Functional Petrosectomy Via a Suboccipital Retrosigmoid Approach: Guidelines and Topography.

OBJECTIVE: Recent reports have validated the use of retrosigmoid approach extensions to deal with posterior fossa lesions extending laterally extracranially or superiorly into the petroclival areas. The purpose of our research is to describe the topographic retrosigmoid anatomy of the petrous pyramid and provide guidelines for neurovascular sparing drilling (hence for a functional petrosectomy), via this surgical route.

METHODS: Suprameatal and inframeatal retrosigmoid approach extensions were performed bilaterally in 6 specimens in the semisitting position. Topographic relationships of pertinent labyrinthine landmarks with evident posterolateral cranial base structures were measured by neuronavigation.

RESULTS: Excellent exposure of inframeatal/petroclival regions as well as of the extracranial posterior infratemporal area was achieved in all the specimens. In the inframeatal region, petrous bone drilling was limited by the labyrinth and the internal auditory canal superiorly and by the jugular bulb, the inferior petrosal sinus, and the lower cranial nerves inferiorly. The intrapetrous internal carotid artery represented the anterolateral limit. In the suprameatal area, the drilling was limited laterally by the labyrinth (i.e., by the posterior part of the superior semicircular canal, the upper part of the posterior semicircular canal, and the common crus). The internal auditory canal was the inferior limit, and the superior petrosal sinus and the trigeminal nerve limited the drilling superiorly. Multiple topographic relationships among key landmarks were quantified.

CONCLUSIONS: Knowledge of the topographic anatomy of the labyrinthine structures examined may be useful (combined with careful assessment of the preoperative imaging and with the use of neuronavigation and endoscopy) to accomplish a retrosigmoid neurovascular sparing petrosectomy.