Acoustic neuromas presenting with normal or symmetrical hearing: Factors associated with diagnosis and outcome

Objective: To evaluate the clinical features leading to diagnosis in patien ts with acoustic neuroma (AN) who present with normal or symmetrical hearin g. Underlying tumor characteristics are also studied to identify a possible explanation for this unique presentation in the AN population. Study Design: Retrospective case review comprising patients who were identi fied as having AN that presented with normal audiometry. Setting: A tertiary referral center. Patients: Patients with AN who met the criteria for normal were included in the report. For this study, abnormal audiometry is defined as an interaura l difference of greater than or equal to 15 dB at a single frequency or gre ater than or equal to 10 dB at two or more frequencies, and an interaural-s peech reception threshold difference of greater than or equal to 20 dB, or a speech discrimination score of greater than or equal to 20%. Main Outcome Measures: Presenting symptoms and signs, clinical features tha t led to the diagnosis of AN, auditory brain stem response results, tumor l ocation, size and relationship to temporal bone landmarks, surgical interve ntion, surgical outcome, and results of hearing preservation attempts were tabulated for each patient. Results: A total of 29 patients (5%) were identified who had normal or symm etrical pure-tone audiograms between 500 and 4,000 Hz. The average differen ce in speech reception threshold between tumor and nontumor ear was 3.2 dB, and the average difference in speech detection score was 2.6%, The most co mmon presenting symptoms that led to the diagnosis of the AN were dysequili brium/vertigo (12 cases), cranial nerve V and VIT abnormalities (11 cases), routine screening for families with neurofibromatosis type 2 (5 cases), as ymmetrical tinnitus (4 cases), headaches (4 cases), unilateral subjective h earing difficulty (4 cases), and incidental finding during evaluation for a nother problem (4 cases). The average tumor size was 19 mm, with five cases presenting with tumors of size greater than or equal to 30 mm. Nineteen pa tients underwent a hearing preservation procedure (middle fossa or retrosig moid), II of whom had useful hearing postoperatively. Conclusions: Despite normal audiometry, patients presenting with imbalance or vertigo, Vth or VIIth cranial nerve deficits, or unilateral hearing comp laints may warrant further evaluation to rule out the possibility of AN or other retrocochlear lesion. To seek an explanation for this phenomenon, the incidence of various tumor characteristics (e.g., depth of penetration int o the internal auditory canal and degree of porous erosion) is discussed an d compared with the entire AN population.