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In the human embryo the first anlage of the bile ducts and liver
is the hepatic diverticulum from the proximal gastrointestinal tract,
as described in Chapter 418. The caudal part
of this bud, known as the pars cystica, grows in length and forms
the gallbladder, cystic duct and common bile duct. At about the
eighth week of gestation, the hepatic precursor cells that lie adjacent
to the hilar portal vein vessels form a sleeve-like double layer
of cells that extends toward the periphery along the smaller intrahepatic
portal vein branches. These hepatoblasts strongly expresses biliary
specific cytokeratins and can be considered biliary precursor cells,
that then form a continuous single-layered ring around the portal
mesenchyme, known as the ductal plate.1 Beginning
at 12 weeks of gestation and extending into the postnatal period,
the ductal plate undergoes progressive remodeling. As new ductules
form they are incorporated into the periportal mesenchyme that surrounds
the portal vein branches. Thus, during successive periods of fetal
life, ductal plate remodeling leads to the formation of the intrahepatic biliary
tree. The largest ducts are formed first, followed by segmental,
interlobular, and, finally, the smallest bile ductules. Arrest or derangement
in remodeling leads to the persistence of primitive bile duct configurations
termed ductal plate malformations. The occurrence of ductal plate
malformations at different generations of the developing biliary
tree gives rise to different clinicopathologic entities, such as
congenital hepatic fibrosis and Caroli syndrome.
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Congenital Gallbladder
Abnormalities
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A variety of structural abnormalities of the gallbladder have
been described. Congenital absence of the gallbladder occurs in
one of 7500 to 10,000 people. Failed development of the pars cystica
is the likely etiology. As an isolated abnormality this is often
of little clinical significance, although symptoms of abdominal
pain, nausea and fatty food intolerance may develop because calculi
form in the ductal system. In these patients gallbladder agenesis
is frequently misinterpreted as cholecystitis with cystic duct obstruction.2 In
addition to extrahepatic biliary atresia, which may accompany agenesis
of the gallbladder, other associations with an absent gallbladder
include imperforate anus, genitourinary anomalies, anencephaly,
bicuspid aortic valve, and cerebral aneurysms. Hypoplasia of the
gallbladder has also been described in association with neonatal
diabetes, hypoplastic pancreas, and intestinal atresia.3 There
is also an association with trisomy 18. The incidence of double
gallbladder is 0.1 to 0.75 per 1000. The two cystic ducts may converge
into a single duct, forming a Y-shaped structure. The accessory
gallbladder may lie under the left lobe of the liver, draining into
the left hepatic duct. A “floating gallbladder” is
an anatomic variant observed in up to 5% of individuals.
The gallbladder lacks a peritoneal coat or supporting membrane,
making the pendulous gallbladder susceptible to torsion. This presents
clinically as acute, severe right upper quadrant pain with nausea
and vomiting. Often symptoms follow rapid movements that generate
centrifugal forces causing gallbladder torsion and volvulus. Symptoms
are consistent with an acute cholecystitis requiring operative intervention.4...