What bone part is important to remove in accessing the suprachiasmatic region with less frontal lobe retraction in frontotemporal craniotomies.

Abstract

The anterolateral approach is one of the main routes for accessing suprachiasmatic lesions involving the anterior communicating artery (AComA) complex. Pterional (PT) craniotomy and its alternatives, including orbitozygomatic, orbitopterional, and mini-supraorbital craniotomies, have been developed as tailored frontotemporal craniotomies. One of the main differences between PT craniotomy and its alternatives is the removal of the orbital bone along with the sphenoid wing. However, which bone part is the most important to remove has not been discussed in relation to frontal lobe retraction. We have evaluated how the removal of the supraorbital bar versus the removal of the lateral orbital wall along with the sphenoid wing affects the relationship between the levels of frontal lobe retraction and area of exposure (AOE) in the suprachiasmatic region. We performed three types of craniotomies: PT craniotomy, PT craniotomy with the removal of the supraorbital bar (PT-SO craniotomy), and PT craniotomy with the removal of the lateral orbital wall along with the sphenoid wing, i.e., the frontal process of the zygomatic bone and the orbital and cerebral faces of the greater sphenoid wing (PT-LO-SW craniotomy). For each craniotomy, the AOE around the suprachiasmatic region was measured at four different levels of frontal lobe retraction, namely, 5, 10, 15, and 20 mm, from the cranial base. At 5-mm retraction, PT-LO-SW craniotomy was the only craniotomy in which the AComA complex was visible. At 10-mm retraction, PT-LO-SW craniotomy afforded the greatest AOE among the three craniotomies, and the AOE was significantly greater than that of PT craniotomy (P = 0.025). At 15- and 20-mm retraction, there were no significant differences among the three craniotomies. Treatment of lesions in the suprachiasmatic region via an anterolateral route involving a frontotemporal craniotomy requires sufficient removal of the lateral orbital wall along with the greater sphenoid wing so that brain retraction is minimized.