Increased growth rate of vestibular schwannoma after resection of contralateral tumor in neurofibromatosis type 2

Abstract

Surgical management of bilateral vestibular schwannomas (VS) in neurofibromatosis type 2 (NF2) is often difficult, especially when both tumors threaten the brainstem. When the largest tumor has been removed, the management of the contralateral VS may become puzzling. To give new insights into the growth pattern of these tumors and to determine the best time point for treatment (surgery or medical treatment), we studied radiological growth in 11 VS (11 patients with NF2) over a long period (mean duration, 7.6 years), before and after removal of the contralateral tumor while both were threatening the brainstem. We used a quantitative approach of the radiological velocity of diametric expansion (VDE) on consecutive magnetic resonance images. Before first surgery, growth patterns of both tumors were similar in 9 of 11 cases. After the first surgery, VDE of the remaining VS was significantly elevated, compared with the preoperative period (2.5 ± 2.2 vs 4.4 ± 3.4 mm/year; P = .01, by Wilcoxon test). Decrease in hearing function was associated with increased postoperative growth in 3 cases. Growth pattern of coexisting intracranial meningiomas was not modified by VS surgery on the first side. In conclusion, removal of a large VS in a patient with NF2 might induce an increase in the growth rate of the contralateral medium or large VS. This possibility should be integrated in NF2 patient management to adequately treat the second VS.

Fig. 1.

Preoperative growth of bilateral vestibular schwannomas. Dotted lines and circles represent the growth curve of the first operated tumor. Plain lines and squares represent contralateral vestibular schwannoma (VS) growth. Abscission times correspond to the preoperative follow-up period, with time 0 being the time of the resection of the first VS (the largest). In 7 of 11 patients, mean tumor diameters (MTDs) differed at the beginning of follow-up, but growth rates were similar during follow-up (eg,  patient 4 in A). In 2 patients, MTDs and growth rates were similar from the beginning to the end of follow-up (eg, patient 6 in B). In the last 2 patients, MTDs were similar at the beginning of follow-up, but growth rates varied during follow-up (eg, patient 5 in C). In case C, the contact between the right VS and the homolateral petrous ridge meningioma, having occurred between images 1 and 2, seems to have significantly triggered VS growth and may explain differential growth between the 2 VSs.

Fig. 2.

Changes in vestibular schwannoma (VS) growth rates after surgery for the first tumor. The origin of the timeline corresponds to the surgery of the first VS. Tumor size is expressed as a fraction of the baseline tumor mean tumor diameter (MTD), defined as the MTD of each tumor at the time of first surgery. Tumor groups as defined by regression analysis are represented as follows: group 1, black circles; group 2, gray triangles; and group 3, white circles. Slopes and R² values are indicated.

Fig. 3.

Progression of the radiological growth rate of the remaining vestibular schwannoma (VS) after resection of the contralateral tumor (Patient 9). Each point represents a magnetic resonance imaging examination (gadolinium-enhanced T1-weighted images) before and after removal of the first VS. Before surgery, the tumor grew with a radiological velocity of diametric expansion (VDE) of 4.0 mm/year. After surgery, the radiological VDE increased to 7.9 mm/year.