Magnetic Resonance Imaging Surveillance for Vestibular Schwannoma After Microsurgical Resection Using a Retrosigmoid Transmeatal Approach.

Background: Vestibular schwannoma (VS) is a benign, usually slow-growing tumor. The drawback of radical microsurgical VS resection is the increased likelihood of neurologic injury, forcing surgeons to leave a tumor remnant in some cases. We evaluated the prognostic value of magnetic resonance imaging (MRI) enhancement patterns to determine the risk of tumor regrowth.

Methods: This clinical study included 30 patients (20 women and 10 men) with VS who underwent surgery via a retrosigmoid transmeatal approach. The extent of resection was assessed by MRI 6 months after surgery. Two subtypes of intracanalicular linear enhancement were defined: linear enhancement of the walls of the internal auditory canal (IAC) or in the cerebellopontine angle (CPA) and linear enhancement covering the end of the IAC. All patients included in the study underwent follow-up MRI every year for at least 6 years.

Results: Intracanalicular nodular enhancement suggestive of a tumor remnant was seen in the IAC in 11 patients (36.7%). Volume of nodular enhancements was <0.5 cm when measurable. The enhancement remained stable throughout follow-up except in 2 cases that showed a slight decrease in size and in 1 case with an initial tumor remnant of 0.5 cm showing a slight increase over the years. Eighteen patients (60%) had linear enhancement in the IAC or in the CPA. No patients with linear enhancement showed nodular enhancement.

Conclusions: Although specific monitoring protocols can be designed based on MRI findings 6 months after microsurgical VS resection, follow-up should be maintained indefinitely given the slight possibility of very late regrowth.