The petrosquamosal sinus: CT and MR findings of a rare emissary vein

BACKGROUND AND PURPOSE: Morphologic changes in the dural sinuses and emissa ry veins of the posterior fossa relate closely to the development of the br ain. We report characteristic findings of imaging in six patients with a ra re and forgotten emissary vein called the petrosquamosal sinus (PSS). METHODS: From a larger group of patients with ear abnormalities, we selecte d six patients from three ENT imaging centers, because they had CT features suggestive of a PPS. This was the criterion for inclusion in this retrospe ctive study. They were explored by high-resolution CT (HRCT) of the tempora l bone. MR venography was performed in three patients to determine the pres ence and patency of the emissary vein. RESULTS: The PPS was bilateral in two patients and unilateral in the other four, It affected mainly the left side (left:right ratio, 5:3). Three patie nts had associated inner ear (n = 2) or middle ear malformations (n = 1). F ive of six patients had jugular vein hypoplasia, with development of emissa ry mastoid veins in three patients. CONCLUSION: Petrosquamosal sinus can be identified on HRCT in a typical loc ation. It is encountered more frequently in patients referred for congenita l abnormalities of the skull base. This rare anatomic variant should be ass essed before surgical treatment, because proper identification of these lar ge venous channels would be of interest to the surgeon.