Iliopsoas abscess is an uncommon condition. Diagnostic delays result in high mortality and morbidity. When there is no obvious source of infection the term primary Iliopsoas abscess is used[1-3]. Primary iliopsoas abscesses can occur in patients with diabetes mellitus, renal failure, immunosuppression and AIDS. Secondary abscesses arise from the direct extension of infection from an adjacent organ. Crohn’s disease is the most common cause. Diverticulitis, appendicitis, ulcerative colitis, colorectal cancer, urinary tract infection or cancer, osteomyelitis, septic arthritis, disk infection, trauma, endocarditis, suppurative lymphadenitis, procedures performed in the groin, lumbar, or hip areas are other causes of secondary iliopsoas abscesses. The most common pathogen of primary psoas abscesess is Staphylococcus aureus (80%), while that of secondary psoas abscesses is usually mixed intestinal floras [2-6].
Iliopsoas abscess is common in the young compared with the elderly and it is more common in males than females [2].
The classic triad, fever, back pain and limitation of hip movement, is present in 30% of the patients. Other symptoms are vague abdominal pain, malaise, nausea and weight loss [2, 3, 6].
Plain radiographic signs of psoas abscess are of limited sensitivity and specificity. Ultrasound of the abdomen is diagnostic in only 60% of the cases as it may demonstrate an anechoic or hypoechoic lesion in the iliopsoas compattment but it cannot identify the cause of the abscess. Also bowel gas can obscure the retroperitoneal space. Computed tomography of the abdomen with contrast is the most efficient and accurate imaging study in diagnosing an iliopsoas abscess. At CT, it manifests as a hypodense lesion causing enlargement of the psoas muscle. After intravenous contrast administration a rim enhancement of varying thickness is noticed. Inflammatory obliteration of surrounding tissue planes, gas bubbles, and bone destruction can be secondary findings [1-6].
MRI findings are similar to CT and consist of a fluid-filled lesion expanding the psoas muscle with rim enhancement after contrast administration [2, 6].
Psoas abscesses should be distinguished from other causes of psoas enlargement, including haemorrhages and tumours. Treatment involves the use of appropriate antibiotics combined, in most cases, with drainage of the abscess through a percutaneous CT-guided or an open technique. Surgical drainage is indicated if there is a contraindication to CT-guided percutaneous drainage or abdominal pathology that requires intervention [1-6].
Although the mortality rate in primary iliopsoas abscesses is 2.4% and in secondary abscesses is 19%, in untreated patients it can reach 100% [2, 3, 6].