Colosigmoid junction: a study of its functional activity with identification of a physiologic sphincter and involvement in reflex actions.

The colosigmoid junction (CSJ) marks the termination of the descending colon (DC) and the beginning of the sigmoid colon (SC); it is a fixed area in the retroperitoneum. At this site where two functionally different areas meet, we hypothesized the presence at the CSJ of a physiologic sphincter that regulates the passage of gut contents from the DC to the SC. This hypothesis was investigated for this communication. Eight subjects (mean age 36.6 +/- 4.7 SD years, 6 women) were studied during surgical repair of incisional hernia or laparotomy. The pressure responses of the CSJ to individual distension of the DC and SC were recorded. A balloon-ended tube was introduced per annum to lie in the DC or SC, and the pressure in the DC, CSJ, and SC was measured by saline-perfused catheters. To study whether the CSJ response to individual DC or SC distension was a direct or reflex action, the test was repeated in six of eight patients after separate anesthetization of the DC, CSJ, and SC. The CSJ had a higher pressure than that of the DC or SC; the high-pressure zone measured a mean of 2.1 +/- 0.9 cm. High-volume DC distension effected a significant DC pressure rise (p <.001) and a CSJ pressure decline (p <.05), which lasted a mean of 7.2 +/- 1.2 s. In contrast, the CSJ responded to big volume SC distension by significant pressure elevation (p <.001) which was also momentary. Small volume distension of the DC or SC effected no significant CSJ pressure response (p >.05). The CSJ pressure did not respond to distension of the anesthetized DC or SC. Likewise, the anesthetized CSJ did not react to DC or SC distension. When the test was repeated using saline instead of xylocaine, the CSJ pressure response was similar to that without saline injection. The CSJ is a high pressure zone with a measurable length. It reacts to DC or SC balloon distension by dilatation or narrowing, respectively. These findings presumably denote the existence of a "physiologic sphincter" at the CSJ, which appears to regulate the passage of colonic contents to the SC. We postulate that the CSJ pressure response to DC or SC distension is reflex and mediated through the "colosigmoid reflexes." The role of the colosigmoid sphincter and reflexes in colonic motility disorders remains to be investigated.