Congenital Porto-Azygous Shunt (Abernethy Malformation Type II) in an Elderly Patient: A Too-Often-Forgotten Occult Abnormality

Congenital extrahepatic portosystemic shunts (CEPS) cause portal blood to circumvent the liver and its metabolism, allowing normally detoxified ammonia to accumulate in the systemic circulation. Hyperammonemia in the elderly often manifests clinically as toxic encephalopathy. We present a case of recurrent altered mental status in a 70-year-old patient that eluded diagnosis over several years. Hyperammonemia was the sole abnormality detected upon a thorough liver function evaluation prompted by the patient's history of remote liver disease. Enhanced computed tomography revealed an extrahepatic porto-azygous shunt arising from a hypoplastic portal vein. This case illustrates that, albeit rare, CEPS may express themselves for the first time in the elderly, a patient population that is frequently afflicted by many more common causes of altered mental status. CEPS should be considered in the differential diagnosis of inexplicable hyperammonemia in this age group.