Acoustic Neuroma

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Intro & Pathogenesis - Schwann's Surprise

  • Benign tumor from Schwann cells (PNS myelin) of vestibulocochlear nerve (CN VIII).
    • Aka Vestibular Schwannoma.
    • Most common Cerebellopontine Angle (CPA) tumor (~80-90% of CPA masses).
  • Origin: Usually vestibular portion (inferior > superior).
  • Pathogenesis:
    • Sporadic (95%): Somatic mutation of NF2 gene (chromosome 22q12.2).
    • NF2-associated (5%): Germline NF2 mutation.
    • Leads to loss of merlin (schwannomin), a tumor suppressor.

⭐ Bilateral acoustic neuromas are pathognomonic for Neurofibromatosis Type 2 (NF2). Acoustic Neuroma MRI and Anatomical Diagram

Clinical Presentation - Hearing's Slow Fade

  • Progressive Unilateral Sensorineural Hearing Loss (SNHL):
    • Most common (>90%) & earliest symptom.
    • Insidious onset; patient may not notice initially.
    • Difficulty understanding speech, esp. on phone or in noisy settings (cocktail party deafness).
    • Speech discrimination disproportionately worse than pure tone thresholds (rollover phenomenon).

    ⭐ The most common and earliest symptom of acoustic neuroma is progressive, unilateral sensorineural hearing loss.

  • Unilateral Tinnitus:
    • High-pitched, continuous, or intermittent.
    • Often precedes or accompanies hearing loss.
  • Balance Issues (Disequilibrium):
    • Vague unsteadiness, not typically true rotatory vertigo.
    • Vertigo may occur if tumor compresses labyrinthine artery or causes hydrocephalus.
  • Aural Fullness: Sensation of pressure in the ear.

Audiogram: Hearing Loss in Acoustic Neuroma

Diagnostic Workup - Pinpointing the Problem

  • Audiometry:
    • Pure Tone Audiometry (PTA): Asymmetric high-frequency Sensorineural Hearing Loss (SNHL).
    • Speech Discrimination Score (SDS): Disproportionately poor; rollover phenomenon.
    • Tone Decay Test: Positive (often >30 dB).
  • Auditory Brainstem Response (ABR):
    • Screens for retrocochlear pathology.
    • Finding: Prolonged Wave V latency or interpeak latency I-V (interaural difference >0.2 ms).
  • Imaging (Definitive):
    • MRI with Gadolinium: Gold Standard.

      ⭐ MRI with gadolinium contrast is the gold standard for diagnosing acoustic neuroma, often showing an "ice cream cone" appearance.

    • CT Scan: Assesses bony erosion of Internal Auditory Canal (IAC); less sensitive for small tumors.

MRI showing acoustic neuroma with ice cream cone sign

Management Strategies - Tumor Taming Tactics

  • Observation (Wait & Scan):
    • Small, asymptomatic tumors.
    • Elderly/comorbid patients.
    • Serial MRI monitoring.
  • Microsurgery:
    • Preferred for larger tumors (>3 cm), symptomatic, or younger patients.
    • Aims: Tumor resection, facial nerve (FN) & hearing preservation.
    • Approaches: Translabyrinthine, Retrosigmoid, Middle Fossa.
  • Stereotactic Radiosurgery (SRS)/Radiotherapy (SRT):
    • For smaller tumors (<3 cm), medically unfit for surgery, or recurrent tumors.
    • Aims: Arrest tumor growth, preserve FN & hearing. (e.g., Gamma Knife)

⭐ For large acoustic neuromas (>3cm) causing brainstem compression or for younger patients, microsurgery is generally preferred over radiosurgery.

High‑Yield Points - ⚡ Biggest Takeaways

  • Most common CPA tumor; arises from Schwann cells of CN VIII (vestibular division).
  • Bilateral acoustic neuromas are pathognomonic for Neurofibromatosis Type 2 (NF2).
  • Earliest features: Progressive unilateral SNHL, tinnitus, and vestibular symptoms (disequilibrium).
  • Speech discrimination is characteristically poorer than expected for the degree of hearing loss.
  • Gold standard diagnosis: Gadolinium-enhanced MRI of the brain and IAC.
  • CN V involvement (e.g., decreased corneal reflex) often precedes CN VII weakness.

Practice Questions: Acoustic Neuroma

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The most common tumor of the cerebellopontine angle is -

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Flashcards: Acoustic Neuroma

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Motor fibers of 7th nerve are _____ resistant and are affected late in acoustic neuroma

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Motor fibers of 7th nerve are _____ resistant and are affected late in acoustic neuroma

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