2026 Poster Presentations
P334: TIPS TO PRESERVE OLFACTION IN THE BASAL INTERHEMISPHERIC APPROACH
Seiichiro Eguchi, MD, PhD; Shuhei Morita, MD, PhD; Takakazu Kawamata, MD, PhD; Tokyo Women's Medical University
Objective: With the advent of 4K endoscopes, the indications for transsphenoidal surgery have expanded, and it is now possible to remove tuberculum sellae meningiomas by extended endoscopic transsphenoidal surgery. However, even for the same anterior skull base meningiomas, open surgery is still considered the first choice for olfactory groove (OG) and planum sphenoidalare (PS) meningiomas, and we prefer to use the basal interhemispheric approach (BIH). This approach carries the risk of anosmia, so we report on the innovations we have made to preserve olfaction.
Methods: This study included 26 cases of OG/PS meningiomas (9 OG, 17 PS meningiomas) who underwent BIH resection at our hospital between January 2012 and March 2024. BIH was performed using standard procedures, including bilateral frontal craniotomy with frontal sinus opening, bilateral dura incision near the anterior skull base, ligation and cutting of the superior sagittal sinus (SSS), opening of the lower part of the interhemispheric fissure, detachment of the olfactory tract from the frontal lobe and protecting it in the olfactory fossa.
Results: The mean age was 63.1 ± 11.5 years, 15 were female, and the mean tumor diameter was 42.9 ± 12.8 mm. Two patients had experienced anosmia before surgery. All patients underwent resection using the method described above, and gross total resection (Simpson grade 1-2) was achieved in 23 patients. Three patients had atypical meningiomas, while the rest were WHO grade 1 meningiomas. The median Ki-67 index was 1.9 (IQR 1.7) %, and no patients showed recurrence.Postoperative anosmia was observed in three cases, including transient disorders. After the third case of anosmia, we stopped early resection of the SSS in cases where olfactory preservation was required. Instead, we removed as much of the tumor as possible from one side (mainly the right side), decompressed it, and reduced the size of the contralateral (left) side without cutting the SSS. During this process, we preserved as much of the contralateral olfactory vein and the arachnoid membrane surrounding the vein as possible to prevent traction on the olfactory tract due to frontal lobe subsidence. As a result, we no longer experience cases of anosmia.
Discussions and Conclusions: We have reported on our attempts to preserve olfactory function in BIH at our hospital. The main cause of olfactory impairment is not direct damage to the olfactory tract, but traction of the olfactory tract due to subsidence of the frontal lobe. However, with the BIH, frontal lobe subsidence due to cerebrospinal fluid drainage is unavoidable. Cutting the SSS in the early stages of surgery can cause traction of the olfactory tract, resulting in postoperative anosmia. An unilateral approach and transition to a bilateral approach where necessary is useful for preserving olfaction.