Mastoid diseases imaging

Imaging in diseases of mastoid by Dr. Gobardhan Thapa

1. IMAGING IN DISEASES OF MASTOID Dr. Gobardhan Thapa MD Radiodiagnosis NAMS, Bir hospital

2. Presentation outlines Normal anatomy Imaging modalities Common pathologies conclusions

3. Temporal bone anatomy

4. The squama ( squama temporalis ): forms the anterior and upper part of the bone; scale like thin and translucent. Mastoid portion (pars mastoidea ): forms the posterior portion of the bone. Petrous portion (pars petrosa { pyramis }): pyramidal and is wedged in at the base of the skull between sphenoid and occipital bone. Contains organ of hearing. Parts of the temporal bone

5. 4. Tympanic part (pars tympanica ): Curved plate of bone lying below the squama and infront of the mastoid process. 5. Styloid process ( processus styloideus ): slender, pointed and of varying length; it projects downward and forward, from the undersurface of the temporal bone.

6. Mastoid Part of Temporal Bone Posterior part of the temporal bone. Trabeculated and pneumatized to a variable degree and contains mastoid antrum T he m a s t o i d i s n am e d f o r t h e Gre e k wor d m a s t o s m e a n i n g b r e a s t , and e i d o s m e a n i ng r e s e mb la n c e . T h i s i s r e f l ect i ve o f t h e n i pp l e- l i ke shape o f th e mast o i d p ro c e s s .

7. Embryology of mastoid The first pharyngeal pouch -> tubotympanic recess . tubotympanic recess -> eustachian tube, tympanic cavity, mastoid antrum , and their epithelial lining. The middle ear cavity and mastoid antrum are fluid filled until birth. The mastoid air cells develop as saclike extensions from the mastoid antrum , commencing around the time of birth and continuing for several years.

8. Mastoid Part of Temporal bone Surface: External and Internal Border: Posterior and Superior tegmen mastoideum – roof of the mastoid

9. External Surface of Mastoid Part Continuous to external part of squamous portion posteriorly appoximately 1.5 cm behind supra-mastoid crest Rough surface Continuous as mastoid process inferiorly

10. Mastoid Process Bony prolongation at inferior portion of mastoid part External aspect provides attachment to Sternocleidomastoid muscle Splenius capitis muscle and Longissimus capitis muscle are attached to it behind sternocleidomastoid muscle

11. Mastoid Foramen Foramen present on external surface at the junction of mastoid part and occipital bone. Opening to inner surface of mastoid part Lodges emissary vein which will communicate posterior auricular vein exteriorly with sigmoid sinus interiorly. Also allow passage of meningeal branch of occipital artery.

12. Internal Surface of Mastoid Process Consists of sigmoid sulcus which lodges sigmoid sinus Groove for Occipital Artery Lodges occipital artery

13. Mastoid segment of the facial nerve courses through the medial portion of the mastoid bone until it exits the skull through the stylomastoid foramen and enters the parotid gland. The chorda tympani branches off of the mastoid segment of the facial nerve and returns to the middle ear cavity via the canaliculus of the chorda tympani. Fig. mastoid segment of the facial nerve canal (black arrowheads) is seen in its vertical course. Parts of the lateral SCC and superior SCC are seen. The mastoid antrum and jugular foramen are seen.

14. Mastoid Antrum Air containing space in antero -superior part of mastoid. Variable size.

15. Mastoid Antrum : Boundaries Roof: Tegmen antri , which separates mastoid antrum from middle cranial fossa Lateral Wall: Squamous part by Macewen Triangle. Medial Wall: formed by petrous bone and is related to Posterior semicircular canal Endolymphatic sac Dura of posterior cranial fossa Macewan /Supra- Meatal Triangle

16. Mastoid Antrum : Boundaries Anterior Wall: communicates with attic ( epitympanum ) through aditus and is in relation with facial nerve canal, middle ear and deep bony external auditory canal Posterior Wall: communicates with mastoid air cells; Sigmoid sinus curves downwards Floor: communicates with mastoid air cells; other deeper relations from medial to lateral sides: Jugular bulb medial to facial canal Digastric ridge which gives origin to posterior belly of digastric muscle Origin of sternocleidomastoid muscle

17. Korner’s / Petrosquamous Septum petrosquamosal suture – may persist as bony plate called Korner’s septum. Separates superficial squamosal cells from deep petrosal cells. Mastoid antrum can be entered into only after removal of Korner’s septum. If not recognized, it leads to incomplete removal of disease during mastoidectomy

18. Radiography of the mastoid process Imaging objectives: Are the mastoids cellular or acellular ? If they are cellular, how are cells distributed and do they extend to their normal anatomical limits? If the mastoid process is acellular , is it sclerotic or diploetic ? Is the cortical bone thin or thick? Are both the mastoid processes symmetrical? Asymmetry is usually the result of pathology early in life that interfered with the normal anatomical extension of the mucosa of the antrum . Are there any signs of bone destruction? Is the mastoid cavity preserved? Can the sinus plate and the dural plate be visualized in their normal positions? Is there any cholesteatoma formation?

19. Frontal-occipital 35 degrees caudad Position of patient and cassette: Head adjusted to bring the external auditory meatuses equidistant from the table , so that the median sagittal plane is at right-angles to, and in the midline of, the table. Chin depressed so that the orbito-meatal line is at right-angles to the table.

20. Direction and centring of the X-ray beam: A caudal angulation employed, such that it makes an angle of 35 degrees to the orbito-meatal plane . The beam is centred midway between the external auditory meatuses .

21. Submento -vertical Supine Shoulders raised and the neck hyperextended to bring the vertex of the skull in contact with the grid cassette or table. H ead 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 .

22. Erect The patient sits a short distance away from a vertical Bucky. neck hyperextended to allow the head to fall back until the vertex of the skull makes contact with the centre of the vertical Bucky. The remainder of the positioning is as described for the supine technique.

23. Direction and centring of the X-ray beam: Central ray is directed at right-angles to the orbito-meatal plane and centred midway between the external auditory meatuses .

24. Mastoid – lateral oblique 25 degrees caudad Position of patient and cassette: Sitting position facing the erect Bucky. Head then rotated, such that the median sagittal plane is parallel to the Bucky and the inter-orbital line is perpendicular to the Bucky .

25. Direction and centring of the X-ray beam: A 25-degree caudal angulation is employed and centred 5 cm above and 2.5 cm behind the external auditory meatus remote from the cassette .

26. Mastoid – profile Position of patient and cassette: The patient lies supine on the table, with the orbito-meatal baseline perpendicular to the table top . From a position with the median sagittal plane perpendicular to the table, the head is rotated through an angle of 35 degrees away from the side under examination. The vertical tangent to the skull should now be at the level of the middle of the mastoid process under examination, so that the mastoid process is in profile .

27. Direction and centring of the X-ray beam: The central ray is angled caudally so that it makes an angle of 25 degrees to the orbito-meatal plane and is centred to the middle of the mastoid process on the side under examination . Collimate tightly around the mastoid process.

28. CT High-spatial-resolution CT (HRCT) - best method for evaluating bone and air space anatomy and disorders. MDCT - provides improved quality of the axial source images as well as two- and three-dimensional (2D and 3D) reconstructions. Multiplanar CT reformations can display the complex anatomy of the temporal bone in all planes while exposing the patient to radiation only once . Usually acquired with thin sections (0.5-1 mm) and special bone algorithms for high detail.

29. Fig. CT axial Mastoid antrum level . The aditus ad antrum ( aditus ) is seen connecting the mastoid antrum and epitympanum . Portions of the posterior (PSSC) and superior (SSSC) semicircular canals and their shared common crus are visualized

30. MRI Primarily for soft tissue entities. Much better than CT in characterizing the CSF, brain, and cranial nerves.

31. Mastoid bone pathologies Congenital malformations Infection Neoplasms Fractures/Trauma Post surgical changes

32. Congenital malformations Air cells variation – poorly pneumatized ( diploic ), non- penumatized (sclerotic). Congenital cholesteatoma . Fig. Axial view of the temporal bone showing:  a   well pneumatised mastoid regions ,  b   poorly pneumatised mastoid air cell ,  c   non- pneumatised mastoids (sclerotic type).

33. congenital cholesteatoma {mass of reactive cells } ( Kazahaya & Potsic ) subdivision into four stages. Stage I : only one quadrant of tympanic membrane affected; no ossicular involvement or mastoid extension. Stage II : multiple quadrants affected; no ossicular involvement or mastoid extension Stage III : ossicular involvement; includes erosion of ossicles and surgical removal for eradication of disease; no mastoid involvement. Stage IV : mastoid extension (regardless of findings elsewhere).

34. Infection: Acute Otomastoiditis appears as middle ear and mastoid air cell opacification with fluid and nonspecific debris . Subacute otitis media shows similar findings in the mastoid air cells and middle ear, with the additional finding of focal or diffuse mucosal thickening .

35. Coalescent Mastoiditis : Spread of infection to the bone with erosion of the mastoid septae , lateral mastoid cortex, or cortex over the sigmoid plate. HRCT - for evidence of bone erosion. MRI - for detecting suspected complications such as epidural abscess, subdural empyema, petrous apicitis , or thrombosis of the sigmoid sinus . Fig. Axial CT image of coalescent mastoiditis in a 7-year-old boy with right otalgia and fever demonstrates erosion of the inner and outer cortices of the mastoid (arrows), as well as marked demineralization of the bony septations within. Inflammatory changes are also seen within the middle ear (∗).

36. Complications of otomastoiditis Acute Mastoid Osteitis Destruction of the bone of the mastoid air cells and a subperiosteal abscess may develop. Fig. Otomastoiditis and subperiosteal abscess . Axial HRCT of the left temporal bone - fluid in the middle ear cavity and mastoid air cells , with osseous erosion.

37. Subperiosteal abscess: most commonly in the post-auricular region; zygomatic abscess, Bezold's abscess, Retropharyngeal or parapharyngeal abscess . Subacute ('masked') mastoiditis : incompletely treated AOM after 10-14 days of infection.

38. Bezold abscess Bone defect at the mastoid tip medial to the insertion of the posterior belly of the digastric muscle (digastric notch). Inflammatory changes then directed inferiorly deep to the sternocleidomastoid muscle by the fascial planes. Fig. Coronal contrast-enhanced CT image of Bezold abscess in a 7-year-old child with acute ear infection. Image shows a rim-enhancing collection below the mastoid tip compatible with a Bezold abscess (∗∗). Also note thrombus in the right sigmoid sinus (arrow) .

39. Intracranial complications of acute mastoiditis dural venous sinus thrombosis, most commonly the sigmoid and transverse sinuses, epidural abscess, subdural empyema, meningitis, and brain abscess

40. Petrous apicitis in pneumatized petrous apex (present in 30% of the population). septal and cortical destruction, osteitis , and adjacent meningeal inflammation. Close proximity of the fifth and sixth nerves to the petrous apex - can develop sixth nerve palsy and deep retro-orbital pain in the V1 distribution in association with otomastoiditis and petrous apicitis => Gradinego syndrome .

41. Imaging findings: include opacification of an aerated petrous apex with fluid levels and destruction of the inner septations or the cortex. On MR images, meningeal enhancement is better appreciated. Fig. left petrous apicitis . Contrast MRI – irregular enhancement of left petrous apex Fig. left petrous apicitis . A region of irregular lytic destruction in the left petrous apex

42. Chronic oto-mastoiditis Follows repeated bouts of otitis media - nonspecific opacification of the middle ear and mastoid air cells by granulation tissue and effusion . Reactive sclerosis results in thickening of the bony septa of the mastoid. If chronic otomastoiditis occurs during maturation of the mastoid during childhood , there will be a gradual reduction in the number of mastoid air cells, resulting in poorly developed mastoids .

43. Fig. Right chronic otomastoiditis . Right middle ear soft tissue opacity with corresponding ossicular destruction . Sclerosis and loss of aeration of mastoid air cells.

44. Cholesteatoma conglomerate mass of reactive cells involved in a localized chronic inflammatory process. lined by stratified keratinizing squamous epithelium with subepithelial fibroconnective or granulation tissue and keratin debris . clinically problematic because of their growth over time , the osseous erosions they cause, and their tendency to recur after resection.

45. Most cholesteatomas are intratympanic . Very rarely they may occur in the mastoid. CT: rounded, expansile, soft tissue mass, with erosion adjacent bones. Osseous erosion - may lead to facial nerve canal dehiscence, labyrinthine fistulas, and dehiscence of the tegmen tympani with or without meningoencephalocele formation.

46. “ automastoidectomy ” appearance mural cholesteatomas drain their cystic contents through the tympanic membrane into the EAC, with only the matrix lining remaining. Characteristic extensive bone destructive process in the middle ear/mastoid resembling a surgical mastoidectomy cavity. Axial CT image of automastoidectomy in a 51-year-old man with a history of longstanding chronic otitis media on the left. Image demonstrates a large cavity (∗) in the middle ear and mastoid antrum , with nonvisualization of the ossicles . There is a small amount of residual inflammatory soft tissue. There is no history of surgery.

47. Differentiation of cholesteatoma from a chronic otitis media may be impossible on CT owing to similar appearance of the entities and lack of bony destruction with small cholesteatomas . Standard MRI sequences cannot differentiate cholesteatomas from other inflammatory lesions. However, half-Fourier acquisition single-shot turbo-spin echo (HASTE) diffusion-weighted sequences - helpful in detecting cholesteatomas larger than 5 mm. Cholesteatomas will appear hyperintense on diffusion-weighted imaging (DWI ). Ref: Neuroradiology of cholesteatomas . Barath et al, AJNR, 2011 Feb;32(2):221-9.

48. Neoplasms Benign : Osteomas rare benign tumors that are often incidentally found on CT imaging. commonly located at the tympanosquamous suture within the EAC can also arise in the mastoid process unilateral and solitary pedunculated hyperdense masses on CT Often these lesions are clinically asymptomatic and do not require surgery Fig. CT - pedunculated osteoma (marked with an arrow) arising from right mastoid bone

49. Lipoma Facial nerve lipoma . Incidental detection of focal fat in the distal mastoid segment of the left facial nerve (arrows), bright on T1- (A) and T2-weighted (B) images in a patient being evaluated for dizziness. Rare benign neoplasms in this region.

50. schwannoma Facial nerve schwannomas – rare. Can occur along the entire course of the facial nerve but most commonly involve the geniculate ganglion ; rarely in the mastoid segment. Classic MR features include a fusiform mass with T1 hypo- to isointense signal, T2 hyperintense signal, and avid enhancement along the facial nerve. Modern MR and CT techniques - variety of appearances, including “ dumbbell shape ” in the CPA-IAC, multilobular morphology in the tympanic segment, and an “ invasive ” appearance in the mastoid segment. mastoid-segment schwannomas may also require following the nerve into the parotid gland Fig. facial nerve schwannoma involving the right mastoid segment of the facial nerve canal. axial T1-weighted postcontrast MR image ( left ) shows homogeneous enhancement of the mass ( between arrows ). The bone algorithm CT ( right ) at the same level shows focal enlargement of the descending segment. ( between arrows ). Ref: The Many Faces of Facial Nerve Schwannoma . Wiggins et al,   American Journal of Neuroradiology  March 2006, 27 (3) 694-699 ;

51. Cholesterol granulomas usually in the middle ear and mastoid air cells and less commonly in the petrous apex. Characteristically expansile with hyperintense signal on T1- and T2-weighted images. slow-growing collections and are nonneoplastic Mastoid granulomas : asymptomatic or headache

52. Fig. cholesterol granuloma T1- (left) and T2- (right) weighed axial MRI - well-defined , high-signal-intensity, soft-tissue mass protruding to the left posterior fossa . The left sigmoid sinus (arrow) was compressed by the cholesterol granuloma , compared with the normal right sigmoid sinus (arrowhead). Fig. cholesterol granuloma . CT - large soft-tissue mass in the left temporal region protruding to the posterior fossa with bone erosion. Fig. H&E stain reveals cholesterol clefts, hemosiderin deposits, and granulomatous inflammation with giant cells. Ref: A Large Mastoid Cholesterol Granuloma Eroding the Dura and Sigmoid Sinus. Hsieh et al, J Cytol Histol 5: 236.

53. Malignant Neoplasms Primary malignant neoplasms of the temporal bone are relatively uncommon; Most common - squamous or basal cell carcinoma - most commonly involve the EAC or mastoid region. aggressive when they occur, often extending to the EAC, middle ear cavity, or mastoid air cells, with involvement of the facial nerve and TMJ. Distant metastases are rare for these tumors. Adenocarcinoma can present locally with similar features as squamous cell carcinoma, but lymph node involvement is more common.

54. CT and MRI are considered complementary imaging techniques for evaluation of temporal bone malignancies . CT - highly sensitive in detecting bone erosion , MRI - delineate the tumor extent and differentiate tumor from nonneoplastic soft tissue. Fig. basal cell carcinoma of right ear. A and B, CT shows bone erosion of inferior mastoid and styloid process (arrows).

55. Metastases Metastases of the temporal bone are not uncommon. can spread hematogenously from the breast, lung, stomach, prostate gland, or kidney.

56. Fractures (Traumatic Injuries) Mechanisms Blunt trauma injuries. Penetrating and gun shot injuries. Sport injuries.

57. Battle sign: Postauricular ecchymosis from traumatic rupture of a mastoid emissary vein. Fig. 46-year-old man with head injury A) a subcutaneous hemorrhage in left postauricular region, B) CT: acute epidural hematoma , C) left temporal bone fracture (arrows).

58. Traditional c lassification: by the direction it courses relative to the petrous portion of the temporal bone . Longitudinal temporal bone fractures ( 80-90% of temporal bone fractures) - course parallel to the long axis of the petrous pyramid, whereas transverse fractures course perpendicular to the long axis of the petrous pyramid. Higher risk of facial nerve injury. Complex , with both longitudinal and transverse components

59. Fig. Complex temporal bone fracture in a 26-year-old male trauma patient. Axial HRCT left temporal bone - comminuted oblique fracture involving the left mastoid and petrous segments, left jugular foramen (JF), and left carotid canal (CC). Partial opacification of the left mastoid air cells and middle ear cavity (*) from posttraumatic hemorrhage. Axial CT (a) longitudinal fracture and (b) transverse fracture in two different patients. The longitudinal fracture is parallel to the long axis of the petrous pyramid (arrow, a) and traverses the mastoid portion of the temporal bone. The transverse fracture is oriented perpendicular to the petrous pyramid (arrow, b) and traverses the basal turn of the cochlea (arrowhead, b). a b

60. Newer classification: by Kelly and Tami otic capsule–sparing Fracture : the otic capsule is spared. much more common (94%–97%), results from a temporo -parietal blow, increased incidence of conductive hearing loss due to ossicular injury. otic capsule– violating fracture: otic capsule is violated (3%–6%); results from an occipital blow, higher incidence of facial nerve paralysis (30%–50%), sensorineural hearing loss, and CSF fistula (CSF otorrhea and CSF rhinorrhea ). otic capsule   - dense osseous labyrinth of the inner ear that surrounds the cochlea, the vestibule and the semicircular canals.

61. Post operative imaging Mastoidectomy Mastoiditis , cholesteatoma resection, cochlear implantation, or endolymphatic surgery - resecting variable portions of the mastoid air cells and adjacent structures. Canal wall- up mastoidectomy – exenteration of the mastoid air cells with preservation of the posterior wall of the external auditory canal, creating a mastoid bowl or cavity . Canal wall- down mastoidectomy - performing the same steps as in canal wall- up mastoidectomy , but in addition the posterior wall of the external auditory canal is resected to increase exposure to middle ear contents.

62. Fig. canal wall up mastoidectomy for a patient with history of mastoiditis . Axial CT – intact posterior wall of EAC (arrow) and mastoidectomy bowl (*) Fig. Canal-wall-down mastoidectomy with ossicular preservation. both mastold air cells and posterior wall of the EAC (canal wall down). The ossicles are preserved in this procedure. Postoperative mastoid bowl (M) , with preservation of ossicles (arrows).

63. Radical mastoidectomy for extensive disease of the middle ear cavity with ossicular involvement. removal of the tympanic membrane, malleus , and incus , with attempted preservation of the stapes, in addition to canal-wall-down mastoidectomy . Tympanomastoidectomy mastoidectomy performed in conjunction with a middle ear procedure, such as tympanoplasty and/or ossicular reconstruction. Fig. radical mastoidectomy for extensive middle ear cholesteatoma and ossicular erosion. Axial CT shows a large mastoidectomy bowl (*) with absence of posterior wall of external auditory canal and ossicular chain .

64. Occasionally, the mastoid bowl may be obliterated using bone, cartilage, fat, or hydroxyapatite to minimize the size of the mastoidectomy cavity following canal-wall-down procedures. Otherwise, the mastoid bowl - clear and presence of soft-tissue attenuation material on CT images => may represent granulation tissue or, in the appropriate scenario, recurrent cholesteatoma .

65. Evaluation of recurrent cholesteatoma is an important indication for imaging after mastoidectomy . CT - recurrent cholesteatoma is suspected when there is new bone erosion associated with a soft-tissue focus , although the attenuation characteristics are nonspecific and it can be difficult to differentiate these lesions from granulation tissue.

66. On MR images, cholesteatoma - high T2 and low T1 signal, without central enhancement, while granulation tissue - internal enhancement. Furthermore, cholesteatoma characteristically shows reduced diffusion .

67. Fig. Recurrent cholesteatoma after surgery .  A , Coronal HRCT scan shows the obliterated mastoidectomy cavity ( white arrow ).  B , Coronal FIESTA image distinguishes the slightly hyperintense (to brain) cholesteatoma ( thick white arrow  on  B, C , and  D ) from the strongly hyperintense granulation tissue ( dashed arrow  on  B  and  C ).  C , Coronal contrast-enhanced MR image differentiates as well the nonenhancing cholesteatoma from the strongly enhancing granulation tissue.  D , Coronal DWI with the intensive intralesional diffusion restriction supports the diagnosis.

68. Conclusions: Though a small portion of temporal bone, mastoid can be affected by a variety of pathologies. Conventional radiography may give a initial clue to diagnosis, but rarely used these days. HRCT and MRI, with or without contrast are extensively used to delineate the exquisitely comple x anatomy and related pathologies of mastoid bone.

69. References Gray’s Anatomy for Students , 2/e Clark’s positioning in radiography , 12/e CT and MRI of the whole body , Haaga , 6/e. Imaging Review of the Temporal Bone: Part I. Anatomy and Inflammatory and Neoplastic Processes . Juliano et al; Radiology: Volume 269: Number 1—October 2013 Imaging Review of the Temporal Bone: Part II. Traumatic, Postoperative, and Noninflammatory Nonneoplastic Conditions. Juliano et al; Radiology: Volume 276: Number 3—September 2015 Various internet sources.

70. Thank you