Prevalence of clinically important posterior fossa emissary veins on CT angiography

PURPOSE: We assessed the prevalence of the clinically important posterior fossa emissary veins detected on computed tomography (CT) angiography. MATERIALS AND METHODS: A total of 182 consecutive patients who underwent 64-slice CT angiography were retrospectively reviewed to determine the clinically important posterior fossa emissary veins. RESULTS: Of 166 patients, the mastoid emissary vein (MEV) was not identified in 37 (22.3%) patients. It was found bilaterally in 82 (49.4%) and unilaterally in 47 (28.3%) patients. Only six patients had more than one MEV that were very small (<2 mm), and only five patients had very large (>5 mm) veins. The posterior condylar vein (PCV) was not identified in 39 (23.5%) patients. It was found bilaterally in 97 (58.4%) and unilaterally in 30 (18.1%) patients. Only 15 patients had a very large (>5 mm) PCV. The petrosquamosal sinus (PSS) was identified only in one patient (0.6%) on the left side. The occipital sinus was found in two patients (1.2%). CONCLUSIONS: The presence of the clinically important posterior fossa emissary veins is not rare. Posterior fossa emissary veins should be identified and systematically reported, especially prior to surgeries involving the posterior fossa and mastoid region.