Evaluation of olfactory nerve function after aneurysmal subarachnoid hemorrhage and clip occlusion

In this study, the olfactory nerve function (ONF) in patients with an aneurysmal subarachnoid hemorrhage (SAH) who underwent neurosurgical clip occlusion for intracranial aneurysm was assessed pre- and postoperatively.

In 13 patients with an aneurysmal SAH who underwent a frontobasal or frontotemporal neurosurgical procedure for clipping of a ruptured intracranial aneurysm, ONF was assessed pre- and postoperatively by using a standardized olfactory test battery ("Sniffin' Sticks"). Preoperative testing was performed within the first 72 hours after SAH. For their follow-up visit, patients were tested 3 months after surgery. Olfactory thresholds, odor discrimination, and odor identification were documented. Only cooperative patients were included, and as a result, all patients enrolled in the study were classified in Hunt and Hess Grade II.

After SAH and before surgery, three patients were normosmic, seven were hyposmic, and three were anosmic according to the Sniffin' Sticks test. Thus, 10 of 13 patients with SAH already showed disturbance of ONF preoperatively. Of these 10, however, only two patients experienced reduced smell and taste sensation. At the 3-month follow-up review, 10 patients could be tested. Three normosmic patients remained normosmic. In one patient, ONF had improved from anosmic to hyposmic, whereas in another patient, ONF had worsened from hyposmic to anosmic. Thus, in eight patients, ONF remained unchanged after surgery. Three patients reported disturbed smell and/or taste sensation. One anosmic patient had experienced no smell sensation since surgery; however, he reported his taste to be normal. Another hyposmic patient experienced both reduced smell and taste sensation. One normosmic patient reported normal smelling ability but disturbed taste sensation.

This study provides evidence that aneurysmal SAH causes disturbance of ONF in a substantial number of cases. With the exception of one case, neurosurgical treatment did not alter a preexisting olfactory deficit. Improvement of SAH-induced olfactory dysfunction at follow-up, however, can also be documented. The subjective assessments of the patients do not correspond well with the test battery results.