A rare, anomalously dilated right transverse sinus with involvement of the torcular herophili strongly suggested the appearance of a meningioma on CT scanning. Carotid and vertebral arteriography did not reveal the nature of the abnormality, since there was only faint opacification of the anomalous vessel, which was interpreted as a faint tumor stain. Transjugular venography was necessary to establish this diagnosis. When a similar lesion is encountered on CT scanning and the transverse sinus is not clearly seen on arteriography, venography should be carried out to determine if the appearance is due to occlusion by a mass or, as in this case, anomalous dilatation of the sinus.