On a plain abdominal X-ray, the psoas muscle shadows are typically visible bilaterally. Absence or obliteration of these shadows can be a non-specific sign of:

Explanation

The psoas muscle shadows are formed by the fat planes surrounding the psoas muscles. Their clear visualization indicates a normal retroperitoneal space. Obliteration or absence of one or both psoas shadows suggests the presence of fluid (e.g., hemorrhage, ascites), inflammation (e.g., appendicitis, pancreatitis, retroperitoneal abscess), or a mass in the retroperitoneal space that obscures the fat planes. While severe bowel gas distension can sometimes make them harder to see, it's not the primary cause of obliteration. Renal calculi are calcifications within the kidney and do not directly cause psoas shadow obliteration, although a large perinephric collection associated with a renal pathology could. It is not a normal variant.