Posterior Fossa Skull Base Lesions

U.C. Irvine - Otolaryngology-Head & Neck

Surgery

Posterior Fossa Skull Base Posterior Fossa Skull Base LesionsLesionsAli Sepehr

UCI Department of Otolaryngology- Head and Neck Surgery


Surgery

Posterior fossa skull base lesionsPosterior fossa skull base lesions

Common–Acoustic neuroma (60-92%)–Meningioma (3-7%)–Epidermoid (2-6%)–Non-AN (1%)–Paraganglioma –Arachnoid cyst–Hemangioma

Uncommon–Metastatic tumor–Lipoma–Dermoid–Teratoma–Chordoma–Chondrosarcoma–Giant cell tumor

• CPA


Surgery

CPACPA

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


Surgery

Skull base lesions (cont.)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


Surgery


Surgery


Surgery


Surgery

Acoustic Neuroma (AN)Acoustic Neuroma (AN)Benign schwann cells in collagenous matrix

and don’t 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 nonhereditaryM = FSlow growing (0.2-4mm/yr)


Surgery

Growth phasesGrowth phases IAC

– acoustic and facial nerve compression

Cisternal– blood from brainstem

Brainstem compression– 4th ventricle compression

occurs at 2-3 cm


Surgery

HistopathologyHistopathology– Antoni A – compact

tissue with spindle cells in palisades (most common)

– Antoni B – loose tissue with cyst formation.


Surgery

Hereditary AN’sHereditary AN’s

Type I–Only 5% with AN’s and no bilateral AN’s–Intra and extra-cranial–Appear late–Chromosome 17

Type II–Bilateral AN’s in 96%–Cranial nerve schwannomas–Appear by 2nd decade–Chromosome 22

• Neurofibromatosis


Surgery

Signs and symptomsSigns and symptoms

SNHL (95%),SSNHL (20%), tinnitus (56%)Dysequilibrium (50%), vertigo, nystagmusFacial hypesthesia and loss of corneal reflexLong tract signs, ataxiaHeadaches and nauseaHitselberger sign


Surgery

Diagnostic studiesDiagnostic studies

Auditory and vestibular testing– Audiometry– ABR

Decreasing sensitivity with smaller tumors 90% sensitive with all tumors 58% with tumors < 1cm

– Vestibular tests


Surgery

ImagingImaging

MRICT


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Surgery

MeningiomaMeningioma 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


Surgery


Surgery

EpidermoidEpidermoid

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.


Surgery

EpidermoidEpidermoid

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


Surgery


Surgery


Surgery

Non-acoustic neuromasNon-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


Surgery


Surgery

Glomus tumorsGlomus 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


Surgery


Surgery

HemangiomasHemangiomas

Arise in area of geniculate ganglionPulsatile tinnitusEarly facial weaknessEnhancingHoneycomb bone with irreagular and

indistinct margins and intratumoral bone spicules


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Surgery

Lipomas and Asymmetric Lipomas and Asymmetric petrous apex pneumatizationpetrous apex pneumatization

Fat content on less pneumatized side appears hyperintense on T1

Lack of bone destruction or expansion, non-enhancing, and hypointense on T2


Surgery

Other petrous apex tumorsOther 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


Surgery


Surgery

ChordomaChordoma

Arise from notochord remnantsCause extensive bone destructionUsually 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


Surgery


Surgery

Approach to TreatmentApproach to Treatment

Preservation of life– Mass effect, hydrocephalus

Preservation of function:– Facial nerve– Hearing nerve– Balance nerve


Surgery

ObservationObservation 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


Surgery

Stereotactic RadiosurgeryStereotactic Radiosurgery Examples:

– Gamma knife– Linac

Cyber knife X knife Novalis Peacock

– Proton beam Indications

– Small tumors (< 3 cm) who have very characteristic radiographic appearance– Funtional hearing– Older patients (>75)– Medically unstable patients– Previous resection– Young patients who don’t want surgery


Surgery

Stereotactic RadiosurgeryStereotactic 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


Surgery

Stereotactic RadiosurgeryStereotactic 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)


Surgery

SurgerySurgery

Approaches– Translabyrinthine– Middle Fossa– Retrosigmoid

Considerations– Size– Hearing– Age


Surgery

Trans-labrynthineTrans-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


Surgery

TranslabyrinthineTranslabyrinthine 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


Surgery

Middle FossaMiddle Fossa Indications

– Small tumor– Intracanallicular tumor– Moderate CPA involvement (<1cm)– Adequate hearing (SRT<50 db, Disc >50%)

Contraindications– Large tumors– Extensive CPA involvement ( > 0.5 – 1 cm)– Older patients ( > 60 yrs. may have higher rate of bleeding

or stroke)


Surgery

Middle Fossa ApproachMiddle Fossa ApproachAdvantages

– 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


Surgery

Middle Fossa ApproachMiddle Fossa Approach


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Middle Fossa CraniotomyMiddle Fossa Craniotomy


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Retrosigmoid/SuboccipitalRetrosigmoid/SuboccipitalApproachApproach

Indications– Serviceable hearing– Large tumors– Compression of brainstem

Contraindications– Functional hearing with

extensive IAC involvement– Intracanallicular tumors


Surgery

Retrosigmoid/SuboccipitalRetrosigmoid/SuboccipitalApproachApproach

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


Surgery

Retrosigmoid/Suboccipital Retrosigmoid/Suboccipital ApproachApproach

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Posterior Fossa Skull Base Lesions