Anatomic variations of the superficial middle cerebral vein: embryologic aspects of the regressed embryonic tentorial sinus.

SUMMARY: The embryonic tentorial sinus usually regressses during postnatal development, but its typical prenatal drainage patterns and intradural anastomoses can be depicted as various developmental phenotypic representations. Here, we tried to clarify the variant types of the superficial middle cerebral vein (SMCV) associated with the embryonic tentorial sinus. Total 41 patients and 82 hemispheres were included in this study. CT angiography was performed in all patients as screening for cerebrovascular disease or other intracranial disorders. A separate workstation and 3D software were used to evaluate the cranial venous systems with 3D volume rendering techniques, thin-slice MIP images, and MPR techniques for the analysis of its complicated angioarchitecture. Variations of the SMCV were classified according to the developmental alterations of the embryonic tentorial sinus, including sphenoparietal sinus (cranial remnant of tentorial sinus), basal sinus (floor of middle cranial fossa), petrosal and caudal remnant of the tentorial sinus. Secondary intradural anastomoses of cavernous and superior petrosal sinuses were also evaluated for the efferent pathways. The most frequent type of remnant tentorial sinus, sphenoparietal sinus was present in 49% (40/82) of hemispheres examined. Other regressed patterns of embryonic tentorial sinus were also identified in 38% (31/82): nine caudal remnant type around the transverse sinus, 12 petrosal type, one basal type, five unclassified cases, and mixed type were found in four cases. Secondary intradural cavernous sinus anastomosis was seen in 44% (36/82), however the most prevalent pattern was no anastomosis (46/82) with cavernous sinus. Only one case of superior petrosal sinus anastomosis was found in this series associated with basal sinus type. Anatomic variations of SMCV can be clearly demonstrated with embryologic aspects of the tentorial sinus according to its developmental regression and postnatal secondary adaptations of cerebral venous drainage.