Dural+sinus

= __**Dural Sinuses**__ =

Veins draining the brainstem, cerebrum and cerebellum are like rivers that drain their contents into an estuary, the **dural venous sinus**. There are many of these found throughout the cranial cavity and the blood flowing through them eventually finds its way to the **internal jugular vein** and then on to the heart via the **superior vena cava**.

Veins draining the skull also find their way to the dural sinus, for example **diploic** and **emissary** veins. Diploic veins cross from internal to external surfaces of the skull and emissary veins run from outside the cranial cavity to reach the dural venous sinus. Emissary veins are important clinically in that due to their lack of valves, they may act as a route for infection to spread in to the cranial cavity.

There are several **dural venous sinuses** and i'll breifly describe their routes. They include the **superior sagittal, inferior sagittal, straight, transverse, sigmoid, occipital, the confluence of sinuses, cavernous, sphenoparietal, superior petrosal, inferior petrosal and basilar sinuses**.

Six of these sinuses are paired and they are as follows: 1) Transverse 2) Sigmoid 3) cavernous 4) sphenoparietal 5) Superior petrosal 6) Inferior petrosal

__Mapping out the dural sinuses__



The superior sagittal sinus receives blood from diploic and emissary veins and veins from the superior surface of the cerebral hemispheres. It runs along the superior surface of the falx cerebri from the foramen cecum anteriorly, to the occipital protuberance posteriorly. Here it empties its contents into the confluence of sinuses. The confluence of sinuses also receives blood from the occipital sinus and the inferior sagittal sinus via the straight sinus. The inferior sagittal sinus, which runs along the inferior edge of the falx cerebri, and the great cerbral vein form the straight sinus. Some cerebral veins and veins from the falx cerebri drain into the inferior sagittal sinus.

The transverse sinuses (left and right) begin at the confluence of sinuses and travel horizontally along the lateral walls of the cranial cavity. The superior sagittal sinus usually drains blood into the right transverse sinus and the inferior sagittal sinus drains into the left transverse sinus. Before the transverse sinuses become the sigmoid sinuses, blood is received from the superior petrosal sinus , veins from the inferior surface of the cerebral hemispheres and the cerebellum, diploic veins and emissary veins. The sigmoid sinuses then drain into the internal jugular vein before eventually reaching the heart.

The paired cavernous sinuses lie either side of the sella turcica (fossa in the sphenoid bone where the pituitary gland sits). The sphenoparietal sinuses (which receive blood from diploic and meningeal veins) empty their contents into the cavernous sinuses at the anterior ends. Many important structures pass through the cavernous sinuses, therefore they are very important clinically. Several nerves run through the cavernous sinus including the **abducens (VI)**, **trochlear (IV)**, **occulomotor (III)** and the **ophthalmic (V1)** and **maxillary (V2)** devision of the **trigeminal** nerve (V). In addition the **internal carotid artery** also passes through.The cavernous sinuses receive blood from the cerebral veins, the ophthalmic veins and emissary veins, which can act as a gateway for infection to travel from extracranial locations to intracranial areas.

The cavernous sinuses drain into the transverse sinuses via the superior petrosal sinuses. Cerebral and cerebellar veins also drain into the superior petrosal sinuses. The inferior petrosal sinuses, where cerebellar, internal ear and brainstem veins drain, assist in draining the cavernous sinus but they drain directly into the internal jugular veins. The inferior petrosal sinuses are joined together by the basilar sinuses which lie posterior to the sella turcica on the sphenoid bone.

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