[False-positive diagnostic findings in acoustic neurinomas]

In the period from 1976 to 1990 Tos and Thomsen operated on 520 patients with acoustic neuromas using the translabyrinthine approach and five other patients were operated on via middle fossa approach. The diagnostic work up in all patients included: pure tone audiometry, tympanogram with acoustic reflexes, caloric test and brainstem audiometry. Since the late seventies, CT became the radiological investigation of choice to visualize the tumor. The first generation of CT failed to reveal tumors less than 1.5 cm in the extrameatal diameter, and pantopaque cisternography was necessary in some cases. The following generation of CT did not always reveal small intrameatal tumors, and false-negative results were reported. The incidence of false-positive CT findings in our series is calculated to be 0.6%. Three patients were operated on on account of false-positive CT. Peroperatively, adhesions in and around the internal porus were found in two cases while no pathology was found in the third case. Postoperatively, anacusis was observed in two cases. This could have been avoided if magnetic resonance imaging (MRI) with gadolinium contrast had been performed. In our opinion, MRI should be considered before a definitive surgical procedure is undertaken. Until MRI becomes more widely available, intravenous contrast-enhanced tomography followed by air cisternography is recommended in the diagnosis of small acoustic neuromas.