VESTIBULAR SCHWANNOMA for Undergraduates

powerpoint presentation on Vestibular Schwanomma

1. VESTIBULAR SCHWANNOMA

2. Vestibular schwannoma(VS) Previously called acoustic neuroma , which is a misnomer In 1992 National institute of Health Consensus Conference made vestibular schwannoma as official term Cerebellopontine angle tumors account for 10% of all intracranial tumors Vestibular schwannoma ccounts for 90% of primary neoplasm of cerebellopontine angle(CPA) Differential diagnosis of primary CPA neoplasms are Meningioma(3%) Epidermoid Cyst(2.5%) Facial neve schwannoma(1%)

3. AETIOLOGY Not known Defect in chromosome 22q may be responsible for development of sporadic VS and bilateral VS in neurofibromatosis type 2(NF2) NF2 is characterized by bilateral VS in 96%,schwannomas of other cranial nerves, meningioma, ependymoma Gene responsible for NF2 encodes membrane protein –merlin/ schwannomin

4. PATHOLOGY Vestibular schwannoma(acoustic neuroma, neurinoma, neurilemmoma)-benign, well circumscribed, unencapsulated tumor. Arise from schwann cells of vestibular nerve. Inferior vestibular nerve- predominant site of origin Arise at Obersteiner -Redlich junctional zone of vestibular nerve –region at which schwann cells and neuroglial cells meet Schwann cells accumulate at junctional zone

5. Typically tumors are either yellowish/pinkish grey Rubbery consistency Large tumors –mottled (due to hemorrhage & fibrosis) & cystic regions(due to necrosis & degeneration) Some have intrinsic cystic nature

6. Microscopic examination Well circumscribed ,unencapsulated tumor Composed of 2 histological patterns- Antoni A & Antoni B Antoni A- compact & cellular with elongated spindle cells & palisading nuclei in rows ( Verocay bodies) Antoni B- vacuolated cells, loose & less cellular with spongy appearance

7. Clinical features Age & sex: in 40-60 age group, both sexes equally affected COCHLEOVESTIBULAR SYMPTOMS: - unilateral progressive SNHL with or without tinnitus - marked difficulty in understanding speech( poor speech discrimination ) out of proportion to pure tone hearing loss - sudden hearing loss - imbalance/unsteadiness, true vertigo is rare

8. Cranial nerve involvement: V th nerve : earliest nerve to be involved. reduced corneal sensitivity, paraesthesia of face VIIth nerve : sensory fibres are affected first. Hitzelberger’s sign- hypoesthesia of posterior canal wall loss of taste reduced lacrimation by Schirmer test delayed blink reflex(motor fibres are affected) facial palsy -rare

9. IX th & x th : dysphagia, hoarseness due to palatal, pharyngeal & laryngeal paralysis,aspiration XIth , XIIth , IIIrd , IVth & Vth are affected if tumor is large BRAINSTEM INVOLVEMENT : ataxia, weakness, numbness of arms & legs, exaggerated tendon reflex CEREBELLAR INVOLVEMENT : tested by finger nose test, knee heal test, dysdiadochokinesia, ataxic gait, inability to walk in straight line & tendency to fall to affected side RAISED ICP : headache, nausea,vomiting , diplopia, papilledema with blurring of vision

10. DIAGNOSIS AUDIOMETRIC STUDIES : Pure tone audiometry -SNHL more marked in high frequencies

11. Speech audiometry- Poor speech discrimination ,disproportionate to pure tone hearing - Roll over phenomenon seen(with increase in speech intensity above a particular level SD falls rather than maintaining a plateau) Performance Intensity function for Phonetically Balanced (PIPB) test-evaluate SD at progressively higher sensation levels Recruitment phenomenon(abnormal growth of loudness) is absent Short increment sensitivity index(SISI) test -0-20% in 70-90% cases Threshold tone decay test- a tone of 4000Hz is presented 5 dB above threshold for 60s. a decay of >25dB - retrocochlear type of lesion

12. STAPEDIAL REFLEX DECAY TEST : if sustained tone of 500-1000Hz delivered 10 dB above acoustic reflex threshold for 10s –bring reflex amplitude to 50% indicative of VIII nerve lesion VESTIBULAR TESTS : C aloric Test (modified kobrak test)–to test function of LSCC innervated by superior vestibular nerve small inferior vestibular nerve schwannoma-normal caloric response - Romberg Test-drift may be elicited - Fu kuda stepping rotation- to side of lesion - VEMP(vestibular evoked myogenic potential): helps to identify the origin of VS saccule-> inf.vestibular nerve->vestibular nucleus->ipsilateral vestibulospinal ->spinal accessory nerve->sternocleidomastoid - cVEMP

13. NEUROLOGICAL TEST : cerebellar function- Gait (Ataxic) Tandem(heel to toe) gait speech –ataxic dysarthria finger to nose test dysdiadochokinesia knee jerk reflex heel to shin test brainstem signs of pyramidal & sensory tract Examination of lower cranial nerves - fundus examination-papilledema

14. Auditory brainstem response testing : Brainstem response to 83 dB broadband click(100 microsecond rarefaction/condensation square wave pulse) is recorded while the opposite ear is masked with 78db white noise Latency for wave V for 2 ears is compared Interaural latency for wave V > 0.2 ms is abnormal Prolonged interpeak latencies > 4.4 ms for I-V,>2.3 ms for I-III,>2.1ms for III-V suggest retrocochlear disorder Abnormal wave forms Complete absence of wave V suggest retrocochlear pathology False negative results-intracanalicular tumors Stacked ABR : test audiometric spectrum in frequency specific fashion followed by temporal alignment of result. Calculates wave V amplitude by temporally aligning the wave V of each derived band ABR & summating time shifted responses.

15. Radiology Provide definitive diagnosis Gold standard- contrast enhanced T1 weighted MRI

16. Computed tomography: Advantage Provides excellent details of temporal bone Expansion of IAC from expansion of VS is well visualized Disadvantage Less soft tissue detail than MRI Tumor less than 1cm are often missed by CT

17. Magnetic resonance imaging T1 weighted images show VS –hyperintense relative to CSF & iso-hypointense to gray matter T2 weighted images show-hypointense to CSF & hyperintense to gray matter Cystic tumors have high signal intensity on T2 weighted sequence Gadolinium enhanced T1 weighted reveal marked tumor enhancement

18. Treatment options Observation Stereotactic radiation therapy Microsurgery

19. OBSERVATION - is reasonable for Elderly patient >65yrs Medically infirm Only hearing ear with serviceable hearing with normal brain stem function Patient preference Small tumor

20. STEREOTACTIC RADIATION THERAPY In 1951, Leksell developed first open stereotactic instrument Linear accelerators have also been used to provide stereotactic radiation Advantages :- Decreased hospital stay Considered for elderly or medically infirm patients

21. D isadvantages : Need for prolonged surveillance with repeated MRI Treated tumors may harbor viable tumor requiring salvage microsurgery Radiation induced hydrocephalus Sudden hearing loss due to swelling following radiation Difficulty preserving facial nerve in surgical salvage that had failed radiation Risk of complete deafness in vestibular schwannoma associated with NF2

22. Radiation induced malignancy In 1998 Noren reported 0.1% worldwide rate of malignant transformation of 8000 VS treated with stereotactic radiation since 1969 Histopathology showed spindle cell neoplasm National institute of health consensus development conference report donot recommend radiation unless patients are elderly or medically infirm

23. MICROSURGICAL APPROACHES TRANSLABYRINTHINE APPROACH MIDDLE CRANIAL FOSSA APPROACH SUBOCCIPITAL/RETROSIGMOID APPROACH COMBINED APPROACH RETROLABYRINTHINE APPROACH

24. Outcomes & complications Key determinants are ( i ) size of tumour being removed (ii) experience & surgical skill of operating team

25. Intraoperative complications Cranial nerve injury Bleeding Brain edema Venous air embolism Cardiac arrythmias Brain herniation

26. Postoperative complications Hemorrhage Infarction CSF leak Meningitis Tension pneumocephalus

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