Comparison between olfactory bulb and olfactory tract implantations through an endoscopic supraorbital keyhole...

Since the COVID-19 pandemic, olfactory loss has been recognized as a highly prevalent condition that greatly impacts the quality of life. Similar to other sensory implants, the idea of an olfactory implant has emerged. Evidence indicates that electrical stimulation of specific olfactory structures can evoke smell sensations. However, debates on the most appropriate anatomical target and surgical technique for implantation are still ongoing. By extrapolating data from other surgical indications, transcranial approaches appear to carry a lower risk of cerebrospinal fluid leakage and infection compared with endoscopic endonasal routes. The aim of this study was to compare two electrode placements (dorsal olfactory bulb and ventral olfactory tract) through a supraorbital keyhole craniotomy in human cadavers.

Four fresh human cadavers were dissected in a staged manner. Supraorbital keyhole craniotomy was performed through an eyebrow incision and the frontal lobe was slightly retracted to allow angled (30°) endoscope insertion. An auditory brainstem implant (ABI) from MED-EL was used for electrode placement.

Endoscopic placement of the electrode on the dorsal side of the olfactory bulb was achieved after orbital roof drilling in all cases, but was not stable. On the contrary, endoscopic placement of an electrode under the olfactory tract was easily achieved without drilling and the electrode was stable between the olfactory tract and the planum sphenoidale, behind the olfactory bulb.

Ventral olfactory tract implantation posterior to the olfactory bulb using an ABI is straightforward and is associated with satisfactory electrode stability. Such a procedure could be used for clinical pilot studies evaluating the effects of various stimulation protocols on the olfactory tract in patients with long-lasting olfactory loss.