[Investigation of fat in the dural sinus]

Detection of fat in the cranium usually indicates the presence of a fat-containing tumor such as lipoma, dermoid cyst or teratoma. However, since 1982, Hasso et al demonstrated with CT the presence of normal adipose tissue in the cavernous sinus, the mere existence of fat in the cranium does not necessarily mean the presence of a fatty tumor. The author first described fat deposition in the superior sagittal sinus and torcular Herophili following a CT study performed in 1986. The purpose of this study was to investigate the distribution, frequency, and anatomical correlations of fat in the dural sinus as demonstrated on CT. Fat was detected in the cavernous sinus in 20% of all cases (492/2408), and occurred more frequently (25%) in those older than 50 years. Fat was less frequent in the other dural sinuses (3%; 75/2296). The most common location was the torcular Herophili, followed in decreasing order of frequency by the straight sinus, inferior sagittal sinus, superior sagittal sinus and transverse sinus. Pathological examination was performed in three cases. Fat deposition was composed of normal adipose tissue and was devoid of fibrous encapsulation or infiltration. In one case, the fat seemed to be partly exposed to the subarachnoid space on CT, whereas on autopsy, thin dura mater covering the fat nodule was confirmed. Fat in the dural sinus must be differentiated from cavernous nodule or sinus thrombosis. The Hounsfield unit may be helpful in making a definitive diagnosis.