Gallbladder agenesis describes the congenital absence of the gallbladder. In the absence of congenital malformations of the intrahepatic biliary structures, this is an inconsequential abnormality.
Biliary atresia describes the congenital maldevelopment of intrahepatic biliary structures and is uncommonly encountered. Affected individuals are jaundiced and unthrifty at a young age. Prognosis is poor.
A bilobed gallbladder is occasionally identified in cats during ultrasonography or at surgery as an inconsequential abnormality.
Cystic mucosal hyperplasia of the gallbladder is also known as cystic mucinous hypertrophy, cystic mucinous hyperplasia, and mucinous cholecystitis (although it is not an inflammatory lesion). The role of steroid hormones in lesion induction remains unclear but is suspected. There is no associated inflammation, and the serosal surface of the gallbladder remains intact. These hyperplastic lesions are routinely identified in dogs with gallbladder mucocele, in which "cystic" structures are filled with tenacious viscoelastic mucin.
Gallbladder dysmotility is proposed as an emerging syndrome in dogs and may precede GBM development. The syndrome may be linked to steroid hormones, based on early observations of an apparent link between mucocele development and treatment with progestational compounds. Sex hormones (progestins, androgens) have been shown experimentally (in vitro) to reduce contractility of gallbladder smooth muscle in experimental animal models.