Spinal Cord & Vertebral Column Vascular Anatomy (Artery of Adamkiewicz)

Three longitudinal arteries. A single anterior spinal artery runs in the anterior median fissure, formed superiorly from branches of both vertebral arteries. It supplies the anterior two-thirds of the cord: the corticospinal and spinothalamic tracts and the anterior horns. Two paired posterior spinal arteries run on the posterolateral surface and supply the posterior third, the dorsal columns.

Why the anterior cord is vulnerable. A single artery with watershed dependence feeds the anterior two-thirds, so this is the territory that fails, as anterior cord syndrome. The paired posterior arteries have a richer pial collateral plexus, so the dorsal columns are more resilient and isolated posterior cord syndrome is rare.

Segmental reinforcement. The longitudinal vessels are not sufficient on their own. Radiculomedullary (segmental) arteries from the vertebral, ascending and deep cervical, posterior intercostal and lumbar arteries enter through the intervertebral foramina along the nerve roots and reinforce them at intervals. The cord is not fed as one continuous column from top to bottom.

The watershed. Because the reinforcement is intermittent, some zones are relatively poorly perfused, classically the mid-thoracic cord, around T4-T9. This region is furthest from both ends of the supply and the least collateralised, which is why hypotension does its damage there.

View larger

View larger

The dominant feeder. The artery of Adamkiewicz, the great anterior radiculomedullary artery (arteria radicularis magna), is the dominant segmental feeder of the anterior thoracolumbar cord, the enlargement that supplies the lumbar plexus. Injuring it causes cord ischaemia, which is why its anatomy is high-yield.

The numbers. On meta-analysis of anatomical studies (Taterra), the artery is usually single (about 87%), so there is no redundancy. It is most often on the left (about 77%) and arises between T8 and L1 in about 89%, occasionally higher. It is present in about 85%, a figure better read as "identified in" (see the evidence card), so imaging that fails to find it does not prove the cord safe.

The hairpin. The artery ascends with a nerve root and then makes a characteristic hairpin turn as it joins the anterior spinal artery, which then descends in the midline. The turn is a recognisable sign on spinal angiography and MR angiography. Identifying this feeder before thoracoabdominal aortic or complex spine surgery helps avoid cord ischaemia.

Why it is injured. It can arise over a range of levels and is usually solitary, so it is vulnerable to inadvertent injury in thoracolumbar and aortic surgery. Its usual side and levels, left and T8-L1, are the territory of a thoracolumbar deformity correction or an anterior approach, which makes left-sided segmental vessel ligation in that range the highest-risk manoeuvre.

View larger

View larger

View larger

View larger

The lesion. Compromise of the anterior spinal artery, or of its dominant feeder, infarcts the anterior two-thirds of the cord. Below the level, motor function (corticospinal tracts) and pain and temperature (spinothalamic tracts) are lost, with autonomic dysfunction of bladder and bowel.

The dissociation is the diagnosis. Proprioception, vibration and fine touch are preserved, because the dorsal columns are supplied by the posterior spinal arteries, and that split identifies the syndrome at the bedside. It carries the worst prognosis of the incomplete cord syndromes.

Causes. The causes include aortic surgery and cross-clamping, profound hypotension, embolism or atheroma, thrombosis, and iatrogenic injury during spinal deformity correction.

Imaging. Anterior spinal artery syndrome is a clinical-radiological diagnosis. Sagittal images show longitudinal ventral T2 signal in the cord, and the axial cut shows bilateral anterior horn hyperintensity, the owl's eyes or snake-eyes sign, with the dorsal columns spared.

View larger

View larger

Where the risk lies. Anterior spinal artery syndrome complicates about 0.1-0.2% of abdominal aortic operations. It is a feared complication of thoracic and thoracolumbar aortic repair and of major spinal deformity correction, especially kyphosis correction and vertebral column resection, where the cord is shortened or manipulated and segmental vessels are sacrificed.

Reading the aortic figure. The 0.1-0.2% belongs to abdominal aortic surgery, where the artery usually arises above an infrarenal field and the source review judged cord ischaemia essentially unpredictable and unpreventable. In spinal surgery the level is known, the vessels are seen, and perfusion and neuromonitoring are under the surgeon's control.

Monitor the right tract. Somatosensory evoked potentials monitor the dorsal columns, which are on the other circulation, so anterior cord ischaemia can advance with normal SSEPs. Motor evoked potentials specifically watch the anterior (motor) cord that the anterior spinal artery supplies.

The drainage route. The cord drains through anterior and posterior spinal veins into a pial venous plexus, then through radicular (medullary) veins into the internal vertebral venous plexus (Batson's plexus) in the epidural space. This communicates with the external vertebral plexus and the basivertebral veins draining the vertebral bodies, and freely with the segmental, azygos and hemiazygos, caval and pelvic veins.

Valveless and low-pressure. The system has no valves and runs at low pressure, so flow can reverse, particularly when intra-abdominal or intrathoracic pressure rises with Valsalva, coughing or prone positioning. Three clinical points follow:

• Haematogenous spread. Valveless retrograde flow lets pelvic and abdominal tumour (prostate or breast, for example) and infection (pyogenic discitis, vertebral osteomyelitis) reach the spine, the classic explanation for vertebral and pelvic metastasis.
• Epidural venous bleeding. Engorgement of the plexus, worsened by abdominal compression in the prone position, causes troublesome bleeding in spine surgery. That is why patients are positioned on a frame or bolsters with the abdomen free, to decompress the plexus.
• Collateral return when the inferior or superior vena cava is obstructed.

View larger

The segmental artery. Each posterior intercostal or lumbar segmental artery runs around the vertebral body. It gives periosteal and nutrient branches to the body, branches to the posterior elements and paraspinal muscles, and a spinal (radicular) branch that enters the foramen and supplies the radiculomedullary feeder to the cord, the dominant anterior one being the artery of Adamkiewicz.

Body versus cord. The vertebral body has a rich collateral supply and tolerates segmental ligation. The cord does not, if its dominant feeder is lost.

Where to ligate. Anterior and lateral thoracolumbar approaches expose the spine by ligating the segmental vessels over the vertebral bodies. To avoid cord ischaemia:

• Ligate over the mid-vertebral body, away from the foramen, preserving the foraminal anastomosis and collateral network
• Avoid sacrificing multiple consecutive segmentals, and especially the segmental that carries the Adamkiewicz feeder
• In high-risk cases, temporarily clamp the segmental vessels and check neuromonitoring before permanent ligation

Intraoperative neuromonitoring in detail is covered in our Spinal Cord Monitoring topic.

View larger