Arteries of the Brain · 427 11

supply the paraseptal region, rostral portion of the basal ganglia and diencephalon, and the anterior limb of the internal capsule (Fig. 11.3). The recurrent artery of Heubner is a large branch of the proximal segment of the anterior cerebral artery that supplies the basal ganglia; it is sometimes visible on an angiogram (see Fig. 11.12, p. 434).

In their further course, the anterior cerebral arteries wind around the genu of the corpus callosum and then course posteriorly until they reach the central region, where they make anastomotic connections with the posterior cerebral arteries Along the way, they give off branches to the corpus callosum, the medial surfaces of the cerebral hemispheres, and the parasagittal region. Areas of the brain receiving their blood supply from the anterior cerebral artery include the leg areas of the primary sensory and motor cortices and the cingulate gyrus. The anterior cerebral artery makes anastomotic connections with the middle cerebral artery as well as the posterior cerebral artery.

The major cortical branches of the anterior cerebral artery (Fig. 11.5) are the orbital (I), frontopolar (II), frontal, pericallosal (III), callosomarginal (IV), and internal parietal (V) arteries.

Arteries of the Posterior Fossa

Vertebral Artery

Just after it enters the dura mater, the vertebral artery gives off branches to the cervical spinal cord. The vascular anatomy in this area is variable, but the ante-

Posterior cerebral aa.

Oculomotor n.

Superior cerebellar a.

Basilar a.

Branches to the pons (circumferential branches)

Anterior inferior cerebellar a.

Posterior inferior cerebellar a.

Vertebral aa.

Fig. 11.6 Blood supply of the cerebellum, lateral view

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11 428 · 11 Blood Supply and Vascular Disorders of the Central Nervous System

Basilar a.

Superior cerebellar a.

Anterior inferior cerebellar a.

Posterior inferior cerebellar a.

Anterior spinal a. and paramedian branches of the vertebral a.

Fig. 11.7 Territories of the cerebellar and brainstem arteries in midline sagittal section

Posterior cerebral a.

Superior cerebellar a.

Basilar a.

Anterior inferior cerebellar a.

Posterior inferior cerebellar a.

Vertebral a.

Fig. 11.8 Blood supply of the cerebellum and territories of the cerebellar arteries, inferior view

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Arteries of the Brain · 429 11

rior spinal artery almost always arises from the intradural portion of the vertebral artery.

Posterior inferior cerebellar artery (PICA). The PICA is the largest branch of the vertebral artery (Figs. 11.1, 11.2, and 11.6­11.8) and likewise arises from its intradural portion, just before the vertebral artery joins its counterpart from the opposite side to form the basilar artery. The PICA supplies the basal portion of the cerebellar hemispheres, the lower portion of the vermis, part of the cerebellar nuclei, and the choroid plexus of the fourth ventricle, as well as the dorsolateral portion of the medulla. It makes numerous anastomotic connections with the remaining cerebellar arteries.

The size of the PICA territory is inversely related to that of the anterior inferior cerebellar artery (AICA) territory; furthermore, the PICA and its territory may be of very different sizes on the two sides. If one PICA is particularly small, the basal portion of the cerebellum will be supplied by the AICA ipsilaterally and the larger PICA contralaterally. A congenitally small (“hypoplastic”) vertebral artery may terminate as the PICA and give off no contribution to the basilar artery, which, in such cases, is simply a continuation of the contralateral vertebral artery. This is a fairly common normal variant.

Basilar Artery

The basilar artery arises from the union of the right and left vertebral arteries in front of the brainstem at a lower pontine level (Fig. 11.2). Its major branches are the two pairs of cerebellar arteries and the posterior cerebral arteries. The basilar artery also gives off numerous small perforating branches to the brain- stem—the paramedian branches as well as the short and long circumferential branches (Fig. 4.58, p. 225). Occlusions of these branches produce the brainstem syndromes described in Chapter 4 (p. 223ff.).

Anterior inferior cerebellar artery (AICA). The first major branch of the basilar artery is the AICA (Figs. 11.1, 11.2, and 11.6­11.8), which supplies the flocculus and the anterior portion of the cerebellar hemisphere. Its territory is inversely related in size to the ipsilateral PICA territory: in some individuals, part of the cerebellar hemisphere that is usually supplied by the PICA is actually supplied by the AICA (as discussed above). The AICA also gives off the labyrinthine artery to the inner ear.

Superior cerebellar artery (SCA). The superior cerebellar artery (Figs. 11.1, 11.2, and 11.6­11.8) arises from the basilar artery below its tip and supplies the rostral portion of the cerebellar hemisphere and the upper portion of the vermis. As it curves around the midbrain, it gives off branches to the tegmentum.

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11 430 · 11 Blood Supply and Vascular Disorders of the Central Nervous System

Fimbria of the	Lateral posterior	Artery of
hippocampus	choroidal a.	Ammon’s horn
		Dentate
		gyrus
Choroid		Posterior
plexus of
		cerebral a.
the inferior
horn		Long
		branch (of
		Uchimura)

Collateral sulcus

Tentorium

Temporal branch of posterior cerebral a.

Fig. 11.9 Anatomical relation of the posterior cerebral artery to the tentorial edge; blood supply of Ammon’s horn

The basilar tip (end of the basilar artery) is the site where the artery divides into the two posterior cerebral arteries (Fig. 11.2).

Posterior Cerebral Artery

The posterior cerebral artery (PCA) has connections to both the anterior and posterior circulation. Most of the blood flowing within it is usually derived from the basilar tip, but there is also a smaller contribution from the internal carotid artery by way of the posterior communicating artery (Fig. 11.1). At an earlier stage in ontogenetic development, the posterior cerebral artery is a branch of the internal carotid artery (as discussed above, p. 423). The posterior communicating artery joins the posterior cerebral artery some 10 mm distal to the basilar tip. The segment of the posterior cerebral artery proximal to this point is called the precommunicating segment, or, in Fischer’s terminology, the P1 segment, while the segment distal to this point is the postcommunicating or P2 segment. Both the posterior cerebral artery and the posterior communicating artery give off perforating branches to the midbrain and thalamus

(Fig. 11.3).

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Anterior thalamoperforating a.

Middle cerebral a.

Anterior choroidal a.

Internal carotid a.
Posterior communi-
cating a.
Posterior thalamo-	Basilar a.
perforating a.

Arteries of the Brain · 431 11

Posterior cerebral a.

Thalamogeniculate a.

Lateral posterior choroidal a.

Fig. 11.10 Arterial blood supply of the thalamus

The posterior cerebral artery originates at the basilar bifurcation and then curves around the midbrain and enters the ambient cistern, where it has a close spatial relation to the tentorial edge (Fig. 11.9). Within the ambient cistern, the posterior cerebral artery divides into its major cortical branches, including the calcarine and occipitotemporal arteries and the temporal branches (Fig. 11.5).

The anterior and posterior thalamoperforating arteries (Fig. 11.10). The anterior thalamoperforating artery is a branch of the posterior communicating artery that mainly supplies the rostral portion of the thalamus.The posterior thalamoperforating artery arises from the posterior cerebral artery proximal to the insertion of the posterior communicating artery and supplies the basal and medial portions of the thalamus, as well as the pulvinar. The posterior thalamoperforating arteries of the two sides may share a common trunk, called the artery of Percheron; this is often seen in association with unilateral hypoplasia of the P1 segment and fetal origin of the posterior cerebral artery (cf. p. 423). An alternative nomenclature is sometimes used for the anterior and posterior thalamoperforating arteries, in which the former is called the thalamotuberal artery, and the latter is called the thalamoperforating artery.

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