Pyomyositis: CT appearance

Pyomyositis, spontaneous bacterial abscess in skeletal muscle, is rare in the United States. The clinical diagnosis is difficult to make, as pyomyositis can present as a tumor-like mass, mimicking a soft-tissue sarcoma. Pyomyositis can also mimic muscle hematoma, thrombophlebitis, osteomyelitis, cellulitis, arthritis, and appendicitis. The authors present the CT appearance of 15 cases of pyomyositis. Sarcoma was suspected clinically in the majority of these cases. CT demonstrated an intramuscular mass in all, with a central low-density area in 14 of the 15 cases. Contrast-enhanced CT revealed peripheral enhancement in 11 of 12 cases. Reactive changes in the subcutaneous fat were present in 12 of the 15 cases. In the three exceptions, the abscesses were deep within muscle. Knowledge of the CT appearance of this rare entity may speed accurate diagnosis and the institution of appropriate therapy