Vascular Disorder of Bowel

The largest portion of the gastrointestinal tract is supplied by the celiac, superior mesenteric, and inferior mesenteric arteries. As they approach the intestinal wall, the superior and inferior mesenteric arteries fan out to form the mesenteric arcades. Interconnections between arcades, as well as collateral supplies from the proximal celiac and distal pudendal and iliac circulations make it possible for the small intestine and colon to tolerate slowly progressive loss of the blood supply from one artery. By contrast, acute compromise of any major vessel can lead to infarction of several meters of intestine.

Hemorrhoids

Hemorrhoids are dilated anal and perianal collateral vessels that connect the portal and caval venous systems to relieve elevated venous pressure within the hemorrhoid plexus. Thus, although hemorrhoids are less serious than esophageal varices, the pathogenesis of these lesions is similar. They are common, affecting about 5% of the general population. Common predisposing factors include constipation and associated straining, which increase intraabdominal and venous pressures, venous stasis of pregnancy, and portal hypertension.

Collateral vessels within the inferior hemorrhoidal plexus are located below the anorectal line and are termed external hemorrhoids, while those that result from dilation of the superior hemorrhoidal plexus within the distal rectum are referred to as internal hemorrhoids. On histologic examination, hemorrhoids consist of thin-walled, dilated, submucosal vessels beneath anal or rectal mucosa. These vessels are subject to trauma, which leads to rectal bleeding. In addition, they can become thrombosed and inflamed.

Hemorrhoids often manifest with pain and rectal bleeding, particularly bright red blood seen on toilet tissue. Hemorrhoids also may develop as a result of portal hypertension, where the implications are more ominous. Hemorrhoidal bleeding generally is not a medical emergency; treatment options include sclerotherapy, rubber band ligation, and infrared coagulation. In severe cases, hemorrhoids may be removed surgically by hemorrhoidectomy.

Summary

Vascular Disorder of Bowel

• Hemorrhoids are collateral vessels that form in response to venous hypertension.