Acoustic Neuroma Department of Otorhinolaryngoglogy the 2 nd

Acoustic Neuroma Department of Otorhinolaryngoglogy the 2 nd Hospital affliatted to Medical college Zhejiang University Xu Yaping

Anatomy Cerebellopontine Angle-CPA (in the posterior fossa)

Epidemiology • • 6 % of all Intracranial tumors 80 - 90% of CPA tumors Incidence in US: 10 per million / year Vast majority in adulthood 95% Sporadic (unilateral) 5% Neurofibromatosis type 2 (bilateral) No known race, gender predilection

Pathogenesis • Neither neuroma or acoustic (auditory) • Schwannoma arising from vestibular nerve • Benign tumor. Malignant degeneration exceedingly rare. • Majority originate within the IAC(the internal auditory canal) • Equal frequency on Superior and Inferior vestibular nerves (controversial)

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

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

Intracanalicular Compressive Cisternal Hydrocephalic

Hearing Loss 1. Most frequent initial symptom 2. Most common symptom ~ 95% AN patients 3. Asymmetric SNHL 4. Down-sloping / High Frequency 5. Decreased Speech Discrimination 6. Lack of conclusive correlation between tumor size and hearing

Estimating Tumor Growth • Serial MRI with and without GAD(Gadolinium) ---The only reliable study to estimate tumor growth rate • Gadolinium-enhanced MRI remains the gold standard ---It can detect tumors as small as 1 mm and differentiate AN from many CPA lesions

Delayed Diagnosis Duration of Symptoms Prior to Diagnosis Symptoms • • Hearing Loss Vertigo Tinnitus Headache Dysequilibrium Trigeminal Facial ----Jackler RK. 2000. Tumors of the Ear and Temporal Bone Years 3. 9 3. 6 3. 4 2. 2 1. 7 0. 9 0. 6

History and Physical • • • Hearing Loss Vertigo Dysequilibrium Tinnitus Headache Nystagmus – Early small lesion: Horizontal (vestibular) – Late large: Vertical (brainstem compression) • Cranial neuropathy – CN V, VII – Lower cranial nerves (IX-XII)

Sudden Sensorineural Hearing loss • Idiopathic • 1 -2 % SSNHL patients have AN • 10 - 26 % AN patients have a history of SSNHL • Most experts advocate obtaining MRI in all patients who present with SSNHL

Diagnosis • History and Physical Exam • Audiology testing: – Audiogram – ABR – OAE • Vestibular testings (eg. ENG, rotary chair, posturography) all lack diagnostic value • Radiography – MRI – CT Gold Standard

Pure Tone

ABR: Retrocochlear Pathology (Auditory Brainstem Response) • Increased interpeak intervals – I-to-III interval of 2. 5 ms, III-to-V interval of 2. 3 ms, and I-to-V interval of 4. 4 ms • Interaural wave V latency difference (IT 5) – Greater than 0. 2 ms • Poor waveform morphology ie. only some of the waves are discernible • Absent waveform

ABR patterns in AN • 10 -20 % with only wave I and nothing thereafter • 40 -60 % with wave V latency delay • 10 -15 % have normal findings

OAE(Otoacoustic emissions) Reflect cochlear/ OHC / sensory hearing Not primarily used as screening tool Presence of OAE in SNHL ↔ Retrocochlear However, 50 % AN demonstrate both cochlear and retrocochlear hearing loss • Risk stratification for hearing preservation surgery • •

MRI Brain w. & w/o GAD T 1 pre-Gad T 1: T 2: T 1+Gad: T 2 T 1 post-Gad Isointense to brain, hyperintense to CSF Hyperintense to brain, hypointense to CSF Enhancing

CT Brain with contrast 1. Heterogeneous 2. enhancement on contrast 3. 2. Rare calcification 4. 3. Contraindication to MRI (metallic implants), claustrophobic patients 5. 4. May not be able to detect small tumor < 1. 5 cm 6. 5. Radiation

Treatment options • Observation<5 mm • Surgery : >1 cm – Translabyrinthine – Retrosigmoid – Middle fossa • Radiotherapy – Conventional – Stereotactic: knife <1 -2 cm

Conservative Management • • Advanced age (> 65 ) Short life expectancy (< 10 years) Slow growth rate Poor surgical candidate / poor general health Minimal symptoms Only hearing ear Patience preference

Conclusions • Tumor size has no correlation with audiovestibular symptoms in Acoustic neuroma • Understanding tumor growth rate is important for predicting symptom progression and treatment planning • The study-of-choice to estimate tumor growth is serial MRI

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