General description

The most common causes of hyperammonemia include acute liver failure and portosystemic shunting. Other contributing factors include infections with urease-producing bacteria, gastrointestinal bleeding leading to protein overload and catabolism, urea cycle enzyme deficiencies, organic acidemias, carnitine deficiency, tumors, and certain medications such as valproate, carbamazepine, and high-dose 5-fluorouracil (5-FU).

Symptoms of hyperammonemia can vary but often include vomiting, irritability, seizures, altered consciousness, and encephalopathy, which can progress to coma. In infants, additional signs may include poor feeding and rapid breathing, while in older individuals, behavioral abnormalities, developmental delays, and hallucinations may also occur.

Radiographic features

MRI shows bilateral symmetric T2WI/FLAIR and DWI hyperintensity in the cingulate gyrus and insula. The thalamus and internal capsule may also be affected.