Biliary Atresia Remnants Revisited: Myogenesis, Hepatic Duct-Like Structures, and Fate of Peribiliary Glands

Purpose and Context: Proximal levels of excised remnants from youngest infants may reveal early features of biliary atresia (BA). Method: A targeted IHC survey was applied to 34 most proximal 2 levels in 17 BA remnants excised at age 10–74 days including 7 = Key Results: Severity of inflammation and extent of active fibroplasia do not distinguish proximal remnants in younger (n = 7) and older (n = 10) infants. In 27/34 levels of 14/17 remnants, reactive stroma is focally SM-MHC-2 (+), marking smooth muscle myosin, termed reactive myogenesis (RM), that is absent in controls. RM facilitates identification of 3 novel hepatic duct remnants (HDR): an HD-like collagen collar lined by degenerating cholangiocytes (n = 5); erosion defects in loose reactive stroma (n = 14); solitary foci of hyperplastic squamoid epithelium (n = 4). Peribiliary glands are either hyperplastic or atretic and typically lack RM. Conclusion: Minimally inflammed end-stage lesions in BA remnants occur at youngest ages favoring prenatal onset. Three novel HDR are defined. RM, a useful surrogate for HDR, is a prevalent inappropriate stromal reaction in proximal remnants of uncertain biological significance. RM is the source of mature smooth muscle in BA remnants.