A tumor of the recto-sigmoid junction causes intestinal obstruction. The proximal bowel distends, decompression into the small intestine depends upon the ileo-caecal valve. In some patients the valve prevents decompression (a so called competent ileo-caecal valve) and this aggravates the distension in the colon. The caecum in particular distends due to its larger diameter, and the tension in the caecal wall is greater than in any other part of the large intestine (Law of LaPlace), the tension impedes blood flow to the caecal wall and the combination of ischaemia and increased tension results in caecal perforation.
The importance of recognising the possibility of the patient having a closed loop obstruction is that surgery prior to intestinal perforation is more likely to result in a successful outcome. On clinical examination, tenderness over the caecum should raise the specter of imminent perforation. It may be possible to estimate the size of the caecum on radiographic imaging. A large caecum should accelerate the decision for operative intervention.