1. SHER-I-KASHMIR INSTITUTE OF MEDICAL SCIENCES SOURA Department of radiodiagnosis & imaging 2. Presentation by Dr SAMEER PEER First Year Post-Graduate student 3. Imaging of temporal bone Anatomy & Pathology 4. CONTENTS 1. INTRODUCTION 2. ANATOMY OF TEMPORAL BONE GROSS ANATOMY RADIOLOGICAL ANATOMY EMBRYOLOGY 3. PATHOLOGY CONGENITALANOMALIES INFLAMMATORY CONDITIONS TRAUMA TUMOR AND TUMOR-LIKE CONDITIONS 4. REFERENCES AND FURTHER READING 5. INTRODUCTION The Temporal bone is a complex structure with tiny bony objects such as the crura of the stapes and canals like the vestibular aqueduct which are less than 1 mm in diameter. These are close to the limits of resolution by imaging. Thus the best possible spatial resolution is essential and discrimination of 24 line pairs per cm can be achieved on the latest CT scanners. This imaging is mostly by CT, for showing bone detail, and MRI, for the inner ear and its central connections. Conventional angiography has been almost replaced by MR angiography or CT angiography. Metabolic imagaing such FDG-PET is being used to overcome the problem of distinguishing recurrent tumor from radiation damage. Radioisotope studies are rarely required to assess the activity of malignant otitis externa. 6. ANATOMY OF TEMPORAL BONE GROSS ANATOMY RADIOLOGICAL ANATOMY EMBRYOLOGY 7. GROSS ANATOMY The temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., squama petrous Mastoid tympanic styloid process. 8. The Squama (squama temporalis).The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent. Mastoid Portion (pars mastoidea).The mastoid portion forms the posterior part of the bone. Petrous Portion (pars petrosa [pyramis]).The petrous portion or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital bone. Directed medialward, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. Tympanic Part (pars tympanica).The tympanic part is a curved plate of bone lying below the squama and in front of the mastoid process. Styloid Procss (processus styloideus).The styloid process is slender, pointed, and of varying length; it projects downward and forward, from the under surface of the temporal bone 9. Left temporal bone. Outer surface 10. Left temporal bone. Inner surface. 11. Coronal section of right temporal bone. 12. Left temporal bone. Inferior surface. 13. ANATOMY OF THE EAR External Ear Middle Ear Internal Ear ( Labyrinth) 14. THE EXTERNAL EAR The auricula ( Lateral surface) 15. Cranial surface of cartilage of Right auricula 16. Muscles of the auricula 17. External and Middle ear opened from Front 18. Horizontal section through left ear ; upper part 19. THE MIDDLE EAR ( TYMPANUM) Right Tympanic membrane 20. 1. Tympanic membrane 2. Umbo 3. Handle of malleus 4. Lateral process 5. Anterior Tympanomalleolar fold 6. Posterior Tympanomalleolar fold 7. Pars Flaccida 8. Anterior Pouch of Troltsch 9. Posterior Pouch of Troltsch 10. Fibrocartilaginous ring 11. Petrotympanic Fissure 12. Auditory Tube 13. Iter chordae posterius 14. Iter chordae anterius 15. Fossa incudius for short crus of incus 16. Prominentia styloidea Inner view of Tympanic membrane 21. View of the inner wall of the Tympanum 22. View from within, behind and above 23. Medial Wall, parts of posterior and anterior walls of right tympanum 24. EAR OSSICLES LEFT MALLEUS 25. LEFT INCUS 26. LEFT STAPES 27. OSSICULAR CHAIN 28. EUSTACHIAN TUBE 29. INNER EAR (LABYRINTH) Right Osseous Labyrinth 30. INTERIOR OF THE RIGHT OSSEOUS LABYRINTH 31. COCHLEA AND VESTIBULE AS VIEWED FROM ABOVE 32. MEMBRANOUS LABYRINTH 33. SEMICIRCULAR CANAL & DUCT ( CROSS SECTION) 34. LONGITUDNAL SECTION THROUGH THE CHOCLEA 35. ORGAN OF CORTI 36. RADIOLOGICAL ANATOMY PLAIN FILM FRONTO-OCCIPITAL 35 DEGREES CAUDAD SUBMENTO-VERTICAL MASTOID LATERAL OBLIQUE 25 DEGREES CAUDAD MASTOID PROFILE PETROUS BONE: ANTERIOR OBLIQUE (STENVERS VIEW) 37. FRONTO-OCCIPITAL 35 DEGREES CAUDAD 38. SUBMENTOVERTICAL (SMV) VIEW 39. MASTOID 25 DEGREES CAUDAD VIEW 40. MASTOID PROFILE 41. PETROUS BONE : ANTERIOR OBLIQUE (STENVERS VIEW) 42. CT of TEMPORAL BONE Computed tomography (CT) has revolutionized imaging of the temporal bone. Recent advances in multisection CT scanners allow acquisition of high-resolution volumetric data that enable image reformation in any plane. Protocols vary with different institutions e.g. Axial CT images are acquired through the temporal bones. 0.625-mm axial sections are then reprocessed and reformatted into magnified axial and coronal images and displayed at 0.3-mm intervals with overlap. In addition to the traditional axial and coronal views we can also perform reformation in the Stenvers and Pschl projections. The Stenvers projection is the plane parallel to the long axis of the petrous bone, and the Pschl projection is the plane perpendicular to the long axis of the petrous bone. 43. Sections through a plane 30 degrees to the baseline to limit the radiation dose to the orbit 44. AXIAL PROJECTION 45. Axial CT images show the normal anatomy of the temporal bone from inferior (a) to superior (g). IAC = internal auditory canal, ICA = internal carotid artery, LSCC = lateral semicircular canal, n. = nerve, PSCC = posterior semicircular canal, SCC = superior semicircular canal. 46. CORONAL PROJECTION 47. Coronal CT images show the normal anatomy of the temporal bone from anterior (a) to posterior (f). ant. = anterior, LSCC = lateral semicircular canal, m. = muscle, n. = nerve, SSCC = superior semicircular canal, t. = tendon. 48. Pschl projection CT images in a plane perpendicular to the long axis of the petrous bone show the normal anatomy of the temporal bone from anteromedial (a) to posterolateral (g). LSCC = lateral semicircular canal, n. = nerve, PSCC = posterior semicircular canal, SSCC = superior semicircular canal. 49. Stenvers projection CT images in a plane parallel to the long axis of the petrous bone show the normal anatomy of the temporal bone from oblique anterior (a) to oblique posterior (g). ant. = anterior, LSCC = lateral semicircular canal, n. = nerve, PSCC = posterior semicircular canal, SSCC = superior semicircular canal. 50. 3-D CT of TEMPORAL BONE Helps in better understanding of the spatial orientation of various parts of temporal bone Simplification of complex anatomy Volume rendered images can be sectioned in any plane and rotated in space 51. To obtain good 3D reconstructions, it is absolutely essential to obtain the thinnest possible overlapping slices. 0.75 mm collimation with a 0.75 mm slice thickness at 120 kVp, 200 mAs, a pitch of 0.8, and a 15 cm field of view with a matrix size of 512 x 512. The initial data sets reconstructed at 0.1 mm intervals. While obtaining 3D reconstructions, it is important to remember that any amount of gantry tilt results in distortion of the reconstructed 3D image. A zero degree gantry tilt when obtaining such images ensures no distortion of the post-processed 3D images. Volume-rendered 3D images can be generated from the original 2D data with different soft tissue and bone algorithms e.g TeraRecon Aquarius Workstation v3.3 52. AXIAL PLANE (INFERIOR TO SUPERIOR) 53. sp: styloid process, smf: stylomastoid foramen, ns: nerve to stapedius, ms: mastoid segment of the facial nerve, ct: chorda tympani, c aqueduct: cochlear aqueduct, V aqueduct: vestibular aqueduct, PSCC: posterior semicircular canal, pg: posterior genu, LSCC: lateral semicircular canal, CN: cochlear nerve, IV: Inferior vestibular nerve, IAC: internal auditory canal, ts: tympanic segment of the facial nerve, SV: superior vestibular nerve, fc: fallopian canal of the facial nerve, ag: anterior genu, SSCC: superior semicircular canal. 54. CORONAL PLANE ( ANTERIOR TO POSTERIOR) 55. ag: anterior genu, ts: tympanic segment of the facial nerve, fc: fallopian canal of the facial nerve, CN: cochlear nerve, SV: superior vestibular nerve, SSCC: superior semicircular canal, IAC: internal auditory canal, LSCC: lateral semicircular canal, ms: mastoid segment of the facial nerve, c aqueduct: cochlear aqueduct, smf: stylomastoid foramen, PSCC: posterior semicircular canal, V aqueduct: vestibular aqueduct. 56. Volume-rendered 3D CT image of the auditory system. 57. (Left image) Volume-rendered 3D CT image shows the relative positions of the malleus, incus, oval window and the inner ear. B) (Right image) Widening the window level reveals the stapes sitting on the oval window, thereby allowing transmission of sound waves to the inner ear. 58. Volume-rendered 3D CT image of the inner ear. Volume-rendered 3D CT image of the cochlea, having dissected open the overlying bony wall of the cochlea to expose the osseous spiral lamina. 59. Volume-rendered 3D CT image of the temporal bone revealing the dissected (cut) first portion of the facial nerve canal and the canal for the superior vestibular nerve. Volume-rendered 3D CT image of the temporal bone showing the canal for the cochlear nerve. 60. Volume-rendered 3D CT image of the canal for the facial nerve as it traverses the temporal bone. The facial nerve exits the anterosuperior aspect of the internal auditory canal as the labyrinthine segment housed within its own bony channel, the fallopian canal. It then makes a hairpin turn (the anterior genu) and courses as the tympanic segment along the medial wall of the tympanic cavity below the lateral semicircular canal. At the posterior genu, it makes another turn and heads vertically down as the mastoid segment to exit the temporal bone at the stylomastoid foramen. The canal for the chorda tympani, a branch of the mastoid segment of the facial nerve, is also present. 61. MR IMAGING OF INNER EAR POSITIONING Head first Supine Position the head in the head coil and immobilise with coushions Give Coushins under the legs for extra comfort Centre the Laser beam Localizer over the glabella 62. SUGGESTED PROTOCOLS, PARAMETERS AND PLANNING LOCALISER A three plane localizer must be taken in the beginning to localise and plan the sequences. These are low resolution T1 weighted scans AXIAL SAGITTAL CORONAL 63. T2 tse AXIAL Plan the axial slices on the sagittal plane; angle the position block parallel to the anterior and posterior margin of the corpus callosum. Slices must be sufficient to cover the whole brain from the vertex up to the line of Foramen Magnum. Check the positioning block in the other two planes An appropriate angle must be given on coronal plane on tilted head (perpendicular to the line of 3rd ventricle and brain stem). 64. PARAMETERS TR = 3000 4000 msec TE = 100-200 msec SLICE = 5mm FLIP = 130-150 MATRIX = 320X320 FOV 210-230 65. T2 TSE CORONAL Plan the coronal slices on the axial plane Angle the position block parallel to the line along right and left IAMS Check the position block in the other two planes. An appropriate angle must be given in the sagittal plane ( parallel to the brain stem) Slices must be sufficient to cover IAMS from the posterior border of sphenoid sinus upto the line of the fourth ventricle. 66. PARAMETERS TR = 3000-4000 msec TE = 110 msec FLIP = 130 SLICE = 3 mm MATRIX = 256X256 FOV = 150-180 67. 3D CISS ( 3D SPACE OR 3D FIESTA) AXIAL Plan the axial slices on the coronal plane Angle the position block parallel to the line along the right and left IAMS Check the positioning blocks in the other two planes. An appropriate angle must be given in the sagittal plane ( perpendicular to the brain stem). Slices should be sufficient to cover IAMS from hippocampus to the line of C1 vertebral body. 68. PARAMETERS TR= 12-15 msec TE = 6-7 msec SLICE = 0.8 mm FLIP = 80 MATRIX = 384X320 FOV = 210-230 69. T1 PRE AND POST CONTRAST SCANS FOR TUMOR EVALUATION T1 TSE CORONAL Plan the coronal slices on the axial plane Positioning box angled parallel to the line joining the Right and left IAMS Check the positioning blocks in the other 2 planes An appropriate angle should be given along the sagittal plane ( parallel to the brain stem) The slices should be sufficient to cover the IAMS from the posterior border of Sphenoid sinus upto the line of the fourth ventricle. 70. PARAMETERS TR = 400-500 msec TE = 15 msec FLIP = 150 SLICE= 3mm MATRIX = 256X256 FOV = 150-180 71. T1 TSE AXIAL Plan the axial slices on the coronal plane Angle the position block parallel to the line along the right and left IAMS Check the positioning blocks in the other two planes. An appropriate angle must be given in the sagittal plane ( perpendicular to the brain stem). Slices should be sufficient to cover IAMS from hippocampus to the line of C1 vertebral body. 72. PARAMETERS TR = 400-600 msec TE = 150 msec SLICE = 3mm FLIP = 90 MATRIX = 256X256 FOV= 170-180 73. MR CONTRAST GADOLINIUM-DTPA RECOMMENDED DOSAGE = 0.1 mmol/kg i.e. 0.2 ml/kg 74. POST CONTRAST T1 TSE AXIAL 75. Post Contrast T1 TSE CORONAL 76. MR IMAGING Coronal T2 weighted MRI through the cochleae. 77. Coronal T2 weighted MRI through the vestibules. 78. Axial T2 weighted MRI to show the facial (VIIth cranial) and vestibulocochlear (VIIIth cranial) nerves within the internal auditory meatus 79. EMBRYOLOGY The temporal bone is ossified from eight centers, exclusive of those for the internal ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just before the close of fetal life the temporal bone consists of three principal parts: 1. The squama is ossified in membrane from a single nucleus, which appears near the root of the zygomatic process about the second month. 2. The petromastoid part is developed from four centers, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month 3. The tympanic ring is an incomplete circle, in the concavity of which is a groove, the tympanic sulcus, for the attachment of the circumference of the tympanic membrane. . 80. The three principal parts of the tempora bone at birth. 1. Outer surface of petromastoid part. 2. Outer surface of tympanic ring. 3. Inner surface of squama. 81. Temporal bone at birth. Outer aspect 82. Temporal bone at birth. Inner aspect. 83. The embryologic development of the ear is a multistage and anatomically complex process. The outer ear structures develop from the first branchial cleft and the first and second branchial arches during the 6th through 12th weeks of intrauterine life. The external auditory canal (EAC) initially develops as a solid core of epithelium, termed the meatal plate, which migrates toward the first pharyngeal pouch and subsequently hollows out during the 2nd through 7th months of intrauterine life. The eustachian tube and tympanic cavity arise from the first pharyngeal pouch between 10 and 30 weeks gestation. The tympanic membrane is derived from three germ cell layers, including ectoderm from the first branchial groove and mesoderm and endoderm from the first branchial pouch. The ossicular chain and supporting ligaments arise from the first and second branchial arches. 84. The membranous portion of the inner ear arises from neuroectoderm (otic placode) in the 4th week of gestation. The otic placode invaginates, forming the otic pit, and subsequently forms the otic vesicle (otocyst). The otocyst divides into the dorsal and ventral pouches (pars superior and inferior, respectively), which are the precursors to the utricle, semicircular canals, cochlear duct, and saccule. The bony labyrinth (otic capsule) develops from mesenchyme around the membranous labyrinth between 4 and 8 weeks gestation, continues to grow between 8 and 16 weeks gestation, and ossifies by the 24th week of gestation. 85. Imaging findings of developing Temporal bone by Nemzek et al. AJNR september 1996 Comparison of adult and early fetal otic capsule structures on T2-weighted fast spin-echo MR images. A, In the adult, there is high signal intensity of endolymph and perilymph in membranous cochlea, and vestibule and semicircular canals are surrounded by signal void of dense bony otic capsule. B, Sagittal image of fetus, gestational age 14 weeks 4 days. Basal turn of cochlea is the first structure that can be readily identified. C, Fetus, gestational age 15 weeks 5 days. Fluid is seen in cochlea and vestibule. Basal turn of cochlea is two thirds of adult size. The upper turns of the membranous cochlea are now visible (arrow) as a single space. Note 86. Fetus, gestational age 17 weeks 4 days. A, CT scan shows ossification in squamous portion (black arrow) and zygomatic process of the temporal bone (white arrow). Note very early ossification of the malleus and incus. B, T2-weighted fast spin-echo MR image shows vestibule and lateral semicircular canal before ossification. CT scan of fetus, gestational age 18 weeks 4 days, shows earliest ossification of otic capsule. Note discontinuous calcification around the apical turn of the cochlea (small arrows). Note interscalar septum and progressive ossification of ossicles. 87. Fetus, gestational age 19 weeks 3 days. A, CT scan shows that cochlea and vestibule are reaching full adult size. There is now a continuous shell of bone surrounding the cochlea. B, CT scan shows short internal auditory canal. The canal for the cochlear nerve (arrowhead) passes directly anteriorly. The labyrinthine segment of the facial nerve canal is present. The common crus is partially encircled by bone. T2-weighted fast spin-echo axial (C) and sagittal (D) MR images show ossification in cochlea and vestibule as decreased signal intensity. Endolymphatic duct is parallel to common crus. 88. Fetus, gestational age 18 weeks 5 days. CT scan shows progressive ossification with thicker layer of bone surrounding cochlea and vestibule. Note canal for the cochlear nerve (arrowhead) is directed anteriorly. Fetus, gestational age 20 weeks 5 days. CT scan (A) and T2-weighted fast spin-echo MR image (B) show tympanic ring as horizontal structure with adjacent ossicles. 89. Fetus, gestational age 21 weeks 4 days. CT scans (A and B) and T2-weighted fast spin-echo MR image (C) show otic capsule structures are of adult dimensions. Bone surrounds the lateral semicircular canal and the common crus. Ossicles are visible by both CT and MR imaging. There is a large subarcuate space. Note all turns of the cochlea are visible on the MR image (C). 90. Fetus, gestational age 22 weeks 3 days. Lateral plain radiograph of the skull shows a large subarcuate space beneath the superior semicircular canal. The tympanic ring is an ossified horizontal structure that is separated from the squamous temporal bone. 91. Fetus, gestational age 23 weeks 3 days. A, Anteroposterior plain radiograph of the skull shows the horizontal tympanic ring is isolated from the rest of the temporal bone. BD, On CT scans, note the tympanic ring and vestibular and cochlear aqueducts. The stapes is now identified in the oval window. There is a large subarcuate space. 92. Fetus, gestational age 24 weeks 4 days. A and B, CT scans show a thickening of bone surrounding the otic capsule and greater definition of the modiolus. The labyrinthine segment of the facial canal is better defined. The internal auditory canal remains short. Note the pyramidal process, the facial nerve recess (straight arrow), and the sinus tympani (curved arrow) on posterior wall of tympanic cavity. On T2-weighted fast spin-echo axial (C) and sagittal (D) MR images, the endolymphatic duct and vestibular aqueduct and all the turns of the cochlea are identified 93. IMAGING OF TEMPORAL BONE PATHOLOGY 94. CONGENITAL MALFORMATIONS Developmental malformations that affect the EAC and middle ear may cause conductive hearing loss, whereas those that affect the membranous and bony labyrinth may result in sensorineural hearing loss (SNHL). Congenital hearing deficits can be nongenetic or genetic in origin. Congenital hearing deficits from genetic causes may occur in isolation or in association with various syndromes, such as the CHARGE (coloboma of the eye, heart anomaly, choanal atresia, retardation, genital and ear anomalies) Klippel-Feil trisomy 21 Goldenhar syndrome Crouzon syndrome. 95. Congenital atresia of the EAC Involves a spectrum of abnormalities in which the EAC fails to develop fully. The resultant abnormality may be classified as osseous, membranous, or mixed depending on the degree of development of the EAC. Furthermore, the atresia may be bilateral or, more commonly, unilateral and is often associated with abnormalities of the pinna. The prevalence of atresia of the EAC is approximately one in 10,000 96. Atresia of the EAC in a 12-year-old boy with left conductive hearing loss and left microtia. Axial CT image shows absence of the left EAC. The left middle ear cavity is small. The right EAC is normal. 97. Imaging abnormalities involving the bony labyrinth are present in 20%40% of patients with SNHL. CT is currently insensitive to abnormalities of the membranous labyrinth, which are responsible for most cases of SNHL. The specific timing of the insult during inner ear development determines the resultant malformation type along a spectrum of congenital inner ear malformations 98. congenital inner ear malformations labyrinthine (Michel) aplasia cochlear aplasia common cavity malformation incomplete partition type I (cystic cochleovestibular malformation) incomplete partition type II (classic Mondini malformation) cochleovestibular hypoplasia. Historically, all abnormalities of partitioning of the cochlea were referred to as Mondini malformation. More recently, Sennaroglu and Saatci categorized incomplete partition of the cochlea into two types. In incomplete partition type I, the cochlea completely lacks partitioning and appears as a cystic structure at CT. In incomplete partition type II, the cochlea contains one and one-half turns, with a normal basal turn and a cystic-appearing dilated apical portion. 99. Cochlear aplasia in a 4-year-old girl with profound left SNHL. Axial CT image shows absence of the left cochlea and vestibular aqueduct. The left vestibule and lateral semicircular canal are dysplastic. 100. Common cavity malformation in a 2-year-old girl with profound bilateral SNHL and cleft palate. Axial (a) and coronal (b) CT images show confluence of a globular left cochlea with a globular enlarged left vestibule and dysmorphic left lateral and superior semicircular canals (SCCs). The right cochlea is absent, and there is an enlarged globular right vestibule with absence of the right lateral and posterior semicircular canals. 101. Incomplete partition type I in a 5-year-old girl with profound right SNHL and mild to moderate left SNHL with a conductive component on the left. Coronal CT image shows a cystic-appearing cochlea bilaterally with absence of partitioning. 102. Incomplete partition type II in a 13-month-old boy with bilateral mixed hearing loss. Axial (a) and coronal (b) CT images show one and one-half turns of the cochlea AND cystic dilatation of the apical turn bilaterally. The vestibular aqueducts are enlarged bilaterally. 103. CHARGE syndrome in a 17-year- old boy with bilateral mixed hearing loss. Axial (a) and coronal (b) CT images show bilateral hypoplastic vestibules and absence of the semicircular canals. The bilateral cochlear nerve fossette and IAC are also hypoplastic. n. = nerve. 104. Enlarged vestibular aqueduct syndrome Is a relatively common cause of SNHL. Enlargement of the vestibular aqueduct is the most frequently seen osseous abnormality in patients with SNHL. An enlarged vestibular aqueduct may be seen in isolation or in association with other abnormalities of the inner ear. A commonly accepted imaging criterion for an enlarged vestibular aqueduct is a caliber of 1.5 mm or greater in the midportion of the aqueduct. Enlargement of the vestibular aqueduct may also be suspected if the aqueduct is larger in caliber than the normal lateral semicircular canal. 105. Enlargement of the vestibular aqueduct in a 23-year-old woman. Axial CT image shows an enlarged right vestibular aqueduct. The left vestibular aqueduct is of normal caliber. 106. Vascular abnormalities of the temporal bone may involve the ICA and its branches or the internal jugular vein. Both an aberrant course of the ICA and a high-riding jugular bulb may manifest as tinnitus. Differentiation of these entities from neoplastic or inflammatory processes with imaging is critical in guiding appropriate clinical management . Persistence of the stapedial artery is rare, with a prevalence of 0.48% , but its identification is crucial if middle ear surgery is planned. A persistent stapedial artery may be seen in association with an aberrant ICA. At imaging, the persistent stapedial artery can be seen arising from the petrous segment of the ICA or aberrant ICA and extending superiorly to supply the middle meningeal artery. Typical findings include apparent expansion of the tympanic segment of the facial nerve and abnormal soft-tissue attenuation adjacent to the cochlear promontory . In addition, the ipsilateral foramen spinosum is absent 107. Aberrant ICA. Axial CT image shows an aberrant ICA passing anterior to the cochlear promontory through a dehiscent carotid plate. 108. Persistent stapedial artery in an 8- year-old boy with microtia, moderate right conductive hearing loss, and a history of canaloplasty for atresia of the EAC. Axial (a) and coronal (b) CT images show a persistent stapedial artery arising from the horizontal portion of the carotid artery. Abnormal soft-tissue attenuation lateral to the cochlear promontory and apparent expansion of the tympanic segment of the facial nerve are seen, findings indicative of the aberrant vessel. The foramen spinosum is absent on the right. 109. Inflammatory Conditions Several inflammatory conditions may affect the temporal bone. At imaging, infectious or inflammatory processes can be described according to the degree of involvement of the four anatomic regions: external ear, middle ear and mastoid, inner ear, and petrous apex. 110. External Auditory Canal EAC cholesteatoma. EAC cholesteatoma is a rare lesion with an incidenceof approximately 0.1% 0.5%. Most cases are spontaneous or idiopathic, although these lesions can also occur secondary to prior trauma, surgery, or radiation . Most patients are in an older age group and present with chronic dull pain and otorrhea, most commonly unilaterally . Pathologically, it is characterized by local invasion of the lining squamous epithelium of the EAC into the underlying bone, resulting in canal wall erosions and periostitis. On CT images, the lesion is characterized by focal soft tissue within the EAC (typically the inferior wall), with erosion extending into the underlying bone . These imaging findings are nonspecific, however, and may be mimicked by entities such as carcinoma and otitis externa 111. Coronal CT image of EAC cholesteatoma in a 73-year-old patient with a history of chronic bone erosion of the EAC. Image shows soft tissue along the inferior wall of the EAC (), causing bone erosion (arrow). 112. Keratosis obturans. Keratosis obturans represents an expansile accumulation of keratin debris within the EAC. In contrast to EAC cholesteatomas, it occurs in younger patients and tends to be bilateral. Clinically, these patients have severe pain and conductive hearing loss, with otorrhea being relatively rare. There is an association of this entity with sinusitis and bronchiectasis On CT images, there is diffuse widening of the EAC by an epidermal plug, which may cause smooth scalloping of the surrounding bone, but there is no erosion or periostitis 113. Coronal CT image of keratosis obturans demonstrates a soft-tissue plug in the external canal (), with mild expansion of the canal but no bone erosion. 114. Malignant otitis externa. Necrotizing or malignant otitis externa occurs most commonly in elderly diabetic patients and other patients in immunocompromised states. The patients present with severe otalgia and otorrhea, and there is a high mortality rate . The infection is usually caused by Pseudomonas aeruginosa. Clinically one sees granulation tissue in the inferior EAC at the bone- cartilaginous junction. Infection can then spread via fissures of Santorini into the soft tissues beneath the skull base, leading to skull base osteomyelitis, which can be heralded by cranial neuropathies. 115. On images, soft-tissue thickening in the external canal is noted, often with bone destruction and inflammatory changes in the mastoid. Skull base osteomyelitis results from extension of the destructive process into the clivus, jugular foramen, and prevertebral soft tissues . Abscesses can develop in the epidural space, brain parenchyma, and the prevertebral space as a complication. MR and CT are complementary modalities for evaluation of this entity, with the bone windows at CT showing the destructive process to greater advantage, and MR imaging better demonstrating associated soft tissue complications. The imaging differential diagnosis includes nasopharyngeal carcinoma with secondary obstruction of the eustachian tube orifice causing a secondary otomastoiditis 116. Images of malignant otitis externa in a 93-year-old diabetic woman. (a) Axial CT image shows opacification of the right mastoid air cells. There are erosive changes in the petroclival region on the right (arrows). (b) Axial T1-weighted gadolinium-enhanced MR image in the same patient better demonstrates the prevertebral abscess (large ). There is thrombosis of the inferior petrosal sinus with a filling defect within (arrow). Notice the abnormal hypointensity in the right mastoid air cells, representing inflammatory changes (small ). 117. Middle Ear The most common inflammatory condition affecting the temporal bone is acute otitis media (AOM). It usually occurs as the sequela of a viral upper respiratory infection with disruption of the mucosal barrier that prevents bacteria in the nose and nasopharynx from spreading to the middle ear. The imaging findings of uncomplicated AOM are nonspecific, with partial or total fluid-attenuation opacification of the middle ear seen at CT. Chronic otomastoiditis typically occurs as a result of long-standing eustachian tube dysfunction. 118. Imaging is typically performed in AOM when a complication is suspected. Important complications to consider when evaluating acute otomastoiditis include coalescent mastoiditis , Bezold abscess, dural sinus thrombosis , subperiosteal abscess, intracranial abscess and empyema , meningitis, facial nerve involvement, labyrinthitis, and petrous apicitis. These same complications can occasionally occur superimposed on chronic otomastoiditis. 119. Coalescent mastoiditis in a 49-year-old woman. Axial (a) and coronal (b) CT images show complete opacification of the mastoid air cells with fluid-attenuation material and loss of internal bone septa. A large defect in the sigmoid sinus plate is present, and there are bone defects in the tegmen mastoideum (white arrowheads in b) and the external cortex of the mastoid bone (black arrowheads in b). 120. Dural sinus thrombosis. (a) Axial contrast-enhanced CT image shows a filling defect in the left sigmoid sinus. (b) Axial nonenhanced two-dimensional time- of-flight MR venographic image shows absent flow in the left jugular bulb and sigmoid sinus. 121. 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). 122. CT images of petrous apicitis in a 78-year-old man with right ear infection. (a) Axial image demonstrates opacification of the right petrous apex air cells with soft-tissue attenuation (arrow). There is also scattered mastoid opacification. Note normally aerated petrous apex air cells on the left. (b) Coronal image better demonstrates destruction of the petrous bone (arrows). 123. Epidural abscess in a 23-year-old woman. Axial contrast-enhanced CT (a) and coronal contrast-enhanced T1-weighted MR (b) images show a rim-enhancing fluid collection in the left temporal epidural space. There is adjacent enhancement of parenchyma and dura. 124. CHOLESTEATOMA Both AOM and chronic otitis media can result in the development of aquired cholesteatomas in the middle ear. A cholesteatoma is a sac lined with ectopic stratified squamous epithelium and filled with exfoliated keratin debris. Most cholesteatomas of the middle ear are acquired (98%); only a minority are congenital. Acquired cholesteatomas typically arise in the pars flaccida of the tympanic membrane and less commonly in the pars tensa region. Pars flaccida cholesteatomas are typically centered in the Prussak space, whereas pars tensa cholesteatomas are typically centered in the sinus tympani or facial recess. All types of cholesteatomas may erode the ossicular chain, scutum, mastoid bone, or Krner septum 125. Coronal CT image of a pars flaccida cholesteatoma in a 56-year-old woman with a deep retraction pocket at clinical examination. Image demonstrates lobulated soft tissue in Prussak space (arrowhead) and the attic (), displacing the ossicles medially and eroding the scutum (arrow). 126. Coronal CT image of a pars tensa cholesteatoma in a 31-year-old man with left- sided hearing loss and retraction pocket at clinical examination. Image demonstrates a lobulated soft-tissue mass medial to the ossicles (), displacing the ossicles laterally. The scutum remains sharp (arrow), in contrast to that in the case of the pars flaccida cholesteatoma. 127. 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. 128. MR images of cholesteatoma in a 15-year-old male patient with a history of draining ear. (a) Axial T2 weighted image demonstrates a heterogeneously hyperintense lesion in the left middle ear/mastoid (). (b) Axial gadoliniumenhanced T1- weighted image demonstrates the lesion to be nonenhancing (). (c) Coronal DW image demonstrates reduced diffusivity within the lesion (arrow). 129. CHOLESTEROL GRANULOMA Pneumatization of the petrous apex occurs in 9%30% of persons . When pneumatized, the petrous apex can become involved by middle ear infections. A cholesterol granuloma results from a foreign-body giant cell reaction to the deposition of cholesterol crystals in the air cells with fibrosis and vascular proliferation. The characteristic CT appearance of a cholesterol granuloma is an expansile lesion with smooth margins. MR imaging shows high signal intensity on T1-weighted images and often high signal intensity on T2-weighted images owing to the cholesterol crystals and methemoglobin from repeated hemorrhage 130. Cholesterol granuloma of the petrous apex in a 52-year-old man. Axial nonenhanced (bone window) (a) and contrast-enhanced (brain window) (b) CT images show bony expansion of the petrous apex by a nonenhancing mass. 131. Cholesterol granuloma of the petrous apex in a 52-year-old man. (a) Axial T1- weighted MR image shows a hyperintense mass in the petrous apex. (b) On an axial T2-weighted MR image, the mass has heterogeneous signal intensity. (c) Axial diffusion- weighted MR image shows no diffusion restriction in the mass. 132. Axial CT image of petrous apex effusion in a 36-year-old man with right-sided sensorineural hearing loss demonstrates opacification of the pneumatized right petrous apex (). It does not have expansile margins, distinguishing it from a petrous apex mucocele or a cholesterol granuloma. The internal septations and cortex are intact, distinguishing it from petrous apicitis. 133. INNER EAR Labyrinthitis has three radiologic stages: acute, fibrous, and labyrinthitis ossificans. In the acute stage, contrast-enhanced T1-weighted MR imaging may show abnormal enhancement of the labyrinth. MR imaging also allows detection of cochlear obstruction in the fibrous stage, before abnormalities are detectable with CT . Labyrinthitis ossificans involves pathologic ossification of the bony labyrinth and cochlea and is well-depicted with CT 134. Labyrinthitis ossificans in a 45-year-old woman. (a, b) Axial (a) and coronal (b) CT images show abnormal sclerosis of the bony labyrinth and cochlea (*). n. in b = nerve. (c) Axial T2-weighted MR image shows absence of fluid signal intensity in the left cochlea and semicircular canals. 135. TRAUMA Historically, temporal bone fractures were classified into two main categories, longitudinal and transverse, on the basis of the fracture plane relative to the long axis of the petrous bone. It is now generally recognized that temporal bone fractures may be complex with mixed features of both longitudinal and transverse fractures. A common complication associated with temporal bone fractures is hearing loss, which may be sensorineural, conductive, or mixed. Other complications related to temporal bone fractures include facial nerve injury perilymphatic fistula vertigo cerebrospinal fluid leak meningitis, and acquired cholesteatoma. 136. Bilateral longitudinal fractures of the temporal bone in a 47-year-old man. Axial CT images show fracture lines (fx in a) parallel to the long axis of the petrous bone. Bilateral malleoincudal abnormalities (disruption on the left, subluxation on the right) and hemotympanum are noted with fluid attenuation surrounding the ossicles. Air attenuation is faintly seen within the left petrous ICA canal. Arrowheads in a = tiny amount of intracranial air. 137. Transverse fracture of the left temporal bone with ossicular injury in a 39-year-old man. Axial (a) and coronal (b) CT images show a fracture line (fx) (arrowheads in a, arrows in b) perpendicular to the long axis of the left petrous bone, traversing the IAC and bony labyrinth. Malleoincudal disruption and hemotympanum are noted. Air attenuation is seen within the cochlea. 138. Complex (mixed) fracture of the right temporal bone in a 16-year-old boy. Axial CT image shows oblique, longitudinal, and transverse fracture lines (fx). The oblique fracture traverses the middle ear cavity; there is associated malleoincudal subluxation and hemotympanum. The transverse fracture involves the vestibule and vestibular aqueduct. The longitudinal fracture extends through the base of the cochlea. There is pneumovestibule and gas in the IAC. 139. Tumors and Tumorlike Conditions Many types of tumors may affect the temporal bone. A temporal bone tumor may be clinically suspected in several clinical scenarios. Four common clinical presentations suspicious for a tumor are (a) SNHL, tinnitus, or vertigo, which may indicate a vestibular schwannoma or other cerebellopontine angle mass; (b) pulsatile tinnitus or cranial neuropathy involving the jugular foramen; (c) peripheral facial nerve dysfunction ; and (d) a previously clinically identified tumor of the temporal bone. There are also nonneoplastic conditions, including various otodystrophies, that can mimic a neoplasm at imaging. 140. To assess a tumor in the temporal bone region, it is helpful to localize the lesion to one of the following areas, each of which houses a unique set of pathologic conditions: (a) IAC/CPA, (b) middle ear, (c) EAC and mastoid, and (d) petrous apex 141. IAC/CPA The most common masses in this area are vestibular schwannomas, meningiomas, epidermoids, and nonvestibular posterior fossa schwannomas (such as trigeminal, facial, and glossopharyngeal). Less frequently seen are arachnoid cysts, lipomas, dermoids, and malignancies such as lymphoma, melanoma, and metastases. In addition, tumors related to the petrous bone (eg, chondrosarcoma) and brain (eg, glioma) may extend into the IAC/CPA. 142. Axial contrast-enhanced T1-weighted MR image of vestibular schwannoma. This 51 yearold man presented with sudden asymmetric sensorineural hearing loss on the right. Image demonstrates an avidly enhancing tumor in the IAC extending through an expanded porus acousticus (between arrows) into the CPA, where it forms an acute angle with the posterior petrous ridge. 143. IAC schwannoma and meningioma in a 24-year-old man with neurofibromatosis type 2. (a) Axial CT image shows a partially calcified meningioma in the middle cranial fossa with adjacent hyperostosis of the petrous apex. The ipsilateral IAC is widened from the patients known vestibular schwannoma. (b) Axial gadolinium-enhanced T1-weighted MR image shows varying degrees of relatively homogeneous enhancement of the meningioma and bilateral vestibular schwannomas. 144. Facial nerve schwannoma. (a) Axial CT image shows a mass centered in the geniculate ganglion with widening of the geniculate fossa and anterior portion of the tympanic segment of the facial nerve (n.) canal. (b) Coronal gadolinium- enhanced T1-weighted MR image shows homogeneous enhancement of the mass, which extends into the middle cranial fossa. The labyrinthine segment of the facial nerve (n.) canal also appears widened. 145. Axial T2-weighted MR image of epidermoid in a 40-year-old woman who presented with left sensorineural hearing loss, pressure sensation in the head worse with exertion, and tendency to drift to the left. Image shows an epidermoid in the CPA insinuating around the basilar artery (white arrow) and causing mass effect on the brainstem and cerebellum (black arrows). It does not enhance and is hyperintense on DW images 146. Middle Ear When a soft-tissue mass is seen in the middle ear, a vascular structure must be excluded. This includes a persistent stapedial artery, a laterally placed or aberrant carotid artery, a carotid artery aneurysm, and an exposed dehiscent jugular bulb. True neoplasms include paraganglioma (most common); facial nerve lesions extending into the middle ear, such as schwannomas and geniculate region hemangiomas, choristomas, meningiomas; adenomatous tumor of the mixed pattern type; and malignancies such as carcinomas and metastases (rare). 147. Coronal CT image of glomus tympanicum demonstrates a small, rounded nodule in the middle ear abutting the cochlear promontory (arrow). This 50-year-old woman had a history of chronic otitis media. At otoscopic examination, a 2-mm erythematous mass was appreciated and clinically suspected to represent a glomus tympanicum. 148. Glomus tympanicum tumor in a 54- year-old man. (a) Coronal CT image shows a soft- tissue mass along the cochlear promontory and hypotympanum with preservation of the ossicular chain. (b) Coronal gadolinium-enhanced T1-weighted MR image shows that the mass has homogeneous enhancement. 149. Glomus jugulare tumor in a 36-year- old man. (a) Axial CT image shows bone destruction from a mass in the posterior petrous apex and mastoid region near the jugular foramen. There is soft-tissue extension into the middle ear. (b) Axial gadolinium-enhanced T1- weighted MR image shows avid enhancement of the mass. 150. Images of glomus jugulotympanicum. (a) Axial CT image demonstrates the moth-eaten, permeative bone destruction around the tumor. On this image through the right temporal bone, one can appreciate destruction of the margins of the jugular foramen (), the caroticojugular spine (arrowhead), and the carotid canal (small arrow). Note the tumor extending into the middle ear (large arrow). (b) Axial contrast-enhanced T1-weighted MR image shows the large enhancing tumor with internal flow voids (arrows), creating the so called salt-and-pepper appearance. This patient initially presented at age 56 years with right ear fullness, hearing loss, and audible whooshing sound that correlated with heart beat. 151. EAC and Mastoid Tumors in the EAC and mastoid region are often malignant, with squamous cell carcinoma being by far the most common. Patients with EAC squamous cell carcinoma frequently have a long history of chronic ear infections. There is aggressive bone destruction, and there may be invasion of surrounding soft tissues including intracranial, inframastoid, middle ear, parotid, carotid, and temporomandibular joint involvement. Other malignancies such as basal cell carcinoma, melanoma, lymphoma, myeloma, metastases, chondrosarcoma, and osteosarcoma occur much less frequently Aggressive bone destruction may be seen with some benign processes and should be considered in the differential diagnosis. These include granulomatous diseases such as Langerhans cell histiocytosis, tuberculosis, and Wegener granulomatosis. Aggressive infections such as malignant otitis externa and radiation necrosis are additional considerations. 152. Axial CT image of squamous cell carcinoma of the EAC with extension to the mastoid. Patient was a 64-year-old woman with recurrent and persistent left ear infection not improved with antibiotics; biopsy revealed the diagnosis. CT image demonstrates extensive bone destruction involving the EAC margin and mastoid (black arrowheads), extending to the petrous apex (large arrow). The dense otic capsule is relatively spared (white arrowhead). Abnormal soft tissue fills the EAC, middle ear, and mastoid, extending into the posterior cranial fossa (small arrows). The auricle is also thickened, with ulcerated margins. 153. Axial contrast-enhanced T1-weighted MR image of Langherhans cell histiocytosis shows solid enhancing tissue involving the EAC and mastoid (black arrows). There is also involvement of the middle ear (white arrow) and sigmoid sinus (arrowhead). Patient was a 2-year-old boy with otitis media starting at 8 months of age, now with pus and bloody discharge and diffuse swelling in the ear region. Biopsy revealed Langherhans cell histiocytosis. 154. Petrous Apex True neoplasms in the petrous apex include chondrosarcoma, chordoma, osteosarcoma, and meningioma. Myeloma, lymphoma, and metastases may also occur. The petrous area may be secondarily involved by regional tumors such as trigeminal schwannoma, jugular paraganglioma, and nasopharyngeal carcinoma. The latter is usually seen along the petrooccipital fissure, superior to the fossa of Rosenmller. 155. Axial contrast-enhanced T1-weighted MR image of petrous apex chondrosarcoma. Image shows the tumor mass in the petrous apex causing displacement of the petrous carotid artery (arrow). It is hyperintense on T2-weighted images and enhances avidly. 156. ELST in two patients. (a) Axial CT image shows bone destruction along the right posterior petrous apex in the region of the vestibular aqueduct. (b) Axial T1-weighted MR image in another patient, a 60-year-old woman, shows a mass in the posterior petrous apex. The mass is isointense to adjacent brain tissue with peripheral high signal intensity from methemoglobin. (c) Axial T2-weighted MR image in the same patient as in b shows that the mass has heterogeneous signal intensity with multiple small flow voids (arrows). 157. Aneurysmal bone cyst. (a) Axial CT image shows an expansile bone lesion arising from the inner table of the squamosal temporal bone with internal osseous septa. (b) On an axial T2-weighted MR image, the lesion has mixed signal intensity with fluid-fluid levels 158. Osteochondroma in a 53-year-old woman. Axial CT image shows a pedun-culated osteochondroma (arrow) arising from the petrous apex with apparent narrowing of the adjacent IAC. 159. Otospongiosis, also known as otosclerosis, is an unusual disease that affects the otic capsule, resulting in progressive hearing loss. The disease typically affects women more than men, with a female-to-male ratio of 2:1 In otospongiosis, the normal endochondral bone of the otic capsule is replaced by spongy vascular irregular bone. There are two categories of otospongiosis: fenestral and retrofenestral. The more common fenestral type affects the lateral wall of the bony labryinth, including the oval and round windows, promontory, and facial nerve canal. The less common retrofenestral type primarily involves the otic capsule but usually has fenestral involvement OTOSPONGIOSIS 160. Early otospongiosis. Axial CT image shows subtle demineralization involving part of the otic capsule and cochlea from early retrofenestral otospongiosis. 161. Fibrous dysplasia is an inherited disorder affecting the bones and can be monostotic or polyostotic. The disease is characterized by inability to form mature lamellar bone owing to disordered osteoblastic activity. As a result, there is gradual replacement of normal bone by an abnormal proliferation of isomorphic fibrous tissue elements intermixed with irregular trabeculae of woven bone. This results in bone expansion, which can cause osseous narrowing of the vascular channels and neuroforamina and structurally weakened bone. There are three types of fibrous dysplasia, with variable appearances depending on the proportions of fibrous tissue and osseous elements: pagetoid, sclerotic, and cystic FIBROUS DYSPLASIA 162. Fibrous dysplasia in a 23- year-old woman. Axial CT image shows expansion of the temporal bone with a ground-glass matrix, as seen in the pagetoid subtype of fibrous dysplasia (FD). There is narrowing of the IAC and the tympanic segment of the facial nerve canal. Involvement of the incus is noted. 163. COCHLEAR IMPLANT 164. REFERENCES AND FURTHER READING 1. 165. 2. 166. 3. 167. 4. 168. 5. 169. 6. 170. 7. 171. 8. 172. 9. 173. 10. 174. 11. 175. 12. 176. ANATOMY AND PHYSICS ARE THE TWO MOST IMPORTANT PILLARS OF RADIOLOGY