Absent round window reflex: possible relation to step-wise hearing loss.

The diagnosis of perilymphatic fistula can be confusing and prone to error. The signs and symptoms can be extremely varied, and currently there is no clinical or laboratory test that accurately predicts the presence of this entity. The only reliable method of diagnosis, namely surgical exploration, is often frustrating as, commonly, no evidence of an active fistula is found. Four children initially believed to have a perilymphatic fistula were found on exploration instead to have an absent round window reflex with normal mobility of the ossicular chain. These children presented with a history of abrupt, step-wise decreases in their hearing thresholds that frequently progressed from a mixed to a purely sensorineural loss. No anatomic abnormalities were found on high-resolution computed tomography. The authors theorize that this finding may represent altered fluid dynamics within the inner ear. Whether it signifies a prior fistula that has spontaneously healed remains to be confirmed. A review of the literature along with possible pathophysiologic mechanisms is presented.