An abscess in the psoas muscle of the abdomen may be caused by lumbar tuberculosis. Owing to the proximalattachments of the iliopsoas, such an abscess may drain inferiorly into the upper medial thigh and present as a swelling in the region. The sheath of the muscle arises from the lumbar vertebrae and the intervertebral discs between the vertebrae. The disc is more susceptible to infection, from tuberculosis and Salmonella discitis. The infection can spread into the psoas muscle sheath