Most commonly, a psoas abscess results from a tuberculous abscess of the lumbar vertebra that tracks from the spine inside the sheath of the psoas muscle. Other causes include extension of renal sepsis and posterior perforation of the bowel.
Patients present with a tender swelling below the inguinal ligament. They are usually apyrexial.
The condition may be confused with a femoral hernia or enlarged inguinal lymph nodes.