Teaching Case

A 49-year-old Caucasian male consulted his general practitioner with a 3-week history of intermittent right-sided dull groin pain following a mechanical fall. The pain was exacerbated upon running and alleviated with rest. On physical examination, the abdomen was soft with tenderness on palpation in the right iliac fossa and groin.

An outpatient ultrasound of the groin/abdomen and a further triple phase contrast-enhanced computed tomography (CECT) of the pancreas were unremarkable. However, an incidental right common iliac artery was discovered between the right psoas muscle and the L4 vertebral body. This artery originated from the abdominal aorta at the level of the L4 vertebra at an acute angle, approximately 90 degrees, with no significant narrowing. The right internal iliac artery was found to arise from the distal portion of the anomalous artery. The right external iliac artery was not included in this study. The right psoas major muscle was normal in morphology and insertion. The contralateral iliac arteries demonstrated conventional anatomy. There were two accessory renal arteries on the right, one accessory renal artery on the left and a retroaortic left renal vein. The patient did not have subsequent radiological imaging.

Background

Anomalous retro-psoas artery was first reported in scientific literature by Honkasalo et al in 1983 [1]. The common iliac artery was described to be situated between psoas muscle and the lumbar vertebral bodies posterior to the inferior vena cava. Conventionally, the common iliac artery lies anteromedially to the psoas muscles and bifurcates anterior to the sacroiliac joint at the pelvic brim into the internal and external iliac arteries [2].

Clinical Perspective

In most cases, patients were asymptomatic and had presented with non-vascular symptoms or follow-up for renal cell carcinoma or abdominal aortic aneurysm requiring radiological investigation where this anatomical variant were identified as an incidental finding [1, 3, 4]. Most cases reported a right anomalous retro-psoas iliac artery, with only one case of an anomalous left iliac artery with no associated clinical signs and symptoms [4]. In some instances, patients presented with vascular-related symptoms where the retro-psoas iliac artery was implicated in contributing to lower extremity pain and neuralgia [2] and in one case this iliolumbar vascular anomaly resulted in severe right leg claudication [5].

Imaging Perspective

Congenital vascular anomaly of the iliac arteries is rare, and the embryological origin of a retro-psoas iliac artery remains uncertain. The common iliac artery is believed to embryologically derive from the umbilical artery and a dorsal aorta arterial branch. However, it has been postulated that this retro-psoas muscle artery seen arising from the abdominal aorta is a variant lumbar artery that has been established in the context of an aplastic right common iliac artery to allow for normal perfusion of the right lower abdomen and extremity [6]. There are lumbar arteries demonstrated at all other levels. But at the level of L4, the right lumbar artery is replaced by the retro-psoas iliac artery.

Outcome

Retro-psoas iliac artery is a rare congenital anatomical anomaly of uncertain embryological origin. It is often an incidental finding on abdominal CT imaging, however some subsequent vascular symptomatology has been reported.

Take home message/Teaching points

Although retro-psoas iliac artery is asymptomatic for the most part, knowledge of this anatomical variant is of clinical importance for surgical planning and to minimise complications in prospective neurosurgical or orthopaedic interventions.

Written informed patient consent for publication has been obtained.