The dura mater was obtained from fresh cadavers at autopsy in a series of 52 specimens from 31 males and 21 females, ranging in age from 31 to 80 years. By dissecting the superior wall of dural venous sinuses, the courses and connections of all the major venous channels were examined. The configuration of the torcular herophili was divided into 11 types and four variations. The most frequent type was ScRc (29%), in which four major venous sinuses (that is the superior sagittal sinus, rectal sinus, and two transverse sinuses) joined at the same place. When the transverse or sigmoid sinus is obstructed at the time of surgery, there is a potential risk of developing brain edema. From that aspect, the variety and complexity of the torcular herophili configuration were divided into three groups. It was thought that the “freely communicating” type (63%), in which these channels possess open and unobstructed communication, had the least likelihood of brain edema, but that the “partially communicating” type (13%) and “non-communicating” type (23%) are more dangerous. Especially, the SrRr or SIRI type with complete atresia of the transverse sinus would certainly cause a marked congestion of the venous return. Light and electron microscopic observations clearly demonstrated the presence of smooth muscle cell layers in the subendothelial connective tissues. They varied in each sinus, but in the transverse and sigmoid sinuses, cell layers were thicker than in others. In 16 instances of the 52 specimens (31%), trabeculae were disclosed in and around the torcular herophili. The significance of smooth muscle cells and trabeculae is uncertain, but it is speculated that they regulate the venous blood flow to some extent by contractions and relaxations.
The Japan Neurosurgical Society