Dural Sinuses

The dural sinuses are blood channels situated between the two layers of the dura mater and covered by endothelium that is continuous with that of the veins. They are:

Superior sagittal, inferior sagittal, straight, transverse, sigmoid, occipital, cavernous, superior petrosal, intercavernous, inferior petrosal, basilar plexus.

1. The superior sagittal sinus occupies the convex margin of the falx. It starts at the foramen cecum, where it receives a vein from the nasal cavity. It runs backwards, lying in midline, in the inner surface of the skull, until the occipital protuberance, where it deviates (usually to the right side), and continues with the corresponding transverse sinus. The confluence of the sinuses (confluens sinuum; torcular Herophili) is its dilated extremity, located in correspondence with the internal occipital protuberance. The transverse sinus derives from it. The superior sagittal sinus is triangular in section, narrow in the front, and gradually increases in size as it passes backwards. Small openings communicate with irregular venous spaces (venous lacunae) in the dura mater near the sinus; there are usually three, on either side: a small frontal, a large parietal, and a medium-size occipital. Most cerebral veins and arachnoid granulations (pacchionian bodies) open into these lacunae.

2. The inferior sagittal sinus (sinus sagittalis inferior; inferior longitudinal sinus) is in the posterior half or two-thirds of the free margin of the falx cerebri and ends in the straight sinus. It increases in size towards the back, as it receives several veins from the falx cerebri, and some inconstant ones from the medial surfaces of the hemispheres.

3. The straight sinus (sinus rectus; tentorial sinus) lies at the line of junction of the falx cerebri with the tentorium cerebelli. It proceeds backwards and runs downward and backwards from the end of the inferior sagittal sinus to the transverse sinus opposite to the one into which the superior sagittal sinus is prolonged, communicating through a cross branch with the confluence of the sinuses. It drains blood from the inferior sagittal sinus, being its natural prolongation, the great cerebral vein (great vein of Galen), and the superior cerebellar vein.

4. The transverse sinus (sinus transversus; lateral sinus), is paired in number and large. It begins at the internal occipital protuberance, one (usually the right) being the direct continuation of the superior sagittal sinus, the other, of the straight sinus. Each transverse sinus passes laterally and forward to reach the base of the petrous portion of the temporal bone, and lies in the attached margin of the tentorium cerebelli;

5. The sigmoid sinus is the continuation of the transverse one, beginning when it leaves the tentorium and curving downward and medially to reach the jugular foramen. Before it ends in the internal jugular vein, there is an enlargement called the jugular bulb. In its course it rests upon the squama of the occipital, the mastoid angle of the parietal, the mastoid part of the temporal. They receive blood from the superior petrosal sinuses, from the veins of the pericranium by means of the mastoid and condyloid emissary veins, and from the inferior cerebral and inferior cerebellar veins.

6. The occipital sinus (sinus occipitalis) is the smallest of the cranial sinuses. It is situated in the attached margin of the falx cerebelli, begins around the margin of the foramen magnum from several small veins, and ends in the confluence of the sinuses.

7. The cavernous sinus (sinus cavernosus) is paired and has a reticulated structure due to numerous fibrous filaments that traverse it. It is irregular, placed on either side of the body of the sphenoid bone, from the superior orbital fissure to the apex of the petrous bone. On its medial portion, it contains the internal carotid artery and the abducent nerve; on its lateral wall are the oculomotor, the trochlear, and the ophthalmic and maxillary nerves. The cavernous sinus drains blood from the superior ophthalmic vein through the superior orbital fissure, from some of the cerebral veins, and from the small sphenoparietal sinus, which courses along the lower surface of the small wing of the sphenoid. It communicates with the transverse sinus by means of the superior petrosal sinus; with the internal jugular vein through the inferior petrosal sinus; with the pterygoid venous plexus through the foramen Vesalii, foramen ovale, and foramen lacerum, and with the angular vein through the ophthalmic vein. The two sinuses also communicate with each other by means of the anterior and posterior intercavernous sinuses.

8. The intercavernous sinuses (sini intercavernosi) are two, an anterior one and a posterior one, and connect the two cavernous sinuses passing in front of, and behind, the pituitary gland. Together with the cavernous sinuses, they form a venous circle (circular sinus) around the hypophysis.

9. The superior petrosal sinus (sinus petrosus superior) is small and narrow, and connects the cavernous with the transverse sinus going lateralward and backward in the attached margin of the tentorium cerebelli and in the superior petrosal sulcus of the temporal bone. It receives some cerebellar and inferior cerebral veins, and veins from the tympanic cavity.

10. The inferior petrosal sinus (sinus petrosus inferior) is located in the inferior petrosal sulcus formed by the junction of the petrous bone with the occipital bone. It begins in the cavernous sinus and ends in the superior part of the bulb of the internal jugular vein. The inferior petrosal si- Internal nus receives the internal auditory veins and veins from jugular vein the medulla oblongata, pons, and lower surface of the cerebellum. Sigmoid sinus

11 .The basilar plexus (plexus basilaris; transverse or basilar sinus) consists of several interlacing venous channels between the layers of the dura mater. It connects the two inferior petrosal sinuses lying over the basi-occipital bone.

Transverse sinus

- Superior sagittal sinus

Torcular Herophiii (sinus confluence)

Cortical veins

Transverse sinus

Sigmoid sinus

Internal jugular vein

Cortical veins

Transverse sinus

Sigmoid sinus

Internal jugular vein

Cortical veins —

Vein of Trolard

Vein of Labbé

Sigmoid sinus —

- Superior sagittal sinus

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