Significance of pelvic retroperitoneal pneumography in the assessment of extramural invasion of rectal carcinoma.

Pelvic retroperitoneal pneumography (PRP) and barium enema were performed simultaneously in 34 patients with rectal carcinoma in an attempt to assess whether there was extramural cancer invasion. In 9 patients, no free air was visualized in the retroperitoneal cavity surrounding the mass, and histological evaluation of the excised specimens showed extramural invasion in all 9. The mean maximum diameter was 4.1 cm. In 25 patients, free air was seen around the mass, and 10 had tumors limited to the rectal wall, the remaining 15 manifested extramural invasion, however, the mean diameter was small (2.0 cm). In a mass whose center was located along the anterior rectal wall, it was difficult to assess from the free air findings whether there was extramural invasion. Based on the present findings, we concluded that PRP is useful in determining preoperatively whether there is extramural invasion in cases with rectal carcinoma involving the posterior and lateral walls.