Invagination of intra-abdominal structures in the lumbar intervertebral disc space.

Invagination of peritoneal or retroperitoneal structures into the intervertebral disc space of the lumbar spine is extremely rare. In this article the imaging features and clinical findings are demonstrated in four patients with intervertebral invagination of intra-abdominal structures. Plain radiographs, CT scans, and MR images showed disruption of the anterior ligamentous complex (ALC) and invagination of various structures into the disc space, including the vena cava, iliac vessels, intestine, the torn redundant anterior longitudinal ligament, retroperitoneal fat, and the psoas muscle. The invaginations occurred at the level of L3-L4 and L4-L5 in one case each and at L5-S1 in two cases. Follow-up imaging in three cases (1, 5, and 8 years respectively) showed the progression of the invagination. These cases demonstrate that a close evaluation of this condition is necessary, particularly for older patients who show disruption or laxity of the ALC, degenerative spondylosis with chronic segmental instability, and osteoporosis of the lower lumbar spine.