Introduction

Although thrombosis of the gastrointestinal and visceral vasculature, including hepatic vein and inferior vena cava thrombosis (Budd–Chiari syndrome) and splanchnic vein thrombosis (portal, splenic, or mesenteric vein thrombosis) is a rare phenomenon in childhood, it is associated with considerable morbidity and mortality. The overall incidence is unknown in children, but portal vein thrombosis (PVT) and Budd–Chiari syndrome are the most frequently reported. In general, the natural history of these thrombotic disorders is not well described in the pediatric literature; thus risk factors, diagnostic strategies, and therapeutic interventions are often extrapolated from the adult literature to supplement the experience reported in children.

An anatomical understanding of the abdominal venous vasculature is critical in identifying risk factors and recognizing signs and symptoms of gastrointestinal VTE. The portal vein originates behind the pancreas in the right upper quadrant of the abdomen and is formed by the confluence of the splenic and superior mesenteric veins (Figure 4.1). The inferior mesenteric vein drains directly into the splenic vein. The portal vein typically ascends behind the common bile duct and hepatic artery and divides into the right and left portal branches at the porta hepatis, delivering nearly two-thirds of the blood flow to the liver. In neonates, the umbilical vein traverses the portal vein to connect with the ductus venosus, which enables blood to bypass the liver to flow directly to the inferior vena cava (Figure 4.2) [1,2]. A thrombus may form anywhere along the portal vein as well as along any associated tributaries and/or branches. Veno-occlusion may be described as either partial or complete obstruction of the vessel. Nearly two-thirds of PVT are isolated to the portal vein, while 28% of PVT are found to involve the splenic vein and 15% involve the superior mesenteric vein [3]. Patients may also have isolated splenic or isolated mesenteric vein thrombosis.