A 49-year-old woman with a known m.3243A>G tRNALeu(UUR) mutation (ie, the most frequent mutation in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS)) diagnosed in the presence of migraine, diabetes mellitus, neurosensory hearing loss, short stature, cognitive deficit, ataxia and elevated lactate levels, presented with subacute aphasia and right hemiplegia. Brain MRI showed a typical stroke-like lesion in the left temporal and parietal lobe and prerolandic cortex. At this time, gradient-echo T2-weighted imaging showed hyperintensities in the involved regions (also visible on T2-weighted and FLAIR imaging, probably due to the T2 effect), in absence of cortical hypointensities. EEG showed no epileptic activity. Clinical spontaneous resolution was seen during the following 10 days. Seven months later, MRI showed brain atrophy in the earlier involved brain areas, together with cortical hypointensities in these regions on both gradient-echo T2-weighted and susceptibility-weighted imaging (SWI) in the absence of signal abnormalities on T1-weighted and diffusion-weighted imaging (figure 1).

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Figure 1

Brain 3-Tesla MRI showing cortical hypointensities in the left-sided rolandic and the postrolandic cortex on axial gradient-echo T2-weighted imaging (A and B), axial (C and D), coronal (E) and sagittal (F) SWI imaging.

SWI is especially interesting (and probably superior to gradient-echo T2-weighted imaging) for showing mineral deposition (eg, iron, calcium), vascular structures, haemorrhage and blood degradation products, all seen as hypointensities. In MELAS, basal ganglia calcifications are often seen on brain imaging, and both calcium and iron deposition in the basal ganglia have been demonstrated earlier on autopsy.1

Cortical haemorrhage has been suspected in an earlier report in a MELAS patient showing gyral hyperintensities on T1-weighted imaging (typically seen in cortical laminar necrosis due to lipid-laden macrophages) without signal suppression on fat-suppressed imaging.2 In another patient in the same report, small foci of microhaemorrhages were seen on neuropathological examination in the occipital cortex (although radiologically not involved during the stroke-like episode).2

The exact pathophysiology of stroke-like episodes is unclear. Different proposed hypotheses include an ischaemic vascular mechanism, a generalised cytopathic mechanism (caused by an oxidative phosphorylation defect in neurons and/or glia cells), and a neuronal hyperexcitability (possibly epileptic) mechanism.3 In our case, a process of haemorrhage and/or mineral deposition (iron, calcium) secondary to the initial process provoking the stroke-like event could be evoked to explain the SWI abnormalities. The absence of cortical T1-weighted hyperintensity is more in favour of an iron and/or calcium deposition than a haemorrhagic process.