Psoas sign: a reevaluation

In general, the psoas sign has been known to be a reliabler index of presence of a retroperitoneal pathology. However, obliterated psoas margin may be caused by various other conditions in so far as the amount of fat around the psoas muscle is not enough to be visualized. On the other hand, retroperitoneal pathology does not always obliterates the psoas margin. Authors analyzed obliterated psoas margins in 72 patients by comparing simple radiographs and computed tomography, and attempted to explain the mechanism of obliterated psoas margin, on simple radiograph. The results are as follows : 1. The psoas margin is obliterated by the retroperitoneal pathology and various other conditions such as kidney-psoas contract, scanty extraperitoneal fat, scoliosis, bowel interposition and angled psoas muscle. 2. The psoas margin is preserved as far as the perinephric fat is intact and X-ray beam strikes the lateral margin of the psoas muscle tangentially. 3. The psoas sign is considered not to be a reliable index of a retroperitoneal pathology