Lateral arcuate ligaments of the diaphragm: anatomic variations at abdominal CT

The authors have occasionally observed nodular areas abutting the lateral diaphragmatic surface and extending into the posterior pararenal space on computed tomographic (CT) scans. Review of the anatomy literature revealed that this finding represents inferolateral extension of the lateral arcuate ligaments, which reflect over the quadratus lumborum muscles to fuse with the diaphragm. CT scans from 100 consecutive patients were reviewed to determine the frequency, relationship to habitus, and appearance of this finding. Nodularity was found in five patients (bilateral in three, unilateral in two). The average size was 9.4 mm in the transverse plane, 6.3 mm in the anteroposterior plane, and 4.3 cm in the cephalocaudal plane. The extent of retroperitoneal fat was normal in all five patients. In one patient, there were easily visible lobulations; three patients had prominent lobulations, and one patient had few lobulations. It is important to recognize this anatomic variant to avoid confusion with disease.