Sonographic appearance of fecal masses.

Fecal impaction, caused by incomplete evacuation of feces over an extended length of time, may lead to the formation of a fecaloma, a large, firm mass of stool. Sonography is commonly used as the first imaging procedure in patients presenting with abdominal masses. In the five cases cited, fecaloma was suspected by sonography in four cases; confirmation was obtained by rectal examination in three cases and by radiographic studies in two cases. A representative case report is presented of a 74-year-old woman who had a large pelvic mass detected on physical examination. Sonographically, the fecaloma had a highly echogenic surface and a posterior acoustic shadow. Radiographic examination showed a "soap bubble" appearance, suggestive of stool. Thus, fecaloma should be considered in the differential diagnosis of patients with highly reflective and shadowing abdominal and/or pelvic masses.