Abstract

Introduction/Objectives: The cause of rectal diverticula is still unknown and its incidence is very low when compared to the incidence of diverticular disease in the colon. The aim of this work is to propose an angiomorphological etiology to complement the theories already described to explain the low incidence of diverticular disease of the rectum and the rare occurrence of diverticula in the mesocolicside of the sigmoid colon: a hypothesis based on the location and course of the arteries through the colon wall and in the diameter of the lumen of the colon.

Material and methods: Eighty specimens retrieved from donated human cadavers were used. They were all injected via the inferior mesenteric artery with colloidal barium sulfate with red colored gelatin. Ten cases were also injected via the two internal iliac arteries. All of them were then preserved using the Spalteholz diaphanization technique. In four cases was also used a micro-angiography technique.

Results: The vasa recta longa (VRL) course through only one muscle layer, the inner circular muscle layer, during a short tract, almost perpendicular to the greater axis of the colon, and then end in the submucosa. Most of the vasa recta brevia (VRB) cross the two muscle layers at the level of the mesocolic taeniae. The terminal branches of the superior rectal artery cross the two muscular layers of the rectum, from the external towards the inner layer, oriented longitudinally and obliquely during a long tract through the rectal wall until they reach the submucosa.

Conclusion: The areas where the VRL course only through the circular muscle layer are weak points of the colon wall where the diverticula can frequently occur. We think that the lower incidence of diverticula in the mesocolic border of the colon is due to the fact that the VRB have a smaller caliber than the VRL, they cross more often the two muscle layers (at the mesocolictænia level) and, in the cases where they cross only the muscle circular layer, they have an oblique path for a longer tract. Diverticula are rare in the rectum not only for the various reasons already described but also because the arteries that supply the rectum cross the wall of the organ in an oblique and longitudinal way, for a long tract.