Postoperative anosmia after microsurgery for anterior circulation aneurysms

Objective. To analyze the factors contributing to postoperative anosmia and to evaluate the effectiveness of preventive strategies in microsurgery for cerebral aneurysms. Material and methods. The study included 117 patients with unruptured anterior circulation aneurysms who underwent surgery at the Burdenko Neurosurgery Center in 2024—2025. All patients underwent olfactometric assessment preoperatively, after 5—7 postoperative days and 6 months after surgery. Clinical, anatomical (CT angiography) and intraoperative factors were analyzed. Results. Postoperative anosmia occurred in 55 (47%) patients with bilateral involvement in 11 (20%) cases. Anosmia developed in 70.2% of patients with anterior communicating artery (ACoA) aneurysms. Significant anatomical predictors were superior (p=0.01) and anterior (p=0.01) ACoA aneurysm dome orientation. Intraoperative risk factors included nerve compression by brain spatula (p<0.001) and arachnoid dissection of the nerve. In some cases, we noted a single-stage flow of blood along anterior cranial fossa base from olfactory tract during frontal lobe traction and arterial dissection. This «red drop» sign was an intraoperative marker of nerve injury (p=0.04). Transsylvian approach for middle cerebral artery aneurysms ensured 100% preservation of olfactory function (p<0.001). After 6 months, olfactory function recovered in 33.3% of patients. Previous COVID-19 was associated with worse recovery (p=0.05). Conclusion. Postoperative anosmia is a frequent complication in aneurysm surgery. The main predictors are ACoA aneurysm and intraoperative traction-induced avulsion of the nerve. Preventive strategies include selection of less traumatic approach and minimized pressure on olfactory nerve. Arachnoid dissection of the nerve is not recommended.