20.5 Circulatory pathways  (Page 13/162)

Veins of the head and neck

Blood from the brain and the superficial facial vein flow into each internal jugular vein    ( [link] ). Blood from the more superficial portions of the head, scalp, and cranial regions, including the temporal vein    and maxillary vein    , flow into each external jugular vein    . Although the external and internal jugular veins are separate vessels, there are anastomoses between them close to the thoracic region. Blood from the external jugular vein empties into the subclavian vein. [link] summarizes the major veins of the head and neck.

Venous drainage of the brain

Circulation to the brain is both critical and complex (see [link] ). Many smaller veins of the brain stem and the superficial veins of the cerebrum lead to larger vessels referred to as intracranial sinuses. These include the superior and inferior sagittal sinuses, straight sinus, cavernous sinuses, left and right sinuses, the petrosal sinuses, and the occipital sinuses. Ultimately, sinuses will lead back to either the inferior jugular vein or vertebral vein.

Most of the veins on the superior surface of the cerebrum flow into the largest of the sinuses, the superior sagittal sinus    . It is located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri and, at first glance in images or models, can be mistaken for the subarachnoid space. Most reabsorption of cerebrospinal fluid occurs via the chorionic villi (arachnoid granulations) into the superior sagittal sinus. Blood from most of the smaller vessels originating from the inferior cerebral veins flows into the great cerebral vein    and into the straight sinus    . Other cerebral veins and those from the eye socket flow into the cavernous sinus    , which flows into the petrosal sinus    and then into the internal jugular vein. The occipital sinus    , sagittal sinus, and straight sinuses all flow into the left and right transverse sinuses near the lambdoid suture. The transverse sinuses    in turn flow into the sigmoid sinuses    that pass through the jugular foramen and into the internal jugular vein. The internal jugular vein flows parallel to the common carotid artery and is more or less its counterpart. It empties into the brachiocephalic vein. The veins draining the cervical vertebrae and the posterior surface of the skull, including some blood from the occipital sinus, flow into the vertebral veins. These parallel the vertebral arteries and travel through the transverse foramina of the cervical vertebrae. The vertebral veins also flow into the brachiocephalic veins. [link] summarizes the major veins of the brain.