A rare case of pseudohyponatremia in a type IA choledochal cyst due to biliary obstruction

Abstract

A Type IA choledochal cyst is a cystic or fusiform dilatation of the common bile duct affecting the extrahepatic biliary tree. Here, we present a case report of a 3-year-old girl with a prenatal asymptomatic choledochal cyst that in size, leading to intermittent clay-colored stools and aggravated jaundice. Magnetic resonance cholangiopancreatography revealed a large choledochal cyst of 184 cm3 obstructing the extrahepatic biliary tree and pancreatic duct. Clinical chemistry screening revealed asymptomatic hyponatremia of 124 mmol/l, analysed by an indirect ion selective electron (ISE)-based method. Furthermore, the patient had extreme hypercholesterolemia (1975 mg/dl), and an elevated lipoprotein X level (11.9 g/dl). Serum sodium was confirmed by using two additional independent methods: (i) centrifugal ultrafilter with indirect ISE and (ii) blood gas analyze, In contrast to indirect ISE, both methods indicated normal sodium levels, consistent with pseudohyponatremia. Following Roux-en-Y-Hepatojejunostomy, sequential serum sodium levels measured by indirect ISE gradually normalized, but remained within the normal range by direct ISE method. This case shows that biliary obstruction can lead to falsely elevated cholesterol and lipoprotein X analyses and that alternative methods are needed to avoid unnecessary treatments .