A psoas (or iliopsoas) abscess is a collection of pus in the iliopsoas muscle compartment . It may arise via contiguous spread from adjacent structures or by the hematogenous route from a distant site. The incidence is rare but the frequency of this diagnosis has increased with the use of computed tomography (CT), prior to which most cases were diagnosed at post mortem . The anatomy, pathogenesis, microbiology, clinical manifestations, diagnosis, and treatment of psoas abscess will be reviewed here.
Understanding the clinical manifestations, complications, and management of psoas abscess requires knowledge of the anatomy of the psoas muscle and its adjacent structures.
The psoas muscle arises from the transverse processes and the lateral aspects of the vertebral bodies between the twelfth thoracic and the fifth lumbar vertebrae. From this origin it courses downward across the pelvic brim, passes deep to the inguinal ligament and anterior to the hip joint capsule to form a tendon that inserts into the lesser trochanter of the femur. The iliacus muscle joins the psoas to insert via the same tendon. The iliacus and psoas muscles are the main hip flexors.
The psoas and iliacus are sometimes considered together as the iliopsoas muscle, located in an extraperitoneal space called the iliopsoas compartment. The tendon is separated from the hip capsule by the iliopsoas bursa. This bursa is in communication with the hip joint space in up to 15 percent of persons, which may facilitate spread of infection between these sites.
The psoas muscle is situated near a number of important anatomical structures including the vertebral bodies, the abdominal aorta, the sigmoid colon, the appendix, the hip joint, and iliac lymph nodes. Infection may spread directly between these structures and the psoas muscle.