gms | German Medical Science

Objective: Emissary veins are often neglected in their clinical relevance. However, during the retrosigmoid approach, especially during semi-sitting positions, these transosseous venous connections become potentially life-threatening. Therefore, knowledge of the presence and configuration of emissary veins is essential for preoperative planning.

Methods: Two-hundred consecutive patients planned for the retrosigmoid approach due to a cerebello-pontine-angle pathology were evaluated by computed-tomography in the standard technique (5 mm slices) and the spiral technique for the posterior fossa (1 mm slices). The presence and size of emissary veins, the entry point in the sigmoid sinus, the predilecting side and the visibility in either CT technique were evaluated.

Results: Emissary veins were present in 80% of the patients, varying from 0.3 to 4 mm in diameter, whereas 1% (right side) and 2% (left side) of the patients have more than one emissary vein. The mean length of the intraosseous course of the vein to the entry point in the sigmoid sinus was 7.6 mm (right side) and 5.1 mm (left side). The study shows that with the standard CT technique, only emissary veins larger than 1.0 mm can be identified and that either entry point in the skull base or sigmoid sinus cannot be securely visualized. On the other hand, the spiral technique CT scans visualized emissary veins within 0.3 mm of their exact course from the skull to the entry point in the sigmoid sinus.

Conclusions: Thin-slice CT scans are inevitable in the preoperative planning of the retrosigmoid approach in order to identify the presence and the course of emissary veins in order to reduce unnecessary morbidity during surgery.