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A term female neonate (birth weight 3.5 kg) with an antenatally suspected ovarian cyst presented with jaundice, pale stools, and hepatomegaly. Postnatal ultrasound revealed a 6.4 cm cystic lesion in the porta hepatis region, ruling out the prenatal diagnosis. A tubular anechoic structure adjacent to the cyst could not be clearly identified as either a collapsed gallbladder or dilated biliary duct. Laboratory investigations showed conjugated hyperbilirubinaemia with elevated AST, ALT, and total bilirubin levels , features that may support cystic biliary atresia over choledochal cyst in the appropriate clinical context. 3 MRCP demonstrated a well-circumscribed cystic lesion at the porta hepatis with prominent intrahepatic ducts. Neither an extrahepatic duct nor a normal gallbladder structure was identified, which is unusual for a choledochal cyst and should raise suspicion for biliary atresia.1 2 4 5 8 However, based on probability (choledochal cyst being more common), a presumptive diagnosis of choledochal cyst was made. A preoperative HIDA scan and liver biopsy were not performed, as imaging was deemed diagnostic. The infant underwent exploratory laparotomy at 44 days of age for planned cyst excision. An intraoperative cholangiogram revealed the cyst was associated with an obliterated extrahepatic biliary tree, confirming cystic biliary atresia.1 2 Kasai portoenterostomy was performed with excision of the fibrotic cyst and anastomosis of a Roux limb to the liver hilum. Postoperatively, the infant recovered well with gradual resolution of jaundice and normalisation of stool colour. Growth improved dramatically from the 9th centile pre-surgery to above the 75th centile by 26 weeks of age. Follow-up at 3 months showed stable liver function with no signs of cholangitis. This case highlights that cystic biliary atresia can mimic a choledochal cyst on ultrasound and MRCP, even with cyst sizes exceeding 2.5 cm.1–3 5 8 The absence of a visible gallbladder on MRCP should raise suspicion for biliary atresia.1 4 5 Retrospectively, HIDA scintigraphy and liver biopsy could have clarified the diagnosis preoperatively.6 7 Key learning points include that cystic biliary atresia can mimics choledochal cyst on ultrasound and MRCP1 2 5 8; elevated transaminases and bilirubin with pale stools warrant urgent evaluation for biliary atresia regardless of cystic features3 4; intraoperative adaptability is essential in paediatric hepatobiliary surgery2; and additional diagnostics, including HIDA scan and liver biopsy, should be considered in ambiguous cases despite apparent diagnostic imaging.6 7References Schooler GR, Mavis A. Cystic biliary atresia: a distinct clinical entity that may mimic choledochal cyst. Radiol Case Rep. 2018;13(2):415–418.Chen YT, He X, Wang H, et al. Differentiation of cystic biliary atresia and choledochal cysts using prenatal ultrasonography. Ultrasonography. 2021;40(4):566–574.Chen YT, Gao MJ, et al. Comparative analysis of cystic biliary atresia and choledochal cysts: clinical features and outcomes. Front Pediatr. 2022;10:947876.Kasahara M, Kudo M, Nishida M, et al. Choledochal cyst with or without biliary atresia in neonates and young infants: US differentiation. Radiology. 1998;209(2):465-469.Zhou L, Shan Q, Tian W, et al. Ultrasound-based differential diagnosis between cystic biliary atresia and choledochal cysts associated with different outcomes: five case reports. Medicine (Baltimore). 2019;98(8):e14641.Tanaka H, Sasaki H, Wada M, et al. Histological differentiation between prenatally diagnosed choledochal cyst and type I cystic biliary atresia using liver biopsy specimens. Eur J Pediatr Surg. 2007;17(1):19–23.Berrocal T, Luque R, Gámez M, et al. Scintigraphic features of choledochal cyst. J Nucl Med. 1989;30(5):622–628.Caponcelli E, Knisely AS, Davenport M. Cystic biliary atresia: an etiologic and prognostic subgroup. J Pediatr Surg. 2008;43(9):1619–1624. doi:10.1016/j.jpedsurg.2007.12.058.