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vestibular schwannoma

Neurology / OncologyNervous systemEar (auditory and vestibular)Cranial nerves

Summary

Vestibular schwannoma (acoustic neuroma) is a benign Schwann cell tumor of the vestibular portion of CN VIII, arising at the cerebellopontine angle. It presents with unilateral sensorineural hearing loss, tinnitus, and disequilibrium. Bilateral tumors are pathognomonic for neurofibromatosis type 2 (NF2, merlin/chromosome 22q mutation).

Detail

**Pathophysiology:** Benign (WHO grade 1) tumor of Schwann cells, usually arising from the vestibular division of CN VIII near the transition zone (Obersteiner-Redlich zone) within the internal auditory canal. Caused by inactivation of the NF2 tumor suppressor gene on chromosome 22q12, which encodes merlin (schwannomin). Sporadic cases have somatic biallelic NF2 loss. Bilateral tumors occur in NF2 (germline mutation, autosomal dominant).

**Histology:** Spindle cells with two patterns: Antoni A (dense, hypercellular, palisading nuclei with Verocay bodies) and Antoni B (hypocellular, loose, myxoid). Stains S-100 positive (neural crest origin).

**Clinical features:** - Unilateral progressive sensorineural hearing loss (most common, first symptom), often with poor speech discrimination - Tinnitus - Vertigo or disequilibrium (less prominent, since slow growth allows central compensation) - Larger tumors at the cerebellopontine angle: - CN V compression: facial numbness, decreased corneal reflex (often the first sign) - CN VII compression: facial weakness - Cerebellar signs: ataxia - Brainstem compression, obstructive hydrocephalus (4th ventricle)

**Diagnosis:** MRI of the brain with gadolinium (the gold standard) shows an enhancing mass in the internal auditory canal/CPA with an "ice cream cone" appearance. Audiometry shows asymmetric SNHL. Auditory brainstem response (ABR) shows prolonged wave I–III latency.

**Treatment:** Options are observation with serial MRI (small, asymptomatic tumors), stereotactic radiosurgery (Gamma Knife), or microsurgical resection (translabyrinthine, retrosigmoid, or middle fossa approach). Surgical risk includes facial nerve injury. In NF2, bevacizumab (anti-VEGF) can be used for progressive tumors.

**High-yield associations:** - Bilateral vestibular schwannomas = NF2 (also meningiomas, ependymomas, juvenile posterior subcapsular cataracts) - NF1 (chromosome 17, neurofibromin) is NOT associated with vestibular schwannomas - CPA tumor differential: schwannoma (~70–80%), meningioma, epidermoid cyst - Unilateral SNHL in an adult should prompt MRI to rule out a retrocochlear lesion - The name "acoustic neuroma" is a misnomer: the tumor is a schwannoma, and arises from the vestibular rather than cochlear division

Sources

  • First Aid for the USMLE Step 1 (Neurology: Brain tumors; Neurocutaneous disorders)
  • Robbins & Cotran Pathologic Basis of Disease (Tumors of the nervous system, Schwannoma)
  • Pathoma (Fundamentals of Pathology), Central Nervous System chapter
  • UpToDate: Vestibular schwannoma (acoustic neuroma)
  • Harrison's Principles of Internal Medicine (Nervous system tumors)

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