Arterial Anatomy of the Spine and Spinal Cord

Arteries of the Vertebral Body

The vertebral body is vascularized by anterolateral and posteromedian osseous branches ( Fig. 57.9 ). The anterolateral arteries originate from the stem of the ISA; they are divided into ascending, descending, and recurrent branches. Because of the leftward position of the aorta, they are more numerous on the right side than on the left. Ascending and descending branches connect with corresponding vessels from adjacent levels; these anastomoses often act as collateral supply pathways. They also participate in several anatomic variations described later in this chapter. After a short ascending course, the recurrent branch curves medially with a typical 90-degree angle to establish an anastomosis with the contralateral recurrent artery ( Fig. 57.10 ).

The spinal branch of the ISA usually divides into a radicular artery, coursing medially along the corresponding nerve root, and a retrocorporeal artery that provides the posteromedian osseous branches. Over the posterior aspect of the vertebral body, the retrocorporeal artery participates in the formation of a rich anastomotic network by joining analogous branches from adjacent levels. The retrocorporeal artery is frequently targeted during preoperative spinal embolization, so the presence of dangerous anastomoses within this network has to be kept in mind ( Fig. 57.11 ). The cluster of posteromedian osseous branches is often associated with a prominent blush that can mimic a vascular anomaly ( Fig. 57.12 ). Similarly, an enhancing Schmorl node can simulate a more aggressive pathology such as a metastasis ( Fig. 57.13 ). The three branches of the ISA passing through the neural foramen are also known as the anterior, intermediate, and posterior spinal canal arteries. The anterior and intermediate branches are the retrocorporeal and radicular arteries, the posterior one is the prelaminar artery. These branches can have a common origin (i.e., the spinal branch in its complete form ) or originate separately ( Fig. 57.14 ). The left and right prelaminar arteries establish an anastomotic network along the anterior aspect of the posterior vertebral arch that is often difficult to differentiate from the retrocorporeal network on angiographic projections. A modification of the retrocorporeal anatomy is seen at the level of the odontoid process, which is principally vascularized by two branches of the VA, the anterior and posterior ascending arteries (see Fig. 57.7 ). The posterior ascending artery is a cranial extension of the C2 retrocorporeal artery that courses upward within the anterior epidural space. It assumes a typical ogival shape around the odontoid process as it connects with the contralateral posterior ascending artery to form the apical arcade (see Fig. 57.29B ). The odontoid process receives additional supply from the ascending pharyngeal artery, notably a branch joining the apical arcade via the hypoglossal canal.

A selective ISA angiogram usually results in visualization of a hemivertebral blush. The extent and conspicuity of that blush varies among individuals. Anastomoses linking osseous branches from adjacent/opposite ISAs explain the common visualization of partial or even complete hemivertebral blushes in adjoining vertebrae, or of a bilateral blush at the studied level. In children the vertebral blush appearance depends upon the maturation of the growth plate and the progressive dominance of the anterolateral group of osseous branches over the posterior median one ( Fig. 57.15 ) (Gailloud, unpublished data). The evolution of the blush also reflects the transition of the vertebral vascularization from the rich arterial network seen in children to the end-artery configuration of adults, a switch completed at about age 15. The conspicuity of the hemivertebral blush decreases with age as bone marrow is progressively replaced with fat.

Muscular and Cutaneous Branches

The stem of lumbar ISAs gives several superficial and deep branches to the psoas muscle (see Fig. 57.4B ). The paraspinal musculature is principally vascularized by the dorsal component of the DA via its medial, intermediate, and lateral muscular branches. Posterior perforators of the lateral branch of the ISA also contribute, either directly or by anastomosing with the lateral muscular branch of the DA (see Fig. 57.4B ). Despite extensive interconnections, the muscular branches continue to exhibit a segmental pattern at the adult stage. The terminal skin arteries, on the other hand, have less predictable territories owing to cutaneous shifting and vascular redistribution. Anastomoses between the osseous, muscular, and cutaneous branches of adjacent or opposite ISAs offer a wide range of potential collateral pathways. Fig. 57.16 illustrates some typical connections, in particular the anterior and posterior laterovertebral anastomoses, which are commonly involved in anatomic variations and represent potential dangerous anastomoses during endovascular procedures.

Intersegmental Artery Trunks

ISA trunks can be ipsilateral (i.e., involving arteries from two or more consecutive vertebral levels) or bilateral (i.e., providing the left and right ISAs for a single level). Bilateral trunks are most common in the lower lumbar region but exceptional in the mid- and upper thoracic regions (except in the Japanese population, according to Adachi ) ( Fig. 57.17 ). A bilateral trunk is often falsely suggested by the origin of L4 or L5 ISAs from the MSA (see Fig. 57.5B ); a bilateral trunk must show a common stem arising from the MSA itself ( Fig. 57.18 ).

Ipsilateral trunks can be seen at any vertebral level. They are common in the upper thoracic region. Caudally, they are generally seen at L3, L4, or L5; they can involve several consecutive levels, with a complex interplay of spinal and muscular branches. The most extreme form of trunk reported so far consists of a single ascending midline vessel providing bilateral ISAs from T12 to T3. Ipsilateral trunks are divided into complete and incomplete types. To be complete, an ipsilateral trunk must have a full set of branches for each vertebral level it supplies. These include (1) an anterior component (or stem) providing the anterolateral osseous branches, (2) a lateral component (i.e., the lumbar, subcostal, or intercostal artery), (3) a dorsal component supplying the paraspinal musculature, and (4) a spinal component branching off the radicular artery ( Fig. 57.19 ). The dorsal and spinal components, when sharing a common origin, form a DA.

In the classic form of incomplete unilateral trunk, a DA missing at one of the levels supplied by the trunk arises separately from the aorta. This configuration, reported by Chiras and Merland in 1979, is known as an isolated DA or direct emergence of the DA from the aorta ( Fig. 57.20 ). Isolated DAs frequently contribute to the vascularization of the spinal cord. A subtler variant in which only the ISA stem and its spinal branch originate separately from the aorta can be observed ( Fig. 57.21 ). The incomplete nature of this trunk is more difficult to identify because the presence of a dorsal branch falsely suggests a complete configuration. Absence of vertebral blush at one of the levels supplied by the trunk is an important clue, but one must remember that a blush is not always observed, in particular in older patients. Identifying the spinal component of the ISA or one of its branches, a radicular or a retrocorporeal artery in particular, remains the most reliable angiographic criterion to distinguish between complete and incomplete unilateral trunks.