Psoas abscess is a collection of pus (abscess) in the iliopsoas muscle compartment. It can be classified into primary psoas abscess (caused by hematogenous or lymphatic spread of a pathogen) and secondary psoas abscess (resulting from contiguous spread from an adjacent infectious focus). Psoas abscess may be caused by lumbar tuberculosis. Owing to the proximal attachments 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. Treatment may involve drainage and antibiotics.

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