To document an extracranial fenestration of the mastoid emissary vein (MEV) and to clarify its drainage pattern and potential procedural relevance. A 46-year-old male underwent multidetector CT angiographic evaluation of the cervical carotid system. DICOM data were post-processed in Horos using multiplanar reconstructions and three-dimensional volume-rendered images; morphometric measurements were obtained on the reconstructions. A large left MEV (6.6 mm) exited through a single mastoid foramen situated 2.95 cm postero-supero-medially to the mastoid tip. The vein divided 2.2 mm distal to the foramen into an anterior limb (5.0 mm) and a posterior limb (1.1 mm) that rejoined 2.33 cm inferiorly, forming a long fenestration. Three deep communicating veins connected the fenestrated segment to the suboccipital venous plexus, and the distal MEV continued as the deep cervical vein. Extracranial fenestration is a plausible variant of a prominent MEV. Recognition on CT may prevent misinterpretation as vascular duplication or pathology and may influence mastoid, retrosigmoid, and endovascular planning in the mastoid–suboccipital region.
Rusu et al. (Fri,) studied this question.