Acoustic Neuroma

Vestibular Schwannoma

1. VESTIBULAR SCHWANNOMA Dr Harjitpal Singh Assistant Professor(ENT), Dr RKGMC, Hamirpur

2. INTRODUCTION Also known as acoustic neuroma, neurilemmoma or eighth nerve tumour . 10% of brain tumors. 80 % of CP angle tumors. Arises from the schwann cells overlying the vestibular division of the eighth cranial nerve. Historically, known to arise from the superior vestibular nerve. More recent studies advocate that it arises from the inferior vestibular nerve.

3. HISTORY First observed on autopsy in 1777. First clinical case report in 1833 by Charles Bell. First successful excision by Charles Balance in 1894. Term CP Angle tumor introduced in 1902 by Henneberg and Koch. Staging according to symptoms by Cushing.

4. RELEVANT ANATOMY

5. IAC - 1.2 to 1.4 cm

6. CEREBELLOPONTINE ANGLE Extra-axial area containing CSF, arachnoid tissue, cranial nerves VII, VIII and anterior inferior cerebellar artery. Borders Anterior: VI cranial nerve, lateral aspect of clivus . Medial: pons,middle cerebellar peduncle,ventral surface of cerebellum. Lateral : petrous bone Superior : cranial nerve V. Inferior : arachnoid tissue of lower cranial nerves IX,X and XI. Posterior : cerbellar floccules

7. PATHOLOGY Benign, unencapsulated , well circumscribed, slow growing tumors. Grow from the Obersteiner - Redlich zone: junction of Schwann cells and supporting glial cells. Originate in the IAM and progress towards CP angle where involvement of cranial nerves leads to symptoms Schwann cells accumulate and form whorl like cell nests. Eosinophilic bodies and ganglion cells are seen. These act as precursors for development of schwannomas .

8. PATHOLOGY( cont ) Color and consistency depends on size and degree of degeneration. Rubbery, yellowish or pinkish. Mottled appearance if hemorrhage. Cystic consistency: necrosis and degeneration. Cystic tumors grow faster.

9. HISTOLOGY 2 PATTERNS: Antoni-A: compact cellular spindle cells with whorling nuclei alligned in rows: verocay bodies Antoni -B: loose, less cellular, spongy appearance. Usually mixed pattern is seen.

10. HISTOLOGY( cont ) Antoni A Antoni B

11. GENETICS Seen commonly in families with NF-2. Autosomal dominant. High penetration. 95% chance of bilateral lesions in NF-2. Chromosome 22q12. Cytoskeleton protein: Schwannomin / merlin . NF2 gene is inhibitory. Sporadic or inherent inactivation causes cell proliferation and tumor formation.

12. GENETICS( cont ) It is necessary to know the growth pattern of the tumour as it determines the chronology of symptoms. The growth patterns are: Slow growth : 0.02cm per year Medium growth : 0.20cm per year Fast growth : 1.00cm per year

13. SYMPTOMS Earliest symptom: tinnitus and unilateral hearing loss. Sudden SNHL 5% cases Depends on site. Further symptoms according to spread and involvement of other cranial nerves. Vestibular symptoms maybe missed due to compensation. Facial asymmetry, visual disturbances, cerebellar dysfunction, headaches: late.

14. CRANIAL NERVE INVOLVEMENT 5th nerve first involved – 2.5cm. 7 th nerve: sensory then motor. 9 th 10 th and 11 th . 12 th ,3 rd , 4 th and 6 th involved when tumour size is large.

15. CUSHINGS STAGES 1: auditory and labyrinthine symptoms. 2: occipito -frontal pains and discomfort. 3: incoordination due to cerebellar origin. 4: involvement of adjacent cranial nerves. 5: raised ICT and papilledema . 6: dysarthria , dysphagia , cerebellar crisis.

16. PHASES OF TUMOR GROWTH Intracanalicular: Hearing loss, tinnitus, vertigo Cisternal: Worsened hearing and dysequilibrium Compressive: Occasional occipital headache CN V: Midface, corneal hypesthesia Hydrocephalic: Fourth ventricle compressed and obstructed Headache, visual changes, altered mental status

17. JACKLER STAGING SYSTEM Stage Tumor Size Intracanalicular Tumor confined to IAC I (small) < 10 mm II (medium) 11-25 mm III (Large) 25-40 mm IV (Giant) > 40 mm

18. DIFFERENTIAL DIAGNOSIS Vestibular Schwannoma (acoustic neuroma ). Most Common Cause Meningioma Epidermoid Non acoustic neuroma Paraganglioma Arachnoid cyst hemangioma Metastases Dermoid,lipoma,teratoma , chordoma chondrosarcoma

19. DIAGNOSIS Diagnosis can be made on basis of history, clinical examination, audiometric evaluation and radiology. Pts with long term unilateral tinnitus and SNHL with or without balance disturbace should be evaluated.

20. HISTORY Unilateral tinnitus. Unilateral hearing loss – progressive or sudden. Balance disturbances. Aural fullness. Decreased sensations over face, tremors, ataxia, vision loss, aspiration, dysphagia, hoarseness, shoulder and tongue weakness – later stages.

21. EXAMINATION Complete examination: Ear examination Vestibular assessment CNS examination Cranial nerve function testing.

22. EAR EXAMINATION Otoscopy. Loss of touch sensation in posterior meatal wall (house and hitselberger’sign ) Tuning fork tests. Nystagmus – spontaneous – helps to localise : Horizontal – fast component towards normal ear. Rotatory and positional – afected ear dependent position Vertical – central causes Loss of corneal reflex Caloric test: diminished or absent response.

23. CNS - EXAMINATION Cerebellar function tests: Rhomberg test Finger nose test Knee heel test Gait test Dysdidochokinesia Raised ICP Fundus examination

24. CRANIAL NERVE EXAMINATION 5 th nerve: facial sensation, corneal reflex. 7 th nerve: facial symmetry, taste sensation. 9 th nerve: tongue sensation. 10 th nerve: gag reflex, indirect laryngoscopy . 11 th nerve: shoulder movements. 12 th nerve: tongue movements. 3 rd , 4 th , 6 th : eye movements.

25. AUDIOMETRY Tuning fork tests – evaluate type of hearing loss. PTA – degree and type of hearing loss. Special tests – to differentiate cochlear from retro-cochlear lesion. BERA – to locate site of lesion in the nerve.

26. PTA AND SPECIAL TESTS Suggestive of SNHL with retro-cochlear lesion. SDS: poor speech discrimination. Roll over phenomenon present. TDT: decay more than 25 dB. SISI: less than 20%. Recruitment: absent.

27. BERA Most sensitive test. Greater than 90 %. Features suggestive of retro-cochlear lesion: Interaural wave V latency > 0.2 msec. Inter peak latency I-V > 4.4 msec. Cannot be done for hearing loss more than 70 dB. Decreased sensitivity for tumors less than 1cm.

28. VESTIBULAR STUDIES Caloric tests: diminished or no response in the affected ear. Electro Nystagmo Graphy (ENG) is used to detect minimal nystagmus in response to caloric testing which cannot be seen by naked eye.

29. ENG Advantage :When imaging studies fail to demonstrate the nerve of origin of the tumor, ENG can be done. Signifies superior vestibular nerve function. Helps in pre operative planning and counselling regarding nerve and hearing preservation.

30. VEMP Vestibular Evoked Myogenic Potentials. Functional testing of Inf vestibular nerve. Elicited by high intensity stimulation of saccule ( supplied by the inferior vestibular nerve) and measuring the vestibulaspinal reflex in the SCM. Negative VEMP with normal ENG indicates inf vestibular nerve involvement.

31. IMAGING STUDIES For definitive diagnosis. For localizing site and size of tumor. Earlier, X rays: trans-orbital view, stenver’s view, towne’s view and submento -vertical views were used – obsolete. Posterior fossa myelography : obsolete.

32. CT High resolution computerized tomography with 1 mm cuts of the temporal bone. Bony erosions can be visualized. Better visualization by using contrast.

33. CT( cont ) Soft tissue mass in the IAM on the right temporal region

34. CT( cont ) Advantages: Faster. Better for larger tumors with compression symptoms Better differentiation of tumor from bleed. When MRI is contraindicated.

35. CT( cont ) Disadvantages: Contrast is must. Radiation exposure Soft tissue delineation is less. Small tumors of 1cm or less are missed.

36. IMPROVISATIONS IN CT Air – contrast CT: Lumbar puncture is done. CSF is drained and 7-10 cm 3 air or oxygen is injected into sub arachnoid space. Patient is positioned in a way that the air rises to the posterior fossa and outlines the tumor. CT is taken and both sides are examined. Complication: headache, complications associated with lumbar puncture.

37. MRI Gold standard imaging technique. Better soft tissue delineation. Localization of the nerve of origin. Pre operative counselling and prediction of hearing and nerve damage. Helps in determining approach Prognostic indicator.

38. MRI( cont ) Tumor is seen as iso - intense to gray matter and hyper intense to CSF. T1 weighted images

39. MRI( cont ) Tumor is seen hypo- intense to CSF and hyper- intense to gray matter T2 weighted images

40. MRI( cont ) Cystic lesions show fluid filled tumors with peripheral enhancement on T2 images.

41. MRI( cont ) Gold standard for diagnosis of acoustic neuroma. Tumor shows marked enhancement. Can detect tumors of 1- 2 mm size. Gadolinium enhanced T1 images

42. GROWTH RATE PREDICTION Factors: Size at detection. Association with NF2. Patient age. Interval growth over initial observation period. Cystic / solid nature of tumor.

43. TREATMENT OPTIONS Observation. Stereotactic radiotherapy. Microsurgery.

44. APPROACH SELECTION Depends on: Size of tumor at presentation. Growth rate. Consistency. Patient general condition. Patient choice. Surgeon’s preference. Hearing status of the patient. Post operative hearing preservation possibility.

45. OBSERVATION Indolent, slow growing tumors. Patient selection: If critical growth unlikely in patient’s lifespan: older patients. Pt not fit for surgery/ radiotherapy. Pt’s choice. Slow growing tumor with predominant solid component. Only hearing ear.

46. OBSERVATION( cont ) Baseline MRI. MRI after 6 months to assess growth rate. MRI every year if there is no evidence of brain stem compression.

47. OBSERVATION( cont ) Disadvantages Patients may loose the salvageable hearing as tumor progresses. Smaller tumors are easier to excise. Risk of neural injury more in later stage. Sudden rapid increase of tumor size may occur.

48. STEREOTACTIC RT Focused multiple radiation beam therapy. Introduced in 1951 in Sweden. Closed cranial treatment. Gamma knife / cyber knife.

49. STEREOTACTIC RT( cont ) The word stereotaxis is derived from two Greek words: Stereos - “three-dimensional,” Taxis - “orderly arrangement.” A high dose of radiation can be delivered to a defined region, usually within a well- immobilized system that conforms closely to the 3D shape of the target volume.

50. STEREOTACTIC RT( cont ) Goals: Arrest or regression of tumor growth by focused radiation. Avoidance of surgery and thereby neural injury. Minimal collateral damage to brain and nerve tissue.

51. STEREOTACTIC RT( cont ) Goals: Radiation source: Cobalt-60, linear accelerator. Reduction of radiation dose to peripheral zone reduces nerve damage. Standard dose 20Gy – reduced to 18 Gy – 16Gy – 12 Gy .

52. STEREOTACTIC RT( cont ) Advantages: Decreased hospitalization time. Elderly and patients unfit for surgery. Minimally invasive. Salvage surgery still an option. Near normal neurological function.

53. STEREOTACTIC RT( cont ) Disadvantages: Radiation induced malignancy. Radiation induced hydrocephalous. Radiation induced edema(persist for 6month) – sudden hearing loss. Prolonged surveillance with repeated MRI

54. GAMMA KNIFE Fixed dose radiation therapy. Fixed machine. Delivered through collimator helmet. Extensive pre- op preparation.

55. GAMMA KNIFE( cont ) Contraindication: Tumor that extend too far inferiorly to enable placement into centrum of collimator helmet. Large tumor causing life threatening brain stem and central aqueduct compression. Tumor size >3.0 cm with in cp angle

56. CYBER KNIFE Modified Gamma knife. Pre-op planning similar to gamma knife. Uses Linear accelerator mounted on robotic arm. 6 degrees of freedom. Increases accuracy. Fractionated RT can be given. Shielding of vital structures can be done.

57. MICROSURGERY Direct neuro-otological surgery. Tumor excised under vision. Approaches: Middle cranial fossa approach Trans-labyrinthine approach Sub-occipital / retrosigmoid approach Combined approach

58. MICROSURGERY( cont )

59. MICROSURGERY( cont ) lntraoperative Complications : Cranial Nerve Injury Bleeding Brain Edema Venous Air Embolism Cardiac Arrhythmias Brain Herniation

60. MICROSURGERY( cont ) Postoperative Complications: Hemorrhage Infarction Cerebrospinal Fluid Leak Meningitis Tension Pneumocephalus

61. Thank you…