Classification and presentation of iliopsoas abscess

Iliopsoas abscess (IPA) is an infection involving the iliopsoas compartment. Three muscles make up the iliopsoas compartment: the iliacus, psoas major and psoas minor. The iliopsoas compartment is retrofascial (ie posterior to the retroperitoneum) but is in close proximity to the retroperitoneal structures. It is also contiguous with both the axial and the appendicular musculoskeletal system. These complex anatomical relationships explain why different disease processes may involve the iliopsoas compartment, which acts as a conduit allowing the spread of diseaseShields, 2012Van Dyke, 1987.

Iliopsoas abscess can be classified as primary or secondary. Primary iliopsoas abscess occurs when the iliopsoas compartment becomes infected from haematogenous seeding. Secondary iliopsoas abscess is more common and occurs when the iliopsoas compartment is infected by contiguous spread from adjacent structures (eg kidneys, pancreas, gastrointestinal tract, vertebral body, posterior paraspinal muscles, lesser trochanter of the femur).

The clinical presentation varies depending on the source of infection; however, common symptoms include fever, lower back pain and limitation of hip movement. Early clinical features are often nonspecific with diagnosis and effective management often delayed. A contrast-enhanced computed tomography (CT) scan is required for diagnosis. The nature of the clinical presentation and the CT scan results are important to exclude alternative conditions that also affect the iliopsoas compartment, including haemorrhage and malignancy. To identify the causative pathogen, blood cultures and direct abscess aspirate are required.

See advice on management of iliopsoas abscess.