Primary pyogenic abscess of the psoas muscle.

Nine children who were less than nine years old and had a primary pyogenic abscess of the psoas muscle were treated in a five-year period. This rare lesion often simulated septic arthritis of the hip. Ultrasonography was found to be the most reliable and easily performed diagnostic study. Because of the rarity of the lesion, the diagnosis requires a high index of suspicion. The best treatment is early operative drainage and administration of systemic antibiotics.