Tumor Induced Surgical Anatomical Variations of Cranial Nerves in Anterior Petrosal Approach

Objectives: Numerous surgical approaches have been devised to address the petroclival region. Anterior petrosal approach through the middle fossa is a well-established option for addressing cranial base lesions of the petroclival region. Datas about the variations of anatomical structures in different petroclival pathologies help the surgeon to perform such an approach more confidently.

Method: We reviewed retrospectively videos, operation records and histological findings of 40 petroclival tumors between Jan 2009 and September 2013 in which Kawase's approach was performed. The anatomical variations of Cranial nerves IV-VI related to the tumor divided into the following categories: superior lateral (SL), inferior lateral (IL), superior medial (SM), inferior medial (IM), encased (E).

The datas were analyzed considering the different pathological subgroups (Meningioma cases; Epidermoid cases and Schwannoma cases).

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 but not encased. In 38% of meningioma, trochlear nerve is encased by the tumor. Abducens nerve is not always visible.

In epidermoid and trigeminal or abducens nerve schwannoma, the pathological nerve's pattern is totally different from meningioma.

Conclusions: The pattern of cranial nerves IV-VI is various in different types of petroclival tumors. In meningioma, the origin (attachment) of the tumor (cavernous, upper clival, tentorial and petrous apex) is the most important predictor of nerve's location.