Petrosectomy and Topographical Anatomy in Traditional Kawase and Posterior Intradural Petrous Apicectomy (PIPA) Approach: An Anatomical Study.

OBJECTIVE: To compare the anatomical exposure and petrosectomy extent in the Kawase and posterior intradural petrous apicectomy (PIPA) approaches.

METHODS: Kawase and PIPA approaches were performed on 4 fixed cadaveric heads (3 alcohol-fixed, 1 formaldehyde-fixed silicone-injected; 4 Kawase and 4 PIPA approaches). The microsurgical anatomy was examined by means of Zeiss Opmi CS/NC-4 microscopes. HD Karl Storz Endoscopes (AIDA system) were used to display intradural exposure. Petrosectomy volumes was assessed by comparing pre- and postoperative thin-slice computed tomography scans (Analyze 12.0; AnalyzeDirect Mayo Clinic).

RESULTS: The Kawase approach exposed the rhomboid fossa with Meckel's cave extradurally, the upper half of the clivus, superior cerebellopontine angle, ventrolateral brainstem, the intrameatal region, basilar apex, and the preganglionic root of cranial nerve (CN) V, CN III-IV-VI intradurally. The PIPA approach exposed the cerebello-pontine angle with CN VI-XII, Meckel's cave, CN III-V, and the middle and lower clivus intradurally from a posterior view. The area of surgical exposure is wide in both approaches; however, the volume of petrosectomy, the working angle, and surgical corridor differ significantly.

CONCLUSIONS: The Kawase approach allows wide exposure of the middle cranial fossa (MCF) and posterior cranial fossa, requiring extradural temporal lobe retraction and an extradural petrosectomy with preservation of the internal acoustic meatus and cochlea. No temporal lobe retraction and direct control of neurovascular structures make the PIPA approach a valid alternative for lesions extending mostly in the Posterior cranial fossa with minor extension in the MCF. The longer surgical corridor, cerebellar retraction, and limited exposure of the anterior brainstem make this approach less indicated for lesions with major extension in the MCF and the anterior cavernous sinus.