Figure 7-6
Dural septa and associated sinuses.

Review the dural infoldings and the various venous sinuses they create. We will also look at some venous sinuses that are separate identifiable structures which are not part of any particular dural infolding.

The falx cerebri is one such dural infolding. This mid-sagittal infolding separates the two cerebral hemispheres and houses the superior sagittal and inferior sagittal sinus.

The tentorium cerebelli (the roof or tent of the cerebellum) is a transverse dural infolding separating the cerebellum from the cerebrum and houses the transverse sinuses and the superior petrosal sinuses. The free anterior border of the tentorium cerebelli is concave and bounds a large oval opening called the tentorial incisure. This opening allows the brain stem to pass through the tentorium cerebelli.

The straight sinus is formed at the junction between the posterior portion of the falx cerebri and the superior portion of the tentorium cerebelli. This sinus receives blood from the inferior sagittal sinus and the great cerebral vein.

At the most posterior part of the straight sinus the superior sagittal sinus joins the straight sinus to form the confluens of sinuses. The two transverse sinuses originate from either side of the confluens and continue anteriorly, eventually leaving the tentorium inferiorly and changing names to the sigmoid sinuses. These two sigmoid sinuses then pass through the jugular foramina and form the internal jugular veins.

Not all of the brain's venous sinuses are found in the dural infoldings just described. Other venous sinuses are found where the dura separates just enough to form a venous channel. The cavernous sinuses found on either side of the hypophysial fossa are two such sinuses. Both the superior petrosal and inferior petrosal sinuses drain the cavernous sinuses and eventually empty into the transverse sinus and the internal jugular vein, respectively. Try to visualize the path of blood through these sinuses. (Figure 7-6)