Intraoperative Sneezing Secondary to Indirect Olfactory Nerve Stimulation.

Sneezing is a poorly understood, protective reflex response. It's characterized by the following sequence: eye closure, inspiration, glottic closure, forced expiration with sudden glottic opening, and release of an elevated intrathoracic pressure creating a flow of explosive air through the nose.1 Studies have indicated an anatomic sneezing area of the brainstem corresponding to the central recipient zone of the nasal sensory neurons in the lateral medulla.2 The traditional pathophysiology of the sneeze is thought to begin by stimulation of the distal branches of the trigeminal nerve within the nasal mucosa. Afferent neural stimuli are transmitted to the trigeminal ganglion and then the lateral medulla. The efferent phase then begins, giving rise to the sneezing sequence described earlier.1 In addition to direct nasal irritation, sneezing has been shown to be triggered by several other causes (Table 1). This suggests that alternative mechanisms of sneeze induction other than direct nasal stimulation exist. We report a case of a 34-year-old man undergoing an awake craniotomy for a recurrent World Health Organization grade 2 oligodendroglioma (IDH-mutant, 1p19q-codeleted, ATRX preserved). During the operation we elicited a sneeze response on 3 occasions on stimulation of the olfactory nerve (Video 1). Although we cannot completely exclude costimulation of the sensory trigeminal terminations in the anterior fossa floor, the actual sneezing occurred during tumor peeling away from the arachnoid surface overlaying the olfactory nerve. This suggests a potential accessory route of sneeze stimulation involving the olfactory nerve distinct from the previously described trigemino-related, autonomic (sympathetic and parasympathetic systems) and psychogenic etiologies.