Benign Anorectal: Hemorrhoids

Abstract

Hemorrhoids are cushions of specialized, highly vascular tissue found within the anal canal in the submucosal space. The term “hemorrhoidal disease” should be reserved for those vascular cushions that are abnormal and cause symptoms. These cushions of thickened submucosa contain vascular spaces (sinusoids), elastic tissue, connective tissue, and smooth muscle (see Fig. 11.1).Some of the vascular structures within the cushion when examined microscopically lack a muscular wall. The lack of a muscular wall characterizes these vascular structures as sinusoids and not veins. Studies have shown that hemorrhoidal bleeding is arterial and not venous. Hemorrhage occurs from dammaged presinusoidal arterioles that communicate with the sinusoids in this region. The hemorrhage is bright red in appearance and has an arterial pH. The venous plexus and sinusoids below the dentate line, constitute the external hemorrhoidal plexus which drain primarily via the inferior rectal veins into the pudendal veins and then to branches of the internal iliac veins. Venous drainage also occurs to a lesser extent via the middle rectal veins to the internal iliac veins. The overlying tissue is somatically innervated and is therefore sensitive to touch, pain, stretch, and temperature.