Plain film analysis in sigmoid volvulus

Abstract

The plain film findings in a series of 40 proven cases of sigmoid volvulus have been analysed. Approximately one-third of the cases were considered to be diagnostically difficult, with marked distension of the proximal colon. The difficulty was sometimes compounded by gas-filled loops of small bowel, excess fluid in the sigmoid loop, superimposition of the limbs of the sigmoid loop, a low lying transverse colon and by radiographic shortcomings. The essential radiological exercise in the plain film diagnosis of sigmoid volvulus lies in the identification of the walls of the enlarged sigmoid loop. The loop was characterised in the great majority of cases by an ahaustral margin, an apex below the left hemidiaphragm and above the level of D10, an inferior convergence lying to the left of the midline at the level of the upper sacral segments and by a contained air : fluid ratio in excess of 2 : 1. The radiographic appearance of the medial walls of the sigmoid loop is not specific to sigmoid volvulus. The peripheral walls of the loop may be obscured by proximally dilated colon, particularly when there is radiographic overpenetration. The inferior convergence of the limbs of the sigmoid loop, although usually identified in retrospect, are frequently inconspicuous. The smooth margin of the radiolucent sigmoid loop projecting beyond the haustrated proximal colon in the flanks and particularly in the right upper quadrant, was found to be of considerable diagnostic aid in those cases where the greater part of the sigmoid loop was obscured by proximal colonic distension.