Cerebellopontine Angle Masses

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Cerebellopontine Angle Masses

• ALI SAFAR - PGY4
• November 09, 05
• University of Ottawa
• ENT Dept. Grand Rounds

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Introduction

• 10 of all intracranial tumors.
• Fatal without treatment.
• 78 are acoustic neuromas- mostly on vestibular
  branch.
• Other CPA masses
• Meningiomas
• CN schwannomas
• Dermoid tumors
• Arachnoid cysts
• Lipomas, metastatic tumors
• Vascular tumors

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Anatomy

• Potential space in the posterior fossa of the
  brain.
• CPA boundries
• Anterior posterior surface of temporal bone
• Posterior anterior surface of the cerebellum
• Medial lateral surface of brainstem
• Lateral petrous bone
• Superior inferior border of pons cerebellar
  peduncle
• Inferior cerebellar tonsil

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• Cranial nerves
• VII VIII
• V
• IX, X, XI
• Important structures
• Flocculus
• Lateral aperture of 4th ventrical
• AICA

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Differential

• Acoustic Neuroma 60 - 92
• Meningioma
• Epidermoids
• Rare CPA lesions
• Petrous Apex masses
• Vascular malformations
• Intra-axial masses

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Acoustic Neuroma

• Comprises 60-92 of CPA lesions.
• Usually unilateral.
• Arise from schwann cells, commonly within IAC.
• Occur with equal frequency on the Superior
  Inferior vestibular nerves.
• Greatest density of S. cells at scarpa ganglion.
• Majority of cases (95) are sporadic.
• Rarely occur on the cochlear division of the 8th
  CN.

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Acoustic Neuroma

• Type 2 NF
• Genetic defect on long arm of chromosome 22.
• Autosomal-dominant.
• Bilateral or early in life.
• Assoc. with intracranial meningiomas spinal
  cord tumors.
• Tumors supressor gene is absent.

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Pathology

• Composed of Antoni AB tissue.
• Antoni A compact tissue with spindle cells in
  palisades (most common).
• Antoni B loose tissue with cyst formation.

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AN Manifestations

• Cochlear
• Asymmetric SNHL
• SSNHL
• Up to 26 of AN may present with SSNHL
• Only 1-2.5 of SSNHL is due to AN
• Tinnitus
• Decreased discrimination
• Rollover phenomenon
• Vestibular
• Dysequilibrium (more common)
• Vertigo (less common)
• Facial
• Facial weakness (suspect other tumors -
  epidermoid)
• Hitselbergers sign decreased sensation of EAC
  due to compression of CN VII sensory roots

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AN Manifestations

• Cerebellar
• Wide gait
• Falling to side of lesion
• Brainstem
• Headache
• Visual Loss
• Other Cranial nerves
• V facial numbness (large tumors, trigeminal
  schwannoma)
• VI lateral rectus palsy (rare)
• IX dysphagia (large tumors, J F S)
• X hoarseness, aspiration (large tumors, J F S)
• XI shoulder weakness (large tumors, J F S)

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Diagnostic Tests

• Audiometric Testing.
• Electrophysiologic Testing.
• Vestibular Testing.
• CT MRI.

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Audiometric Testing

• Pure-tone testing
• SNHL- most commonly high frequency (65).
• Normal hearing (5).
• Speech discrimination
• Scores out of proportion with pure-tone
  thresholds.
• Some may score well.
• Rollover phenomenon improve the sensitivity.
• Acoustic reflex thresholds
• typically elevated or absent.
• If present then reflex decay measured.
• The sensitivity is 85 for detecting
  retrocochlear problem.

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Electrophysiologic Testing

• ABR
• Most sensitive specific audiologic test.
• Abnormalities seen
• Interaural difference in latency of wave 5 with
  delay of more than 0.2 msec (40-60).
• No identifiable wave forms in 20-30.
• Wave 1 present but all remaining waves are absent
  in 10-20.
• Normal in 10-15.

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Vestibular Testing

• ENG
• Abnormal in 70-90.
• Unilateral weakness in caloric testing.
• Spontaneous nystagmus.
• Only test superior nerve.
• No abnormality for smaller tumors.
• Computerized dynamic posturography.
• Rotary chair testing.

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Imaging Techniques

• CT
• Non-contrasted
• Iodine based contrast - uptake by selected
  lesions
• CT air cisternogram no longer performed
• MRI
• T1W Fat density is bright
• T2W Water density is bright
• FLAIR (Fluid Attenuated Inversion Recovery)
• Gadolinium

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Radiologic Features of AN

• CT
• Non-contrast usually isodense to brain,
  calcification is rare
• IV Contrast Over 90 of non-treated tumors
  enhance homogeneously
• MRI
• T1W isointense to brain, hyperintense to CSF
• T2W hyperintense to brain, iso/hypo-intense to
  CSF
• Gadolinium Intense enhancement of tumor on T1W

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AN Features Centered on Porus acousticus. Acute
angles to petrous bone Often involves the
IAC Homogeneous enhancement No dural tail No
calcifications
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Meningioma

• Second most common CPA lesion 3-7 .
• Arise from cap cells near arachnoid villi which
  are more prominent near cranial nerve foramina
  and venous sinuses.
• Usually arise from posterior surface of the
  petrous bone and usually do not extend into IAC.
• Symptoms
• Ataxia.
• Nystagmus.
• Facial hypesthesia.
• Audiologic findings may show retrocochlear
  pattern or may be normal.

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Meningioma

• Radiologic features
• Tumors generally hemispherical with obtuse angles
  to petrous bone
• Dural tail often present (50-75)
• May herniate into middle fossa (50)
• May show calcification (25)
• Pial blood vessels with flow voids may be present
  at the margins.
• Treatment
• Surgical removal is treatment of choice
• XRT if complete excision not possible

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• Meningioma Features
• Arise from surface of petrous
• bone.
• Obtuse angles to petrous bone.
• Uncommonly involves the IAC.
• Frequently with dural tail.
• Calcifications common.
• Pial vessel flow voids.

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Epidermoid

• Accounts for 2-6 of CPA masses
• Physiology
• Congenital lesions that present in adulthood
• Rests of ectodermal tissue containing stratified
  squamous lining and keratin
• May arise within the temporal bone or in the CPA
• Benign and slow growing
• Symptoms
• Similar to acoustic neuroma and meningioma
• Facial nerve paresis and facial twitching may
  occur

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Epidermoid

• Radiologic Features
• May dumbell into middle fossa or contralateral
  cistern
• Highly variable in shape with a cauliflower
  surface appearance
• CT
• mass hypodense to CSF
• Do not enhance
• MRI homogeneous lesion
• T1 isointense to CSF
• T2 isointense to CSF
• Differentiation from arachnoid cyst may be
  difficult
• Diffusion weighting will show moderate intensity
  for epidermoids, but low intensity for arachnoid
  cysts.

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Arachnoid Cyst
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Other Extra-axial Masses

• Primary
• Arachnoid Cyst
• Schwannomas (CN V-XII)
• Hemangiomas
• Lipoma
• Dermoid/Teratoma
• Secondary
• Paraganglioma
• Chondroma
• Chordoma
• Extension of Petrous bone tumors

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Schwannomas

• CN VII
• Symptoms may be identical to acoustic schwannoma
• Differentiation from acoustic schwannoma may not
  be possible by radiography unless lesion extends
  distal to geniculate ganglion.
• CN IX XI
• Jugular Foramen syndrome
• Dysphagia
• Hoarseness
• Shoulder weakness
• Enlargement of Jugular Foramen
• CN XII
• Hemiatrophy of tongue
• Enlargement of hypoglossal

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CN V Schwanoma
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CN VII Schwanoma
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CN X Schwanoma
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Vascular

• Vertebrobasilar dolichoectasia
• Enlongation and dilatation of the vertebrobasilar
  artery.
• Symptomas - Facial spasm, trigeminal neuralgia
• AICA loop
• May loop over, under, or between CN VII CN
  VIII.
• Symptoms - vertigo
• Giant Aneurysms
• Hemangioma
• Paragangliomas (may extend to CPA)
• Glomus Jugulare
• Glomus Tympanicum

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Vertebrobasilar Dolichoectasia
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AICA loop
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Giant Aneurysms

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Glomus Jugulare
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Petrous Apex

• Cholesterol granulomas (most common)
• Epidermoid cyst
• Trigeminal schwannoma
• Carotid artery aneurysm
• Chondroma
• Chondrosarcoma

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Cholesterol Granulomas
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Intra-axial

• Astrocytoma
• Ependymoma
• Medulloblastoma
• Hemangioma / Hemangioblastoma
• Choroid plexus papilloma
• Metastasis

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Treatment

• Observation
• Surgery
• Translabrynthine
• Retrosigmoid
• Middle Fossa
• Radiotherapy
• Conventional radiation therapy
• Stereotactic radiosurgery

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Observation

• Indications
• Advanced age (over 65 or 75)
• Poor health
• Lack of symptoms
• Non-progression of symptoms
• Only hearing ear
• Isolated IAC tumors in the elderly
• Contraindications
• Young patient
• Healthy patient
• Symptomatic progression
• Compression of brainstem structures

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Trans-labrynthine

• Indications
• Extension into CPA gt 0.5 - 1cm
• Non-serviceable hearing
• Adequate contralateral hearing in large tumors
• Contraindications
• Serviceable hearing

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Middle Fossa

• Indications
• Small tumor
• Intracanallicular tumor
• Moderate CPA involvement
• Adequate hearing (SRTlt50 db, Disc gt50)
• Contraindications
• Large tumors
• Extensive CPA involvement ( gt 0.5 1 cm)
• Older patients ( gt 60 yrs. may have higher rate
  of bleeding or stroke)

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Retrosigmoid

• Indications
• Serviceable hearing
• Large tumors
• Compression of brainstem
• Contraindications
• Functional hearing with extensive IAC involvement
• Intracanallicular tumors

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Stereotactic Radiosurgery

• Indications
• Small tumors
• Functional hearing
• Older patients (gt75)
• Medically unstable patients
• Previous resection
• Contraindications
• Tumors gt 3 cm
• Prior radiotherapy
• Tumor compressing brainstem

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Stereotactic Radiosurgery

• Outcome
• Local control (non-progression) 94
• Hearing preservation 47 77
• Complications
• Facial nerve injury 5 - 17
• Trigeminal nereve injury 2 - 11
• Hyrodcephalus 3

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