Objective: The natural history of sporadic vestibular schwannoma (VS) is unpredictable, as tumors may or may not grow and can even spontaneously regress. A spontaneous VS shrinkage MRI-based pattern has been proposed with either a scalloped tumor aspect in the cerebellopontine angle or the appearance of a CSF-filled space surrounding the intracanalicular (IC) tumor within an enlarged canal. The authors of this retrospective study aimed to describe the evolution of sporadic VSs with radiological signs of VS regression and to identify prognostic factors for tumor shrinkage.
Methods: All MRI scans obtained during patient follow-up were reviewed for extracanalicular (EC) and IC size and tumor characteristics. Volumetric measurements were performed on the first and last MRI scans. Shrinkage was considered to have occurred if the tumor size had decreased by ≥ 2 mm in its largest diameter and/or if the volume had decreased by ≥ 20%. Audiometric data were also collected.
Results: Among 512 patients under observation for sporadic VSs, 66 (13%) had at least one radiological sign of VS regression and 31 of these (6% overall) had confirmed tumor shrinkage. The mean follow-up was 4 ± 2.5 years. One radiological sign was present on initial MRI in 58% of patients and appeared during the follow-up period in the remaining 42%. Two groups were identified: 31 patients (47%) demonstrated progressive tumor regression during follow-up, and tumors in 35 patients (53%) remained stable once signs of regression were identified (assuming a stabilized regression). The prognostic factors for VS regression were as follows: EC VS extension (p = 0.02), cystic lesion (p = 0.002), and central necrosis (p = 0.02). The mean pure-tone average (PTA) was 43 ± 26.2 dB at the time of diagnosis and 53 ± 28.3 dB at the last visit (p < 0.0001). Among patients with an observed tumor shrinkage, ∆PTA was lower if the inner ear signal on the high-resolution T2-weighted image had improved (-3 ± 8.9 dB, n = 11) than if the inner ear signal had not improved (-10 ± 6.9 dB, n = 20) (p = 0.02) between the initial and last MRI scans.
Conclusions: Spontaneous shrinkage of sporadic VSs could be suspected based on two radiological aspects that are indicative of VSs in progressive or stabilized regression and is an additional argument for the conservative management of these tumors. During follow-up, recovery from a reduced to a normal cochlear fluid MRI signal is a good indicator for hearing preservation.
Keywords: MRI; pure-tone audiometry; speech discrimination score; spontaneous regression; sporadic vestibular schwannoma; surveillance.