[Guided surgery in a subtemporal approach in CPA tumors?]

Computer assisted surgery (CAS) permits the visualization of hidden bony covered structures invisible for the human eye with radiological 3d data sets. The surgeon might be able to orientate anatomically during surgery without having to prepare the according landmarks. This would mean less surgical traumatization and a shorter and smaller operation corridor.

We determined the use of CAS in a quality assurance analysis with the subtemporal approach in 8 patients with supra-meatal tumors type A of the cerebellopontine angle. Various navigation systems and methods for referencing for the registration of the patients' heads were used. The question was whether it is possible intraoperatively without preparation of known anatomical landmarks to define the borders of an optimal positioned temporary bone cap and to identify the bony covered inner auditory canal and its neuronal structures without orienting neurostimulation.

It was possible with CAS to assess intraoperatively the borders of a temporary bone cap above the cranially positioned mastoid cell. However, the objective inaccuracy of 2 to 28 mm observed during surgery did not allow a secure identification of the inner auditory canal.

CAS with the subtemporal approach cannot replace the conventional preparation of known anatomical landmarks nor neurostimulation to identify neural structures, due to the expected high inaccuracy with the non-invasive referencing systems that are available today.