Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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August 15, 2019
Acute Hyperammonemic Encephalopathy
- Background
- Hyperammonemia is a neurotoxic, metabolic condition. Acute hepatic dysfunction is the most common etiology in adults.
- Other causes include: inborn errors of metabolism, drugs, infections, multiple myeloma, and post-lung or bone marrow transplantation.
- Clinical Presentation
- Non-specific and ranges from mild alteration in mental status to seizures, coma and death.
- Key Imaging Features
- Bilateral symmetrical cortical T2 prolongation and diffusion restriction. Insular and cingulate involvement is characteristic. Perirolandic and occipital cortices are commonly spared.
- Other areas of involvement include: periventricular white matter, thalami, dorsal brainstem, and posterior limbs of internal capsules.
- Imaging findings can be reversible with early diagnosis and aggressive treatment.
- Differential Diagnosis
- Hypoxic-ischemic encephalopathy: Involvement of perirolandic and occipital cortices and deep grey matter structures is more characteristic.
- Herpes encephalitis: Cingulate and insular cortices involvement is unilateral or bilateral but asymmetrical. Extension to medial temporal and inferior frontal lobes as well as leptomeningeal and cortical enhancement are common.
- Creutzfeldt-Jakob disease: Common pattern is deep grey matter involvement, in addition to diffuse cortical involvement with predilection for insular, cingulate and superior frontal cortices, as well as cortical areas near the midline. Pulvinar sign is characteristic.
- Hypoglycaemic encephalopathy: Bilateral cortical involvement of insulae, parieto-occipital lobes and hippocampi. Basal ganglia and posterior limbs of internal capsules are typically involved.
- Possible involvement of the callosal splenium.
- Treatment
- Lactulose with rifaximin or neomycin to lower ammonia levels. Hemodialysis in severe cases.