Acoustic Neuroma

FACTS

  • Pathology: Benign, slow-growing Schwann cell tumor of the vestibular division of CN VIII.
  • ~8% of all intracranial tumors; most common cerebellopontine angle (CPA) mass.
  • Associations: Usually sporadic, but may be bilateral in NF2 (Neurofibromatosis type 2).

HPI

universal ROS
  • Most common symptom: Unilateral sensorineural hearing loss (gradual onset).
  • Other symptoms:
    • Tinnitus (unilateral).
    • Imbalance or vertigo (usually mild, as compensation occurs).
    • Facial numbness or paresthesias (compression of CN V).
    • Facial weakness (late sign, CN VII involvement).
    • Headache, nausea, vomiting → raised ICP or hydrocephalus from large tumor.
  • Ask
    • Onset and progression of hearing loss or tinnitus.
    • Facial or trigeminal symptoms.
    • Balance issues, falls.
    • Family history of NF2 (bilateral tumors, early onset).

PHYSICAL EXAM

  • Universal exam
  • Careful attention to cranial nerve exam
    • CN VIII: Unilateral hearing loss (test with tuning fork or audiometry).
    • CN VII: Facial weakness or asymmetry.
    • CN V: Decreased corneal reflex, facial numbness.
    • CN VI: Lateral rectus palsy if large mass with brainstem compression.
    • CN IX–X: Dysphagia or dysarthria (rare, with very large tumors).
  • Gait/Coordination: Mild ipsilateral ataxia or unsteadiness (cerebellar compression).
  • Fundoscopy: Papilledema if hydrocephalus present.

IMAGING

Modality
Findings
MRI brain with contrast (IAC protocol)
Gold standard. Shows enhancing mass in internal auditory canal extending into CPA, typically iso-/hypointense on T1, hyperintense on T2.
CT temporal bone
Useful for assessing bony erosion of IAC and preoperative planning.
Audiometry
Confirms sensorineural hearing loss pattern (asymmetric).
Auditory brainstem response (ABR)
Screening tool if MRI unavailable; shows prolonged I–V interpeak latency.
Consider NF2 work-up
If bilateral tumors or age <30 → MRI spine for additional schwannomas/meningiomas.
Koss Grades
1: intracanalicular
2: minimal tumor extension into CPA < 2cm
3: occipies CPA but not displacing cerebellar trunk <3cm
4: large tumor w/ brainstem displacement > 3cm
NOTE:  acoustics usually displace the facial nerve VENTRALLY as the facial nerve enters facial canal anterior suprerior quadrant of meatus
Internal Acoustic Meatus Facial Nerve

A/P

GKRS
  • 4% rate facial neuropathy
  • 60% hearing preservation at margin 12-13 Gy, the lower the dose to cochlea the better
  • takes weeks to months/1 year to show any effect
 
Approach
Ideal Tumor Size / Location
Hearing Preservation
Facial Nerve Visualization
Advantages / Best For
Limitations
Middle Fossa
Small, intra-canalicular tumors (<1.5 cm)
Best (≈70–80%)
Excellent (nerve identified early in IAC)
- Preserves hearing- Avoids labyrinth injury- Ideal for small canal tumors
- Limited CPA exposure- Technically demanding
Retrosigmoid (Suboccipital)
Small–medium tumors (up to ~2.5–3 cm) extending from IAC into CPA
Moderate (≈40–60%)
Good (direct CPA view)
- Versatile access to CPA and brainstem- Useful if hearing still serviceable
- Risk of CSF leak, headache- Less hearing preservation with larger tumors
Translabyrinthine
Large tumors or non-serviceable hearing
None (labyrinth sacrificed)
Excellent (entire course visualized)
- Maximal exposure of IAC + CPA- Minimal cerebellar retraction- Good for complete removal
- Hearing loss inevitable- Only for non-hearing ears

Pathology

Figure 1: Pathology features: S100 positive and biphasic, eliciting compact hypercellular Antoni A areas and myxoid hypocellular Antoni B areas. Cells are narrow and elongated with wavy with tapered ends and interspersed with collagen fibers. Verocay bodies, or nuclear palisading around a fibrillary process, can be seen in cellular areas.