Date Published: June 4, 2019
Publisher: Public Library of Science
Author(s): Ghizlene Lahlou, Mathieu Rodallec, Yann Nguyen, Olivier Sterkers, Michel Kalamarides, Jonathan H. Sherman.
The natural history of sporadic vestibular schwannoma is unpredictable, with tumors growing, non-growing and even showing spontaneous regression in some rare cases.
This retrospective study aims to describe the radiologic signs characterizing and identifying the shrinking vestibular schwannoma.
Involution was considered to have occurred if tumor size had decreased by 2 mm or more on its largest diameter. All magnetic resonance imaging scans were reviewed for tumor size, internal auditory meatus size, and tumor characteristics. Volumetric measurements were performed on the first and last scan. Audiometric data were collected at the first and last visit.
Fourteen patients with a confirmed spontaneous regression were included, with a mean follow-up of 5 ± 2.6 years. The mean shrinkage rate was 0.9 ± 0.59 mm/year on 2D measurements, and 0.2 ± 0.17 cm3/year on volumetric measurements, with a relative shrinkage of 40 ± 16.9%. Two remarkable radiologic features were observed: First, a festooned aspect, defined by multiple curves in the tumor outline, noticed in 12 cases (86%); second, the appearance of cerebrospinal fluid filling the internal auditory meatus, associated with an enlargement of the internal auditory meatus compared to the contralateral side, and observed in 10 out of 13 cases with internal auditory meatus invasion (77%). Those two aspects were associated in 64% of cases.
These two newly reported radiologic features could help neurosurgeons, oto-neurosurgeons and neuroradiologists to identify a spontaneous vestibular schwannoma involution at first visit. This could allow any treatment to be postponed, monitoring to be more widely spaced, and patients to be reassured.
Vestibular schwannoma (VS) is the most frequent tumor of the cerebellopontine angle (CPA) and internal meatus, and arises from Schwann cells around the vestibular nerve and ganglia. The widespread use of magnetic resonance imaging (MRI) has increased the number of VSs diagnosed during the last decades, especially among patients with few or no symptoms. Accordingly, Stangerup and Caye-Thomasen showed that the incidence of sporadic VS in Denmark had increased from 7.8 per 1 million per year in 1976 to 19 per 1 million per year in 2008.1 The tumor size at diagnosis had decreased over time, from a mean extrameatal size of about 30 mm in the mid-1970s, before CT scanning and MRI were available, to 10 mm in the period from 2003 to 2008 , a period with easy access to MRI in most countries.
Spontaneous shrinkage of VS has been reported in 3–11% of VS managed conservatively [2–4,6,7,13], but few studies have characterized these tumors in detail with accurate imaging and volumetric analysis.
The natural history of sporadic VSs includes growth, stabilization, and spontaneous regression. This study describes for the first time two radiological features of shrinking tumors that could allow neurosurgeons, neuro-otologists and neuroradiologists to recognize them at an early stage, since the first visit if shrinkage had already occurred, and so to postpone any treatment and space the MRI monitoring. It is still necessary to define an internationally standardized method to assess tumor growth and regression during observation, and in a larger series, to characterize more precisely the tumors that had shrunk.