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Introduction
Perilymph fistula is defined as an abnormal connection between the perilymph compartment of the inner ear and the middle ear. Some cases are caused by trauma or erosive disease (e.g. cholesteatoma), or following ear surgery, particularly stapedectomy. Twenty per cent of cases have been reported to be spontaneous; however, many of these were associated with a preceding pressure-increasing event.1
There is no agreed 'gold standard' diagnostic tool, and currently diagnosis of a perilymph fistula is based on a compatible history, examination and investigations. Direct observation at tympanotomy may be the only way to definitively identify a perilymph fistula, but even this is controversial, with a wide range of positive identification rates reported in the literature (24-100 per cent).2
Patient history features which may be suggestive of a perilymph fistula include a pressure-increasing precipitating event that causes episodic vertigo, and fluctuating hearing loss sometimes associated with tinnitus and aural fullness. These can be provoked by further pressure-increasing events such as coughing, straining or sneezing. Some patients report vertigo in the presence of loud sounds (Tullio phenomenon). It is notable that this clinical picture may be similar to Ménière's disease and superior semicircular canal dehiscence. The former is not usually associated with pressure-increasing events, and has specific diagnostic criteria set out by the American Academy of Otolaryngology - Head and Neck Surgery.3Superior semicircular canal dehiscence is diagnosed on computed tomography (CT) scans.
Clinical examination findings are often normal, particularly if the patient presents some time after the precipitating event; they may, however, have a positive 'fistula test' result. The Fraser positional test may yield positive results, wherein audiometric thresholds improve after lying with the affected ear uppermost for 30 minutes.
Imaging is often not sensitive enough to detect a small leak, but high resolution CT scanning may show abnormalities predisposing to a perilymph fistula and may show superior semicircular canal dehiscence. Magnetic resonance imaging (MRI) with intrathecal gadolinium has been used to detect leaks, but is not without complications.4
In light of this diagnostic uncertainty, management decisions can be difficult. The options include conservative measures, such as bed rest with head elevation to 30° and the avoidance of pressure-increasing...