Acoustic neuroma

Acoustic neuromas are NOT actually tumours of neuronal tissue but of Schwann cells (schwannoma) in the vestibular nerve (most commonly- occasionally cochlear nerve).  They are intracranial, extra-axial tumours that arise with no apparent risk factors (other than neurofibromatosis II).

Pathophysiology

  • These are slow growing tumours that occur at the relatively spacious cerebellopontine angle.  They continue to grow until they fill this space (3-5cm)- and then commonly begin to cause problems as they compress the vessels and cranial nerves in the area (mainly cochlear nerve, vestibular nerve, trigeminal nerve, facial nerve).  If they continue to grow they may press on the cerebellum and brain stem.
  • Bilateral cases can be associated with neurofibromatosis type II

Presentation

  • Progressive/fluctuating, unilateral sensorineural hearing loss is the most common symptom/sign.  This may resolve itself or in response to steroid therapy.  Tinnitus (unilateral) is also a common symptom and may be present with or without associated hearing loss. Headache and other signs of raised ICP can also present (although rarely without the ear symptoms above).
  • Vertigo is (surprisingly) a very rare complaint in acoustic neuroma although some patients may complain of some dysequilibrium (a sense of unsteadiness or imbalance).  This is because the destruction of vestibular fibres is usually slow enough to allow compensation.
  • Facial numbness (CN V involvement) may be a symptom or a sign (if the patient is unaware of it).  It is more common in larger tumours but a reduced corneal reflex may be present in smaller ones too.
  • Facial weakness is very rare but can occur.

Investigations

  • An MRI is the main mode of imaging for patients with suspected acoustic neuroma.
  • The patient may have a disproportionate reduction in scores for speech discrimination compared to pure tone tests (CN VIII injury- retrocochlear lesions).

Management

  • Surgery can be difficult and may not be suitable for some patients (consider anaesthetic risk and risk of local injury carefully and the duration of further growth in older patients especially).
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