Presentation and Clinical Course of Asymptomatic Incidental Vestibular Schwannomas

Objective: Greater access to advanced imaging combined with the high-resolution of modern contrast-enhanced magnetic resonance imaging (MRI) has resulted in a growing number of incidentally diagnosed vestibular schwannomas (VS). Cadaveric studies have demonstrated that the true incidence of VS is much greater than clinically derived estimates suggest. Thus, several patients harbor asymptomatic VS that may never manifest clinically or require treatment during their lifetime. Currently, little data are available regarding the clinical course of incidentally diagnosed VS. Specifically, it is unknown whether these tumors represent a more indolent biological variant. Such information would be beneficial toward patient counseling regarding treatment strategy and surveillance intervals during observation.

Methods: A retrospective chart review was performed at a single tertiary academic referral center. Patients with incidentally diagnosed VS that were evaluated between January 2000, and July 2015 were analyzed. Only cases where imaging was obtained for unrelated indications among patients that denied attributable symptoms such as hearing loss, dizziness, facial numbness or facial motor dysfunction, were included. All patients had confirmed symmetrical pure tone thresholds and word recognition scores. Data regarding presentation, clinical course, treatment strategy and outcome were analyzed.

Results: Between 2000 and 2015, a total of 56 incidental VS were evaluated, representing ~2.5% of all VS evaluated during this time. There were more than twice as many cases of incidental VS evaluated in the past 5 years compared with the first 5 years of the study period. The mean age at diagnosis was 49.6 years (range 16–76 years), 29 (51.8%) patients were women, and 29 (51.8%) VS were right-sided. The most common indications for head MRI included surveillance of other neurological conditions (e.g., multiple sclerosis) (17%), and chronic headache (14.3%). At time of diagnosis, 39 (69.6%) VS were confined to the internal auditory canal (mean size 4.9 mm; range 2–10 mm), while 17 (30.4%) involved the cerebellopontine angle (mean size 14.5 mm; range 7–35 mm). Ultimately, 11 (17.9%) patients received microsurgery, 11 (17.9%) radiosurgery and 34 (60.7%) were observed with serial MRI. Among patients that elected initial observation, 15 tumors (39.4%) demonstrated radiological growth at a mean of 46 months after diagnosis. The median growth rate among enlarging tumors was 1.0 mm/year (range 0.3–19 mm); notably, one tumor demonstrated exceptionally fast growth of 19mm/year. Of these, 9 received radiosurgery, 4 microsurgery, and one continues to be observed. Of patients who have remained in the observation cohort, all but one have maintained Class A hearing at their last audiometric evaluation at a mean of 33.0 months (range 3.4–97.1 months).

Conclusion: The number of incidentally diagnosed VS is rising. Patients with incidental tumors commonly maintain excellent hearing and rarely experience symptom progression with observation. Approximately 40% of incidental tumors demonstrate growth during the first 5 years of observation, which parallels natural history data from unselected small to medium sized VS. These data suggest that patients with incidental VS should be counseled similarly to the general VS population regarding the risk of growth and need for treatment.