Value of systematic analysis of the olfactory cleft in case of cerebrospinal rhinorrhea: incidence of olfactory arachnoid dilatation.

To report on the presence of olfactory arachnoid dilatations (OAD), a previously undescribed radiologic feature of spontaneous cerebrospinal fluid (CSF) rhinorrhea originating from the cribriform plate of the ethmoid bone. The medical records of all patients treated between 2001 and 2011 at a tertiary care center for a spontaneous CSF rhinorrhea originating from the cribriform plate were retrospectively reviewed. The radiological work-up included high-resolution computed tomography and magnetic resonance imaging with at least the following sequences: T1, T2, and T2 with fast imaging employing steady state acquisition (FIESTA). Thirty cases were identified. The mean age at diagnosis was 49. Fourteen patients (47 %) had a body mass index (BMI) of 30 or more and 3 patients (10 %) had a BMI between 25 and 29.9. Five patients had a history of meningitis. The imaging work-up revealed a bone defect of the cribriform plate in 6 cases (20 %), associated to a typical meningocele in 14 cases (47 %). In ten patients (33 %), there was no defect of the cribriform plate, but ultrathin coronal T2-FIESTA sequences revealed an OAD, i.e. a dilatation of the arachnoid sheath of the olfactory fibers, in nine cases (30 %), or a "pseudo-polyp" outlined by a thin layer of arachnoid (1 patient, 3 %). Preoperative imaging should be carefully analyzed for the presence of OAD or "pseudo-polyp" in patients presenting with a CSF rhinorrhea without bony defect of the cribriform plate.