Microangioarchitecture of haemorrhoids

SummaryHaemorrhoids are normal physiological structures (vascular cushions), which lead to haemorrhoidal disease when they enlarge pathologically. These vascular cushions are located in the submucosa of the lower rectum and are an important part of the continence organ. The cushions contain enormously dilatable veins which, when filled, enable a gas- and water-tight closure of the anal canal. As vascular cushions require rapid filling and haemorrhoid-associated anorectal bleeding is bright red, it is suggested that dilated veins are filled with arterial blood delivered via arteriovenous (AV) anastomoses. To specify blood supply and microvascular anatomy of the anorectum we analyzed vascular corrosion casts of human recta made from excised post mortem specimens. We found wide dilated veins and venules in the submucosa. Dilatations were often associated with sphincters capable to block venous outflow. Though careful analyses of completely filled vascular corrosion casts we could not confirm the existence of large AV-anastomoses in the anorectum postulated by previous authors. Conclusion: From our findings we conclude that the swelling of the dilatable veins is rather the result of blockage of venous outflow from these veins by the sphincters found than their filling via arteriovenous anastomoses as proposed sofar.