Venous Supply

The venous system of the head and neck is extensive. Emphasis is made here only to those vessels that are relevant to cerebrovascular syndromes (.Fig.22-7, ). The blood from the brain is drained by the cerebral veins, which empty into dural sinuses that are primarily drained by the internal jugular veins. The extracranial draining veins of the neck consist of the external jugular vein, the internal jugular vein, and the vertebral vein.

The venous drainage of the brain and meninges can be divided into the diploic veins, the meningeal veins, the dural sinuses, and the cerebral veins. The diploic veins run between the tables of bone of the skull to drain the diploe. These vessels communicate extensively with the extracranial venous system, the meningeal veins, and the dural sinuses. The meningeal veins are epidural vessels that supply drainage for the falx cerebri, the tentorium, and the cranial dura mater. The major dural sinuses include the superior and inferior sagittal sinuses, the cavernous and intracavernous sinuses, the superior and inferior petrosal sinuses, the occipital sinus, and the straight, transverse, and sigmoid sinuses. y

The dural sinuses that are most often affected by thrombosis are the superior sagittal sinus (SSS), the lateral sinuses (LS), and the cavernous sinuses (CS). The SSS originates

Figure 22-7 Major veins of the cerebral venous system. (© 1996 Indiana University Medical Illustration Dept.)

near the crista galli where it communicates with the facial and nasal veins. y It courses posteriorly in the midline along the falx cerebri, and then courses backward toward the occipital protuberance, where it joins the lateral and straight sinuses to form the torcular Herophili. The SSS drains a major portion of the cortex. Due to its connection with the diploic veins that drain the scalp through the emissary veins, the SSS can be affected by infections or contusions of the face and scalp.

The LS course from the torcular Herophili to the jugular bulbs. They have a transverse portion that lies in the attached border of the tentorium and a sigmoid portion that runs on the mastoid process. Due to the latter anatomical configuration, this sinus can be affected by mastoiditis and otitis media. The drainage territory of the LS includes the cerebellum, brain stem, and the posterior portion of the cerebral hemisphere.

The CS are paired venous structures that lie next to the sphenoid bone. There are several important structures that lie within the CS, including cranial nerves (CNs) III, IV, V! , and V2 in the lateral wall, and CN VI and the carotid artery with its sympathetic plexus in the central portion of the sinus. The CS drain blood from the orbits and the anterior portion of the base of the brain. They drain via the superior and inferior petrosal sinuses into the internal jugular veins.

The three important groups of veins that drain blood from the brain are the superficial cerebral veins, the deep cerebral veins, and the veins of the posterior fossa. The superficial cerebral veins lie along the cortical sulci. These vessels drain the cerebral cortex and portions of the white matter. The frontal, parietal, and occipital cortical veins drain into the SSS, while the middle cerebral veins drain into the LS. The middle cerebral veins run along the sylvian fissure to drain the opercular region. These veins are unique because they have no muscular layers or valves, which enables them to dilate and reverse the direction of blood flow if a sinus into which they drain is occluded. The deep cerebral veins, including the internal cerebral and basal veins, drain blood from the deep white matter of the cerebral hemispheres and the basal ganglia. These veins join to form the great vein of Galen, which subsequently drains into the straight sinus. The veins of the posterior fossa are divided into three major systems. The superior group drains into the galenic system. The anterior group drains the anterior cerebellum, pons, and medulla. The posterior group drains into the torcular Herophili and adjacent dural sinuses. They supply the cerebellar tonsils and the posteroinferior cerebellar hemispheres.

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