The authors report a 3-year 8-month-old girl presenting with episodic hyperammonemic encephalopathy probably due to a proximal urea cycle disorder. The magnetic resonance imaging (MRI) of the brain performed during the third episode revealed extensive and diffuse cerebral cortical signal changes with sparing of occipital cortex. It is believed that intracerebral accumulation of glutamine mainly in astrocytes is the major cause of the encephalopathy. This results in astrocyte swelling, brain edema, intracranial hypertension, and cerebral hypoperfusion.
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