Is Navigation Useful in the Resection of Small Intrametal Vestibular Schwannomas?

Introduction: Navigation is generally accepted as an optional additional procedure in skull base surgery. The precise imaging by MR and CT and the correct transforming of these data by the referencing procedure of the navigation system is mandatory. Due to individual differences of the petrous bone it is sometimes difficult to identify the anatomical landmarks near the inner ear canal. Therefore the use of navigation can reduce drill work to progress directly to the optimal target point of uncovering the inner ear canal in small intrameatal vestibular schwannomas (stage I and II, grade 1, 2, or 3 according to Zini and Magnan) by navigation.

Material and Methods: Intrameatally located vestibular schwannomas stages I and II were resected by a subtemporal approach. This was supported by navigation (Stryker-Leibinger®) if requested by the patients. In a retrospective analysis we evaluated the duration of surgery and of drill work, complications, and morbidity in patients treated surgically with or without navigation by the subtemporal approach.

Results: Navigation does not reduce morbidity or surgical time. In three patients accuracy decreased during surgery. In the other cases navigation allowed a direct opening of the inner ear canal in the posterior part near the geniculate ganglion. The anterior part of the bony wall in the inner ear canal was partially preserved to protect the facial nerve. The overall time of surgery was not reduced by navigation. In the 1-year follow-up, no recurrency or residual tumor mass was detected in the MRI.

Conclusions: In contrast to the enlarged subtemporal approach according to Wigand, small tumors can be resected by a limited partial uncovering of the inner ear canal, preserving the bony petrosal trailing edge. However, the set-up time for the registration procedure may prolong the overall surgical time. On the other hand, navigation is a good instrument with which to visualize and to teach the surgical approach.