Abstract
The P2 bypass is one of the most difficult procedures in cerebrovascular surgery. Creating an anastomosis between the arterial graft and the P2 segment of the posterior cerebral artery is challenging because the P2 segment is located deep and high within the ambient cistern.
We describe the application of a skull base technique, mastoidectomy and partial rhomboid drilling of the middle fossa, in order to achieve the anastomosis deep in the ambient cistern without temporal lobe injury. Mastoidectomy with hearing preservation creates a presigmoid space, which enables a presigmoid transtentorial approach to the ambient cistern. After complete skeletonization of the semicircular canals, rhomboid drilling of the middle fossa can be performed, confirming the landmarks of the rhomboid, arcuate eminence, greater superficial petrosal nerve, posterior margin of the third branch of the trigeminal nerve, and petrous margin.
Partial rhomboid drilling, in which the posterior half of the rhomboid is drilled away, helps to reduce the requirement for temporal retraction during P2 bypass.
