Radiological Features and Pathognomonic Sign of Stapes Footplate Fistula in Inner Ear Malformations.

Objective: Some inner ear malformations may cause recurrent meningitis, which may be fatal. The etiology is usually a stapes footplate fistula which enables microorganisms to pass into the inner ear containing cerebrospinal fluid (CSF), causing repeated attacks of meningitis. Radiological signs of the fistula are not obvious and are not reported in detail in the literature. The aim of the study is to investigate the radiological features of stapes footplate fistula in inner ear malformations.

Methods: Radiological findings were analyzed for seventeen patients with inner ear malformations (IEMs) operated on because of recurrent meningitis. Using this information, images of 1,010 patients with IEMs were retrospectively reviewed to investigate the radiological findings of stapes footplate fistula and their relationship to IEMs. They were classified according to the Sennaroglu classification system, and according to different stages of stapes footplate fistula.

Results: In the case of a stapes footplate cyst, computerized tomography shows an opacity at the oval window. On magnetic resonance imaging, a fluid filled cystic structure continuous with and having similar signal characteristics to the CSF in the inner ear is a pathognomonic finding of a stapes footplate cyst. It is most commonly found in common cavity anomaly (18.2%); the second most frequent finding is incomplete partition type I (15%). And it can even be seen in cases of cochlear aplasia where only the vestibule is present.

Conclusion: If the history reveals recurrent meningitis, particular attention should be given to the oval window area, where an opacity, cyst or a leaking lesion should be looked for on the imaging. It is the responsibility of the otolaryngologist to notice these findings, and to operate on the patient to prevent further attacks of meningitis.