Among the numerous causes of abdominal pain, vascular causes comprise an extremely important group that requires prompt recognition and detection. Although some of these abdominal events may be acute, others often present as a chronic debilitating disorder. Compromise of blood flow to and from the gastrointestinal tract may result in ischemia of varying degrees. Although most events are arterial in nature, 5% to 15% of cases involve the mesenteric venous structures. This vascular source of abdominal pathology often goes unrecognized and has a wide gamut of presentations. Most involve the superior mesenteric vein (SMV), but other processes involve the portal vein, splenic vein, hepatic vein, or inferior mesenteric vein (IMV). This chapter discusses the anatomy, etiology, pathophysiology, clinical presentation, diagnosis, and management of splanchnic venous disease. Furthermore, arteriovenous malformations (AVMS) of the gastrointestinal tract and certain rare vascular disorders are examined as related entities to splanchnic venous disease.
NORMAL SPLANCHNIC VENOUS ANATOMY
The venous anatomy parallels that of the splanchnic arterial system. The venous blood from most of the gastrointestinal tract drains into the liver via the portal venous system. The portal vein is formed by the confluence of the SMV and splenic vein. This vein is approximately 2 inches (5 cm) long and is formed behind the neck of the pancreas. The IMV joins the splenic vein before the portal venous confluence. The other tributaries of the portal vein include the left gastric vein, which drains the left portion of the lesser curvature of the stomach and distal esophagus. The right gastric vein also drains directly into the portal vein and drains from the right portion of the lesser gastric curvature. The cystic veins drain the gallbladder blood flow directly into either the portal vein or the liver.
The SMV is vital for drainage of blood flow from the small intestine, cecum, ascending colon, and transverse colon. It is formed by the jejunal, ileal, ileocolic, right colic, and middle colic veins. The pancreas and the duodenum receive venous drainage from the inferior pancreaticoduodenal vein. The IMV drains blood flow from the descending and sigmoid colon and the rectum. Specifically, the left colic vein and sigmoid branches flow into the IMV. The superior rectal vein drains blood flow from the rectum into the IMV.
In normal circumstances, the portal venous blood traverses the liver and drains directly into the inferior vena cava (IVC). However, in conditions that impede portal venous blood flow by this direct route, indirect communications become common between the portal and systemic circulations. These include the following communications. The left gastric vein portal tributary may form an anastomosis with the esophageal veins, which drain the middle third of the esophagus into the azygous vein. The paraumbilical veins connect the left branch of the portal vein with superficial systemic tributaries of the anterior abdominal wall. The superior rectal venous portal tributaries may communicate with the middle and ...