Specific Imaging Findings

The typical finding is that of cerebral infarct-like lesions, both territorial and crossing territories. The posterior temporal lobes and the parietal and occipital lobes are most frequently involved. Involvement of the cortex and deep gray matter nuclei with a swollen appearance is typical. Diffusion MR imaging may show increased or reduced ADC values. Hemorrhage does not occur and MRA shows the large and medium-size arteries to be normal. MR spectroscopy shows low n-acetyl aspartate and lactate in the regions of infarctions and even more typically in those areas of the brain which are normal on MRI. Selective involvement of the cortex with laminar necrosis is frequently present. Some of the cortical lesions may almost completely resolve after the acute phase. Severe cortical atrophy is found in the chronic stage.

Pertinent Clinical Information

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is an uncommon disorder but needs to be considered in the differential diagnosis of children with cerebral infarctions, particularly those with more than one. The overall incidence of mitochondriopathies is about 1 in 20 000 persons. Most patients are diagnosed before reaching 15 years of age and MELAS is more common in males. Acute symptoms include stroke-like episodes, headaches, seizures, hearing loss and visual deficits. Chronic symptoms are generalized weakness, cognitive impairment and, lastly, dementia.