gms | German Medical Science

Objective: Surgery of petroclival and petrous apex lesions is very challenging, due to the complexity of the vascular and neural structures present in this anatomical region. The aim of this study is to compare extent of petrosectomy, anatomical exposure, and exposition of neurovascular structures of the Kawase approach versus the "inverted Kawase approach" (i-Kawase approach: retrosigmoid approach with anterior suprameatal petrosectomy) in the anatomical lab.

Method: Kawase and i-Kawase approaches were performed on 4 fixed cadaveric heads without known intracranial pathology (3 alcohol-fixed specimens, 1 silicone-injected specimens for vessels), respectively (4 heads bilaterally, 4 Kawase and 4 i-Kawase approaches). The microsurgical anatomy was examined and photographed by means of Zeiss Opmi CS/NC-4^® microscopes. HD Karl Storz Endoscopes (AIDA system) were also used to display intradural exposure and maneuverability. Amount of petrous bone drilling was assessed comparing pre- and post-operative thin-slices CT scans and calculating the petrosectomy volume (Analysis 12, Mayo Clinic).

Results: Kawase approach exposed the rhomboid fossa with Meckel's cave extradurally, the upper half of the clivus, superior cerebellopontine angle, ventro-lateral brainstem, the intrameatal region, basilar apex, the preganglionic root of CN V, CN III-IV-VI intradurally. i-Kawase approach exposed the cerebello-pontine angle with CN VII-XII, Meckel's cave, CN III-VI and the middle and lower clivus intradurally from a posterior view. The volume of petrosectomy is comparable between the two approaches, angle and direction, however, differ significantly.

Conclusions: Kawase approach is a commonly used approach with wide exposure of the MCF and PCF, requiring extradural temporal lobe retraction and an extradural petrosectomy with preservation of the internal acoustic meatus and cochlea. No temporal lobe retraction, a direct control of lower cranial nerves and vessels make the i-Kawase approach a valid alternative for lesions extending mostly in the PCF with minor extension in the MCF. Conversely, 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.