Chapter 7

Vasculature of the central nervous system

Vasculature of the spinal cord

Arterial supply of the spinal cord

Three longitudinal arterial vessels run the length of the spinal cord (Fig. 7.1). These are the single anterior spinal artery and the paired posterior spinal arteries. The anterior spinal artery arises in a Y-shaped configuration from the two vertebral arteries at the level of the medulla oblongata (Fig. 7.2) and descends along the ventral surface of the cord in the midline. The posterior spinal arteries arise from either the vertebral arteries or the posterior inferior cerebellar arteries and run caudally on the posterolateral surface of the cord.

Figure 7.1 The arterial supply and venous drainage of the spinal cord.

Figure 7.2 The arrangement of arterial vessels on the base of the brain. The diagram shows the circulus arteriosus (circle of Willis.)

The anterior and posterior spinal arteries alone are insufficient to supply the cord below cervical levels and, therefore, they receive serial reinforcement by anastomosis with radicular arteries derived from segmental vessels, including the ascending cervical, intercostal and lumbar arteries. Radicular arteries pass through the intervertebral foramina and divide into anterior and posterior branches, which run with the dorsal and ventral spinal nerve roots, respectively. One particularly large radicular artery (the great radicular artery, or artery of Adamkiewicz) may arise from a lateral intercostal or lumbar artery at any level between T8 and L3.

Disorders of the blood supply of the spinal cord

The blood supply of the spinal cord is most vulnerable in the thoracic region and in the anterior portion of the cord. Occlusion of the anterior spinal artery leads to an acute thoracic cord syndrome with paraplegia and incontinence. The spinothalamic modalities of pain and temperature are preferentially lost, whereas the proprioceptive functions of the dorsal columns are relatively preserved.

Venous drainage of the spinal cord

The venous drainage of the cord follows a basically similar pattern to the arterial supply (Fig. 7.1). Six longitudinal interconnecting venous channels exist. These consist primarily of anterior and posterior spinal veins, which run in the midline. More irregular, sometimes incomplete, bilaterally paired anterolateral and posterolateral veins are situated near the lines of attachment of the ventral and dorsal nerve roots, respectively. All of these vessels drain via anterior and posterior radicular veins into the internal vertebral venous plexus (epidural venous plexus), which is situated between the dura mater and the vertebral periosteum. The internal venous plexus communicates with an external vertebral venous plexus and thence with the ascending lumbar veins, the azygos and hemiazygos veins.

Vasculature of the spinal cord

▪ The spinal cord is supplied by the anterior and posterior spinal arteries, supplemented by radicular arteries.

▪ Venous drainage is by anterior and posterior spinal veins which drain, via radicular veins, into the internal vertebral venous plexus.

Vasculature of the brain

Arterial supply of the brain

The brain is supplied with blood by two pairs of vessels, the internal carotid arteries and the vertebral arteries (Figs 7.2, 7.3 and see Fig. 7.7). The internal carotid artery arises from the common carotid artery and enters the middle fossa of the cranial cavity through the carotid canal. Its course then follows a series of characteristic bends, known as the carotid syphon (Fig. 7.4), after which it passes forwards through the cavernous sinus and then upwards on the medial aspect of the anterior clinoid process, reaching the surface of the brain lateral to the optic chiasm. Along its course, the internal carotid artery gives rise to a number of pre-terminal branches.

▪ Hypophyseal arteries arise from the intra-cavernous section of the internal carotid to supply the neurohypophysis. They also form the pituitary portal system of vessels by which releasing factors are carried from the hypothalamus to the adenohypophysis (Ch. 16).

▪ The ophthalmic artery passes into the orbit through the optic foramen. It supplies the structures of the orbit, the frontal and ethmoidal sinuses, the frontal part of the scalp and dorsum of the nose.

▪ The anterior choroidal artery supplies the optic tract, the choroid plexus of the lateral ventricle, the hippocampus and some of the deep structures of the hemisphere, including the internal capsule and globus pallidus.

▪ The posterior communicating artery passes backwards to join the posterior cerebral artery, thus forming part of the circle of Willis.