IMAGING OF INFRATENTORIAL BRAIN TUMORS.pptx

Imaging of Infratentorial brain tumors.

1. INFRATENTORIAL BRAIN TUMORS

2. ANATOMY OF POSTERIOR CRANIAL FOSSA Anterior Postero -laterally

3. Infratentorial tumors Common in children. In children: Cerebellar astrocytoma (1/3 rd ) and Medulloblastoma(1/3 rd ) > Brain stem gliomas (1/4 th ) > Ependymoma (1/8 th ) Adults: Mostly extra-axial. Schwannoma> Meningioma > Epidermoid. Intra-axial neoplasm: Metastasis> Hemangioblastoma>Glioma

4. IMAGING Primary imaging modality : Magnetic resonance imaging (MRI). Superior delineation of the extent of tumor. Computed tomography: Better demonstration of small or subtle calcifications within tumors.

5. Determine whether the mass is intra-axial or extra-axial in location. Features suggesting that the mass is extra-axial include: Bone and meninges Dural tail sign. Erosion, invasion or destruction of adjacent bone. Hyperostosis. Brain parenchyma Absence of claw sign. Intervening cortex between mass and white matter. Subarachnoid space: CSF cleft sign. Widening of adjacent subarachnoid space/cistern. Intervening pial arteries/veins.

6. Classification of Infratentorial tumors Location Tumors Cerebellar hemisphere and vermis Medulloblastoma Ependymoma Pilocytic Astrocytoma Hemangioblastoma Atypical teratoid/rhabdoid tumor Metastasis Dysplastic Cerebellar Gangliocytoma Rare tumors (Glioblastoma multiforme, Gliosarcoma) Brainstem and cervicomedullary junction Brainstem Gliomas Primitive Neuroectodermal Tumor (PNET) Rare tumors (Ganglioglioma)

7. Location Tumors Cerebellopontine angle and internal auditory canal Vestibular Schwannoma Meningiomas Epidermoid and dermoid Facial nerve schwannomas Metastatic disease Primary exophytic parenchymal neoplasms Arachnoid Cyst Rare (endolymphatic sac tumor , lipoma, chordoma, melanocytoma, paraganglioma) Fourth Ventricle Medulloblastoma Ependymoma Epidermoid Choroid plexus papillomas Subependymoma Posterior Fossa and skull base Paraganglioma Meningioma Schwannoma

8. Cerebellar hemisphere and vermis

9. Medulloblastoma Malignant primitive neuroectodermal tumor. Midline tumors Most common site: Vermis and Inferior medullary velum. Less common: Cerebellar hemisphere(Older patients) Most common malignant posterior fossa tumor in children(one-thirds of childhood pediatric tumors). Age group: 5-15 years. Clinical presentation: With features of raised intracranial pressure. CSF seeding and Leptomeningeal metastatic spread +.

10. Histologically Defined Medulloblastomas: Classic medulloblastoma and Medulloblastoma histopathologic variants: (1) Desmoplastic/nodular medulloblastoma. (2) Medulloblastoma with extensive nodularity. (3) Large cell/anaplastic medulloblastoma. Genetically Defined Medulloblastomas • WNT-activated medulloblastoma • SHH-activated medulloblastomas ○ TP53 mutant ○ TP53 wild-type • Non-WNT/non-SHH medulloblastomas ○ Group 3 medulloblastoma ○ Group 4 medulloblastoma

11. Imaging features Well-circumscribed midline mass filling the fourth ventricle. Midline extension through the foramen of magendie into the cisterna magna may occur. Lateral extension is uncommon. Peritumoral edema. Obstructive hydrocephalus with periventricular accumulation of CSF(Best delineated on FLAIR.) Calcification + (in 20%). Cystic and necrotic degeneration common in adult MBs.

12. Imaging features CT Isodense or moderately hyperdense. Strong but heterogeneous enhancement on CECT. MRI Isointense or hypointense on T1WIs and T2WIs. Signal heterogeneity on T2-WI due to cysts, hemorrhage , necrosis and clump-like calcifications. Moderate enhancement. High signal intensity on DWI. Low ADC. Proton MR spectroscopy : Show taurine, detectable at short echo time, and a massive choline peak.

13. Ependymoma Age group: 1-5 years. Arise from differentiated ependymal cells lining the fourth ventricle and foramina of Luschka. Can present within the cerebellopontine angle. Clinical features: Fill and distend the fourth ventricle, resulting in hydrocephalus and symptoms of nausea and vomiting. Insinuate around and within structures, encasing vessels and lower cranial nerve --> Cause cranial neuropathies.

14. Ependymoma 4 types: Ependymoma (grade 2) Anaplastic ependymoma (grade 3)(Greater incidence of CSF dissemination at the time of diagnosis and a poorer prognosis) Subependymoma (grade 1), and Myxopapillary ependymoma (grade 1).

15. imaging CT : Irregular and lobulated isodense masses with calcification (up to 45%). MRI: Heterogeneous with T1 hypointensity . T2 iso/hyperintensity and heterogeneous enhancement. Demonstrate intratumoral microcysts, necrosis or hemorrhage . Peritumoral edema usually absent. Following contrast administration: Inhomogeneous enhancement +. Rarely, ependymomas do not enhance. CSF seeding is found in small percentage of the cases, less frequent than PNET.

16. Typical feature: Extension through the foramina of Luschka into the cerebellopontine angle (15%) and/or Inferiorly through the foramen of Magendie (60%) onto the posterior aspect of the upper cervical cord. MB: More bulbous extension rather than thin tongues of tissue through the foramina as in ependymomas. Proton MR spectroscopy: Elevated choline Reduced N- acetylaspartate (NAA) imaging

17. Subependymoma Biologically benign, slow-growing intraventricular tumors. Origin: Astrocytes and ependymal cells. Mean age ~ 50 years. Location: Fourth ventricle(floor)- MC Lateral ventricle(attached to the septu m p ellucidum) Third ventricle and even in the spinal cord.(Rare) Rarely produce symptoms. Hydrocephalus is the most common presentation.

18. SUBEPENDYMOMA CT: Fourth ventricular subependymomas : Variable density compared to gray matter with calcifications(50-100%) and enhancement. Lateral ventricle subependymomas : Vary in density. More often hypodense. Do not enhance and Calcifications in less than 10 percent.

19. SUBEPENDYMOMA MRI: Fourth ventricular subependymomas : Origin from the floor of the fourth ventricle. Extension through the foramina of Luschka or Magendie. Hypointense or isointense to gray matter on T1. Isointense or hyperintense to gray matter on T2. Heterogeneous enhancement. Do not demonstrate paraventricular extension, unlike other ventricular tumors. PET using 18F-FDG : Hypometabolic tumor (Low cellular density and slow growth.)

20. Pilocytic Astrocytoma Benign tumors of CNS (WHO Grade 1). Specific histologic type. Present in first two decades of life. Sites: Cerebellum(vermis or hemisphere) Hypothalamus Optic nerve optic chiasm. Brain stem Cerebral hemispheres.(Less common)

21. Imaging Cystic mass with an enhancing mural nodule or a solid-cystic mass. MRI: Variable and non-specific. Solid portion is hypointense on T1WI (higher than CSF intensity) and hyperintense on T2WI. MR with contrast shows enhancement of the solid component. Absent accompanying edema or intratumoral calcification. Proton MR spectroscopy: Lactate peak.

22. Atypical Teratoid/Rhabdoid Tumor Extremely rare. Highly malignant neoplasm of undetermined histogenesis. May arise at any site within the central nervous system. Non-specific features. Large lesions at presentation, with moderate- to- marked surrounding edema. CT: Solid(hyperdense) or mixed lesions. Areas of necrosis, cyst formation, hemorrhage and calcification may occur with varying pattern of enhancement.

23. MR: Hypointense on T1WI and iso-hypo on T2WI with inhomogeneous enhancement. Meningeal enhancement and spinal tumor seeding common . Lower ADC values in MB and AT-RT compared with juvenile pilocytic astrocytomas and ependymomas. Restricted diffusion + Not in the midline + CPA involvement: AT-RT > MB

24. Hemangioblastoma Benign (WHO grade 1) tumor. Sporadic or manifestation of von Hipple -Lindau disease (VHL) in 25 percent. Location Cerebellum (83-86%) Brain stem (2-5%) Spinal cord (3- 13%) Cerebrum (1.5%). Other manifestations of VHL: Retinal angioma Renal cell carcinoma Adrenal pheochromocytoma Benign cysts in the lungs, liver, kidneys, and pancreas.

25. imaging NCCT: Well marginated, cystic lesion(hypodense) with a mural nodule( isodense with the brain parenchyma). Edema is usually absent. The mural nodule abuts the pial surface - Shows strong homogeneous contrast enhancement. Solid hemangioblastomas - Hyperdense on NCCT with strong homogeneous enhancement.

26. MRI: Cystic component of hemangioblastoma: Iso- or slightly hyperintense relative to CSF on T1WI and hyperintense on T2WI. The nodule - Hypointense on T1WI and hyperintense on T2WI with intense enhancement. DWI: Solid portions give low signal with increased ADC values. Extensive hypervascular tumor. Flow voids within and at the periphery of the tumor.

27. Perfusion MR imaging : High rCBV ratios in these lesions (around 11)- Significantly higher than metastases (around 5). Cerebral angiography: Dilated feeding arteries and a prolonged tumoral blush corresponding to the solid portion. Main differential diagnosis – Pilocytic astrocytoma- Typically occurs in younger age group.

28. Metastases Most common infratentorial intra-axial neoplasms in the adult population. Well-defined round masses. Nodular or ring enhancement (due to central necrosis). Multiple. Primary in adults : Lung and breast carcinoma > Melanoma > Renal cell carcinoma > Thyroid carcinoma > Gastrointestinal malignancies.

29. CT: Typically hypodense. MRI: Hypointense on T1WI and hyperintense on T2WI. Varying pattern of enhancement. Edema + Areas of hemorrhage and calcification - Variable signal on T2WI.

30. imaging Increased T1 signal intensity before contrast administration: Melanoma, kidney, lung, choriocarcinoma, and bowel (because of the presence of mucin). MR spectroscopy: Significantly elevated choline and very low NAA ( may represent contamination from adjacent tissues due to partial averaging). High lactate and lipids. The tissues surrounding the enhancing mass usually are normal by spectroscopy (unlike high grade gliomas).

31. Dysplastic Cerebellar Gangliocytoma (Lhermitte-Duclos) Rare space occupying lesion of cerebellum. Clinical presentation: Headache and hydrocephalus. Range in age from newborn to 74 years, with an average age of 34 years.

32. IMAGING Reflect the generally benign biologic behavior of these lesions. NCCT: Hypodense May be isodense . Calcification +/-. MRI: Cerebellar mass typically involving one hemisphere. Highly characteristic folial pattern (laminated, corduroy, lamellar, or striated ). Do not enhance(Majority).

33. BRAINSTEM AND CERVICOMEDULLARY JUNCTION

34. Brainstem Gliomas Location: Pons(MC) and less frequently in the medulla. Clinical features: No sex predilection. Age group: 3-10 years. Multiple cranial nerve palsies, pyramidal tract signs, ataxia and nystagmus.

35. Brainstem Gliomas NCCT: Subtle enlargement or morphologic distortion of brainstem on CT. Contrast enhancement -patchy, irregular, homogeneous or absent. CPA cistern widening due to exophytic component producing extra-axial effect. MR Imaging: Useful for diagnosis and localization of the tumor. Diffuse glioma: Poorly defined regions of low intensity on T1WI and high intensity on T2WI. Intratumoral heterogeneity +/-.

36. Brainstem Gliomas The basilar artery often engulfed by the anterior extension of the tumor. Contrast enhancement + in one-half of the cases - Often focal and nodular. Focal brainstem gliomas : Well circumscribed/ sometimes markedly exophytic. Dorsally exophytic lesions are grossly multicystic and often enhance intensely. Other subtypes of focal gliomas : Tectal plate and cervicomedullary glioma.

37. CEREBELLOPONTINE ANGLE AND INTERNAL AUDITORY CANAL

38. CPA tumors Frequent and represent 6–10 percent of all intracranial tumors. Most common: Vestibular schwannomas and meningiomas(~ 85–90 percent of all CPA tumors.)

39. Vestibular Schwannomas Benign and slow growing. NF-2 - Bilateral CN VIII schwannomas. Malignant degeneration – Rare- Associated with NF-1. Arise from the inferior vestibular nerve within the internal auditory canal (IAC). Clinical feature: Hearing loss or tinnitus. Can be: Entirely intracanalicular Intracanalicular and cisternal components(‘‘Ice-cream cone’’ tumor) Purely intracisternal.(Rare).

40. Histologically: Antony type A tissue(Compact)- low T2 signal relative to CSF. Antony type B tissue(Loose textured). MRI: Larger lesions: Heterogeneous appearance(internal necrosis/cyst formation). Higher signal intensity than CSF(Hemorrhagic byproducts, necrotic material, or colloid-rich fluid). Predominance of Antoni Type B cells. Associated Extramural(arachnoid) cysts +.

41. IAC involvement: Flaring of the porous acousticus . Expansion of the IAC. Acute angle with the dura.

42. Low T2 signal intensity in vestibule. (Larger lesions) Small lesions - Homogeneous enhancement. Larger lesions: Heterogeneous enhancement( cystic spaces). Degeneration of the vestibular nucleus. Extent into the cochlea and “dural tails” of enhancement. After surgery, linear or somewhat nodular enhancement in the IAC may be seen.

43. Meningiomas Second most common CPA tumor. Extra-axial neoplastic lesion. 10 percent of all intracranial meningiomas arise in the posterior fossa. Origin: Arachnoidal cap cells. Arise from the posterior petrous surface or the underside of the tentorium. Intense enhancement is the rule. Relative T2 hyposignal - Characteristic of most of the lesions(especially transitional and fibroblastic varieties)

44. IMAGING NCCT: Hyperdense with focal areas of calcification. Dural tail(not pathognomonic) Bony reaction Obtuse angle with the dura. Center of the lesion located away from the IAC. Necrosis and cystic degeneration uncommon. May originate within the internal auditory canal, or even within the labyrinth. Differentiate from schwannoma

45. Epidermoid and Dermoid Congenital/ developmental masses. Arises from ectodermal heterotopia. Both cysts are lined with stratified squamous epithelium. Dermoids : Additional mesodermal elements such as hair, sebaceous and sweat glands +.

46. Epidermoid CYST More common. Become quite large before becoming symptomatic. Extension into the middle cranial fossa results in a dumb-bell shape. Spread along the basal surfaces. Location: CPA > Parasellar region. CT: CSF density and do not enhance. Calcification + Can have a faintly enhancing border.

47. Epidermoid CYST MRI: Isointense to CSF on both T1 and T2WI.(Cholesterol in solid/crystalline state). The adamantinomatous craniopharyngioma typically contains cholesterol in liquid state. Lamellated appearance because of surface desquamation. Do not enhance ( Minimal rim enhancement occurs in approximately 25 percent of cases.) Malignant transformation of an epidermoid (squamous cell carcinoma) is rare - Considered if follow-up scans show significant increase in the amount of enhancement.

48. ‘‘White epidermoid’’ : Hyperintense on T1WI, and hypointense on T2WI High protein content, hemorrhage or the presence of saponified keratinized debris or cholesterol in the liquid state. DD’s: Dermoid Lipoma. Chemical shift artifact absent. Fat saturation pulse sequence will not suppress the high signal in epidermoid. EPIDERMOID

49. Arachnoid cysts Lamellate appearance. Insinuate rather than displace. On FLAIR: Mixed iso- to hypersignal intensities, but with poor demarcation. DWI: Hyperintense due to restricted diffusion (low ADC) Useful for detecting postoperative residual epidermoid. EPIDERMOID

50. Dermoid cyst Extremely rare. Midline lesions. Locations: Parasellar , Frontobasal region or posterior fossa (vermis or fourth ventricle). CT: Fat density Do not enhance on contrast administration. Associated with bone defect in nasofrontal or occipital region- Dermal sinus tract.

51. MRI: Unruptured cysts – Hyperintense. Heterogeneous signal intensity on T2WI(hypo- to hyperintense.) Chemical shift artifact + DD: Lipoma Rupture of the cyst --> Chemical meningitis. Fat-like leptomeningeal and intraventricular deposits. Less lobulated than lipomas. Displace blood vessels and neural structures(encasement in lipomas.) DERMOID

52. Arachnoid cysts Congenital, benign, intra-arachnoid pouchlike lesions filled with normal CSF. Origin : Uncertain. Usually supratentorial(70 percent in the temporal fossa, mostly on the left side,anterior to the temporal poles.) 10 percent in the posterior fossa(CPA). Clinical presentation: Mostly: Asymptomatic and incidental finding. Compromise of cranial nerve functions. Spontaneous or traumatic intracystic hemorrhage.

53. IMAGING Attenuation and signal intensities of uncomplicated arachnoid cysts exactly match those of CSF on all sequences. No enhancement. DD: Epidermoid cyst. Complete suppression of signal intensity on FLAIR sequence. DWI: Lack of diffusion restriction. ARACHNOID CYST

54. Facial Nerve Schwannomas Arise anywhere along the course of the nerve from the CPA to the stylomastoid foramen. Arising in the IAC or CPA – Difficult to differentiate from vestibular schwannoma. Enhancing component extending along the labyrinthine segment of the facial nerve to the geniculate ganglion. FACIAL NERVE SCHWANNOMA

55. Cerebellopontine Angle/Internal Auditory Canal Lipomas Rare lesions. Mesodermal inclusions. MRI: T1 hyperintense. DD: Hemorrhagic masses.

56. Metastatic Disease Leptomeningeal( Diffuse, nodular or mass-like) OR Parenchymal (brainstem, cerebellum). Breast and lung primaries predominate.

57. Primary Parenchymal Neoplasms Infiltrative intraaxial component with an exophytic component resulting in a CPA mass. Childhood neoplasms - MB, astrocytoma(MC), and ependymoma.

58. Endolymphatic Sac Tumor Papillary adenomatous tumors. Origin: Endolymphatic sac(Distal portion of the vestibular aqueduct of the petrous bone.) Sporadic Frequent in von Hippel–Lindau disease. Hypervascular tumor . CT: Destruction of retrolabyrinthine petrous bone. Geographic or moth-eaten margins. Intratumoral spiculated or reticulated bone.

59. Endolymphatic Sac Tumor MRI: Heterogeneous on both T1 and T2WIs. Focal high signal intensity due to subacute hemorrhages. Low signal intensity due to calcification or hemosiderin. Blood-filled cysts and protein-filled cysts - Hyperintense on T1 and T2WIs. Heterogeneous enhancement. Flow voids within and around( > 2 cm in diameter) - Hypervascular .

60. Paraganglioma Extension of paragangliomas arising at : Jugular foramen (glomus jugulare tumor) or Middle ear (glomus tympanicum tumor) Benign, locally aggressive tumor CT: Destroy the bones of the skull base with a moth-eaten erosion pattern.

61. MRI: Highly vascular soft tissue lesions. Mix of multiple punctuate and serpentine signal voids (High-flow intratumoral vessels) Foci of high-signal intensity ( Intratumoral hemorrhages with methemoglobin). Perfusion MR imaging: High vascularity patterns with high rCBV . Conventional angiography: Intense tumoral blush with enlarged feeding arteries. Salt-and-pepper appearance

62. FOURTH VENTRICLE

63. Choroid Plexus Papilloma Origin: Choroid plexus epithelium. Most frequent in first year of life. Hydrocephalus. Common site of origin : Lateral ventricles. Commonest site of adult CPP: Fourth Ventricle

64. Choroid Plexus Papilloma Well-defined lobulated masses. Enlargement of the involved ventricles. Foci of small hemorrhages and calcification may be found. Anaplastic papillomas , frequently invade the brain – Difficult to differentiate from carcinomas. Metastasis through CSF pathways is common for both anaplastic papillomas and carcinomas.

65. Choroid plexus papilloma NCCT: Typically isodense to hyperdense with occasional foci of calcification. Homogenous enhancement is seen following intravenous contrast. Anaplastic CPP: Invade the ependyma and grow into the surrounding white matter, producing vasogenic edema. Irregular in outline and closely resemble CPC. Hydrocephalus.

66. Choroid plexus papilloma MRI: Either homogeneous or heterogeneous cauliflower-like tumors. Iso/hypointense on T1 and T2WI and strongly enhance after contrast injection.(Unless highly calcified). Areas of low signal intensity(Calcifications). Foci of high signal intensity( Intratumoral hemorrhage). Flow voids(high flow vessels).

67. Choroid plexus carcinoma More aggressive than papillomas . Irregular in contour. NCCT: Mixed density on pre-contrast study. Variable enhancement. Cysts and hemorrhage is frequent. Grow through the ventricular wall into the brain with associated edema .

68. Posterior fossa tumor Location Cerebellar hemispheres Brainstem Fourth ventricle Foramen of Luschka/CPA What is the ADC What is the ADC What is the ADC Low ADC High ADC Low ADC High/Intermediate ADC Low ADC Almost extraaxial Extra-axial +/- multiple enhancing nodules Medulloblastoma SHH Desmoplastic Medulloblastoma SHH Solid and /or cystic areas Pilocytic astrocytoma Not enhancing <3 years Multiple enhancing nodules Enhancing >3 years Cystic/Hemorrhagic/Calcific areas Age < 3 years Group 4 MB or AT-RT Desmoplastic Medulloblastoma SHH Medulloblastoma all the subgroups Ependymoma AT-RT Medulloblastoma WNT Yes No

69. references AIIMS-MAMC-PGI IMAGING COURSE SERIES DIAGNOSTIC RADIOLOGY Neuroradiology Including Head and Neck Imaging. OSBORN’S BRAIN IMAGING, PATHOLOGY, AND ANATOMY, SECOND EDITION.

70. Thank you