Introduction Encephalopathy secondary to hyperammonemia due to Congenital Extra-hepatic Porto-systemic shunt (CEPS) in the absence of liver cirrhosis is an exceptionally unusual condition. We describe the case of a 54-year-old woman admitted to the Emergency Department complaining of recurrent episodes of confusion and worsening cognitive impairment. At admission, the patient displayed slowing cognitive-motor skills with marked static ataxia and impaired gait. Hyperammonemia was detected in the serum. An abdominal computed tomography (CT) excluded portal hypertension and liver cirrhosis, detecting a congenital extra-hepatic porto-systemic shunt which is a highly unusual vascular malformation. The patient was treated by interventional radiologists with a successful endovascular closure. Areas Covered We have performed a review of the last three decades of the literature, starting from the introduction of CT scanning in common clinical practice. Eighteen studies (case reports) described 29 patients with encephalopathy secondary to hyperammonemia due to CEPS in the absence of liver cirrhosis: They underwent treatment similar to our case report of CEPS. Expert Commentary Encephalopathy secondary to hyperammonemia in the absence of hepatic dysfunction is an important diagnostic dilemma to many clinicians. An interventional radiologic approach is currently preferred.