Olfactory bulb ventricles as a frequent finding--a myth or reality? Evaluation using high resolution 3 Tesla magnetic resonance imaging.

Data on the prevalence of persistent olfactory bulb ventricles (OBV) in humans remain contradictory. The aim of this study was to investigate the hypothesis of large cystic-like OBVs filled with cerebrospinal fluid (CSF) as a frequent finding in magnetic resonance imaging (MRI). Fifty normosmic volunteers (25 men and 25 women, mean 40 years) underwent 3 Tesla MRI of the anterior skull base. Normal smell function was determined by testing of the odor threshold discrimination identification score using the Sniffin' Sticks test kit. The voxel size of the constructive interference in steady state (CISS) sequence was 0.4×0.4×0.4 mm (TR 12.18 ms, TE 6.09 ms) using a 12-channel head coil. Image quality was rated by three observers according to predefined criteria on an ordinal scale. Additionally, contrast-to-noise (CNR) and signal-to-noise (SNR) ratios were calculated. Quantitative signal intensity (SI) measurement of olfactory bulb (OB) structures and small Virchow-Robin spaces (VRS) was performed using multi planar reconstruction mode. Ninety-one OBs were eligible for evaluation. Image quality was rated as adequate in 55% and as excellent in 36% of cases. CNR and SNR calculations resulted in values of 21.59 and 19.06, respectively. Wilcoxon signed rank test revealed significant higher SI values for OB center compared to OB surface (P<0.001) and to OB base (P<0.001) but also significant lower SI values compared to small VRS (P<0.001) in 94.5%. In 5.5%, SI measurement revealed signs for CSF-filled structures in the OB. High-resolution 3 Tesla MRI did not verify the hypothesis of large cystic CSF-filled OBVs as a frequent finding although evidence is growing that the hyperintense signal in the center of OBs might be associated with interstitial or finely dispersed CSF/fluid or with tiny, histologically detectable remnants of OBVs.