Volvulus of the Sigmoid: A New Radiologic Sign

Abstract

ACCORDING TO statistics, volvulus of the sigmoid is responsible for 45 per cent of obstructions in the large intestine; it is therefore one of the most frequent causes of intestinal obstruction in general. Volvulus of the sigmoid is the result of torsion of the sigmoid colon around its mesenteric axis. The pivot of this torsion is the rectosigmoid, the anatomic characteristics of which permit the twisting of the mobile pelvic colon. With the growth and development of the individual, certain changes take place in the pelvic colon. The wide mesocolon of the fetus and newborn infant becomes the narrow mesocolon of the adult, while the coil elongates. Frequently, however, the evolution of these two structures is not parallel, and the length of the coil may become excessive in relation to the mesentery. Under these conditions torsion is very probable. To the anatomic conditions predisposing to volvulus are to be added certain pathological processes which may affect either the mesocolon or the sigmoid coil. The base of the mesocolon, normally small, may be still further reduced by inflammatory processes (a retractile mesosigmoiditis) , being transformed into a mere pedicle. A megacolon may also involve the coil and facilitate torsion. Having outlined thus briefly the anatomical and pathological causes that contribute to the frequency of torsion of the sigmoid, we may proceed to a discussion of the radiological signs that aid in its diagnosis. The study of a case, from this point of view, begins with two roentgenograms, one with the patient standing and the other in the supine position. A detailed study of these two films sometimes permits a diagnosis without resort to the barium enema. Radiologic Signs Of Sigmoid Volvulus In any case of volvulus we have (a) a strangulation of an intestinal coil and above this (b) an obstruction. In a particular case, the picture will depend upon the competence of the ileocecal valve. With an incompetent valve, we have what is regarded as the typical image of sigmoid volvulus, a huge arched coil with a uniform and ample connection between the two sides of the arch. At first, it may seem as if this coil represents a distention of the whole colon, such as can be seen roentgenographically in cases of sigmoid cancer. When we study the character of the coil, however, we find that it is a segment of the colon only, distended as a result of mechanical obstruction. There is one sign which we have found useful in arriving at a correct diagnosis in these cases. In the “hermetically shut coil” in the presence of a neoplasm, the diameter of the right-hand portion is larger than that of the left-hand portion (Fig. 1). The explanation of this is clear, if we consider that the former represents the cecum and ascending colon, classically known to be very distensible, while the left-hand segment is formed by the more rigid descending colon.