A rare case of an unusual presentation of flank pain

Abstract

Iliopsoas abscess (IPA) is an uncommon retroperitoneal infection with insidious onset and nonspecific clinical features. Image-guided percutaneous catheter drainage (PCD) is widely regarded as first-line therapy, but multiloculation, viscous pus, gas formation, and extensive anatomic spread predict PCD failure and warrant open surgical drainage. A 67-year-old woman with hypertension, treated breast cancer, prior stroke, and remote deep venous thrombosis presented with right-sided flank pain and a large fluctuant, tender subcutaneous mass. Computed tomography revealed a 14×2×5.8 cm multiloculated retroperitoneal collection involving the entire length of the right iliopsoas muscle from the crus of the right hemidiaphragm to the iliacus, with extension through the right posterolateral abdominal wall into the subcutaneous fat. She had undergone two unsuccessful interventional radiology-guided drainages at an outside facility. The white blood cell count was 29,000/µl and blood cultures grew methicillin-resistant Staphylococcus aureus (MRSA); there was no evidence of osteomyelitis or endocarditis. After culture-directed antibiotics were initiated, the patient underwent staged open exploration through a right flank incision, with drainage of more than one litter of purulent material. Penrose drains were placed and the wound was left open for daily dressing changes. A two-week follow-up computed tomography (CT) demonstrated near complete resolution. Primary IPA is rare and prone to recurrence when initial drainage is incomplete. In multiloculated, anatomically extensive, or PCD-refractory disease, early conversion to open surgical drainage is essential to achieve definitive source control and prevent the cumulative morbidity of repeated unsuccessful intervention.