Imaging description

The diaphragmatic crura fuse with each other medially to form the single midline median arcuate ligament, behind which the aorta passes from the thorax into the abdomen. Laterally, the crura extend in front of the psoas muscles as the paired medial arcuate ligaments, which provide a ligamentous attachment for the diaphragm. The medial arcuate ligament is classically described as attaching to the transverse process of L1, although a dissection study suggests it actually attaches to the transverse process of L2 [1]. More laterally still, the crura continue in front of the quadratus lumborum muscles as the paired lateral arcuate ligaments, which pass from the spinal attachment to the 12th rib. Prominent lateral arcuate ligaments may be seen as distinct soft tissue nodules of 1 cm or more in diameter in continuity with the diaphragm and projecting into the posterior pararenal space of the retroperitoneum on cross-sectional imaging (Figure 3.1) [2].

Importance

A prominent lateral arcuate ligament may simulate a retroperitoneal mass, or suggest peritoneal metastases in the hepatorenal pouch (if right-sided).

Typical clinical scenario

Nodular projections into the retroperitoneum due to prominent lateral arcuate ligaments were seen in 5 of 100 unselected CT scans, and were bilateral in 3 patients [2]. No particular association with age, sex, or respiratory position has been described.