A 27-year-old man visited with the chief complaint of back pain, right thigh pain, lower back pain and fever with a 3 week duration. He had severe pain on the right lower quadrant of the abdomen, and a fever of 38.5℃. The physical examination revealed a tender, palpable 15×10 cm² size mass, accompanied by local heat, in the RLQ. In addition, he reported pain with an external rotation of the right hip. The laboratory findings revealed an elevated WBC count (19,410/L with 83.8% neutrophils; the normal levels are: WBCs; 3,400-9,300/L, neutrophils; 33.0-74.0%) and ESR (erythrocyte sedimentation rate) (88 mm/h; the normal level is 0-20 mm/h). The abdominal CT scan revealed a multiseptated cystic mass along the right psoas-iliacus muscle (Fig. 1). Upon admission, CT-guided percutaneous aspiration and drainage were performed using a catheter. On day 8, the follow-up abdominal CT scan revealed a marked reduction of the right psoas-iliacus abscess (Fig. 2). On day 9, the catheter was removed. The total amount of drainage was 1,800 ml. A microbiological examination revealed Klebsiella pneumoniae. Antibiotic therapy was performed using cefamezine.

Six months later, the patient presented with a history of anorexia, malaise, epigastric pain, lower back pain and a fever of 37.8℃ for one week. The physical examination revealed tenderness in the RLQ region of the abdomen. The laboratory findings showed a hemoglobin level of 9.5 g/dl (the normal level is 11.7-17.1 g/dl), a Hematocrit level of 29.5% (the normal level is 35.5-51.4%), a WBCs count of 20,000/L with 81% neutrophils, and an ESR of 63 mm/hr. The abdominal CT scans revealed an abscess cavity on the inferior side of the right psoas-iliacus muscle. In addition, retrocecal appendicitis accompanying the periappendiceal abscess was observed on the abdominal CT scans. (Fig. 3) Magnetic resonance imaging of the pelvis revealed a psoas-iliacus between L3 and S1. An appendectomy and laparotomywas performed. The culture yielded Escherichia coli in the psoas abscess. Ceftazidim was administered to our patient based on the results of the sensitivity test. The drain was removed on day 10. After 3 months antibiotic treatment, the patient was discharged. At the 2-year follow-up, the patient showed no recurrent episodes.

An Iliopsoas abscess can be classified as primary or secondary according to the presence or absence of the underlying disease. Primary psoas abscess is caused by Staphylococcus aureus in 80-95% of cases5). A prior trauma to the psoas muscle is observed in 18-20% of cases. Intravenous drug abusers or HIV-positive people are at increased risk of developing a primary psoas abscess6). In some cases, the causative agents are coupled with Escherichia coli, Staphylococcus and Streptococcus, in which Bacteroides species are predominant5). Presumably, percutaneous drainage with antibiotic therapy might be the first treatment of choice in cases of primary psoas abscess. Before starting this treatment, the occult blood must be cultured once the blood supply is stabilized. In cases of a psoas abscess, with percutaneous drainage, complete drainage of the abscess can be performed and the abscess membrane can be debrided. This increases the recovery rate to 97%5). In addition, it is advantageous to shorten the length of hospital stay and lower the recurrence rate. In the management of a secondary psoas abscess, abscess drainage must be carried out in combination with a treatment for the primary infectious focus3). In cases of a secondary psoas abscess in which only percutaneous drainage was performed, the recurrence rate was at most 50%4). In conclusion, antibiotic therapy must be continued for 2-3 weeks after defervescence and the cessation of drainage2).