Posterior Fossa Skull Base Lesions

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Posterior Fossa Skull Base Lesions

• Ali Sepehr
• UCI Department of Otolaryngology- Head and Neck
  Surgery

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Posterior fossa skull base lesions

• CPA

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CPA

• Borders
• Medial lateral surface of the brainstem
• Lateral petrous bone
• Superior middle cerebellar peduncle
  cerebellum
• Inferior arachnoid tissue of lower cranial
  nerves
• Posterior inferior cerebellar peduncle

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Skull base lesions (cont.)

• Petrous apex
• Cholesterol granuloma
• Epidermoid
• Asymmetric pneumatization
• Retained mucus or mucocele
• Petrous carotid artery aneurysm
• Intra-axial
• Hemangioblastoma
• Medulloblastoma
• Astrocytoma
• Glioma
• Fourth ventricle tumor

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Acoustic Neuroma (AN)

• Benign schwann cells in collagenous matrix and
  dont invade (usually cause symptoms by
  encroaching)
• Usually arise from vestibular (95) nerve in IAC
  but if they arise medial then symptoms develop
  later
• 95 are unilateral and nonhereditary
• M F
• Slow growing (0.2-4mm/yr)

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Growth phases

• IAC
• acoustic and facial nerve compression
• Cisternal
• blood from brainstem
• Brainstem compression
• 4th ventricle compression occurs at 2-3 cm

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Histopathology

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

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Hereditary ANs

• Neurofibromatosis

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Signs and symptoms

• SNHL (95),SSNHL (20), tinnitus (56)
• Dysequilibrium (50), vertigo, nystagmus
• Facial hypesthesia and loss of corneal reflex
• Long tract signs, ataxia
• Headaches and nausea
• Hitselberger sign

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Diagnostic studies

• Auditory and vestibular testing
• Audiometry
• ABR
• Decreasing sensitivity with smaller tumors
• 90 sensitive with all tumors
• 58 with tumors
• Vestibular tests

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Imaging

• MRI
• CT

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Meningioma

• Originate cap cells near arachnoid villi which
  are more prominent near cranial nerve foramina
  and venous sinuses.
• Grossly appear speckled due to psammoma bodies
• 25 Cause hyperostosis
• Same symptoms as AN but arise from posterior
  surface of petrous bone so audiometric (75 HL)
  and vestibular testing is less sensitive.
• Only 75 have abnl ABR
• Histopathologic subtypes
• Syncitial
• Transitional
• Fibrous
• Angioblastic
• Sarcomatous

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Epidermoid

• Originates from epithelial rests within temporal
  bone or CPA.
• Stratified squamous epithelial cells lining
  desquamated keratin
• Same symptoms as AN but facial tic and paresis
  more common
• Expand along least resistance so irregular shapes
  and borders and discovered in 2nd-4th decades.

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Epidermoid

• DDX
• Cholesterol granuloma - Hemorrhage into petrous
  apex air cells with foreign body reaction and
  granuloma formation
• Arachnoid cysts
• smooth surfaced sac containing CSF
• Low intensity on DWI MR whereas epidermoid has
  moderate intensity

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Non-acoustic neuromas

• V
• VII
• Facial weakness is a late finding unless location
  is intratemporal
• Facial tic
• IX-XI
• Smooth enlargement of the jugular foramen
• Jugular foramen syndrome soft palate
  (dysphagia) vocal cords (hoarseness,
  aspiration) shoulder (numbness and weakness)
• XII enlargement of hypoglossal canal and
  hemiatrophy of the tongue

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Glomus tumors

• Order of symptoms pulsatile tinnitus,
  conductive loss.
• Deficits of the cranial nerves of the jugular
  foramen
• Irregular destruction of jugular foramen on CT
• Flow voids cause salt and pepper appearance on
  T1 and T2
• Characteristic angiography pattern

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Hemangiomas

• Arise in area of geniculate ganglion
• Pulsatile tinnitus
• Early facial weakness
• Enhancing
• Honeycomb bone with irreagular and indistinct
  margins and intratumoral bone spicules

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Lipomas and Asymmetric petrous apex pneumatization

• Fat content on less pneumatized side appears
  hyperintense on T1
• Lack of bone destruction or expansion,
  non-enhancing, and hypointense on T2

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Other petrous apex tumors

• Mucocele Nonenhancing mass hypointense on T1
  and hyperintense on T2,
• Petrous carotid aneurysm can be confused with
  chondrosarcoma
• Giant cell tumors originate from supporting
  connective tissue cells and consist of
  multinucleated giant cells in spindle-shaped
  stromal cells

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Chordoma

• Arise from notochord remnants
• Cause extensive bone destruction
• Usually present with frontoorbital headaches and
  changed vision (diplopia, decreased acuity,
  visual field deficits)
• Homogeneous and enhance on CT with bony
  destruction
• Isointense on T1 and hyperintense on T2

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Approach to Treatment

• Preservation of life
• Mass effect, hydrocephalus
• Preservation of function
• Facial nerve
• Hearing nerve
• Balance nerve

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Observation

• Indications
• Advanced age (over 65 or 75)
• Poor health
• Small tumors, especially if hearing is good
• Lack of symptoms
• Non-progression of symptoms
• Only hearing ear
• Isolated IAC tumors in the elderly
• Slow growth 1-3mm/yr
• Contraindications
• Young patient
• Healthy patient
• Symptomatic progression
• Compression of brainstem structures
• Cystic tumors

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Stereotactic Radiosurgery

• Examples
• Gamma knife
• Linac
• Cyber knife
• X knife
• Novalis
• Peacock
• Proton beam
• Indications
• Small tumors (characteristic radiographic appearance
• Funtional hearing
• Older patients (75)
• Medically unstable patients
• Previous resection
• Young patients who dont want surgery

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Stereotactic Radiosurgery

• Contraindications
• Tumors 3 cm
• Prior radiotherapy
• Tumor compressing brainstem
• Uncertain diagnosis
• Dizzy patients
• Facial nerve symptoms
• Cystic Tumors
• Outcome
• 94 Local control 62 smaller, 32 unchanged,
  6 larger
• 51 no change hearing
• Complications
• Early
• Facial nerve injury 5 - 17
• trigeminal hypesthesia 27
• Hyrodcephalus 3
• 7 imbalance

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Stereotactic Radiosurgery

• Complications
• Early
• Facial nerve injury 5 - 17
• trigeminal hypesthesia 27
• Hyrodcephalus 3
• 7 imbalance
• Early
• Benign tumor formation (16-30 yrs)
• Malignant tumor formation (4-5 yrs)

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Surgery

• Approaches
• Translabyrinthine
• Middle Fossa
• Retrosigmoid
• Considerations
• Size
• Hearing
• Age

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Trans-labrynthine

• Indications
• Extension into CPA 0.5 - 1cm
• Non-serviceable hearing
• Average hearing 50dB
• Speech discrim 50
• Adequate contralateral hearing in large tumors
  (2.5cm)
• Contraindications
• Serviceable hearing

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Translabyrinthine

• Advantages
• No retraction of cerebellum
• Allows good identification of CN VII
• Allows good exposure of IAC
• Less risk of CSF leak
• Disadvantages
• Hearing is sacrificed

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Middle Fossa

• Indications
• Small tumor
• Intracanallicular tumor
• Moderate CPA involvement (
• Adequate hearing (SRT50)
• Contraindications
• Large tumors
• Extensive CPA involvement ( 0.5 1 cm)
• Older patients ( 60 yrs. may have higher rate
  of bleeding or stroke)

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Middle Fossa Approach

• Advantages
• Excellent for intracanalicular tumors, especially
  at the lateral end of the IAC
• Hearing preservation is possible
• Extradural with low risk of CSF leak
• Disadvantages
• Lack of access to CPA and posterior fossa
• Need to retract temporal lobe

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Middle Fossa Approach
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Middle Fossa Craniotomy
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Retrosigmoid/SuboccipitalApproach

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

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Retrosigmoid/SuboccipitalApproach

• Advantages
• Hearing preservation is possible
• Access to CPA
• Disadvantages
• Limited access to lateral IAC/Fundus
• Difficulty repairing or grafting CN VII
• Increased risk of air embolism/CSF leak/
  post-op headache
• Cerebellar retraction is necessary

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Retrosigmoid/Suboccipital Approach