Electrocochleography in the diagnosis of perilymphatic fistula: intraoperative observations and assessment of a new diagnostic office procedure.

The intraoperative electrocochleogram (ECochG) was investigated during stapedectomy surgery and during cochleostomy surgery. This provided the justification for obtaining recordings with the oval window (OW) or round window (RW) intact and then when there was a definite fistula. It was noteworthy that no ECochG changes occurred on merely opening the OW or RW, but that marked changes occurred on removing perilymph, even by gentle suction. On raising the intrathoracic pressure and replacing the perilymph, the ECochG potentials usually recovered. Based on these intraoperative observations, an office procedure was designed. The subject was asked to raise the intrathoracic pressure on several occasions and changes in the amplitude of the ECochG potential were noted. An increase of over 15 percent in the action potential (AP), with or without a decrease in the negative summating potential (SP) during the period of raised intrathoracic pressure, was used as the diagnostic criteria for a perilymphatic fistula. A decrease in the AP with or without an increase in the negative SP immediately on relaxing after a period of raised intrathoracic pressure was also treated as a positive diagnostic criterion. Seventy-one normal ears were investigated and a positive result was recorded in two ears (false positive rate: 2.8%). Two hundred and six ears, strongly suspected as having a perilymph leak on the basis of the clinical history and vestibular signs have been investigated over the past 4 years. Ninety positive diagnoses have been reached and 46 of these ears have been surgically explored.(ABSTRACT TRUNCATED AT 250 WORDS)