Reevaluation of psoas sign analyzed by CT

The lateral margin of the psoas muscle, contrasted by retroperitoneal fat, is usually visualized o plainabdominal radiography. Failure to visualize all or segment of lateral margin of the psoas muscle, so called psoassing, has been emphasized as reliable finding of retroperitoneal pathology. But the significance of psoas sign hasbeen controversial. The authors reevaluated ‘psoas sign’ by comparing 160 abdominal radiography with CT. Theresults were as follows: 1. In 160 supine radiographys, good visualization was present in 106 cases(66.3%), faintvisualizatin in 24(15.0%), segmental nonvisualization in 18(11.3%), and completer nonvisualization in 12(7.5%). In113 erect radiographs, good visualization was present in only 36 cases(31.9%). 2. Asymmetric visualization waspresent in 84 out of 160 cases. In patient with scoliosis, lateral margin of convex side was seen more clearlythan concave side, and this finding was statistically significant (p<0.005). 3. Ascites did not directly influenceto psoa visualization contrary to common belief. 4. In 54 cases of faint or nonvisualization, normal was16(29.6%), intraperitoneal pathology was 16(29.6%), and retroperitoneal pathology was 22(40.7%). 1) In normalpatient, psoas contact with kidney or intestine and deformed psoas muscle were responsible for poor visualization. 2) The major cause of poor visualization in intraperitoneal pathology were psoas contact with displaced kidney byhepatomegaly, ascites with scanty retroperitoneal fat and derformed psaos muscle. 3) The major cause of poorvisualization in retroperitoneal pathology were psoas invasion by tumor or inflammation, psoas conntact withenlarged kidney or perirenal lesion. 5. In summary, the mechanism of faint or nonvisualization of psoas marginwere: 1) psoas contact with normal or pathologic organs 2) psoas invasion by tumor or inflammation 3) deformedpsoas muscle 4) scanty retroperitoneal fat