Endoscope-Assisted Microsurgical Resection of a Petroclival Artificial Tumor Model with Retrosellar Extension Using a Retrosigmoid Approach: A Cadaveric Study and Analysis of Supratentorial Working Area

Background: Petroclival tumors present a management challenge to the neurosurgeon to carefully select the appropriate operative approach. The retrosigmoid approach has been advocated for certain petroclival tumors. One of the limitations of the retrosigmoid approach is limited access to the retrosellar space. We have previously described the concept of endoscope-assisted microsurgery. Our hypothesis is that an endoscope-assisted technique would allow a safe corridor into the retrosellar space to augment exposure and resection of a petroclival tumor extending into the retrosellar space during a retrosigmoid approach. Methods: Fresh cadaveric heads underwent an orbitozygomatic approach to gain access to the interpeduncular fossa. From here, an artificial tumor model was prepared using a combination of 5 mL water, 1 mL stratathane polymer (ST-504), 1 mL radio-opaque contrast (Omnipaque, iohexol solution), and approximately 0.1 mL coloring dye. While the polymer was just starting to solidify, it was injected using a 15-cm long catheter into the petroclival and retrosellar space. A thin slice CT was then performed to ensure adequate tumor placement. A retrosigmoid approach was then performed. A small opening was made in the lateral tentorium after adequate visualization of the trochlear nerve. Tumor, oculomotor nerve, posterior cerebral artery, and superior cerebellar artery were visualized. The tentorial opening was widened to allow passage of endoscopic instruments. Tumor resection was then performed using endoscopic technique. Additionally, neuronavigation was used to compute the working area and limits of exposure on the clivus and brainstem in the supratentorial working space after full opening of the tentorium comparing both the endoscope and microscope. Results: CT scans of implanted artificial tumor appropriately mimicked a petroclival tumor with retrosellar extension. With some concern that tumor caused lateral displacement of neural and vascular structures of the anterolateral incisural space to near proximity of the tentorium, the endoscopic-assisted technique allowed small lateral opening and visualization of these structures endoscopically, then permitting further opening the tentorium. Various endoscopes and endoscopic instruments were used to resect the retrosellar portion of the tumor and fully visualize the retrosellar space to ensure no residual tumor existed. Results of the working area analysis supplement previous studies already demonstrati