Primary psoas abscess. A review of 16 cases

OBJECTIVE: Most psoas abscesses are secondary. The objective of this study was to report on the clinical features, diagnosis and treatment of primary psoas abscess. METHODS: We retrospectively studied 16 cases seen over a ten-year period (1987-1997) and compared our findings to published data. RESULTS: There were 14 men and two women, with a mean age of 6 years (range, 17-57 years). The right side was affected in nine cases, the left side in six, and both sides in one. Fever, pain and psoas spasm were the presenting symptoms. Laboratory tests for inflammation were positive; four patients had a high neutrophil count. Ultrasonography demonstrated a fluid collection in the psoas in 13 patients. A computed tomography scan was done in 14 patients and showed either a fluid collection (n = 11) or a presuppurative abscess (n = 3). Magnetic resonance imaging was not used. The organism was recovered in nine patients and was a Staphylococcus aureus in seven, an Escherichia coli in one and a Pseudomonas aeruginosa in one. The Brucella agglutination test was strongly positive in two patients. Findings were negative from investigations done to look for a cause (discitis, urinary tract infection, Crohn's disease, ulcerative colitis, malignancy or infection in the vicinity of the psoas muscle). All patients received antimicrobial therapy. Drainage was percutaneous in six patients and surgical in ten. The outcome was favorable in every case.