Acoustic Neuroma

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).

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.

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.

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.