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

To evaluate the clinical features leading to diagnosis in patients with acoustic neuroma (AN) who present with normal or symmetrical hearing. Underlying tumor characteristics are also studied to identify a possible explanation for this unique presentation in the AN population.

Retrospective case review comprising patients who were identified as having AN that presented with normal audiometry.

A tertiary referral center.

Patients with AN who met the criteria for normal were included in the report. For this study, abnormal audiometry is defined as an interaural difference of > or =15 dB at a single frequency or > or =10 dB at two or more frequencies, and an interaural speech reception threshold difference of > or =20 dB, or a speech discrimination score of > or =20%.

Presenting symptoms and signs, clinical features that led to the diagnosis of AN, auditory brain stem response results, tumor location, size and relationship to temporal bone landmarks, surgical intervention, surgical outcome, and results of hearing preservation attempts were tabulated for each patient.

A total of 29 patients (5%) were identified who had normal or symmetrical pure-tone audiograms between 500 and 4,000 Hz. The average difference 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 common presenting symptoms that led to the diagnosis of the AN were dysequilibrium/vertigo (12 cases), cranial nerve V and VII abnormalities (11 cases), routine screening for families with neurofibromatosis type 2 (5 cases), asymmetrical tinnitus (4 cases), headaches (4 cases), unilateral subjective hearing difficulty (4 cases), and incidental finding during evaluation for another problem (4 cases). The average tumor size was 19 mm, with five cases presenting with tumors of size > or =30 mm. Nineteen patients underwent a hearing preservation procedure (middle fossa or retrosigmoid), 11 of whom had useful hearing postoperatively.

Despite normal audiometry, patients presenting with imbalance or vertigo, Vth or VIIth cranial nerve deficits, or unilateral hearing complaints 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 into the internal auditory canal and degree of porous erosion) is discussed and compared with the entire AN population.