Overview
A psoas or iliopsoas abscess is a collection of pus in the iliopsoas muscle compartment that may emerge due to the haematogenous or lymphatic spread of an infection/abscess from a distal site (a primary abscess) or spread from adjacent structures (a secondary abscess).
Causes
Primary psoas abscesses tend to be monomicrobial:
- Staphylococcus aureus is the most common organism found
- Mycobacterium tuberculosis is another notable cause
Causes of secondary psoas abscesses include:
- Lumbar vertebrae (e.g. discitis, osteomyelitis)
- Hip (e.g. replacement)
- Gastrointestinal tract (e.g. Crohn’s disease, diverticulitis, malignancy)
- Genitourinary tract (e.g. urinary tract infection)
- Intravenous drug use
- Infective endocarditis
Presentation
Overview
Features of a psoas abscess include:
- Fever
- Flank pain
- Limp
- Weight loss
- Psoas sign – patients may have a lumbar lordosis and flexed hip and extending the hip exacerbates pain as the psoas muscle is stretched
Diagnosis and Management
Overview
The diagnostic test is a CT scan and treatment involves drainage and empirical IV antibiotics that are adjusted according to culture results.
Drainage may be performed percutaneously under ultrasound guidance, however, in some cases, surgery may be necessary (e.g. if percutaneous drainage fails, the abscess is too large, or concomitant abdominal pathology exists).
