Anatomic Comparison of the Endonasal and Transpetrosal Approaches for Interpeduncular Fossa Access

Object: The interpeduncular cistern (IPC), including the retrochiasmatic area, is one of the most challenging regions to approach surgically. Various conventional approaches to the IPC have been described; however, only the endoscopic endonasal approach (EEA) transdorsum sellae and the transpetrosal approach (TPA) provide ideal exposure with a caudal-cranial view. Therefore we compared the EEA and transpetrosal approach to clarify the their limitations and intrinsic advantages of these approaches to the IPC.

Methods: Four fresh cadaver heads were studied. An EEA transdorsum sellae with pituitary transposition was performed to expose the IPC. A transpetrosal approach was performed bilaterally combining a retrolabyrinthine presigmoid and a subtemporal transtentorium approach. Water balloons were used to emulate a space-occupying lesion. “Water balloon tumors” (WBT), inflated to two different volumes (0.5 ml and 1.0 ml), were placed (volume 0.5 ml and 1 ml) in the IPC to compare their visualization by the two approaches. The distance between Cranial Nerve III (CN III) and the posterior communicating artery (PcomA), and between CN III and the edge of the tentorium, were measured through a TPA to determine the width of surgical corridors using 0- 6 ml WBT in the IPC (n = 8).

Results: Both approaches provided sufficient adequate exposure of the IPC. The EEA yielded a good visualization of both CN III and the PcomA when a WBT in the IPC. Visualization of the contralateral anatomical structures was impaired when we used the transpetrosal approach. The surgical corridor to the IPC via the transpetrosal approach was narrow when the WBT volume was small, and its width increased as the volume of the WBT increased. There was a statistically significant increase in the maximum distance between CN III and the PcomA (p = 0.047) and between CN III and the tentorium (p = 0.029) when the WBT volume was 6 ml.

Conclusions: While both approaches are valid surgical options for retrochiasmatic pathology, such as craniopharyngiomas. The EEA via the dorsum sellae provides a direct and wide exposure of the IPC with negligible neurovascular manipulation. The transpetrosal approach also allows direct access to the IPC without pituitary manipulation; however, the surgical corridor is narrow due to the surrounding neurovascular structures and affords poor contralateral visibility. Conversely, in the presence of large or giant tumors in the IPC, that widen the spaces between neurovascular structures, the transpetrosal approach becomes a superior route whereas the EEA may have limited freedom of movement in the lateral extension.