Congenital Diseases of Intrahepatic Bile Ducts: Variations on the Theme “Ductal Plate Malformation”

Abstract

Congenital diseases of intrahepatic bile ducts (IHBDs) can be divided into two main groups: diseases characterized by necroinflammatory destruction of IHBDs and diseases characterized by a variable degree of ectasia of IHBDs and associated with a variable degree of fibrosis.This review will emphasize that in mostif not allof these conditions, persistence or lack of remodeling of the embryonic ductal plate (so-called "ductal plate malformation" [DPM]) is an essential precursor of the lesions (1). EMBRYOLOGY OF IHBDs AND DPMDuring the fourth week of human gestation, the liver arises as a bud of cells (the hepatic diverticulum) from the ventral wall of the most cephalad portion of the foregut, near the junction with the yolk sac (2).In the human, as in the mouse, the hepatic diverticulum comprises two parts: a pars cranialis or pars hepatica and a pars caudalis or pars cystica.The former gives rise to liver precursor cells that grow into the mesenchyme of the septum transversum, which consists of a mass of loosely arranged mesodermal cells separating the pericardial and peritoneal cavities.The caudal part of the hepatic diverticulum develops into the gallbladder and the common bile duct.The cranial or hepatic part of the diverticulum acquires a T-shaped cephalic end, with more pronounced growth of epithelial sprouts from the lateral walls, creating the early outline of the right and left lobes of the liver.The liver precursor cells grow between small endothelium-lined spaces in the septum transversum that connect with the capillary plexus of the vitelline (or omphalomesenteric) veins, thus establishing the basic architecture of liver parenchyma: parenchymal cords and plates alternating with hepatic sinusoids.During the first 7 wk or so of embryonic life, no intrahepatic bile duct system exists in the developing liver.Its formation begins around the eighth gestational week.