Anatomical variations of the posterosuperior dural venous sinuses and, in particular, the absence or hypoplasia of one of them has been described in several studies. However, no recent detailed analysis on the subject exists. Cerebral venous thrombosis is quite often evoked, although rarely confirmed, when the physician is faced with patients having various neurological problems. In fact, for a number of cases the image interpreted as thrombosis is nothing but the total or partial absence of a dural sinus. It was considered of interest to undertake an anatomical study in order to define these variations. The results of anatomoradiological investigations of 70 fresh cadavers were compared to those obtained by angiographic examination of 100 patients not suffering from any kind of venous pathology (patients explored angiographically for glioma, meningioma or aneurysm). Our conclusions and a review of the embryology literature enabled us to demonstrate that a number of radiological findings, quite often considered pathognomonic of venous thrombosis (i.e. 'delta sign'), are in fact the result of anatomical variations.