Olfactory bulb ventricles as a frequent finding in magnetic resonance imaging studies of the olfactory system

Background. In some species an embryologic cavity inside the olfactory bulb (OB) persists and is called olfactory bulb ventricle (OBV). It is generally assumed that OBVs in humans are solitary findings representing remnants of embryologic structures that were not fully regressed, although the incidence of OBVs was never examined. Using magnetic resonance imaging (MRI), the present study aimed to study the incidence of OBVs in healthy human subjects. Material and methods. A total of 122 individuals participated. Volumes of the right and left OB were determined using MRI scans and a standardized protocol for OB analysis. For comparison, OBs of 42 cadavers were collected and sectioned. Results. The main finding of this study was the high incidence of OBV-like structures in our study group. Seventy-two out of 122 (59%) participants yielded signs for an OBV whereas three out of 42 postmortem OBs contained histologically detectable OBV. Discussion: This stands in disagreement with the previous assumption of complete obliteration at the time of birth. This discrepancy may be explained by the fact that our present findings are based on modern MRI techniques with much higher resolution than 10 or 20 years ago. Another possible explanation for the discrepancy between studies based on MRI and histopathology might relate to postmortem resorption of cerebrospinal fluid from OBVs. Especially with a long postmortem interval OBVs may collapse and may no longer appear as an open cavity.