Imaging in Skull base

Imaging in Skull base

1. The Skull Base Rakesh C A

2. The Normal Skull Base

3. Normal skull base Concept of fossa does not work well for the skull base, because the bony anatomy spills over from one fossa to the next. Perspective of individual bones Components Apertures Transmitted structures

4. Normal skull base Extend root of nose anteriorly to the superior nuchal line posteriorly

5. Normal skull base 5 bones: Frontal Ethmoid Sphenoid Temporal Occipital

6. Ethmoid

7. Normal skull base Most important part: Basisphenoid (anterior aspect of sella ) Basiocciput (posterior lip of the foramen magnum) The cranial nerves and cerebral vasculature traverse the skull base here.

8. Bones Of Skull Base

9. Occipital bone Floor of the posterior fossa 3 distinct areas: Basiocciput ( clivus and jugulare tubercles) Condylar (lateral) portion Squamous (posterior) portion

10. Occipital bone Floor of the posterior fossa 3 distinct areas: Basiocciput ( clivus and jugulare tubercles) Condylar (lateral) portion Squamous (posterior) portion

11. Occipital bone Apertures: Foramen magnum Posterior condylar canal Hypoglossal canal

12. Temporal bone Petrous pyramid and mastoid process form most of the skull base between the posterior and middle skull base. Apex of the petrous pyramid joins the anterolateral margin of the clivus (i.e., basiocciput ) and the posteromedial aspect of the greater wing of sphenoid along the basisphenoid synchondrosis .

13. Apertures: Jugular foramen Internal auditory canal Facial nerve canal Petrous carotid canal Eustachian tube

14. Sphenoid bone Mid section of the skull base Anterior wall of middle cranial fossa

15. Sphenoid bone 3 compartments: Basisphenoid : Dorsum sella , posterior clinoids , sella turcica , tuberculum sella , sphenoid sinus Fused to clivus in adult Greater wing of sphenoid Medial two-thirds and anterior wall of the middle cranial fossa floor Lesser wing of sphenoid Medial and superior aspects of the anterior wall of the middle cranial fossa and the anterior clinoids Superior and medial edges of the superior orbital fissure

16. Sphenoid bone 3 compartments: Basisphenoid : Dorsum sella , posterior clinoids , sella turcica , tuberculum sella , sphenoid sinus Fused to clivus in adult Greater wing of sphenoid Medial two-thirds and anterior wall of the middle cranial fossa floor Lesser wing of sphenoid Medial and superior aspects of the anterior wall of the middle cranial fossa and the anterior clinoids Superior and medial edges of the superior orbital fissure

17. Sphenoid bone Apertures: Foramen ovale Foramen spinosum Foramen rotundum Optic canal Superior orbital fissure Precavernous carotid canal Foramen lacerum Not a true foramen Thinning of skull base, filled with fibrocartilage in life

18. Frontal bone Anterior cranial fossa is anteriorly and laterally bound by frontal bone; majority by orbital plate of frontal bone

19. Foramen caecum Indentation in the medial anterior frontal bone Normal ( should not be confused with cephalocoele ) Complete bony floor ( protrude through a gap in the frontal bone ) Prominent at birth and gradually shrinks over first 10 years of life Frontal bone

20. Ethmoid bone 2 distinct pieces: Cribriform plate Crista galli

21. Ethmoid bone Cribriform plate is perforated by approx 20 holes on each side of the crista galli Nerve fibres of olfactory nerve (CN I) pass from nasal mucosa to olfactory bulb Crista galli serves as the anchor for anterior margin of the falx cerebri

22. Ethmoid bone Cribriform plate is perforated by approx 20 holes on each side of the crista galli Nerve fibres of olfactory nerve (CN I) pass from nasal mucosa to olfactory bulb Crista galli serves as the anchor for anterior margin of the falx cerebri

23. Bones of Base of skull in ct

24. Embryology

25. Development of the skull base Development of the skull base begins only after the spinal cord, cranial nerves, and blood vessels have formed. The cranial base is relatively stable during development as compared with the rapid growth and expansion of the calvaria . Study of fetal developmental anatomy may lead to a better understanding of congenital skull base disorders.

26. The skull base originates predominately from cartilaginous precursors with a small contribution from membranous bone.

27. The components of the skull base are derived from neural crest cells and mesoderm during the fourth week of fetal life to form the cartilaginous and bony components of the cranial base .

28. Ossification of the skull base progresses in an orderly pattern from posterior to anterior.

29. RADIOGRAPHY OF SKULL BASE

30. Submento -vertical Position of patient and cassette The patient may be imaged erect or supine . If the patient is unsteady , then a supine technique is advisable. Supine The patient’s shoulders are raised and the neck is hyperextended to bring the vertex of the skull in contact with the grid cassette or table. The head is adjusted to bring the external auditory meatuses equidistant from the cassette. The median sagittal plane should be at right-angles to the cassette along its midline. The orbito-meatal plane should be as near as possible parallel to the cassette. Erect The patient sits a short distance away from a vertical Bucky. The neck is hyperextended to allow the head to fall back until the vertex of the skull makes contact with the centre of the vertical Bucky .

31. Submento -vertical Position of patient and cassette The patient may be imaged erect or supine. If the patient is unsteady , then a supine technique is advisable. Supine The patient’s shoulders are raised and the neck is hyperextended to bring the vertex of the skull in contact with the grid cassette or table. The head is adjusted to bring the external auditory meatuses equidistant from the cassette. The median sagittal plane should be at right-angles to the cassette along its midline. The orbito-meatal plane should be as near as possible parallel to the cassette. Erect The patient sits a short distance away from a vertical Bucky. The neck is hyperextended to allow the head to fall back until the vertex of the skull makes contact with the centre of the vertical Bucky .

32. Submento -vertical Direction and centring of the X-ray beam The central ray is directed at right-angles to the orbito-meatal plane and centred midway between the external auditory meatuses .

33. Submento -vertical

34. Essential image characteristics A correct projection will show the angles of the mandible clear of the petrous portions of the temporal bone. The foramina of the middle cranial fossa should be seen symmetrically either side of the midline.

35. Essential image characteristics POSITIONING No rotation is evidenced by  The lateral borders of the foramen magnum are equidistant from the lateral borders of the skull. No tilt is evidenced by  The vomer and the bony nasal septum are aligned with the long axis of the film .

36. Jugular foramina: S ubmento -vertical 20 degrees caudad The jugular foramina lie in the posterior cranial fossa between the petrous temporal and occipital bones on each side of the foramen magnum . Both sides are imaged simultaneously on a -single image by undertaking a submento -vertical (SMV) 20 degrees caudad projection .

37. Jugular foramina: Submento -vertical 20 degrees caudad Position of patient and cassette As per the SMV projection described previously.

38. Jugular foramina: Submento -vertical 20 degrees caudad Direction and centring of the X-ray beam Using a well-collimated beam, the central ray is angled caudally so that it makes an angle of 70 degrees to the orbitomeatal plane and centred in the midline to pass midway between the external auditory meatuses.

39. Notes: Alternative Technique With the patient’s neck less extended , the head can be positioned with the orbito-meatal plane at an angle of 20 degrees to the Bucky , in which case a horizontal central ray will make the required angle of 70 degrees to the base plane (see photograph).

40. Jugular foramina: Submento -vertical 20 degrees caudad

41. The Pathological Skull Base

42. Role of imaging Diagnosis Extend of disease – criteria of surgical resectability Treatment planning – surgical approach Follow up – recurrence vs post ttreatment changes

43. Anterior skull base lesions Bones: Orbital plates of frontal bones Cribriform plate of ethmoid bone Planum sphenoidale

44. Anterior Skull Base Lesions Common: Malignant sinonasal tumor ( eg ., SCC, RMS) Meningioma Metastases Uncommon Mucocoele Osteoma Polyposis Inverted papilloma Esthesioneuroblastoma Lymphoma Complicated sinusitis (bacterial, fungal, granulomatous) Rare Cephalocoele Dermoid cyst

45. Lesions arise: Extracranially From the nasal vault, frontal and ethmoid sinuses Intrinsically From the skull base itself Intracranially From the brain, meninges and CSF spaces

46. Lesions arise: Extracranially From the nasal vault, frontal and ethmoid sinuses Intrinsically From the skull base itself Intracranially From the brain, meninges and CSF spaces

47. Extra cranial lesions Most arise from the nose and paranasal sinuses Common Benign Lesions Mucocoele Polyposis Inverted papilloma Osteoma Common Malignant Lesions Squamous cell carcinoma Rhabdomyosarcoma Adenoid cystic carcinoma Esthesioneuroblastoma

48. Mucocoele Accumulation of impacted mucus behind an occluded draining sinus ostium . Obstruction - Inflammatory > post traumatic, neoplastic Frontal > Ethmoid > Maxillary > Sphenoid

49. Mucocoele - Imaging Well delineated soft tissue mass with bony expansion and remodelling. Low density on NECT; inspissated secretions may appear hyperdense . MR signal is variable. Aggressive bone erosion seen in 10 – 12% of cases.

50. Mucocele A : Coronal T1 magnetic resonance image. The sphenoid sinus is enlarged and its contents are of high signal . Mucocele also involves the left anterior clinoid (arrow), which is markedly expanded and filled with the same high-signal contents as the rest of the sinus. B : Sagittal T1 magnetic resonance image again shows marked enlargement of the left anterior clinoid (large arrow).

51. Mucopyocoele Mucocoeles when infected Axial T1 C+ MR shows left frontal mucopyocoele with thick, peripheral enhancement. Note linear enhancement of the anterior fossa dura (arrows) consistent with meningitis .

52. Inverted Papilloma Benign slow growing epithelial neoplasm. 1 to 4% of sinonasal neoplasms Arise near the nasal vault near the junction of ethmoid and maxillary sinuses . The surface epithelium proliferates by inverting into underlying stroma rather than growing outward.

53. Inverted Papilloma Benign slow growing epithelial neoplasm. 1 to 4% of sinonasal neoplasms Arise near the nasal vault near the junction of ethmoid and maxillary sinuses . The surface epithelium proliferates by inverting into underlying stroma rather than growing outward. Inverted sinonasal or Schneiderian papilloma shows endophytic or “ inverted ” growth pattern. These nests of squamous epithelial cells grow down into the myxomatous to fibrous stroma with chronic  inflammatory cells and vascularity 

54. Inverted Papilloma - Imaging A unilateral, polypoid nasal fossa soft tissue mass widens the nasal vault s ometimes destroying bone and extending into the adjacent ethmoid and maxillary sinuses Focal erosion of the cribriform plate with cephalad extension occassionally occurs. (DD: sinonasal malignancies) No definitive MR findings to differentiate from various malignant tumors .

55. Inverted Papilloma - Imaging A unilateral, polypoid nasal fossa soft tissue mass widens the nasal vault s ometimes destroying bone and extending into the adjacent ethmoid and maxillary sinuses Focal erosion of the cribriform plate with cephalad extension occassionally occurs. (DD: sinonasal malignancies) No definitive MR findings to differentiate from various malignant tumors .

56. Osteoma Benign bony tumor Mature well delineated cortical bone as their primary component. Most common site: frontal sinus Expands and erodes the posterior and superior frontal sinus walls

57. Malignant Sinonasal Tumors Intracranial extension occurs in upto one-third of cases Squamous cell carcinoma Esthesioneuroblastoma Adenocarcinoma Melanoma Non-Hodgkin Lymphoma

58. Rhabdomyosarcoma In children the most common extracranial malignancy that affects the skull base is Rhabdomyosarcoma . It is the most common soft tissue sarcoma in children. Head and neck is the most common site. Orbit & nasopharynx > PNS & middle ear

59. Anterior skull base invasion or cavernous sinus invasion - approx. 35% of nasopharyngeal RMS. Bulky soft tissue mass with areas of bone destruction. Isointense to muscle on T1, hyperintense on T2; some contrast enhancement. Meningeal and perineural spread are common

60. Nasal cavity RMS with extension through sinonasal roof, along the anterior cranial fossa

61. Intracranial extension of masticator fossa RMS through foramen ovale

62. Other Malignancies 98% of n asopharyngeal tumors in adults are carcinomas . Squamous cell carcinoma accounts for 80% of these tumors , and adenocarcinoma (most commonly from minor salivary glands) represent 18%. Nasopharyngeal carcinomas spread directly into skull base as well as along muscles and their tendinous insertions . They extend intracranially along neural and vascular bundles via osseous foramina.

63. A nasopharyngeal mass with obliterated soft tisssue p lanes and adjacent bone destruction are the typical imaging findings with direct tumor invasion. Serous otitis media can be seen because the eustachian tube is frequently obstructed. T1C+ : NP Ca has destroyed large area of skull base bone (arrows) surrounding the foramen ovale . Opposite foramen ovale has V3 traversing it (open arrow).

64. Perineural tumor spread most commonly involves the second and third divisions of trigeminal nerve and facial nerve. Sometimes no dominant mass is present. Enhancement of the affected nerve or denervation atrophy of the muscles of mastication and face may be the only detectable abnormalities.

65. Esthesioneuroblastoma Olfactory neuroblastoma Bipolar sensory receptor cells in the olfactory mucosa. (neural crest origin) Any age – bimodal peak (2 nd and 4 th /5 th decade)

66. Esthesioneuroblastoma - imaging Often confined to nasal cavity; may extend to PNS or anterior cranial fossa (through cribriform plate) High nasal vault with focal bone destruction Variable signal intensity on MR Moderate but inhomogenous enhancement CNS dissemination as a late manifestation CECT - right nasal cavity ENB with destruction of the cribriform plate (arrow) and lamina papyracea (open arrow).

67. Esthesioneuroblastoma - imaging Often confined to nasal cavity; may extend to PNS or anterior cranial fossa (through cribriform plate) High nasal vault with focal bone destruction Variable signal intensity on MR Moderate but inhomogenous enhancement CNS dissemination as a late manifestation

68. Miscellaneous Bacterial or fungal sinusitis

69. Misc Sarcoidosis

70. Misc Sinonasal lymphoma

71. Misc Cocaine granulomatosis History of coccaine abuse Septal perforation with nasal inflammatory changes

72. Misc Wegner granulomatosis Soft tissue mass in nose with septal and non-septal bone destruction Enhancing soft tissue in maxillary sinuses extending into nasopharynx (arrows) with large septal perforation .

73. Lesions arise: Extracranially From the nasal vault, frontal and ethmoid sinuses Intrinsically From the skull base itself Intracranially From the brain, meninges and CSF spaces

74. Intrinsic anterior skull base lesions Intrinsic anterior skull base lesions Fibrous dysplasia Paget disease Osteopetrosis

75. Lesions arise: Extracranially From the nasal vault, frontal and ethmoid sinuses Intrinsically From the skull base itself Intracranially From the brain, meninges and CSF spaces

76. Intracranial lesions Arise from: Meninges CSF spaces Brain

77. Meningioma Most common meningeal lesion to i nvolve anterior skull base Planum sphenoidale and olfactory groove – 10-15% of all meningiomas Broad based, anterior basal subfrontal mass that enhances strongly and relatively uniformly after contrast administration is typical. Presence of tumor -brain interface or cleft with compressed cortex and white matter buckling indicate extraaxial location. Blistering and hyperostosis of the adjacent bone. Enlargement of the air-containing ethmoid sinus ( pneumosinus dilatans ) or even frank bone destruction is sometimes observed.

78. Figure. (A) Enlarged, air-filled ethmoid sinus extending into an isointense intracranial mass on T1-weighted MRI, which enhances uniformly on contrast agent administration (B). (C) Axial CT shows expansion of sinus beyond its normal boundaries into the meningioma , where the plate of bone lining the pneumosinus dilatans is preserved Mai A et al. Neurology 2003;60:1861-1861 ©2003 by Lippincott Williams & Wilkins

79. Cephalocoele The most common anterior skull base lesion that arises from the brain is nasoethmoidal cephalocoele . 15% of basal cephalocoeles occur in the frontonasal area.

80. Cephalocoele The most common anterior skull base lesion that arises from the brain is nasoethmoidal cephalocoele . 15% of basal cephalocoeles occur in the frontonasal area .

81. Misc Nasal dermoid sinuses and nasal cerebral heterotopias ( nasal gliomas ) are less common congenital lesions that occur in this location. Occasionally, a slow growing peripherally located primary brain neoplasms such as ganglioneuroma cause pressure erosion of the adjacent skull. Frank dural invasion or calvarial destruction can occur with anaplastic astrocytoma and glioblastoma multiforme , but uncommon.

82. Destructive Central Skull Base Lesions Common Metastases Nasopharyngeal malignancy Haematogenous Uncommon Osteomyelitis Fungal sinusitis Non fungal granulomas Wegner granulomatosis Cocaine abuse Midline granuloma (probably a lymphoma variant) Aggressive pituitary adenoma Lymphoma Myeloma Meningioma Juvenile nasopharyngeal angiofibroma Chordoma Rare Leprosy Rhinoscleroma Syphilis Sarcoidosis

83. Middle skull base

84. Central skull base It includes: Upper clivus Sella turcica Cavernous sinuses Sphenoid alae

85. Central Skull Base Lesions Lesions affecting the central skull base originate from: Cavernous sinus Pituitary gland Basisphenoid bone Nasopharynx

86. Cavernous sinus Multiseptated , extradural venous spaces that lie on both sides of the sella turcica . They communicate extensively with each other, the intracranial dural sinuses, and deep facial venous plexuses.

87. Lateral wall is composed of 2 layers: Thick outer dural layer Thin inner membranous layer The inner layer is formed by the perineurium of CNs III, IV, V 1 and sometimes V 2. T hese nerves lie within the lateral wall, whereas the internal carotid artery and CN VI are inside the cavernous sinus proper.

88. Medially , a thin poorly delineated medial dural wall separates the cavernous sinus from sella turcica . Meckel’s cave and its contents, the trigeminal ganglion, CSF, and investing arachnoid, invaginate into the cavernous sinus posteriorly .

89. Cavernous Sinus Masses Unilateral Bilateral Common Common Schwannoma Invasive pituitary adenoma Meningioma Meningioma Metastasis Metastases Aneurysm (Cavernous ICA) Carotid-cavernous fistula Uncommon Uncommon Chordoma Lymphoma Lymphoma Cavernous sinus thrombosis Rare Lipoma Epidermoid Cavernous haemangioma Osteocartilagiomnous tumors Plexiform neurofibroma (NF 1)

90. Central skull base lesions

91. Congenital/Developmental lesions Neoplasms Cephalocoele Benign Encephalocoele Pituitary adenoma Meningocoele Meningioma Trauma Nerve sheath tumors Fractures Juvenile nasopharyngeal angiofibroma CSF fistula Chordoma Infection and Inflammatory disease Osteocartilaginous tumors Osteomyelitis Tumor like lesions Bacteral sinusitis Epidermoid tumor Fungal sinusitis Lipoma Wegner granulomatosis Malignant tumors Leishmaniasis Nasopharyngeal carcinoma Sarcoidosis Rhabdomyosarcoma Leprosy, Treponemes , Mycobacteria, Rhinoscleroma Multiple myeloma or Solitary plasmocytoma Cocaine abuse Osteosarcoma Midline lethal granuloma (T-cell lymphoma) Chondrosarcoma Miscellaneous Metastatic disease Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas Radiation necrosis Lymphoma – primary / secondary

92. Congenital/Developmental lesions Neoplasms Cephalocoele Benign Encephalocoele Pituitary adenoma Meningocoele Meningioma Trauma Nerve sheath tumors Fractures Juvenile nasopharyngeal angiofibroma CSF fistula Chordoma Infection and Inflammatory disease Osteocartilaginous tumors Osteomyelitis Tumor like lesions Bacteral sinusitis Epidermoid tumor Fungal sinusitis Lipoma Wegner granulomatosis Malignant tumors Leishmaniasis Nasopharyngeal carcinoma Sarcoidosis Rhabdomyosarcoma Leprosy, Treponemes , Mycobacteria, Rhinoscleroma Multiple myeloma or Solitary plasmocytoma Cocaine abuse Osteosarcoma Midline lethal granuloma (T-cell lymphoma) Chondrosarcoma Miscellaneous Metastatic disease Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas Radiation necrosis Lymphoma – primary / secondary

93. Cephalocoele Axial CT scan (b ) photographed with bone window and coronal CT scan (c) photographed with soft-tissue window reveal the presence of a persistent craniopharyngeal canal (arrow) in the sphenoid bone. Coronal (d) and midsagittal (e) Ti -weighted MR images through the central skull base demonstrate herniation of the pituitary gland into the craniopharyngeal canal through the sphenoidal defect (arrow ) . Note the proximity of the pituitary gland to the roof of the nasopharynx .

94. Congenital/Developmental lesions Neoplasms Cephalocoele Benign Encephalocoele Pituitary adenoma Meningocoele Meningioma Trauma Nerve sheath tumors Fractures Juvenile nasopharyngeal angiofibroma CSF fistula Chordoma Infection and Inflammatory disease Osteocartilaginous tumors Osteomyelitis Tumor like lesions Bacteral sinusitis Epidermoid tumor Fungal sinusitis Lipoma Wegner granulomatosis Malignant tumors Leishmaniasis Nasopharyngeal carcinoma Sarcoidosis Rhabdomyosarcoma Leprosy, Treponemes , Mycobacteria, Rhinoscleroma Multiple myeloma or Solitary plasmocytoma Cocaine abuse Osteosarcoma Midline lethal granuloma (T-cell lymphoma) Chondrosarcoma Miscellaneous Metastatic disease Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas Radiation necrosis Lymphoma – primary / secondary

95. Fractures Most commonly occur as extensions of cranial-vault fractures. Petrous temporal bone > orbital surface of the frontal bone > basiocciput . Multiple skull-base fractures in a 23-year-old man after an automobile accident .

96. CSF fistula The most common cause of CSF fistula is skull-base trauma Fractures through the frontoethmoidal complex and middle cranial fossa. Nontraumatic cause of leakage: Tumors , especially those arising from the pituitary gland congenital anomalies , such as encephaloceles Coronal CT scans through the sphenoid sinus were obtained before (a) and after (b) the intrathecal instillation of water-soluble contrast material . A mass with attenuation values of soft tissue (arrow in a) is seen involving the right lateral floor of the sphenoid sinus. After contrast enhancement increased attenuation is seen in this region, consistent with the accumulation of contrast material (curved arrow in b) . This finding confirms the presence of a CSF fistula .

97. Congenital/Developmental lesions Neoplasms Cephalocoele Benign Encephalocoele Pituitary adenoma Meningocoele Meningioma Trauma Nerve sheath tumors Fractures Juvenile nasopharyngeal angiofibroma CSF fistula Chordoma Infection and Inflammatory disease Osteocartilaginous tumors Osteomyelitis Tumor like lesions Bacteral sinusitis Epidermoid tumor Fungal sinusitis Lipoma Wegner granulomatosis Malignant tumors Leishmaniasis Nasopharyngeal carcinoma Sarcoidosis Rhabdomyosarcoma Leprosy, Treponemes , Mycobacteria, Rhinoscleroma Multiple myeloma or Solitary plasmocytoma Cocaine abuse Osteosarcoma Midline lethal granuloma (T-cell lymphoma) Chondrosarcoma Miscellaneous Metastatic disease Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas Radiation necrosis Lymphoma – primary / secondary

98. Osteomyelitis Potentially lethal complication of: Immunocompromised states Diabetes Chronic mastoiditis Paranasal sinus inection Trauma Necrotising otitis externa Occasionally in the absence of predisposing factors

99. Bacterial sinusitis complicating Osteomyelitis Infection can extend : Directly from frontal, ethmoid or sphenoid sinuses Intracranially via emissary veins and the cavernous sinus. May result in: Cerebral infarct Meningitis Subdural empyema Brain abscess

100. Left frontal SDE with leptomeningeal enhancement in a patient with left pansinusitis

101. Paranasal sinus fungal infections 4 different patterns: Extramucosal disease with cavitating mycetoma (fungus ball) Allergic fungal sinusitis Mucosal thickening from indolent, penetrating fungal sinusitis Fulminant invasive mycosis

102. Manifestations include: Multiple cranial nerve palsies Septic cavernous sinus thrombosis Internal carotid occlusion Brain infarction Brain abscess

103. Fungal sinusitis - Imaging Multisinus nodular mucoperiosteal thickening High attenuation foci in soft tissue masses on CT

104. 17-year-old boy with allergic fungal sinusitis complicated by compression of right optic nerve. Painless decreased vision had been present in the right eye for 2 months. Coronal (A–C) and axial (D) CT images show high-attenuation opacification of left maxillary, left ethmoidal , and bilateral sphenoidal sinuses with bone expansion and thinning . Compression of right optic nerve (straight arrow, B and D) is caused by expanded right anterior clinoid process (asterisk, B and D). Bone dehiscence is present at left lamina papyracea (curved arrow, A and D) and around left optic nerve (arrowhead, B and D), and internal carotid arteries (arrows, C). These structures are at risk of injury during functional endoscopic sinus surgery.

105. Mycetomas Best diagnostic clue: single PNS contains high density mass with fine round to linear matrix calcifications Very hypointense on MR with a high signal rim surrounding the fungal ball.

106. Aggressive mycosis Extensive skull base destruction Cavernous sinus thrombosis, blood vessel invasion and rapid intracranial dissemination can occur CEMR / CECT – multiple filling defects within the cavernous sinus. Extensive skull base erosion is indistinguishable from nasopharyngeal malignancy

107. Biopsy-proved aspergillosis in a 23- year oId black woman with right-sided facial pain . Axial (a ) and coronal (b, c) non-contrast-enhanced CT scans show a large soft-tissue mass (*) with extensive bone destruction of the right maxillary sinus (m ), nasopharynx (n), pterygoid plate ( p ), and sphenoid sinus (s) . The central high attenatuation may represent calcium deposits in mycetoma . T1-weighted MR images obtained before (d) a nd after (e) administration of gadopentetate dimeglumine show the extent of skull base and sinus ivolvement . The central low-signal-intensity areas within the sinus may represent inspissated secretions or fungal mycetoma containing metals.

108. Sarcoidosis Due to its propensity for leptomeningeal invasion , sinus and nasopharyngeal sarcoidosis is recognized as a more common cause of cranial nerve neuropathy . Central nervous system involvement occurs in 3%-8% of patients with sarcoidosis . The most frequent problem is cranial neuropathy secondary to facial , acoustic, optic, or trigeminal nerve involvement. Sarcoidosis should be considered when both the meninges and the cranial nerves are involved in a pathologic process.

109. Other granulomatous diseases Wegner granulomatosis Leishmaniasis Leprosy Rhinoscleroma Mycobacteria Treponemes Cocaine abuse Midline lethal granuloma (T-cell lymphoma)

110. Congenital/Developmental lesions Neoplasms Cephalocoele Benign Encephalocoele Pituitary adenoma Meningocoele Meningioma Trauma Nerve sheath tumors Fractures Juvenile nasopharyngeal angiofibroma CSF fistula Chordoma Infection and Inflammatory disease Osteocartilaginous tumors Osteomyelitis Tumor like lesions Bacteral sinusitis Epidermoid tumor Fungal sinusitis Lipoma Wegner granulomatosis Malignant tumors Leishmaniasis Nasopharyngeal carcinoma Sarcoidosis Rhabdomyosarcoma Leprosy, Treponemes , Mycobacteria, Rhinoscleroma Multiple myeloma or Solitary plasmocytoma Cocaine abuse Osteosarcoma Midline lethal granuloma (T-cell lymphoma) Chondrosarcoma Miscellaneous Metastatic disease Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas Radiation necrosis Lymphoma – primary / secondary

111. Pituitary Adenoma Usually indolent, non agresssive tumors that expand and slowly erode the bony sella turcica . Typically extend superorly through the diaphragma sellae and laterlally into the cavernous sinus. Occasionally, some variants behave more aggressively and may cause extensive destruction of the central skull base.

112. Meningioma Meningiomas of the central skull base are located along the sphenoid wing, diaphragma sellae , clivus and cavernous sinus Focal, globose or flat, en-plaque lesions Occasionally, bony destruction or hyperostosis. Cavernous sinus meningiomas cause multiple cranial nerve palsies.

113. Medial sphenoid wing meningioma

114. Clival meningioma

115. Nerve Sheath Tumors Those involving the central skull base often affects the cavernous sinus and Meckel’s cave. Plexiform neurofibromas Schwanommas

116. Plexiform neurofibromas Unencapsulated diffusely infiltrating masses that originate along peripheral nerve, usually ophthalmic division of trigeminal nerve, and involve BOS by central extension. Extension along mandibular and maxillary divisions of trigeminal nerve is also common.

117. Schwannoma Encapsulated , well delineated tumors . Most are quite vascular Haemorrhage or necrosis may occur

118. Trigeminal Schwannoma Most common schwannoma to involve the central BOS and cavernous sinus is a trigeminal schwannoma. Its symptoms, signs, and imaging appearance varies with the part of the nerve involved, direction and extent of tumor growth. Meckel’s cave – extend into skull base Cisternal – CP angle mass Cisternal and ganglion – “dumbbell” configuration Circumscribed, rounded or lobulated soft tissue masses that enhance strongly but heterogenously . Most are isodense with brain on CT Isointense on T1WI, hyperintense on T2WI

119. On an axial T1-weighted image, a normal nonenhancing Meckel’s cave is seen on the right side (arrow). In the left Meckel’s cave, a heterogeneous enhancing mass arrowheads) is depicted, extending in the cavernous sinus: trigeminal schwannoma .

120. Juvenile Angiofibroma Highly vascular, locally invasive lesion Originates near sphenopalatine foramen Adolescent males Most common benign nasopharyngeal tumor Typically spread along natural foramina and fissures into pterygopalatine fossa, orbit, middle cranial fossa, sphenoid sinus, and cavernous sinus.

121. Imaging – strongly enhancing, highly vascular nasopharyngeal soft tissue mass.

122. Chordoma Slowly growing destructive tumor Histologically benign, but locally invasive One-third in sphenooccipital region Most in midline; primarily involve clivus Other – petrous apex and Meckel’s cave

123. Destructive lesion in the central skull base – T1 hypontense and T2 hyperintense

124. Osteocartilaginous neoplasms Clivus and skull base – cartilaginous neurocranium by endochondral ossification vs Calvarium – mesenchymal membranous neurocranium by intramembranous ossification Therefore, a spectrum of benign and malignant osteocartilaginous neoplasms can arise in the central skull base.

125. Enchondroma The most common benign osteocartilaginous tumor in this location. CT Expansile lobulated soft tissue mass with scalloped endosteal bone resorption and curvilinear matrix mineralisation MRI isointense on T1; hyperintense on T2 Post contrast – enhancement of scalloped margins and curvilinear septae ( ring-and-arc pattern )

126. Multiple myeloma Diffuse skull vault and calvarial vault destruction. Solitary plasmacytoma Focal destructive sphenoid sinus or calvarial vault mass is typical, though nonspecific Best diagnostic clue: CT shows solitary intraosseous osteolytic soft tissue mass with nonsclerotic margins

127. Osteosarcoma Craniofacial osteosarcomas are uncommon - when present, present in older patients, and commonly affect the maxilla or mandible . Skull base osteosarcomas are rare. May occur spontaneously or In association with Paget disease or previous radiation therapy. A soft tissue mass with tumor matrix mineralisation and aggressive bone destruction is characteristic. DD: Radiation osteitis , metastatic carcinoma, myeloma

128. MRIs of a radiation–induced osteosarcoma in a patient with severe fibrous dysplasia of the skull and skull base. ( A) Gadolinium–enhanced, T1–weighted axial image with fat suppression shows a large tumor in the region of the sphenoid and sella . ( B) T2–weighted fast spin–echo, axial and (C) gadolinium–enhanced, T1–weighted coronal image with fat suppression of the same lesion.

129. Chondrosarcoma Rare in skull base Slow growing, locally invasive tumors Soft tissue mass with focal bone destruction is typical. Matrix mineralisation in half of cases. MR: low to intermediate signal on T1 Hyperintense on T2 Strong but heterogeneous enhancement

130. Chondrosarcoma in a 65-year-old man with epistaxis and facial pain. ( a) Axial CT scan with bone windows reveals the presence of a midline destructive lesion involving the sphenoid body and extending anteriorly to the ethmoid bones and nasal fossa with tumor calcification (arrow) , within the mass. ( b) Axial T1 -weighted MR image a relatively homogeneous midline mass (*) that is slightly less intense than brain and associated destruction of the clivus (arrows) . ( c) Midsagittal T1-weighted MR image shows a destructive mass in the midline of the ethmoid bones and nasal fossa extending posteriorly and causing destruction of the sphenoid body and clivus (*).

131. Metastatic disease Central skull base metastases are more common than primary bone neoplasms . Arise via regional extension of head and neck malignancies or perineural spread from regional or remote malignancies or haematogenous spread from extracranial sites

132. Prostate, lung and breast carcinomas are the most common. Lung and breast – focal or diffuse lytic destructive lesions Prostate – mixed hyperostoses and bone destruction with an associated soft tissue mass (resembles meningioma). Lateral orbital wall – favourite site

133. Lymphoma CNS involvement – primary or secondary Leptomeningeal involvement (most common type) Cranial nerve palsies (most common presenting signs) Focal masses or perineural tumor can occur MR: Replacement of normal high signal marrow with infiltrating soft tissue that has decreased signal intensity Cavernous sinus lymphoma can be unilateral or bilateral.

134. Unenhanced (A) and contrast-enhanced (B) axial T 1 -weighted images reveal homogeneous infiltrating lesions (arrow) in cavernous sinus , which exhibits homogeneous , intense enhancement .

135. Posterior Cranial Fossa Largest and the deepest of the 3 cranial fossae. Roughly two-fifths of the base of skull. Surrounds the foramen magnum

136. Includes: clivus below the sphenooccipital synchondrosis petrous temporal bone pars lateralis and squamae of occipital bone

137. NOTE!!! MR signal of normal clivus and posterior skull base depends on the amount and nature of the marrow elements the comprise the cancellous bone. Red marrow ( haematopoetic tissue) predominates upto approximately 3 years of age and results in low and high intensity portions mixed in various proportions on T1WI. Enhancement of normal clivus marrow sometimes follows contrast administration. This is mild and infrequent in adults, but is common and may even be quite striking in young children. The skull base in children normally has signal irregularity and patchy enhancement .

138. Posterior Skull Base Lesions

139. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

140. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

141. Cerebello pontine angle – Intenal auditory canal cistern

142. Normal anatomy CPA cistern lies between the anterolateral surface of pons & cerebellum and the posterior surface of the petrous temporal bone. Important structures: Nerves – CNs V, VII and VIII Arteries – SCA, AICA Tributaries of superior petrosal veins Others – Flocculus , choroid plexus

143. CPA-IAC cistern lesions

144. Normal variants in CPA- lAC Normal structures, when unusually prominent, trouble radiologist evaluating CPA – lAC . AICA loop flow void on high-resolution T2 MR Will not prominently enhance on Tl1C + MR Subtle enhancement in lAC on TI C+ MR may be mistaken for small acoustic schwannoma Choroid plexus protruding through lateral recess of 4th ventricle T1 C+ MR shows enhancing bilateral tear-shaped masses of CPA cistern Symmetry &. characteristic appearance make diagnosis Cerebellar flocculus is a lobule of cerebellum projecting into posterolateral aspect of CPA cistern Signal follows intensity of cerebellum on all MR sequences Marrow space foci in walls of lAC can mimic lAC tumor on Tl C+ MR images Correlate location of foci with lAC cistern Bone CT of T-bone may be necessary to identify this normal variant High jugular bulb Prominent jugular tubercles

145. Normal variants in CPA- lAC Normal structures, when unusually prominent, trouble radiologist evaluating CPA – lAC . AICA loop flow void on high-resolution T2 MR Will not prominently enhance on Tl1C + MR Subtle enhancement in lAC on TI C+ MR may be mistaken for small acoustic schwannoma Choroid plexus protruding through lateral recess of 4th ventricle T1 C+ MR shows enhancing bilateral tear-shaped masses of CPA cistern Symmetry &. characteristic appearance make diagnosis Cerebellar flocculus is a lobule of cerebellum projecting into posterolateral aspect of CPA cistern Signal follows intensity of cerebellum on all MR sequences Marrow space foci in walls of lAC can mimic lAC tumor on Tl C+ MR images Correlate location of foci with lAC cistern Bone CT of T-bone may be necessary to identify this normal variant High jugular bulb Prominent jugular tubercles

146. Cerebellopontine angle cistern masses Uncommon in children; very common in adults Cerebellopontine angle cistern masses Common Uncommon Acoustic schwannoma (75%) Arachnoid cyst Meningioma (8 to 10%) Lipoma Epidermoid (5%) Demoid Other schwannomas Exophytic cerebellar/brainstem astrostoma Vascular (VB ectasia , aneurysm, VM) Chordoma Metastases Osteocartilaginous tumors Paraganglioma Ependymoma Choroid plexus papilloma

147. Internal Auditory Canal Masses Internal Auditory Canal Masses Common Uncommon Intracanalicular acoustic schwannoma Neuritis ( eg ., Bell’s palsy, Ramsay Hunt syndrome) Post operative fibrosis Haemangioma Lymphoma Metastases Sarcoidosis Meningioma

148. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

149. Temporal bone lesions

150. Primary temporal bone lesions: Gradenigo’s syndrome Malignant otitis externa Cholesterol granulomas Paraganglioma ( glomus tympanicum )

151. Gradenigo’s Syndrome Osteomyelitis of petrous apex with sixth nerve palsy, otorrhea , and retroorbital pain. NECT: Destructive lesion of the petrous apex with fliud in the adjacent middle ear and mastoid.

152. Gradenigo’s Syndrome Osteomyelitis of petrous apex with sixth nerve palsy, otorrhea , and retroorbital pain. NECT: Destructive lesion of the petrous apex with fliud in the adjacent middle ear and mastoid.

153. Malignant otitis externa Uncommon but fulminant form of temporal bone osteomyelitis Typical in insulin-dependent diabetics and immunocompromised patients Extension into parotid and masticator spaces, skull base, and occassionally the CPA cistern may occur.

154. Malignant otitis externa Uncommon but fulminant form of temporal bone osteomyelitis Typical in insulin-dependent diabetics and immunocompromised patients Extension into parotid and masticator spaces, skull base, and occassionally the CPA cistern may occur.

155. Cholesterol granulomas Expansile cystic lesions of petrous apex that contain haemorrhage and cholesterol crystals. Hyperintense on T1 and T2

156. Paragangliomas Slow growing hypervascular tumors Arise from neural crest cells Locaised to cochlear promontory in the middle ear cavity – glomus tympanicum tumors

157. Paragangliomas Glomus jugulotympanicum tumors extend from the jugular foramen into middle ear cavity. Large masses also extend into CPA cistern. The axial post-gadolinium T1-weighted image above shows an enhancing lesion involving almost the entire petrous temporal bone and extending through the external auditory canal to protrude from the external ear (green arrow). The tumour extended beyond the skull base into the carotid sheath, and bulged into the posterior fossa

158. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

159. Clival and Paraclival Lesions Chordoma and Metastasis are the most common causes of destructive clival masses. The same infectious and inflammatory processes and primary and metastatic tumors that affect the anterior and central skull base can also involve the clivus. Replacement of the normal marrow that forms the cancellous clival bone by soft tissue masses is easily identified on MR studies in these cases. Compared to brain, most abnormalities exhibit low signal on T1 and high signal on T2WI.

160. Axial computed tomography shows a large midline chordoma involving the petrous apex bilaterally.

161. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

162. Jugular foramen Jugular foramen: Located in the floor of the posterior fossa, between the petrous temporal bone anterolaterally and the occipital bone posteromedially . Anterior and inferior to it is the hypoglossal canal Hypoglossal nerve

163. Divided into: Pars nervosa ( smaller anteromedial compartment ) CN IX Pars vascularis ( larger posterolateral compartment) CN X and XI Jugular vein

164. Jugular Foramen Masses Non Neoplastic Masses Common Large jugular bulb (normal variant) Jugular vein thrombosis Uncommon Osteomyelitis Malignant otitis external Neoplasms Common Paraganglioma Metastasis Nasopharyngeal carcinoma Haematogenous Uncommon Scwannoma neurofibroma Epidermoid tumor

165. Prominent jugular bulb Normal variant Most common “ pseudomass ” in the jugular foramen.

166. Glomus Jugulare The glomus jugulare is situated in the jugular bulb adventitia immediately below the middle ear. .

167. Glomus Jugulare Expand the jugular foramen, eroding the jugular spine and surrounding cortex .

168. Glomus Jugulare T1  : low signal T2 :  high signal T1 C+ ( Gd ) :  marked intense enhancement Salt and pepper appearance is seen on both T1 and T2 weighted sequences; the salt representing blood products from haemorrhage or slow flow and the pepper representing flow voids due to high vascularity.

169. Glomus Jugulare T1  : low signal T2 :  high signal T1 C+ ( Gd ) :  marked intense enhancement Salt and pepper appearance is seen on both T1 and T2 weighted sequences; the salt representing blood products from haemorrhage or slow flow and the pepper representing flow voids due to high vascularity.

170. Glomus Jugulare Carotid arteriography is necessary for preoperative evaluation and/or embolization

171. Nerve Sheath Tumors Jugular foramen is uncommon location for nerve sheath tumors . Schwannomas of CNs IX to XI smooth well delineated rounded or lobulated soft tissue masses that expand the jugular foramen. Pressure erosion is common (frank invasion is rare; c.f. paragangliomas ) Isointense to brain on T1; hyperintense on T2 Strong homogenous contrast enhancement

172. Nerve Sheath Tumors Jugular foramen is uncommon location for nerve sheath tumors . Schwannomas of CNs IX to XI smooth well delineated rounded or lobulated soft tissue masses that expand the jugular foramen. Pressure erosion is common (frank invasion is rare; c.f. paragangliomas ) Isointense to brain on T1; hyperintense on T2 Strong homogenous contrast enhancement

173. Nerve Sheath Tumors Jugular foramen is uncommon location for nerve sheath tumors . Schwannomas of CNs IX to XI smooth well delineated rounded or lobulated soft tissue masses that expand the jugular foramen. Pressure erosion is common (frank invasion is rare; c.f. paragangliomas ) Isointense to brain on T1; hyperintense on T2 Strong homogenous contrast enhancement

174. Posterior Skull Base Lesions - location CP Angle – IAC cistern Temporal bone Clival and paraclival Jugular foramen Foramen magnum

175. Foramen Magnum Masses

176. Normal Aantomy Large aperture in the occipital bone though which posterior fossa communicates with the cervical spinal canal . It transmits: Medulla and its meninges Spinal segment of CN XI 2 vertebral arteries Anterior and posterior spinal arteries Vertebral veins Bony elements that contain these structures are collectively termed the craniovertebral junction (CVJ).

177. CVJ Formed by the occiput and the C1 and C2 vertebrae. 4 joints are present here: Atlanto occipital Anterior median atlanto axial Posterior median atlanto axial Lateral atlanto axial joints

178. Pathology Intraaxial ( cervicomedullary ) masses Extramedullary intradural masses Anterior Posterior Extradural masses CVJ Clivus & Skull base

179. Cervicomedullary masses Extradural masses Common Craniovertbral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

180. Cervicomedullary masses Extradural masses Common Craniovertbral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

181. Intraaxial ( cervicomedullary ) masses Non neoplastic intraaxial lesions Syringohydromyelia 25% of patients with Chiari I malformation Acquired syrinxes – trauma, cystic neoplasms Demyelinating diseases Including multiple sclerosis In medulla and upper cervical spinal cord Cervicothoracic ganglioneuroblastoma

182. Intraaxial ( cervicomedullary ) masses Non neoplastic intraaxial lesions Syringohydromyelia 25% of patients with Chiari I malformation Acquired syrinxes – trauma, cystic neoplasms Demyelinating diseases Including multiple sclerosis In medulla and upper cervical spinal cord Demyelination extends from the cervicomedullary junction to the T2 vertebral level. ADEM post liver transplantation

183. Intraaxial ( cervicomedullary ) masses Neoplasms Half of brain stem gliomas occur here Cephalad extension of cervical spinal cord tumors into distal medulla is also common Most are low grade astrocytomas Inferior extension of medulloblastoma in children and haemangioblastoma in adults are common are the common nonglial neoplasms of the cervicomedullary junction. Intraaxial metastases are rare in this location.

184. Cervicomedullary masses Extradural masses Common Craniovertbral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

185. Extramedullary Intradural Masses Anterior foramen magnum masses Most arise anterior to cervicomedullary junction. Posterior foramen magnum masses

186. Cervicomedullary masses Extradural masses Common Craniovertbral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

187. Anterior foramen magnum masses Vascular lesions Ectatic Vertebral Artery Aneurysms Neoplasms Meningioma Schwannoma Epidermoid tumors Paragangliomas Metastases Non-vascular Non-neoplastic lesions Arachnoid, inflammatory and neurenteric cysts Extraosseous intradural chordomas Intradural rheumatiod nodules

188. Anterior foramen magnum masses – vascular lesions Ectatic vertebral artery M ost common intradural mass anterior to the medulla There is no correlation between neurologic deficit and the presence of vascular grooves along the brainstem, regardless of their size. Aneurysms Vertebral artery Posterior inferior cerebellar artery PICA aneurysm

189. Anterior foramen magnum masses - neoplasms Meningioma : The most common primary intradural extramedullary neoplasm in this location. Nerve sheath tumors Second most frequently encountered neoplasms Schwannomas of CNs IX to XI Neurofibromas from exiting spinal nerve segments Misc : Epidermoid tumors Paragangliomas Metastases – cistenal , perineural and skull base

190. Left : Sagittal T 2 -weighted MR image obtained in a 48-year-old man, demonstrating an anteriorly situated foramen magnum meningioma   (long arrow)  causing compression and displacement of the rostral spinal cord   (short arrow). Right :  Axial T 1 -weighted Gd -enhanced MR image obtained at the level of the foramen magnum. The homogeneously enhancing tumor arises predominantly in an anterior location with some left lateral contribution. The large tumor occupies slightly more than half of the transverse diameter of the foramen magnum and affords an adequate surgical corridor of approximately 1 cm. The rostral spinal cord  (arrow)  is compressed and displaced posteriorly.

191. Anterior foramen magnum masses - Non-vascular Non-neoplastic lesions They are uncommon. Arachnoid , inflammatory and neurenteric cysts Extraosseous intradural chordomas or notochordal remnants Intradural rheumatoid nodules

192. Cervicomedullary masses Extradural masses Common Craniovertbral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

193. Posterior Foramen Magnum Masses Herniated tonsils 5 to 10% of all foramen magnum masses Most frequent extramedullary intradural mass posterior to the cervicomedullary junction.

194. Posterior Foramen Magnum Masses Herniated tonsils Congenital Occur with Chiari I malformations Acquired Causd by increased intracranial pressure or posterior fossa masses. After lumboperitoneal shunting of subarachnoid spinal space. Reported with multiple traumatic lumbar punctures

195. Posterior Foramen Magnum Masses Ependymoma Subependymoma Medulloblastoma Are intraaxial neoplastic masses that sometimes extend posteroinferiorly behind the medulla

196. Posterior Foramen Magnum Masses Ependymoma Subependymoma Medulloblastoma Are intraaxial neoplastic masses that sometimes extend posteroinferiorly behind the medulla

197. Cervicomedullary masses Extradural masses Common Craniovertebral junction Syringohydromyelia Trauma Demyelinating disease Arthropathies Glioma Congenital anomalies Fourth ventricle tumor Clivus and skull base Uncommon Metastases Haemangioblastoma Chordoma Metastases Osteocartilaginous tumors Anterior extramedullary intradural masses Posterior extramedullary intradural masses Common Common Vertebrobasilar dolichoectasia Tonsillar herniation Meningioma Ependymoma / subependymoma Aneurysm (VA, PICA) Medulloblastoma Uncommon Schwannoma Epidermoid tumor Paraganglioma Metastases Arachnoid cyst

198. Extradural Masses Most extradural masses at the foramen magnum are osseous lesions . Trauma Arthropathies Congenital malformations Tumors High resolution MR delineates relationship between the osseous abnormalities, neural canal, and spinal cord in CVJ malformations. Plain film tomography and CT with multiplanar 3D reconstruction are helpful for detailing the complicated osseous abnormalities seen in these disorders.

199. Trauma Odontoid fractures Relatively common 20% of all cervical fractures 25 to 40% cause death at the site of accident. Survivors do not experience immediate neurologic impairment. Late-onset myelopathy secondary to non united dens fracture may occur. Chronic instability can lead to spinal stenosis and irreversible cord damage. The Anderson and D’Alonzo classification of odontoid fracture. Type I fractures involve avulsion near the tip of the dens. Type II fractures occur at the base of the odontoid process. Type III fracture lines extend into the body of the axis.

200. Trauma Odontoid fractures CT – delineates the osseous abnormalities. MR – best delineates the relation to the spinal subarachnoid space and cord itself.

201. Trauma Odontoid fractures CT – delineates the osseous abnormalities. MR – best delineates the relation to the spinal subarachnoid space and cord itself.

202. Arthropathies True synovial joints Full spectrum of degenerative and inflammatory arthropathies occur. Rheumatoid arthritis of spine is second in incidence only to that of hands and feet. Cervical spine is affected in 80% of patients. Prominent pannus and atlantoaxial subluxation may cause severe CVJ narrowing with spinal cord compression. Occasionally, rheumatoid nodules may be present within the dura and perineurium . Less common CVJ lesions include: Osteoarthritis, Paget disease, CPPD disorders, osteomyelitis with or without epidural abscess.

203. MRI of rheumatoid arthritis of the cervical spine. A sagittal spin-echo T1-weighted MR image shows inflammatory pannus eroding odontoid ( arrow ), and cranial settling with cephalad migration of C-2 impinging on the medulla oblongata ( open arrow ).

204. Congenital anomalies Congenital CVJ anomalies are relatively uncommon , and include: Vertrabralisation of occipital condyles Arch hypoplasias and aplasias Os odontoideum Odontoid hypoplasia Assimilations and Ligament laxity Occur in isolation or with basilar invagination. May be associated with other congenital abnormalities like Down syndrome, Chiari I malformations, or syringohydromyelia .

205. Neoplasms Primary and metastatic tumors Most extradural tumors affect clivus and are therfore anterior to medulla. Primary neoplasms include: Chordoma Osteocartilaginous tumors ( chondroma , chondrosarcoma ) Metastases Haematogenous Local extensions (nasopharyngeal or skull base tumors ) All lesions r eplace normal fatty marrow Hypointense on T1; hyperintense on T2 (regardless of etiology ) Exception is Chordoma : Very high, but heterogenous signal intensity on T2

206. Metastasis from a renal cell carcinoma at the jugular foramen and FM region Contrast-enhanced computed tomography shows an enhancing mass at the base of the left posterior fossa destroying the lower clivus , occipital squama , and lateral mass of C1. MRI shows large enhancing soft tissue mass in the region of the left jugular foramen and lateral to the foramen magnum .

207. Diffuse skull base masses

208. Lesions that can occur in any or all BOS locations Diffuse Skull Base Lesions Non Neoplastic Masses Uncommon Fibrous dysplasia Paget’s disease Langerhans’ cell histiocytosis Neoplastic Masses Common Metastasis Uncommon Myeloma Anaemias Meningioma Meningioma Lymphoma Rhabdomyosarcoma

209. Fibrous dysplasia Among the most common skeletal disorders. Adolescents and young adults Monoostotic (70%) or polyostotic Skull and facial bone involvement: 25% of patients with monoostotic FD 40 to 60% of patients with polyostotic FD

210. Expands and replaces the normal bone medullary spaces with vascular fibrocellular tissue. Varying degrees of ossification may be seen. CT: Thickened sclerotic bone with a “ground-glass” appearance. Cystic components may be present in the early active stage. MR: Low to intermediate signal on T1 and T2; scattered hyperintense regions may be present. Variable contrast enhancement.

211. Expands and replaces the normal bone medullary spaces with vascular fibrocellular tissue. Varying degrees of ossification may be sen. CT: Thickened sclerotic bone with a “ground-glass” appearance. Cystic components may be present in the early active stage. MR: Low to intermediate signal on T1 and T2; scattered hyperintense regions may be present. Variable contrast enhancement.

212. Paget disease Osseous lesion of unknown etiology Monoostotic or polyostotic Focal or diffuse 3 phases are identified: Early destructive phase Intermediate phase with combined destruction and healing Late sclerotic phase.

213. Imaging findings vary with stage. Both CT and MRI scans show expanded bone of the skull base associated with calvarial involvement. MRI better demonstrates the basilar invagination often seen because of bone softening. CT scan of the skull included an axial view at midcranial level (bone window), which confirmed the asymmetric broadening of the skull , increased density of the calvarium , and disturbance of the trabecular architecture due to diffuse mineralisation of the diploe with corticomedullary dedifferentiation .

214. Imaging findings vary with stage. Both CT and MRI scans show expanded bone of the skull base associated with calvarial involvement. MRI better demonstrates the basilar invagination often seen because of bone softening. MRI of the skullshows on the axial T2- weighted MR-image of the posterior fossa showing thickening of the skull with corticomedullary dedifferentiation and non-homogeneous, low to intermediate signal intensity of the diploe .

215. Langerhan Cell Histiocytosis Solitary or monoostotic Eosinophilic Granuloma is the most common presentation. Children between 5 and 15 years ; occassionally in young to middle-aged adults. Typically affects skull vault However, striking diffuse osteolytic skull base and calvarial lesions can occur. Single or multiple areas of pure osteolysis are seen in the skull base and calvarium of children (i.e., eosinophilic granuloma). A soft tissue mass may be associated (i.e., Hand- Schuller -Christian or Letterer- Siwe disease)

216. Langerhan Cell Histiocytosis Solitary or monoostotic Eosinophilic Granuloma is the most common presentation. Children between 5 and 15 years ; occassionally in young to middle-aged adults. Typically affects skull vault However, striking diffuse osteolytic skull base and calvarial lesions can occur. Single or multiple areas of pure osteolysis are seen in the skull base and calvarium of children (i.e., eosinophilic granuloma). A soft tissue mass may be associated (i.e., Hand- Schuller -Christian or Letterer- Siwe disease)

217. Metastases Most common malignancy of skull base Direct or haematogenous spread MC primary – lung, breast and prostate CT – destructive mass infiltrating the skull base MRI – T1WI show a “muscle” intensity mass within the skull base with loss of normal, low intensity cortical bone signal Metastasis to the sphenoid triangle (greater wing of sphenoid). The tumor (T) expands in all directions, pushing the temporalis muscle laterally, extending into the middle cranial fossa, and impinging on the orbit causing proptosis .

218. Myeloma Multiple myeloma or solitary plasmacytoma is possible Indistinguishable from osteolytic metastases on CT or MRI In the diffuse form, all bones of the skull base are involved, with permeative changes . Bone window images demonstrates destruction of clivus , petrous apex, sphenoid bone, lateral mass of C1, and the pedicle of C2 on left side

219. Anemias CT of the 6 years old with thalassemia showing extensive hypertrophy of the diploic spaces mostly in the maxillary walls, skull base and frontal bones. Note obliteration of the maxillary, sphenoid and frontal sinuses. Also note increased trabeculation in the diploë . This results from bone marrow hypertrophy due to ineffective erythropoiesis.

220. Interventional Neuroradiology in Skull Base

221. Interventional Neuroradiology in Skull Base Image guided biopsy Radio-frequency Ablation and Cryoablation for Tumors Percutaneous Sclerotherapy – venous malformations Preoperative Tumor Embolization Management of Bleeding from the Head and Neck Transarterial Embolization for Epistaxis Bleeding from Carcinoma of the Head and Neck Carotid Blowout Syndrome Other lesions of vascular etiology AVF Dural AVF – Transverse, Sigmoid CCF Aneurysms Intra-Arterial Chemotherapy for Head and Neck Carcinoma

222. Image-Guided Biopsies A, Paramaxillary approach to the left parapharyngeal space mass, proven to be an oncocytoma . Slight turning of the head to the opposite side simplifies the approach to this parapharyngeal space lesion. B , Subzygomatic approach to the masticator space mass via the intercondylar notch. The core specimens in this patient with previously treated squamous cell carcinoma revealed scar tissue with no evidence of malignant cells . C, CT image in a patient with a mass at the C2 level reveals a subtle left-sided epidural soft-tissue (arrow) and cortical irregularity of the vertebral body (arrowhead). This image was acquired with contrast to map the location of the adjacent vertebral A. D , A posterolateral approach to the epidural mass was planned. A 22-gauge Franseen needle is advanced through a guiding needle, and aspiration biopsy is performed . Aspiration biopsy was consistent with a diagnosis of chordoma

223. Radio-frequency Ablation and Cryoablation for Tumors A 59-year-old man with severe dyspnea and dysphagia secondary to a large squamous cell carcinoma treated with radio-frequency ablation. A , Axial contrast-enhanced CT scan demonstrates a large necrotic tumor ( arrows ) in the floor of the mouth and hypopharynx . B , 3D volume-rendered reconstruction demonstrates the radio-frequency probe and electrode deployment within the tumor by means of a submental approach. Note that the tumor anterior and posterior to the hyoid bone could be ablated simultaneously.

224. Left cheek venous vascular malformation ( A ) Clinical picture before treatment showing left cheek mass. ( B ) T2-weighted, fat-saturated axial MR image showing a mass with heterogeneous signal intensity in the left masseter muscle extending to the masticator space . ( C ) Injection of 75% ethanol mixed with Ethiodol under live subtraction mode showing accumulation of the sclerosing agent in the lesion. ( D ) Further injection of the sclerosing agent with compression of the venous outflow of the lesion. ( E ) Non-subtracted image of the head after sclerotherapy showing stasis of the sclerosing agent within the lesion. ( F ) Clinical picture 5 months after treatment showing decreased size of the left cheek mass.

225. Preoperative Tumor Embolization The tumors that require embolization in the head and neck most commonly include glomus tumors , angiofibromas , and meningiomas . Many other types of tumors that may also require preoperative embolization include the following: hypervascular metastases , esthesioneuroblastomas , schwannomas , rhabdomyosarcomas , plasmacytomas , chordomas , and hemangiopericytomas .

226. Preoperative Tumor Embolization The embolic agents in common use are: polyvinyl alcohol (PVA), Embospheres ( Bio- Sphere Medical, Rockland, Mass) , liquid embolic agents ( glue, ethylvinyl alcohol copolymer, or Onyx) , gelatin sponge ( Gelfoam ) , and coils .

227. Glomus jugulare tumor . ( A ) Contrast-enhanced head CT shows an enhancing mass extending into right temporal bone at cerebellar pontine angle level ( arrow ). ( B ) Bony expansion and destruction at jugular fossa level ( arrow ) is seen on thin section temporal bone CT. ( C ) Axial and ( D ) coronal contrast-enhanced MRI shows a corresponding intensely enhancing mass ( arrows ), consistent with glomus jugulare paraganglioma tumor . Diagnostic angiography confirms dense tumor blush , consistent with glomus tumor . Multiple feeding arteries were found, indicating a multicompartmental tumor , and these feeding pedicles were embolized to stasis with polyvinyl alcohol particles . ( E ) Lateral view during injection of a common trunk of the right occipital artery and ascending pharyngeal shows dense stain from ascending pharyngeal artery. AP, ascending pharyngeal artery; Occ , occipital artery. ( F ) Tumor blush seen on selective catheterization of a feeding pedicle from posterior division of the right ascending pharyngeal artery.

228. Juvenile nasal angiofibroma ( A ) Axial and ( B ) coronal T1-weighted MRI with contrast confirms the intensely enhancing mucosal mass in left nasal cavity, with rightward displacement of the nasal septum ( arrows ). ( C ) Unsubtracted and ( D ) subtracted cerebral angiogram demonstrates intense tumor blush in nasal cavity during internal maxillary artery. ( E ) Postembolization angiogram of the sphenopalatine artery shows no residual tumor blush. The tumor subsequently was resected endoscopically , with an estimated total blood loss of 75 cm 3 .

229. Bleeding from Carcinoma of the Head and Neck An elderly man with a recurrent head and neck cancer presenting with pulsatile bleeding through the oral cavity. A , CT angiogram of the neck shows an ulcerated left oropharyngeal mass ( arrowheads ) that encases the left ECA ( arrow ). B , Common carotid angiogram reveals a long-segment tumor encasement of the left ECA . C , The ECA is embolized with fibered and detachable platinum coils . The patient did not have additional episodes of bleeding after the embolization.

230. Maxillary arteriovenous malformation ( A ) Clinical picture before treatment showing a soft tissue pulsatile mass in the left gingiva and palate. ( B, C ) Early ( B ) and late ( C ) phases of the left external carotid artery angiogram in the lateral projection showing a left maxillary arteriovenous malformation with large draining venous channel inside the maxilla. ( D ) Lateral view of the superselective angiogram of the left descending palatine artery showing arteriovenous shunts to the intraosseous vein. ( E ) N-butyl cyanoacrylate (NBCA ) cast injected from the same microcatheter position as in ( D) , showing penetration of NBCA into the vein. ( F ) Lateral view of the external carotid artery angiogram after multiple embolization showing disappearance of the arteriovenous malformation. ( G ) Clinical picture after embolization showing ulceration of the left palate. No further hemorrhagic episodes were experienced.

231. Lower-grade dural arteriovenous fistula of the left sigmoid sinus Study confirms low-grade dural arteriovenous fistula of the left sigmoid sinus, with multiple feeding arteries , including ( A ) occipital artery, ( B ) ascending pharyngeal artery, ( C ) middle meningeal artery, and ( D ), and left vertebral artery. Each of these feeding arteries was embolized to stasis using polyvinyl alcohol particles. Coils were placed in the distal occipital artery to protect the cutaneous branches from the effects of the proximal embolization ( ∗ , seen in B ). Following transarterial embolization of the feeding arteries, transvenous embolization was performed for a combined transarterial-transvenous approach , resulting in complete obliteration of the fistula. This combined transarterial and transvenous treatment results in durable cure of this fistula without open surgery.

232. Higher-grade dural arteriovenous fistula of the torcular region Diagnostic angiogram confirms DAVF of the torcular region, with supply from multiple arteries including the middle meningeal artery and opacification of multiple cerebellar veins. Transvenous embolization of this fistula is not practical. After transarterial embolization with NBCA tissue adhesive, resulting in a glue cast of the distal feeding arteries and proximal recipient veins, the fistula is obliterated . CV , cerebellar veins; MC, microcatheter in middle meningeal artery; MMA, middle meningeal artery.

233. Direct (high-flow) carotid cavernous fistula – post traumatic ( A ) Coronal T1-weighted MRI shows dilated superior ophthalmic vein (SOV). ( B ) Axial image from MR angiogram also shows a dilated superior ophthalmic vein (SOV). ( C ) Angiogram of left internal carotid artery (IAC) (lateral projection) confirms a fistula (CCF) with opacification of cavernous sinus and retrograde flow in superior ophthalmic vein (SOV), draining to facial veins (FV). ( D ) After embolization with detachable balloons , the fistula is closed.

234. Symptomatic mid-basilar aneurysm ( A ) 3-D reconstructions from magnetic resonance angiography. ( B ) Diagnostic cerebral angiogram, anteroposterior projection from ( C ) 3-D rotational angiography. ( D ) Lateral projection from cerebral angiogram obtained after endovascular treatment with a combination of endovascular stents for reconstruction of the arterial lumen, followed by coiling . Patient's symptoms resolved following this treatment.

235. Intra-Arterial Chemotherapy for Head and Neck Carcinoma

236. ADVANCES

237. Advances in Skull Base Imaging Advances in the areas of diagnostic imaging, interventional radiology, surgical approaches and techniques, as well as electrophysiological monitoring, have all advanced the treatment of skull base tumors and disorders.

238. Advances in CT & MR technologies Better and precise diagnosis Facilitated aggressive skull base surgery by allowing precise preoperative delineation of the extent of lesions Post operative follow-up

239. Advanced image-guided skull base surgery .

240. Advanced image-guided skull base surgery . The early localization of the major vessels or neural structures during transtumoral decompression is beneficial.  A:  Instrument points to the petrous portion of the internal carotid artery (ICA) during decompression of a cavernous sinus meningioma .   B :  Instrument points to the basilar artery (BA) during removal of a craniopharyngioma

241. CT/MR Fusion For Skull Base Imaging

242. CT/MR Fusion For Skull Base Imaging A: Axial CT visualized at bone window settings demonstrates lytic lesion with well-defined margins in left petrous apex (M). Note extent of bone erosion involving cortex of the posterior petrous portion of the temporal bone (curved arrow) and bony covering (straight arrows) of the petrous segment of the internal carotid artery (C). B : Axial T1-weighted noncontrast - enhanced MR imaging performed in same patient shows a high signal intensity mass located within the left petrous apex (curved arrow) which is characteristic of a cholesterol granuloma . Note relationship of the mass to the basilar artery (straight arrow ). There is excellent visualization of the soft tissues of the brain and masticator spaces (M); however, the relationship of the mass to the carotid artery (c ) and the extent of bone erosion is better seen on CT than on MR imaging.

243. CT/MR Fusion For Skull Base Imaging

244. Conclusion The central skull base is a highly complex region. Knowledge of the normal development and anatomic relationships will lead to more accurate diagnoses. This in turn helps in decision making, especially regarding challenging surgical procedures.