MR IMAGING OF INNER EAR Sarbesh Tiwari

MR IMAGING IN INNER EAR PATHOLOGY

Moderator-PROF & HOD . DR R.K. GOGOI Presented by :: Sarbesh Tiwari

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Introduction

The ear functions both as an organ of hearing and as an organ of equilibrium2

Ear is the part of auditory system. It not only receives sound, but also aids inbalanceand body position.The external ear consists of auricle and the external auditory canal. The ext auditory canal is 2.4 cm in length in adult. The middle ear lies between the ext and inner ear and contains the ossicles and muscles for sound conduction.Inner ear

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Embryology of earThe ear is the first organ of special senses to become differentiated in man, inner ear reaches full adult size by midtermThe external and middle ear develop from 1st and 2nd brachial archNeural sound perceiving apparatus of inner ear develops from ectodermal otocyst

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The cochlea is developed sufficiently by 20 weeks of gestation and foetus can hear in the womb of the mother. This probably explains how Abhimanyu, while still unborn, could have heard the conversation between his mother and father (Arjuna) in the legend given in the Grear Indian epic of Mahabharata written thousands of years ago. 3

External Ear

PINNA (auricle) : # sixth week of embryonic life, # six tubercles appear around 1st branchial cleft. # They progressively coalesce to form the auricle

External auditory meatus # develops from the first branchial cleft. # 16th embryonic week, # cells proliferate and form a meatal plug. # Recanalisation of this plug forms the epithelial lining of the bony meatus. # External ear canal is fully formed by the 28th week of gestation

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MIDDLE EARTympanic membrane: Develops from all the three germinal layers. Outer epithelial layer by ectoderm, Middle fibrous layer by mesoderm & Inner mucosal layer by endoderm.

Middle ear cavity : # Develops from endoderm of tubotympanic recess which arises from 1st and partially from 2nd pharyngeal pouches. # Head of Malleus and short process of incus are derived from mesoderm of 1st arch # Rest of malleus and incus with stapes suprastructure develop from 2nd arch # footplate and annular ligament which are derived from the otic capsule

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Inner ear Starts by 3rd week of fetal life and completed by 16th wks The inner ear is derived from the ectoderm in the region of the hindbrain. A thickening of the ectoderm, the otic placode becomes invaginated to form the auditory/otic vesicle.

OTIC PLACODE

OTIC PIT

OTIC VESICLE6

Each vesicle divides into -- the dorsal portion which forms theutricle, semicircular canalsandendolymphatic duct, and -- the ventral component, which gives rise to thesacculeand the cochlear duct (scala media).

DIFFERENTIATION OF OTIC VESICLE INTO INNER EAR ELEMENTS 7

Utricular portion3 diverticula for semicircular canalsSaccular portionTubular diverticulum (cochlear duct) grows in spiral fashion to become membranous cochleaThe organ of Corti differentiates from cells along the wall of the cochlear duct.

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Mesoderm around otocyst soon forms a cartilaginous otic capsule.Part of the cartilaginous shell undergoes vacuolization, and twoperilymphatic spaces(scala vestibuli and scala tympani) are formed.Ossifies by 25 weeks

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Development of cochlea is complete by 8th weekVestibule by 11th weekSemicircular canal by 19- 22 wks8

Small group of cells breaks away otic capsule and along with cells of neural creast origin forms the statoacoustic ganglion. The ganglion subsequently splits into vestibular and cochlear nerves.

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Anatomy of inner earIt lies in the petrous part of the temporal boneInner ear consists of osseous labyrinth that encloses membranous labyrinth.

Outer bony labyrinth bony cochleavestibule three bony semicircular canalsVestibular and cochlear aqueduct

Inner membranous labyrinth Cochlear duct Utricle SacculeThree membranous semicircular canalsEndolymphatic system 10

Bony labyrinth Vestibule :- Central rounded portion of labyrinth.

Medial wall has two recesses, a spherical recess for saccule and an elliptical recess for utricle. Continues antero-inferiorly with cochlea and posteriorly with SCC & vestibular aqueduct. 11

The oval window of the vestibule is the interface between the mechanical and neural element of the ear. It is covered by the annular ligament, which surrounds the footplate of the stapes.The round window is bony opening in the basal turn of cochlea covered by fibrous membrance.11

2. Semicircular Canal: They are three in number, the lateral, posterior and superior, and lie in planes at right angles to one another.

3. Cochlea :-The bony cochlea is a coiled tube making 2.5 to 2.75 turns round a central pyramid of bone called the modiolus. The bony cochlea contains three compartments: (a) scala vestibuli, (b) scala tympani, (c) scala media or the membranous cochlea

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Each canal has an ampullated end which opens independently into the vestibule and a nonampullated end. The non-ampullated ends of posterior and superior canals unite to form a common channel called the crus commune.

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4. Vestibular aqueduct

Tubular structure that arises from vestibule and runs along posterior inferior aspect of petrous boneContains endolymphatic duct and sacNormally measures less than 1.5mm in diameter or approximates the size of post. SCC which runs anterior and parallel the aqueduct.

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Membranous labyrinth Cochlear duct : Also called the scala media. It is a blind coiled tube. It appears triangular on cross-section and its three walls are formed by:

(a) the basilar membrane, which supports the organ of corti,(b) the Reissner's membrane which separates it from the scala vestibuli, (c) the stria vascularis, which contains vascular epithelium and is concerned with secretion of endolymph. 14

Endolymphatic duct and sacEndolymphatic duct is formed by the union of two ducts, one each from the saccule and the utricle. It passes through the vestibular aqueduct.Its terminal part is dilated to form endolymphatic sac which lies between the two layers of dura on the posterior surface of the petrous bone15

Utricle and sacculeThe utricle lies in the posterior part of bony vestibule. It receives five openings of the three semicircular ductsThe saccule anterior to the utricle and opposite the stapes footplate

Internal Auditory CanalA bony conduit that transmits VII & VIII cranial nerves from pontomedullary junction to inner ear.

Divided by a bony lamina (falciform crest) into A. Smaller superior partSuperior vestibular N.Facial NerveB. Larger Inferior part Inferior vestibular N. Cochlear nerve.

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Blood supply of labyrinthArterial supply : Labyrinthine artery which is a branch of anterior-inferior cerebellar artery

Venous drainage : through three veins :

internal auditory vein vein of cochlear aqueduct vein of vestibular aqueduct Transverse sinus.17

Inferior petrosal sinus

Cross sectional anatomy of inner ear

White arrowhead : Modiolus with cochleaWhite arrow : I A C

Black arrowhead : VestibuleBlack arrow : Posterior semicircular canal Fig.1.-----Axial HRCT of Inner Ear18

Fig. 2 Axial heavily T2 WIFig. 3 Axial heavily T2 WICross sectional anatomy of inner ear Axial images shows basal turn of cochlea and osseous spiral laminaMiddle and apical turns with the modiolus (arrowhead) and the spiral lamina (curved arrow) dividing the cochlea into scala vestibuli and scala tympani . The nerves are seen in CP angle.19

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Cross sectional anatomy of inner ear

Fig. 3 Sagittal T2 MR ImagesShowing the four nerves within IAC : The facial nerve (arrow head), cochlear nerve (curved arrow) and superior and inferior vestibular nerves (arrowhead) 20

When and why MRIMRI essentially compliments CT because of its excellent soft tissue contrast

MRI is directed toward imaging of # Fluid containing spaces in temporal bone # Vascular structure and their pathologies # Adjacent brain parenchyma # Evaluation of 7th and 8th nerve complex

Loosely, one can state that conductive hearing loss is mainly evaluated by CT scan and sensorineural hearing loss by MRI

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IMAGING PROTOCOL -- MRI1.5 or 3 Tesla MRI is preferredSedation used in most children3D volumetric CISS in axial plane with coronal and sagittal reformation and MIP reconstructionSlice thickness of 0.4 0.7 mmOblique sagittal reformatted images in plane perpendicular to 7th and 8th nerve in IAC Routine axial T2WI of brain to exclude CNS causes of sensorineural hearing loss3D MPRAGE may be added.

Precontrast brain with thin section through the CPA- IAC region

MRA/ MRV as required

Post contrast fat sat.

Inner ear ImagingTumors and infection22

MAGNETIZATION-PREPARED RAPID ACQUISITION WITH GRADIENT ECHO.22

3D CISS Three dimensional (3D) constructive interference in steady state (CISS) is a heavily T2 weighted fully refocused gradient echo MR sequence.Being heavily T2 weighted it is better suited for imaging of structures surrounded by fluid like 7th 8th nerve complex and membranous labyrinth.3D sequence , so reconstruction in any plane possible.Other uses:- 1. Evaluation of cranial nerves 2. Diagnosis of NCC 3. Evaluation of CSF rhinorrhea 4. Evaluation of ventricular system etc.

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A steady state sequence is a type of gradient echo sequence in which residual transverse magnetization is refocused so that a steady magnitude longitudinal and transverse magnetization is achieved after a few repetition times (TR) periods.The same sequence in GE machine is called 3D FIESTA. Philips called DRIVE

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The 3 D reconstruction of inner ear done with post-processing by maximum intensity projection(MIP) and multi-planar reconstruction(MPR) by using 3D-CISS sequence

CONGENITAL ANOMALIES25

Congenital malformation of inner ear

Cochlear abnormalities are numerous and Jackler et al classified them on the basis of arrested development during organogenesis26

Inner ear abnormalities affects the cochlea, semicircular canals, vestibule and the vestibular/ cochlear aqueducts.26

TIMELINE OF CONGENITAL MALFORMATION OF INNER EAR27

COMPLETE LABYRINTHINE APLASIA OR MICHELE APLASIAMost severe inner ear deformityEtiology : Arrested development of otic placode during 3rd gestational weekExtremely rare only 1% of inner ear malformation.Unilateral/ bilateral. Unilateral cases are associated with contralateral inner ear dysplasia.

HRCT :- # Complete absence of inner ear with hypoplasia of petrous bone and narrow atretic IAC. # Absence of round and oval window # Flattening of medial wall of middle ear cavityMRI : 8th cranial nerve not visualized on MR images Associated with skull base, CVJ and vascular anomalies 28

Axial CT : Flat middle ear cavity and hypoplastic petrous boneCoronal CT : Atretic internal auditory canalSagittal MRI : single nerve within the IAC, suggesting absent 8th nerve29

Common cavity Defined by absence of normal differentiation between the cochlea and vestibule 25% of cochlear malformationArrest during 4th arrest of gestation

Associated with poor differentiation of membranous labyrinth as well resulting in severe to profound hearing loss30

Confluence of cochlea and vestibule in a cystic cavity with no internal architectureCommon cavityAbsence of cochlear nerve31

Cochlear Aplasia Cochlea fails to form Due to arrested development in latter part of 5th week The vestibule and semicircular canal are often malformed but may be normal.

Imaging features : 1. Absence of cochlea 2. Dilatation of vestibule 3. Deformity of semicircular canal 4. dense otic bone is present where cochlea would be 32

Axial CT images shows dilated globose vestibule (arrow head) , dense sclerotic bone where cochlea should be (curved arrow) , and a stunted dilated posterior semicircular canal (straight arrow). Coronal CT images shows malformed dilated lateral semicircular canal (straight arrow) with stunted superior semicircular canal (curved arrow)33

Cochlear Hypoplasia

Small rudimentary cochlear bud with normal or malformed vestibule and semicircular canal6th week of gestation -- 15 % of incidence CT scan: # Height around the cochlea is around (3-6) mm as compared to normal height of 12-13 mm # Abnormal Small IAC # Though cochlea is visible it has one turn or partial turn

Diagram shows : Small cochlear bud and abnormally small and deformed vestibule34

Axial CT & MRI :- Small cochlear bud and abnormally small and deformed vestibuleStenotic IAC35

Incomplete partition or dilatation defectDue to development around 7th weekIncludes the Mondinis defect (most common malformation 50%)Here basal turn of the cochlea is formed , however the middle and apical turns are replaced by a common cavity.Imaging : (Triad of ) # Instead of 2.5 turns , only 1.5 turns are present # enlargedvestibulewith normalsemicircular canal # enlarged vestibular aqueductcontaining a dilatedendolymphatic sac.MRI reveals : complete or partial absence of the normal interscalar septum36

Axial CT shows absence of the modiolus with a cystic cochlear apex (straight arrow) , dilatation of vestibular aqueduct (arrowhead) and vestibule (curved arrow)Slightly lower level shows normal basal turnCoronal CT images shows the cystic cochlear apex37

Lateral semicircular canal malformationOf anomalies of SCC, lateral semicircular canal malformations is most frequent. Hypoplasia of semicircular canal can lead to compensatory enlargement of the vestibule (lateral semicircular canal- vestibule dysplasia syndrome)Aplasia of SCC is associated with CHARGE syndrome

Axial CT shows a stenotic IAC (curved arrow) , mildly dilated vestibule with stunted lateral semicircular canal ( straight arrow). The posterior semicircular canal appears normal. 38

coloboma, heart anomalies, choanal atresia, retardation of growth and development, and genital and ear anomalies38

Large vestibular aqueduct syndromeThelarge vestibular aqueduct syndrome(LVAS)refers to the presence of congenital sensorineural hearing loss with an enlargedvestibular aqueductC/F : Sensorineural hearing loss starts in childhood and is progressiveAssociated with Pendred syndrome, vestibular and cochlear anomaliesImaging : # Vestibular aqueduct of 1.5 mmis considered the upper limit of normal. # Usually less than posterior semicircular canal.39

An enlarged vestibular aqueduct is defined by an anterior-posterior diameter greater than 1.5 mm, at the midpoint between its external aperture and the common crus. Hearing loss usually is bilateral, progressive in nature, and may be associated with vertigo. Some cases may be familial.39

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IAC and cochlear nerve anomaliesIAC normal diameter range from 2- 8 mm, average 4mmDiameter less than 2mm, described as StenoticSagittal oblique images obtained in a plane perpendicular to the long axis of IAC provides best depiction of the four major nerves of IACTypes of cochlear anomalies Type I A Stenotic IAC with absent 8th nerve Type 2 A common vestibulocochlear nerve with hypoplasia or aplasia of cochlear branch 2a associated with other inner ear anomaly 2b No associations.

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COMMON VASCULAR ANOMALIES

Aberrant (intratympanic) Internal Carotid ArteryDue to abnormal regression of cervical ICA during embryogenesis Aberrant ICA has a sharp angled posterolateral course where it tracks through the middle ear over the cochlear promontory.Importance : # Produces pulsatile tinnitus in few pt. # May be confused with Glomus tympanicum Paraganglioma43

Difference with paraganglioma is essential because a biopsy in leiu of a malignancy may have a disastrous consequences.43

CT: 1. Posterior carotid plate is absent 2. Horizontal part of carotid canal appears to merge with lateral cochlear promontoryMRI : 1. Routine MR sequence are not helpful. 2. MRA shows unusual posterolateral course of ICA44

Others arterial abnormality are : 44

Other arterial anomalies : 1. Persistant stapedial artery 2. Persistant trigeminal Artery 3. Anomalous artery in the stria vascularis of the cochleaEctatic vascular loops of AICA/PICA or tortous course of vertebral artery may present with tinnitus due to compression of VIII nerve complex.45

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Venous variantsHigh riding Jugular bulb : Large jugular bulb reaching above the internal auditory canal with intact sigmoid plateDehiscent Jugular Bulb : The sigmoid plate is deficient, the bulb protrudes into the middle ear cavity. It is a common cause of aretro-tympanic vascular mass.Jugular bulb diverticulum47

Dehiscent jugular bulbHigh riding jugular bulb48

INFLAMMATORY CONDITIONS

LABYRINTHITISTypes:Tympanic labyrinthitis : Infection spreads from middle ear via oval or round window or labyrinthine fistulaMeningogenic : Infection spreads along CSF spaces via IAC or cochlear aqueduct. Usually bilateral.Hematogenic labyrinthitis : spread of infection by blood-stream. Virus e.g, measles and mumps, syphilis etcPost traumatic labyrinthitis.

Inflammation of membranous labyrinth.

Viruses are the most common etiologic agents, but can be bacterial or autoimmune .50

Imaging features:CT : # Usually normal in acute stage # Ossification of membranous labyrinth in late chronic phaseMRI : contrast enhanced MR is the method of choice # T1- CEMR shows moderate to intense enhancement within normal fluid filled structure of inner ear # Usually viral conditions causes subtle enhancement and bacterial causes intense enhancement.Complication : Labyrinthitis ossificans is a Sequela of chronic labyrinthitis, usually Pyogenic in origin.

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Axial MRI in patient with suppurative labyrinthitis.Enhancement of internal auditory canal, cochlea, and vestibule.52

Labyrinthitis ossificans

Labyrinthitis ossificans (LO) is the pathologic formation of new bone within the lumen of the otic capsule.Etiology :- 1. Sequela of inflammation of the inner ear, e.g bacterial meningitisor purulent labyrinthitis 2. Vascular obstruction of the labyrinthine artery 3. Autoimmune labyrinthitis etc.Imaging : CT scan :- Osseous deposition within the membranous labyrinthMR Imaging :- Loss of the normal high signal on T2-weighted images from displacement of the endolymphatic fluid is suggestive of this diagnosis.53

Labyrinthitis ossificans (LO) is the pathologic ossification of spaces within the lumen of the bony labyrinth and cochlea that occurs in response to a destructive or inflammatory process. Regardless of the etiology, the most common region of cochlear ossification is the scala tympani of the basal turn, with the most extensive disease noted in post-meningitic cases.53

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Axial CT scan reveals at the level of internal auditory canal reveals complete ossification of the vestibule and semicircular canal.54

CHOLESTEATOMA WITH COMPLICATIONMRI features of cholesteatoma ::--

Hypointense on T1WI & Hyperintense on T2 WINo enhancement or faint peripheral rim enhancementDelayed Contrast scan (after 45min) continued enhancement of inflammatory or granulation tissue and not in cholesteatoma.DWI Cholesteatoma shows restricted diffusion and are hyperintense on b= 1000/m2.55

CHOLESTEATOMA WITH COMPLICATIONA . Labyrinthine fistula -- Most frequent complication with middle ear cholesteatoma (prevalence of 5% 10%).

C/F : Episodic vertigo, sensorineural hearing loss, tinnitus

CT Findings :- 1. Dehiscent lateral semicircular canal support the diagnosis 2. Uncommonly , dehiscence of cochlear promontory or fistula in oval window. MRI Findings :- a labyrinthine fistula causing labyrinthitis, shows enhancement of the membranous labyrinth.

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Magnetic resonance imaging (MRI) findings. (A) T2-weighted images revealed cholesteatoma induced inflammation in the right middle ear with abnormal communication with inner ear fluid-filled space. (B) Routine T1 weighted images after intravenous gadolinium administration revealed areas showed pathological enhancement in the lateral canal and cochlea on the right side. (C) High-resolution T1 weighted scans demonstrate prominent enhancement of lateral canal and entire length of cochlea more clearly (Cochlea, indicatedby arrow-heads; lateral semicircular canal, arrows)57

Other complications -B. Perineural extension of cholesteatoma along facial nerve.

C. Erosion of the sigmoid sinus plate and consecutive thrombosis, tympanic tegmen erosion and subsequent intracranial invasion, recurrent\bacterial meningitis, and intracranial abscess are rare complications, which, nevertheless, require an urgent CT/MR imaging examination58

Petrous apex granulomaCholesterol granuloma is an inflammatory granulation appearing in response to the deposits of cholesterol crystals

Etiology: Middle ear disorderscausing mucosal edema and deposition of cholesterol crystal

Site : Middle ear cavity followed by mastoid process and petrous apex

C/F : Hearing loss, vertigo, headaches, tinnitus Any focal neurological deficit, especially of cranial nerves VVIII

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Cholesterol granuloma may occur within any area of pneumautized temporal bone and it is associated with a variety of middle ear disorders followed by chronic obstruction of air exchange and inadequate aeration. Subsequently, absorption of gases, hypoxia, or negative pressure may cause mucosal edema with resultant stagnation and extravasation of blood, which can produce hemosiderin and cholesterol crystals. These substances lead to foreign-body reaction. Thus, cholesterol granuloma develops itself by repeating this process

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A CT of a cholesterol granuloma is nonenhancing, well marginated, and bone erosion is usually present(21). The MRI of a cholesterol granuloma is pathognomonic there is highsignal intensity on both T1 and T2-weighted images and there is no gadolinium enhancement, whereas cholesteatomas and epidermoid cysts show slightly greater cerebrospinal fluid signal intensity

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Petrous apicitisPetrous apicitis is infection with involvement of bone at the very apex of thepetrous temporal bone.Pathology : Osteitis developing from infected and obstructed air cells in a pneumatised petrous apexC/F: Presents with Gradenigos syndrome 1. petrous apicitis, with 2. 6th nervepalsy, and 3. Retro-orbital pain, or pain in the cutaneous distribution of thetrigeminal nerve, due to extension of inflammation intoMeckel's cave.

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CT scan : 1. Erosive lysis with ill-defined irregular edges of petrous apex2. Peripheral enhancement of petrous apex with dural enhancement and thickeningMRI: 1. Fluid signal intensity in petrous apex often with peripheral enhancement 2. More sensitive in detecting dural thickening and enhancement as well asleptomeningitis, cerebritisandcerebral abscess

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FACIAL NERVE LESIONS

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The facial nerve is the nerve of facial expression. It arises from lower border of pons at the pontomedullary junction from three different nucleus.Motor nucleus which hooks around the 6th nerve nucleus.Nucleus tractus solitarius : supplies taste sensation to tongueSuperior salivatory nucleus : Parasympathetic innerveation to salivary glands.The facial nerve is described as having six divisions: 1. Cisternal 2. Intracanalicular 3. Labyrinthine 4. Tympanic 5. mastoid and 6. Extratemporal segment.64

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Within the CP angle, the facial nerve is the most anterior and the vestibulocochlear nerve is the most posterior, with the nervus intermedius between the two.65

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The facial nerve enters the internal ear through the fallopian canal and this segment is callled the labyrinthine segment. At geniculate ganglion, it takes an acute turn posteriorly to form the tympanic portion of the nerve.The nerve than turn at 90 degrees to form the mastoid segment and exit the ear at the stylomastoid foramen. 66

BELLS PALSYBell's palsyis characterized by rapid onsetlower motor neuron facial nerveparalysis, often with resolution in 6 - 8 weeks.Etiology : 1. Idiopathic 2. Reactivation of Herpes Simplex Virus infection in geniculate ganglion. Pathogenesis : Secondary to swelling and edema of the 7th nerve within the facial nerve canalIndication for imaging : MRI not done routinely . Indicated if :- # Decompressive surgery is being planned # Atypical: No recovery in 6 wks, recurrent palsy, multiple cranial nerve involvement. 67

On MRI imaging enhancement of the facial nerve within the tympanic portion of the facial nerve canal supports the diagnosis. Reported enhancement rates vary from 57% to 100%.Typically long segments of the facial nerve enhance in a uniformly linear fashion68

Subtle but definite (asymetrical)enhancement of the left VIIth nerve especiallyat the genu and in thehorizontal portion of the nerve. This indicates an inflammatory process rather than Schwannoma as the enhancement is diffuse rather than focal, and non mass like.68

Facial SchwannomasFacial nerve Schwannoma are uncommon tumors arising from the Schwann cell sheathSite : Geniculate ganglion, followed by labyrinthine and tympanic segment.Pathology : Originate from surface of the nerve, and splay the nerve fibres over their eccentric growthC/F : 1. Persistent and gradually facial paresis. 2. Conductive hearing if tympanic segment involved causing ossicular compression 3. In CP angle or IAC : Presents with sensorineural deafness with facial paresis being rare in these cases. 4. Other like, tinnitus, hemifacial spasm, and otalgia

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Imaging features HRCT : Enhancing soft tissue density lesion along facial nerveIntracanalicular or CP angle tumor can cause bony erosion of anterosuperior portion of IAC

MRI:T1: Iso- to hypo intenserelative to gray matterT2: Hyperintense ;large lesion may show heterogeneous signalT1 C+ (GAD): Homogeneous enhancement with larger lesionsshowing cystic degeneration as focal intramurallow signal intensity

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CT SCAN : focal enlargement of the labyrinthine segment of the facial nerve

MRI: homogeneously enhancing mass filling the internal auditory canal with extension into the CP angle and labyrinthine segment

Diagnosis : Facial Nerve Schwannoma71

The axial T1-weighted post-contrast 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 with extension toward the external auditory canal.Diagnosis : Schwannoma of the mastoid segment of facial nerve.72

FACIAL NERVE HEMANGIOMARare tumor of vascular origin (0.7% of all intra-temporal tumors)This along with other vascular malformations are termed as Intra-temporal Benign Vascular Lesions

Age : 3rd to 6th decade without sex predilection

Site : Geniculate fossa followed by IAC

C/F: Facial nerve paralysis progressing over weeks. Sensorineural hearing loss and pulsatile tinnitus may occur if there is erosion of otic capsule.73

IMAGING FINDINGSMRI : # Intratemporal hemangiomas characteristically havevariable signal intensity on T1-weighted images increased signal intensity on T2-weighted imagesavid contrast enhancement. # Low-signal-intensity foci may be seen on T1- and T2-weighted images, corresponding to the ossic matrix of the lesion

CT Scan : Enables exquisite visualization of associated bone changes Tumor causes erosion which are irregular with indistinct margins giving a Honeycomb pattern of eroded bone.

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, there is abnormal globular signal hyperintensity in the region of the labyrinthine segment of the facial nerve and the inferior aspect of the left geniculate fossa (arrow), with stippled punctate foci of hypointense signal. In b, there is contiguous abnormal signal intensity in the more craniad aspect of the geniculate fossa intense enhancement of the lesion (arrow), with the exception of a few punctate areas of nonenhancement that correspond to the stippled hypointense foci I

There is a mildly expansile lytic lesion with fine internal high-attenuation spiculations in the region of the geniculate ganglion (long arrow). There is involvement of the labyrinthine portion of the facial nerve canal (short arrow) and proximal tympanic segment (*). (b)Coronal targeted reformatted CT image of the left temporal bone at the level of the cochlea (1-mm section thickness). The image is centered on the expansile le-sion shown in a(arrow) and best demonstrates the honeycomb pattern of internal bone spicules within the geniculate fossa75

Tumors in association with Inner ear

Anatomy: Cerebellopontine angle

Boundaries :- - Anterolateral surface of pons & Cerebellum - Posterior surface of petrous temporal bone77CRANIAL NERVE - V , VII & VIII

ARTERIES : SUP. CEREBELLAR A.AICAVEINS : TRIBUTARIES OF SUP PETROSAL V.

Imaging signs of extra-axial CPA cistern massesEnlarged ipsilateral CPA cisternCSF/ Vascular Cleft between mass and cerebellumDisplaced gray-white interface around massBrainstem rotatedFourth ventricle compressed.

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Corresponding drawing depicts a mass emanating from the internal auditory canal, bulging into CPA and impinging upon the middle cerebellar peduncle. 78

Cerebellopontine angle cistern massesAcoustic Schwannoma [75%]Meningioma [10%]Epidermoid [5%]Non acoustic Schwannoma [4%]AneurysmMetastasisParagangliomaEpendymomaChoroid plexus papilloma

Arachnoid cystLipomaDermoidBrain stem gliomaOsteo-cartilagenous tumorCommon tumorUncommon tumor79

Trigeminal scnwannoma is the most common non-acoustic schwannoma.79

Vestibular SchwannomaBenign tumor arising from Schwann cells that wrap vestibulocochlear nerve70- 80 % of CPA lesions Age 5th -6th decade.B/L acoustic Schwannoma pathognomonic for NF-2.

Origin : Most from Inferior Vestibular Nerve, at glial-schwann cell interface

Morphology : # Entirely intracanalicular # Intracanalicular with cisternal component Ice-cream cone appearance. # Rarely purely intracisternal.

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Second most common extra-axial neoplasm in adults80

Pathology : Compact Antoni Type A tissue or loose textured , often cystic Antoni type B tissue

C/F : SNHL or tinnitus, Hydrocephalus, CN palsies (If large)

Imaging findings : CT SCAN:-

# NECT :- Extra axial hypodense to isodense mass with its base on post aspect of petrous temp in region of IAM. # CECT :- Marked enhancement, large lesion m/b heterogeneous. # Erosion & widening of Internal Acoustic canal. # Small lesions c/b missed d/t beam hardening artifact.81

Asymmetry of the internal auditory canals of more than 2 mm suggests the presence of mass. 81

T1WI: 2/3rd are hypointense and 1/3rd are isointense. may contain hypo intense cystic areasT2WI : # Heterogeneously hyperintense # Small leson : "Filling defect" in high signal CSF of CPA-lAC cistern # may have associated peri-tumoural Arachnoid cysts

T1 C+ (Gd) : # contrast enhancement is vivid # Heterogeneous in larger tumors # Occasionally, may show extension into the cochlea and dural tail of enhancement.

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MR IMAGING FEATURES

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MENINGIOMAExtra-axial neoplastic lesions arising from Arachnoid cap cells.

2nd most common CPA tumor (10%)

Site : arises from the meninges covering posterior petrous bone.

Female > Male (2-3:1) , peak age = 60yrs.

C/F : Small Meningioma -entirely asymptomatic Large tumors headache, paresis or neurological deficit.

Morphology :

# "Mushroom cap" (hemispherical) with broad base towards posterior petrous wall (75%)

# Plaque-like : +/- bone invasion with hyperostosis (20%)

# Ovoid mass : mimicking Acoustic Schwannoma

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Imaging features NECT : # Frequently hyperdense with focal areas of calcification # Bony hyperostosis of petrous boneCECT : Presence of broad dural base with dural tail and intense enhancement is typical.MRI : # Isointense to brain parenchyma in T1 & T2WI # Blooming s/o calcification in GRE # Dural tail with other features of extra-axial lesion # May rarely extends into IAC and presents with diagnostic dilemma.

ANGIOGRAPHY : Homogenous blush which lasts till late venous phase (Mother In Law sign)

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Axial T1-weighted MRI image demonstrates a mass isointense to cerebral cortex involving the left cerebellopontine angle. B. Axial T2-weighted MRI image at the same level shows the mass is intermediate high-signal-intensity (higher then cerebral cortex but less than CSF). There is mass effect on the 4th ventricle and the pons without edema.Post-gadolinium MRI images show avid, homogeneous enhancement of the mass. There is a small dural tail (black arrow) and extension into the left IAC via the porus acousticus (white arrow). The IAC is not dilated. Mass effect is again seen on the pons, middle cerebellar peduncle, and 4th ventricle.

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Lipoma of internal auditory canal

Rare congenital lesion often associated with CP angle lipoma.CT Scan: Fat attenuating non enhancing lesionPresents with unilateral sensorineural hearing lossMRI : Non enhancing lesion which is hyperintense on T1WI & T2WI with suppression of SI on fat saturated images.

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Axial T1-weighted image (400/14/2) shows a hyperintense mass in the right vestibule (arrow).B, Axial T2-weighted fast spin-echo image (4000/102/4) shows the intravestibular mass to be hypointense relative to the fluid-filled membranous labyrinth (arrow).C, Coronal T2-weighted fast spin-echo image (4000/102/4) shows the intravestibular mass (large arrow), the horizontal semicircular canal (small arrow), and the basal turn of the cochlea (open arrow).D, Axial T1-weighted image (500/20/4) with fat saturation reveals saturation of the intravestibular mass (arrow), consistent with a lipoma.

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GLOMUS TUMOR (PARAGANGLIOMA)Slow growing, locally aggressive vascular tumor arising from chemoreceptor cellsArising from the 9th & 10th nerve, most common tumor of middle ear 2nd most common tumor of temporal bone

Unique names associated with location: - Jugular bulb Glomus jugulare Middle ear -- Glomus tympanicum Carotid body Carotid body tumor Vagus nerve ganglion-- Glomus vagale

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Clinical feature: Pulsating tinnitus with conductive hearing loss Invasion into cochlea leads to sensorineural hearing loss Otoscopy : Tympanic membrane appears blue Glomus tympanicum : Isolated to middle ear cavity Soft tissue density protruding from cochlear promontory .Homogenous enhancement on post contrast scan. Glomus Jugulare : Confined to jugular fossa and large at presentationInvades the hypo-tympanum and infralabryrinth compartment Tumor can follow the Jugular venous system upto lower cervical jugular vein.

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MRI features : T1WI Low signal intensityT2WI High signal IntensityT1C+ -- Marked intense enhancementSalt pepper appearance (T1 + T2) : Salt represents areas of hemorrhages and pepper represents areas of flow void.

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Perineural Spread of tumorsCommon with head & neck cancer.Nasopharyngeal CA followed by adenoid cystic carcinoma and lymphoma.Trigeminal and facial nerve are the commonest nerves involvement.Features of Perineural spread :- 1. Enlargement and enhancement along the course of nerve 2. Obliteration of the fat surrounding neural foramina 3. Denervated muscles becomes atrophic with time and replaced with fat. 4. Tumor in lateral aspect of pons should raise a suspicion. 91

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LESION OF ENDOLYMPHATIC SAC & DUCT

Endolymphatic hydrops ( Menieres )Refers to increased hydraulic pressure within inner ear endolymphatic system.Etiology: # Idiopathic (Menieres disease) # Association with autoimmune disease , hormonal and metabolic condition noted (Menieres syndrome)C/F : 1. Fluctuating hearing loss 2. Episodic vertigo 3. Tinnitus 4. Aural fullness

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Mnire disease is idiopathic by definition, whereas Mnire syndrome can occur secondary to various processes interfering with normal production or resorption of endolymph (eg, endocrine abnormalities, trauma, electrolyte imbalance, autoimmune dysfunction, medications, parasitic infections, hyperlipidemia).94

Role of MRI in Menieres diseaseBilateral intratympanic GBCA is being used for semi quantitative evaluation of Menieres.1- 1.5 ml of diluted gadolinium is injected into middle ear through a small myringotomy and evaluated after 24 hours.3D FLAIR is used to evaluate inner ear 3Tesla is better. The gadolinium successfully penetrated the round window membrane, entering the perilymphatic space and delineating the contrast-enhanced perilymphatic and contrast-negative endolymphatic spaces of the inner earIf the non-enhancing endolymphatic area exceed the perilymphatic area, it is considered significant.

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gadolinium-based contrast agent (GBCA)95

Normal : Inner ear ; No hydrops3D FLAIR : Significant enlargement [3350%] of the endolymphatic compartment in the cochlea;

in the vestibule and semicircular canal endolymphatic hydrops [>50%] has displaced almost all perilymph. 96

Endolymphatic sac tumorPapillary adenomatous tumors originating form endolymphatic sac. Described by Heffner in 1989.Occurs sporadically or with VHL diseaseAge : Presents early if associated with VHLC/F : Sensorineural hearing loss + Tinnitus +Vertigo

Imaging : CECT a. Heterogeneous lesion with moth-eaten retrolabyrinth petrous bone b. Intratumoral spiculated bone seen c. Intense enhancement in seen

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CT images showing an erosive lesion of the right petrous bone, centered at the right vestibular aqueduct opening (endolymphatic sac). The lesion is eroding the posterolateral wall of the jugular fossa. There is also erosion of the posterior wall of the right IAC, however the right IAC itself is still intact. There are scattered bony spicules seen within the lesion.97

MRI Features :T1 /T2WI : Mixed signal intensity lesion where focal high signal intensity d/t subacute hemorrhage and low signal intensity d/t calcification or hemosiderin.Blood filled cysts and protein cyst, both appearing hyperintense on T1/T2WI suggests the diagnosisMasses larger than 2 cm shows flow voidsT1C+ : Heterogeneous enhancement

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Axial T1 and axial T2 precontrast images, respectively, at the level of Cerebellopontine angle. There is a hyperintense multilobulated lesion occupying the right endolymphatic sac space. There is also a central area of low signal intensity which enhances post-gadolinium.T1-weighted post-gadolinium axial and coronal images, respectively. There is a central area of enhancement indicating hypervascularity. Low-signal intensities within the lesion represent intratumoral bony spicules.

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ISSUES WITH POST COCHLEAR IMPLANT CASESCochlear implants are not safe at 1.5TMR compatible CI are now availableExternal component should be removed in all casesRole of MRI is in preimplant evaluation to exclude cochlear aplasia which is contraindication for surgery. Absent Cochlear nerve is relative contraindication.CT scan is better for post-operative evaluation of these patients.99

ConclusionMR provides accurate anatomical delineation of complex soft tissue of inner ear3D reconstruction improves preimplant evaluationDetailed delineation of 7th & 8th nerve complex in temporal bone as well as membranous labyrinthDepiction of tumor size and extension into CP angle determines the approach to surgical removal.100

References Diagnostic Radiology- Neuroradiology AIIMS MAMC- PGI Course series . 3rd edition. CT and MRI of whole body John R Haaga 5th editionJoshi VM,Navlekar SK et.al -Ct and MRI imaging of the inner ear and brain in children with sensorineural hearing loss. Radiographics.2012 May-Jun;32(3):683-98Jeremy Hornibrook, Mark Coates, Tony Goh, Philip Bird et.al MRI imaging of the inner ear for Menieres disease. Journal of the New Zealand Medical Association. 27 August 2010, Vol 123 No 1321 101

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