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ENT clinic - acoustic neuroma

ENT GPSI Dr Raj Singh on a disease that requires those with unilateral hearing loss to be questioned carefully

 

Case

A 51-year-old woman first presented to her GP 18 months ago, complaining of a ‘ringing' and some unilateral hearing loss in her right ear. She was referred for audiometry, which revealed unilateral deafness. Three months ago, when she was walking back to her office after lunch, she lost consciousness for almost 10 minutes, falling onto the pavement. She was taken to A&E and treated for an injury on her left side caused by the fall. There was no evidence of neurological deficit, but she was given an MRI scan that revealed an acoustic neuroma. When talking to the neurologist she admitted suffering balance problems, but had attributed this to increasingly heavy alcohol use over the past few years. Due to the extent of the tumour, the neurologist recommended microsurgery, which was successful.

The problem

  • Acoustic neuromas are benign, slow-growing tumours arising from the Schwann cells.
  • They represent 6% of all intracranial tumours and the incidence is about two in 100,000 per year.1
  • The term acoustic neuroma is a misnomer as it actually arises from the vestibular nerve, but the more accurate term – vestibular schwannoma – is not commonly used.
  • Some 95% of cases are unilateral and occur sporadically – the remaining 5% are bilateral and associated with neurofibromatosis type II.2

Features

  • Patients generally present with cochlear symptoms – 90% have gradual hearing loss in one ear, 5% have sudden hearing loss and 70% have tinnitus.
  • Some 3% have normal hearing and will present for another reason, but there have been reports of symptomless neuromas.
  • Headache is present in up to 60% of patients at diagnosis, but fewer than 10% have headache as a presenting symptom.
  • Up to 50% of patients report balance disturbance when carefully questioned, but again it is the presenting symptom in fewer than 10% of patients.
  • Less common presentations include:

- facial numbness or pain from irritation of the trigeminal nerve

- earache

- facial nerve weakness.

Rarely, large neuromas may present with symptoms of raised intracranial pressure.

Diagnosis

  • All patients with suspected unilateral or asymmetric hearing loss should be referred for pure tone audiometry, but about 3% of the population have an asymmetry so this is not in itself an indication for ENT referral.
  • Patients with unilateral hearing loss should be questioned closely for other symptoms – such as dizziness, balance problems, headache, tinnitus and facial symptoms – which they may feel are insignificant.
  • MRI is the gold-standard investigation and fine 1mm cuts mean neuromas as small as 6mm can be detected.

Management

  • A watch and wait approach with interval MRI scans may be suitable for elderly patients and those with smaller tumours.
  • Stereotactic radiosurgery – radiotherapy delivered to a precise point to minimise exposure of adjacent tissue – can halt tumour growth and is suitable for patients with small to medium tumours whose symptoms are not debilitating.
  • Microsurgery is the traditional approach and there are three options:

– Translabyrinthine surgery sacrifices hearing in the affected ear but makes it easier to avoid damage to the facial nerve.

–  Retrosigmoid surgery does not destroy the labyrinth and can preserve hearing.

–  Middle fossa surgery monitors the facial and hearing nerves during the procedure.

 

Dr Raj Singh is an ENT GPSI in Manchester

 

References

1 Lin D, Hegarty JL, Fischbein NJ et al. The prevalence of ‘incidental' acoustic neuroma. Arch Otolaryngol Head Neck Surg 2005; 131:241-4

2 Rosenberg SI. Natural history of acoustic neuromas. Laryngoscope 2000;110:497-508

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