Anatomical Variations of the First Vein Draining into the Anterior Superior Sagittal Sinus: Implications for the Transbasal Approach

Introduction: In the subfrontal approach, the anterior superior sagittal sinus is commonly ligated to release the anterior falx. The transbasal skull base approach allows access to the origin of the anterior superior sagittal sinus at the crista galli. Knowledge of anatomical variations of the first frontal vein draining into the anterior superior sagittal sinus may allow preservation of all frontal veins and therefore decrease risk of venous infarction.

Material and Methods: Stepwise dissections for a transbasal level 1 approach were performed on five silicon-injected anatomic specimens. A two-piece craniotomy with an orbital bar removal was made once a nasion osteotomy was performed. The dural opening allowed for visualization of the draining veins into the sinus bilaterally. Measurements in mm were taken from both sides (10 sides in total) from the most anterior part of the sinus, at the level of the foramen cecum, until the first and second veins were encountered and merged into the sagittal sinus. Further specifications were made as to the site of entrance into the sagittal sinus (lateral corner or lateral wall) and the course of the cortical vein along the cortex (dorsolateral or medial).

Results: The distance between the foramen cecum and the first bridging vein of the sagittal sinus varied between 4 and 32 mm on the right side (median: 14 mm) and 5 and 36 mm on the left side (median: 19 mm). The entry points of the first bridging vein into the sagittal sinus was the lateral corner of the sinus in 80%, while 20% entered the sinus on the lateral wall. All veins that entered the lateral corner of the sagittal sinus drained the dorsolateral surface, while those entering the lateral wall drained the medial surface of the frontal lobe.

Conclusion: A nasion osteotomy, that is part of the transbasal skull base approach, is necessary to safely preserve the first and second bridging veins when ligating the anterior superior sagittal sinus. Preservation of these veins may be of clinical importance when approaching large anterior skull base tumors.