imaging approach to & interpretation of findings in

8/22/2019 Imaging Approach to & Interpretation of Findings In

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IMAGING APPROACH TO &

INTERPRETATION OF FINDINGS INLESIONS IN THE CEREBELLOPONTINE ANGLE & INTERNAL

AUDITORY CANALBYDR (MRS) YANJU AKINOLAMBChB, FWACS, FMCR, FICS

ASSOCIATE PROFESSOR OFRADIOLOGY / HONORARYCONSULTANT LASUTH / LASUCOM

02/08/2013CNS UPDATE 2013LUTH

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Objectives

1. To review the process of imaging patientssuspected of harbouring CPA-IAC lesions.

2. To review the anatomy of the CPA-IAC.

3. To identify imaging findings of the commonlesions found in the CPA-IAC.


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Introduction

CPA tumours are the most common neoplasm inthe posterior fossa, constituting 5-10% ofintracranial tumors.

Mostly benign and extra-axial

Vestibular schwannomas (acoustic neuromas),

85%Lipomas,

vascular malformations,

hemangiomas.


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Introduction (Contd.)

The most frequent non-acoustic CPA tumoursinclude,

meningiomas

epidermoids (primary cholesteatomas),

facial or lower cranial nerve schwanomas.

Primary malignancies or metastatic lesionsaccount for less than 2% of neoplasm in the CPA


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DD of CPA LESIONS Vestibular schwannoma (85%)

Meningiomas (3-13%)

Epidermoids (2-6%) Facial and lower cranial nerve

schwannomas (1-2%)

Arachnoid cysts (1%)

Rare tumors

Lipomas Dermoid tumors

Neuroepithelial cysts

Trigeminal schwannoma

Endolymphatic sac carcinomas

Ependymoma

choroid plexus papillomas,

metastatic adenocarcinomas,

metastatic neuroblastoma, ependymoma,

lymphoma,

cholesterol cyst,

angioleiomyoma,

venous hemangioma, cavernous angioma, and

pontine glioma.


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OTHER DD. Brainstem glioma

Astrocytoma

Medulloblastoma

Choroid plexus papilloma Large or giant aneurysms of

anterior inferior cerebellar artery(AICA), superior cerebellar artery(SCA), or the midbasilar artery

Brainstem arteriovenousmalformation (AVM)

Brainstem cavernousmalformation originating in thebrain stem (may reach a pialsurface along the CPA)

Petroclival chondrosarcoma

Clivus chordoma (usually arise inmidline but may extend laterallyinto the CPA)

Osteosarcoma of the lateral skullbase

Metastatic tumors (can reach CPAby hematogenous spread or directextension)

Granulomatous inflammatorymasses


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Anatomy of the CPA & IAC

CPA is the anatomic space between thecerebellum and the pons.

A common site for the growth of acousticneuromas or schwannomas.

Neurologic syndrome / deficits occur due to the

proximity of the CPA to specific cranial nerves


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Anatomy of the CPA & IAC (Contd.) 8th cranial nerve enters the cranial

cavity through the internal auditorymeatus, which is found in thetemporal bone

also entering through this canal arethe facial nerve and thelabyrinthine artery(which providesthe blood supply to the inner ear)

the close relationship between the VIIand VIII cranial nerves can explainsome of the complications of an

ACOUSTIC NEUROMA 8th nerve fibres enter the

ventrolateral surface of the medulla atthe cerebellopontine angle, anterior tothe inferior cerebellar peduncle (25 onthe brainstem) and lateral to the facialnerve


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Anatomy of the CPA & IAC (Contd.)

Lateral view of thebrainstem:

1. medial geniculate body2. brachium of the inferiorcolliculus

4. inferior colliculus

25. Cerebellar Peduncle


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The internal acoustic meatus (also internalauditory meatus, IAM) is a canal within the temporal

bone that transmits nerves and vessels from within theposterior cranial fossa to the auditory apparatus.Contents of the IAM include:Facial nerve, V11Vestibulocochlear nerve, V111

Vestibular ganglionLabyrinthine artery (usually a branch of the Anterior

Inferior Cerebellar Artery or basilar artery) The opening of the IAM is located within the cranial

cavity, near the posterior surface of the temporal bone.


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IACNormal anatomy of the temporal bone.MPR/CT

EAC =External auditory canal,

Carotid canal = CC Jugular bulb =JB,

Malleus = M,

Facial nerve =FN,

Cochlea = C,

Semicircular canals = SCC,

Internal auditory canal = IAC,

Incus = I,

Vestibule = V,

Vestibular aqueduct = VA,

Mastoid air cells = MAC.

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1. Ear drum

2. Malleus

3. Incus4. Stapes

5. Semicircular canals

6. Auditory nerve

7. Facial nerve

8. Vestibular nerve9. Cochlea

10. Eustacian tube


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The margins of the opening are smooth androunded and the canal is short (1 cm), running

laterally to the bone.

At the distal end of the canal, it splits into threedistinct openings, one of which is the facial

canal.


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Anatomy of the CPA & IAC (Contd.)Nerves There are five nerves that run through the IAC:

1. nervus intermedius (sensory component of CN V11)2. facial motor root (motor component of CN V11)3. cochlear nerve (component of CN V111)4. inferior vestibular nerve (component of CN V111)5. superior vestibular nerve (component of CN V111)

Their position is most constant in the lateral portion ofthe meatus which is anatomically divided by thefalciform crescent.

This horizontal ridge divides the canal into superiorand inferior portions.


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Superior: facial nerve and superior vestibularnerve (SVN); the facial nerve is anterior to the SVN and

is separated from it laterally byBills bar, a verticalridge of bone Inferior: cochlear nerve and inferior vestibular

nerve (IVN); the cochlear nerve is situated anteriorlyGanglion

In addition to the three nerves which enter it, it alsocontains the vestibular ganglion (Ganglion of Scarpa)From here three bundles emerge (superior and inferiordivision of the vestibular nerve and the nerve from theposterior semicircular canal


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Imaging The IAC is housed by the petrous temporal bone which

is a complex structure with many tiny bones (crura of

stapes, vestibular acqueduct,


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Imaging (Contd.) Plain radiography, now obsolete except for postop.

assessment of cochlear implants Views include, Stenvers view (Oblique PA)

Periorbital view best for IAM, if tomography isnot available

CT shows intracranial lesions & its extensions

Contrast enhancement required except if lesion isconfined to petrous pyramid

Thin slices with wide window setting, 3000-4000HU Starts with lateral scout film, then axial, coronal &

reformatted images


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Imaging (Contd.)MRI

Bone Negligible signal. Appears same as air

Bone details better seen by CT

Soft tissue details on MRI. Cranial Nerves well seen

TIW intense signal with yellow bone marrow

(high fat content especially in petrous apex) CSF & Labyrinthe fluid low signal intensity on

T1W, Spin echo & high signal on T2W

Flowing blood gives no signal blood vessels are

normally black


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Imaging (Contd.)

Standard MRI studies using TI & T2 Protocol

T1W - better spatial resolution

T2W - poorer spatial resolution & take longer toacquire images.

T2 gives higher signal from water containing

structures (as in tumours) With Gadolinium DTPA, there is significant

enhancement


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Imaging (Contd.)

Angiography

Has a limited role now for vascular anomaliesand tumours. MRA& CTAhave replaced it

Rarely used as diagnostic means now.

More for pre operative assessment and for

therapeutic embolization Aneurysm and vascular malformations require

selective angio.

Gradient echo sequences used


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Imaging Studies Adults suspected to have CPA-IAC disease, usually

complain ofsensorineural hearing loss

(SNHL), can be imaged either withconventional enhanced T1 fat-saturated MR orhigh-resolution T2 MR imaging. CPA-IAC diseases that may be found include

congenital lesions such as epidermoid cyst,arachnoid cyst and CPA-IAC lipoma. Benign tumors found in this location include

acoustic schwannoma, meningioma, facial nerveschwannoma and IAC hemangioma.


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Acoustic Neuroma (VestibularSchwanoma) Benign, primary intracranial tumours of the myelin

forming cells of the vestibulocochlear nerve (CN VIII).

involves the vestibular portion of the 8th

cranial nerve, arises from Schwann cells, which are responsible for

the myelin sheath in the peripheral nervous system. 3,000 cases are diagnosed each year in the US, with a

prevalence of about 1 in 100,000 worldwide.

510% of all intracranial neoplasm in adults. Incidence peaks in the fifth and sixth decades both sexes are affected equally.


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Imaging Studies (Contd.)Site of acoustic N/Intracanalicular Schw.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.) Ipsilateral SNHL/deafness,

disturbed sense of balance and altered gait,

vertigo with associated nausea and vomiting, pressure in the ear, all of which can be attributed to the

disruption of normal vestibulocochlear nerve function.

Tinnitus in > 80%, (usually unilateral, high-pitched

ringing, sometimes a machinery-like roaring or hissingsound, like a steam kettle).

Large tumours that compress the adjacent brainstemmay affect other local cranial nerves.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.) 7th cranial nerves are rarely involved pre-

operatively

Involvement of the trigeminal nerve (CN Vloss of sensation in the involved side's face andmouth.

The glossopharyngeal and vagus nerves are not

usually involved, but their involvementaltered gag or swallowing reflexes. Larger tumors increased intracranial

pressure, with its associated symptoms such asheadache, vomiting, and altered consciousness.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.)Pathogenesis May occur idiopathically or as part ofvon Recklinghausen

neurofibromatosis, in which case the neuroma may take

on one of two forms. InNeurofibromatosis type I, schwannoma may

sporadically involve the 8th nerve, usually in adult life, butmay involve any other cranial nerve or the spinal root.

Bilateral acoustic neuroma are rare in this type. InNeurofibromatosis type II, bilateral acoustic neuroma

are the hallmark and typically present before the age of 21. Tend to involve the entire extent of the nerve and show a

strong autosomal dominant inheritance. Incidence is about 5 to 10%.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.) Usually in the adult, presents as a solitary

tumour, originating in the nerve.

From the vestibular portion of the 8th nerve,just within the internal auditory canal.

Usually extends into the posterior fossa to

occupy the angle between the cerebellum andthe pons (cerebellopontine angle).

may also compress the 5th, 7th, and less often,the 9th and 10th cranial nerves.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.) Later, may compress the pons and lateral medulla,

causing obstruction of the CSF and increased

intracranial pressure. Schwannomas can occur in relation to other cranial

nerves or spinal nerve roots, resulting inradiculopathy or spinal cord compression.

Trigeminal neuroma are the second most commonform of schwannomas involving cranial nerve.

Schwannomas of other cranial nerve are very rare.


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Acoustic Neuroma (VestibularSchwanoma)(Contd.) Contrast-enhanced CT will

detect almost all acousticneuromas that > 2.0 cm indiameter and project furtherthan 1.5 cm into thecerebellopontine angle.

smaller tumors may bedetected by MRI with

gadolinium enhancement.


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http://en.wikipedia.org/wiki/File:Vestibularis-Schwannom.jpg


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Acoustic Neuroma (VestibularSchwanoma)(Contd.)VESTIBULAR SCHWANOMA VESTIBULAR SCHWANOMA

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Acoustic Neuroma (VestibularSchwanoma)(Contd.)VESTIBULAR SCHWANOMA VESTIBULAR SCHWANOMA

02/08/2013

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http://en.wikipedia.org/wiki/File:Akustikusneurinom_Mrt.jpg


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MeningiomaPathophysiology 2nd most common tumour of CPA

Arise from the meninges, the membranous layerssurrounding the CNS.

According to the American Brain Association, theyare the most common primary brain tumour,

representing 1/3 of all such tumors. Arise from the arachnoid "cap" cells of thearachnoid villi in the meninges.

Usuallybenign but may be locally aggresive;however, a small percentage are malignant


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Pathophysiology

Meningioma(Contd.) Many are asymptomatic, producing no symptoms

throughout a person's life, and require no treatmentother than periodic observation.

The 4 histologic variants, (1) meningothelial, (2)fibroblastic, (3) transitional, (4)angioblastic.

Angioblastic variant is more aggressive.

usually arise on the posterior surface of the petrousbone, near the porous acusticus, or along the lateralvenous sinus.

Oval / hemisphericbroad dural-based, attachedto the tentorium/petrous bone dura


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Pathophysiology

Meningioma(Contd.) Displace but do not invade adjacent neural

tissue.

Meningiomas usually have a thin investingcapsule.

They can invade bone without destruction by

extension along haversian canals. 60% extend into the middle fossa.

Intense contrast enhancement

Usually does not extend into the IAC


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EpidermoidPathophysiology Originate from epithelial restswithin the

temporal bone or CPA. Usually grow very slowly with undulating margins. Patients often do not present until the 2nd to 4th

decade of life. Tend to envelop rather than displace adjacent

neural and vascular structures. Variable shapes, with irregular patterns. Usually develop multiple fingerlike projections

between cranial nerves and brainstem fissures, sulciand blood vessels.


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Pathophysiology - Epidermoid(Contd) Lamellated / onion skin appearance

May extend through the tentorium into the middle

fossa, forming a dumbbell shape. Imaging signal is similar to that of CSF

May show a peripheral rim of calcification

No enhancement with Gadolinium on MRI

T1W Hypo / Iso intense

T2W & Flair Iso / Hyperintense

DWI Marked restriction bright

appearance


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Pathophysiology - Epidermoid(Contd) Apparent diffusion coefficient (ADC) values of

epidermoid are significantly lower than that of

CSF and higher than that of deep white matter Unusual imaging findings include,

Hyperdensity on CT, T1W, T2W MRI which may

be due to the high protein content of the cyst


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Facial and lower cranial nerveschwannoma: Arise from Schwann cells anywhere along the

course of the nerve.

May be cystic / solid

Cystic schwanomas are larger, with a thin rimenhancement of the wall

Funnel shaped in axial MRI and club shaped oncoronal images

Half of the solid tumours stronghomogenous enhancement


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Arachnoid cysts CPA is the 2nd most common site for arachnoid

cyst to occur, sylvian fissure being the 1st

These are thin-walled sacs containing yellowcerebral spinal fluid (CSF) that most likelyoriginate as congenital developmentalanomalies.

Smooth walled with CSF intensity on MRI

Dont enhance with contrast


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Arachnoid cysts(Contd.) Similar to epidermoid cysts in that they are well

defined, homogenous low density, similar to CSF on

CT, with no contrast enhancement and on MRI Hypointense on T1Wand hyperintense on T2W

On FLAIR, similar intensity to CSF unlikeepidermoid which is strongly hyperintense

Echo planar diffusion scanning, helpsdifferentiate : Arachnoid cyst is hypointensebut epidermoid is hyperintense


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Presentation of CPA tumours

Hearing loss - 95%

Tinnitus - 80%

Vertigo/unsteadiness - 50-75%

Headache - 25%

Facial hypesthesia - 35-50%

Diplopia - 10% Symptoms can vary according to the size and

location of the lesion.


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Presentation of CPA tumours (Contd.)Meningioma Trigeminal or facial nerve symptoms are likely to occur

earlier than hearing loss.

Patients with larger tumours can present withobstructive hydrocephalus and/or symptoms ofbrainstem compression.

Epidermoid These can become quite large without symptoms.

Facial twitching (hemifacial spasm) and progressivefacial paralysis is more prominent than with othertumors in the CPA.

Patients may present with cranial nerve or cerebellardysfunction that develops over a number of years.


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Presentation of CPA tumours(Contd.)Facial nerve schwannoma Findings depend on the portion of the nerve affected Conductive hearing loss from middle ear involvement, parotid

mass from extratemporal involvement, or sensorineural lossfrom internal auditory canal (IAC) or CPA involvement. CPA lesions do not cause facial weakness until tumor is very large

(hemangiomas of the facial nerve usually cause symptoms at anearlier stage).

Hemifacial spasm is relatively common.

Lower cranial nerve schwannoma Patients may have weakness and hypesthesia of the palate, vocalcord, and shoulder (cranial nerves [CN] IX, X, XI) or hemiatrophyof the tongue (CN XII).

Large tumours may cause deficits of all the lower cranial nerves


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Imaging StudiesMeningioma Computed tomography (CT) scanning findings

Hyperdense compared with the cerebellum on NCE images

May demonstrate calcifications within or at the periphery of the tumor May be a broad attachment to the petrous ridge Less likely to show enlargement of the internal auditory canal (IAC) than

vestibular schwannomas MRI findings

Variable intensity on T2W images and either isointense or slightlyhypointense to brain on T1W images

Can be heterogeneous as a result of calcifications and cystic foci withinthe tumor

Dural tail sign, characterized by enhancement of the dura adjacent toan enhanced primary lesion, possible on contrast-enhanced MRI


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CT / MRI FINDINGSLEFT IAC MASS WITH CALCIFIC. DURAL TAIL


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Imaging Studies (Contd.)IAC MENINGIOMA WITH DURAL T. IAC MENINGIOMA


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Imaging Studies (Contd.)Epidermoid CT scanning findings

Hypointense to brain

Do not enhance (enhancement suggests an associatedmalignancy or infection)

Irregular margins with variable involvement of IAC MRI findings

Heterogeneous and hypointense to brain on T1-weighted

images Homogeneous and isointense or hyperintense to brain on

T2-weighted images Nonenhancing (allows them to be differentiated from

schwannomas, meningiomas, and chondromas, which havesimilar intensity)


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EPIDERMOID CYSTNCE CT T1W MRI


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EPIDERMOID CYST(Contd.)

T1W MRI / T2W MRI T2W MRI / DWI


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Imaging Studies (Contd.)Facial nerve schwanoma CT scanning findings

Identical to vestibular schwannoma within the IACexcept for possible anterosuperior IAC erosion orerosion of facial nerve canal in labyrinthine segment

May have enlargement of geniculate ganglion andfallopian canal (more common)

MRI findings Isointense or mildly hypointense to brain on T1WI Mildly hyperintense to brain on T2WI Enhances with gadolinium contrast


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Imaging Studies (Contd.)Lower cranial nerve schwannoma

Enlargement of jugular foramen with cranial

nerve IX, X, and XI tumours Enlargement of hypoglossal canal with cranial

nerve XII tumours


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Imaging Studies (Contd.)Arachnoid cyst

CT scanning findings

Typically smooth surface lesion isointense withCSF

Non enhancing

MRI findings

Isointense or hypointense with brain on T1-weighted images

Hyperintense to brain on T2-weighted images


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Lipoma Lipomas develop from mesenchymatous cells In the IAC bone erosion, but is atypical for CPA lipomas CT scans show a typical low density mass that has attenuation

characteristics similar to adipose tissue (-50 to -100HU). At MRI lipomas appear similar to fat, hyperintense, compared

to brain, on T1-weighted images and hypointense on standardT2-weighted spin echo frequencies.

With gadolinium no enhancement. DD, hemorrage or highly proteinaceous fluid. Fat suppression techniques in T1-weighted scans can be used

to confirm the diagnosis, when it changes from the high signalintensity to an isointense aspect


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Lipoma (Cond.)T1W T1W


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Lipoma (Contd.)Coronal STIR MRI. Fat suppressed

Contrast enhanced T1W + FatSuppression / T1W


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Cerebral angiography Cerebral angiography is used when involvement of a

large vessel is suspected or preoperative

embolization is required. It is used to assess patency in vessels encased bytumor.

Balloon test occlusion can aid in determininglikelihood of catastrophic stroke if internal carotidartery sacrifice is contemplated.

Preoperative embolization can be performed invascular tumors to effectively decrease amount ofblood loss


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Treatment Surgical intervention remains the most

definitive means for complete tumour removal

for most of these lesions. Radiation therapyhas gained popularity to

arrest tumour growth with specific tumour typesand is also an option for patients who areunwilling or medically unable to undergosurgery


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Contraindications

Occasionally, complete resection is impossiblebecause of the intimate involvement of

surrounding structures, which may causeunnecessary morbidity if complete excision isattempted, and planned partial resection isconsidered.


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WORK UP OF PATIENTS WITH CPA/IACTUMOURSAudiovestibular assessment.

Audiology and vestibular tests should be

concurrently evaluated using air conductionandbone conduction threshold testing toassess for sensorineural versus conductionhearing loss.

MRI: T1W & T2W with or without contast;DWI

CT Scan: CE / NCE


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MORE IMAGES Ac.Neur.


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IAC MASS

Glomus tympanicum (arrow)

in a patient with right-sidedpulsatile tinnitus. Axial CTimage demonstrates lobulatedsoft-tissue attenuation in themiddle ear overlying thecochlear promontory.


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http://www.ajnr.org/content/31/2/211/F1.expansion.html


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Aberrant course of the ICA presenting with pulsatile tinnitus.A, CECT shows an abnormallateral course of the right ICA through the middle ear (white arrow), destruction of the

overlying bony plate.

B, AP from the MR angiogram shows decreased caliber and lateral deviation of the aberrantICA on the right reversed-7 sign (black arrow).


P di f h k ll A i l CT

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http://www.ajnr.org/content/31/2/211/F2.expansion.html


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Paget disease of the skull. Axial CT scandemonstrates diffuse expansion andsclerosis of the bones of the skull base.Note the sparing of the maxillofacial

bones, which is a helpful indifferentiating it from fibrous dysplasia.

Temporal bone Meningioma. Axial CT imagedemonstrates diffuse sclerosis of the temporal boneand soft-tissue attenuation (black arrows) in the leftmastoid and middle ear cavity.

B, Axial enhanced MR image showing enhancementwithin the left middle ear (white arrow).


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THANK YOU&

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