Subclinical portal-systemic encephalopathy in a child with congenital absence of the portal vein.

A 6-year-old girl with congenital absence of the portal vein (CAPV) who had persistent hyperammonemia due to a congenital portosystemic shunt is reported. The patient only exhibited mild intention tremor, without any apparent neurological manifestations of portal-systemic encephalopathy. However, magnetic resonance imaging of the head showed white matter atrophy with ventricular dilatation, which is thought to represent subclinical brain damage caused by chronic hyperammonemia. This is the first report of subclinical portal-systemic encephalopathy in a patient with CAPV. The present case suggests that the effect of a congenital portosystemic shunt on the central nervous system is serious, but can be clinically latent in children with CAPV.