Plain film diagnosis of intussusception: prevalence of the target sign.

We describe a feature of intussusception seen on plain abdominal films that to our knowledge has not been previously described. The abnormality, termed the "target sign," consists of two concentric, circular, radiolucent lines to the right of the spine superimposed on the kidney. Four observers examined 280 plain abdominal films; 180 were of 94 patients who had had 100 episodes of intussusception and 100 films were of 80 control subjects. The target sign was observed by three or four observers on plain films in 24 (26%) of 94 patients with intussusception and on 4% of radiographs of control subjects. There was no concordance between observers on false-positive findings seen in the control subjects. Our experience suggests that circular radiolucent lines superimposed on the right kidney on plain abdominal radiographs (target sign) constitute a useful diagnostic feature of intussusception.