Lumbocostal Trigone

Lateral Lumbocostal Arch (Lateral Arcuate Ligament)
Medial Lumbocostal Arch (Medial Arcuate Ligament)
Left and Right Crura of the Diaphragm
Esophageal Hiatus
Median Lumbocostal Arch (Median Arcuate Ligament)
Aortic Hiatus

The Lateral Lumbocostal Arch is a thickening of the fascia of the quadratus lumborum muscle that extends from the transverse process of the first lumbar vertebra to the tip of the lower margin of the twelfth rib. The Medial Lumbocostal Arch is a thickening of the fascia of the psoas major muscle that extends to the tip of the transverse process of the first lumbar vertebra. The part of the diaphragm arising from the lateral arcuate ligament, and from the 12th rib lateral to this may be deficient in actual muscle tissue. In such cases, this region of the diaphragm will consist essentially of fused endothoracic and transversalis fasciae. The deficient region is said to comprise a Lumbocostal (vertebrocostal) Trigone and is a potential site of herniation of abdominal contents into the thoracic cavity. The Left and Right Crura of the Diaphragm arise from the anterior surfaces of the bodies of the lumbar vertebrae and the anterior longitudinal ligament. The right crus is larger and longer than the left crus. The right crus splits to enclose the esophagus as it pierces the diaphragm, creating the Esophageal Hiatus. The medial tendinous margins of the crura meet in the median line, variably forming the Median Lumbocostal Arch, defining the Aortic Hiatus.