The postulated sites of perilymph fistulae involve otic capsule deficiencies, in particular, at the fissula ante fenestram. Histological studies have revealed this to be a channel extending from the middle ear, and becoming continuous with the inner ear medial to the anterior limit of the oval window. The relationship between a patent fissula and symptoms of perilymph fistula is contentious.

The understanding of the anatomy of the fissula ante fenestram is incomplete. Histopathology is inherently destructive to the delicate ultrastructure of the middle and inner ear. Conversely, X-ray microtomography allows non-destructive examination of the otic capsule. In this study, we used X-ray microtomography to characterise the fissula ante fenestram.

We imaged cadaveric temporal bones with X-ray microtomography. We used the Avizo Fire (Visualization Science Group, Merignac Cedex, France) software to perform post-processing and image analysis.

Three-dimensional modelling of the fissula ante fenestram allowed stratification into four forms: rudimentary pit; partial fissula; complete occluded fissula; and complete patent fissula.

X-ray microtomography showed that the fissula ante fenestram is present in various forms from rudimentary pit to complete deficiency of the otic capsule. This understanding may have implications for otologic surgery and clinical diagnosis of perilymph fistula.

To investigate the feasibility of postauricular hypodermic injection for treating inner ear disorders, we compared perilymph pharmacokinetics for postauricular versus intravenous injection, using magnetic resonance imaging, in an animal model.

Twelve albino guinea pigs were divided randomly into two groups and administered gadopentetate dimeglumine via either a postauricular or an intravenous bolus injection. A 7.0 Tesla magnetic resonance imaging system was used to assess the signal intensities of gadolinium-enhanced images of the cochlea, as a biomarker for changes in gadopentetate dimeglumine concentration in the perilymph. Pharmacokinetic parameters were calculated based on these signal intensity values.

Guinea pigs receiving postauricular injection showed longer times to peak signal intensity, longer elimination half-life, longer mean residence time and a greater area under the signal–time curve (from pre-injection to the last time point) (p < 0.05).

Postauricular injection shows potential as an efficient drug delivery route for the treatment of inner ear disorders.

To investigate whether artificial perilymph can induce neural stem cells, derived from the hippocampus of newborn guinea pigs, to differentiate into inner ear hair cells, in vitro.

Primary neural stem cells derived from the hippocampus of newborn guinea pigs were incubated in medium containing either 10 per cent fetal bovine serum or 5, 10 or 15 per cent artificial perilymph, for three weeks. Differentiated cells were identified using immunofluorescence, Western blot and scanning electron microscopy.

Both fetal bovine serum and artificial perilymph induced the neural stem cells to differentiate into cells with hair-cell-specific antibodies.

Neural stem cells can survive in both fetal bovine serum and artificial perilymph, and within these media can differentiate into cells with hair-cell-specific antibodies. This provides an experimental basis for transplantation of neural stem cells into the inner ear.

A number of authors have suggested that surgery for suspected perilymph fistula is effective in preventing deterioration of hearing and in improving hearing in some cases in the short term. We present long-term hearing outcome data from 35 children who underwent exploration for presumed perilymph fistula at The Children's Hospital, Sydney, Australia, between 1985 and 1992.

The pre-operative audiological data (mean of 500, 1000, 2000 and 4000 Hz results) were compared with the most recently available data (range two to 15 years) and the six-month post-operative data.

The short-term results showed no significant change in hearing at six months, with a subsequent, statistically significant progression of hearing loss in both operated and non-operated ears (Wilcoxon signed rank test: operated ear, p < 0.017; non-operated ear, p < 0.009).

In this case series, exploratory surgery for correction of suspected perilymph fistula did not prevent progression of long-term hearing loss.