Hairpin turn sign | Radiology Signs

Answer:

The hairpin turn is the sharp, near-180-degree reversal of a radiculomedullary vessel at the point where it reaches the midline anterior surface of the spinal cord and joins the anterior spinal artery. It is the defining angiographic signature of the artery of Adamkiewicz, the great anterior radiculomedullary artery that dominates the arterial supply of the thoracolumbar cord. The vessel ascends steeply with a nerve root, turns abruptly caudally at the anastomosis, then descends in the midline as the anterior spinal artery. It was described on, and is classically a sign of, selective spinal digital subtraction angiography (DSA), still the reference standard for spinal vascular anatomy because of its spatial and temporal resolution; the same configuration is now routinely sought non-invasively on CT angiography and contrast-enhanced MR angiography, with reported detection rates around 88% for both against roughly 75% in pooled DSA series. The artery arises between T8 and L1 in about 89% of people and from a left-sided intercostal or lumbar artery in about 77%. Its main mimic is the anterior radiculomedullary vein, which makes an opposite-facing hairpin at the same location.

Why is it called so?

The vessel ascends, reverses direction through almost 180 degrees and descends alongside its own ascending limb, tracing the shape of a hairpin.

Pathophysiology

The great anterior radiculomedullary artery enters through an intervertebral foramen with a nerve root and ascends along the anterolateral surface of the cord to reach the midline. Flow in the anterior spinal artery at that level is directed caudally, so the feeding vessel must reverse direction abruptly to join it, and this geometric necessity creates the hairpin. Above the anastomosis the anterior spinal artery is usually thin and the cord below depends almost entirely on this single feeder, so occlusion, embolisation or surgical sacrifice of the parent segmental artery can infarct the anterior two-thirds of the thoracolumbar cord. The anterior radiculomedullary vein makes a mirror-image hairpin at the same site; it is separated by timing (arterial versus late venous phase on DSA and dynamic MRA) and by the direction of its course, which is descending rather than ascending.

Alternative names: Hairpin curve, hairpin configuration, hairpin sign

Other associated named signs: Owl eye sign and pencil-like hyperintensity of anterior spinal artery infarction, and the coral reef aorta as a source of spinal cord embolism

References

1. Yoshioka K, Niinuma H, Ehara S, Nakajima T, Nakamura M, Kawazoe K. MR angiography and CT angiography of the artery of Adamkiewicz: state of the art. Radiographics. 2006;26 Suppl 1:S63-73. PMID: 17050520.