Tumor-Induced Surgical Anatomical Variations of Cranial Nerves in Anterior Petrosectomy for Petroclival Tumors

Objective: Anterior petrosectomy through the middle fossa is a well-described option for addressing cranial base lesions of the petroclival region. Data about the variations of anatomical structures in different petroclival pathologies help the surgeon to perform such an approach more confidently. Methods: We reviewed retrospectively videos and operation and histological records of 40 petroclival tumors between January, 2009 and September, 2013 in which Kawase approach was performed. The anatomical variations of cranial nerves IV-VI related to the tumor divided into different categories: superior lateral (SL), inferior lateral (IL), superior medial (SM), inferior medial (IM), and encased (E). The data were analyzed considering the different pathological subgroups (meningioma, epidermoid, and schwannoma). Results: In 41% of meningiomas, the trigeminal nerve is encased by the tumor. In 38% of meningioma the trigeminal nerve is in SL part of the tumor and in 20% in IL part of the tumor. In 38% of meningioma, trochlear nerve is encased by the tumor. Abducens nerve is not always visible (35%). In epidermoid and trigeminal or abducens nerve schwannoma the pathological nerve's pattern is different from meningioma. Conclusion: The pattern of cranial nerves IV-VI is various in different types of petroclival tumors. In meningioma tumor type (cavernous, upper clival, tentorial, and petrous apex) is the most important predictor of nerve's location.