Diffusion and perfusion characteristics of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) in thirteen patients

Abstract

Objective: We analyzed the diffusion and perfusion characteristics of acute MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) lesions in a large series to investigate the controversial changes of the apparent diffusion coefficient (ADC) that were reported in prior studies.

Materials and methods: We analyzed 44 newly appearing lesions during 28 stroke-like episodes in 13 patients with MELAS. We performed a visual assessment of the MR images including the ADC and perfusion maps, comparison of the ADC between the normal and abnormal areas, comparison of % ADC between the 44 MELAS lesions and the 30 acute ischemic infarcts. In addition, the patterns of evolution on follow-up MR images were analyzed.

Results: Decreased, increased, and normal ADCs were noted in 16 (36%), 16 (36%), and 12 (27%) lesions, respectively. The mean % ADC was 102 ± 40.9% in the MELAS and 64 ± 17.8% in the acute vascular infarcts (p < 0.001), while perfusion imaging demonstrated hyper-perfusion in six acute MELAS lesions. On follow-up images, resolution, progression, and tissue loss were noted in 10, 4, and 17 lesions, respectively.

Conclusion: The cytotoxic edema gradually evolves following an acute stroke-like episode in patients with MELAS, and this may overlap with hyper-perfusion and vasogenic edema. The edematous swelling may be reversible or it may evolve to encephalomalacia, suggesting irreversible damage.

Keywords: Diffusion weighted imaging; Mitochondrial encephalopathy; Perfusion MR imaging; Stroke.

Fig. 1

11-year-old girl with gradually progressive stroke lesions. A. T2-weighted image obtained three days after first attack shows mild swelling (arrows) of right temporooccipital lobe. B. Follow-up T2-weighted image obtained 11 days after first symptom onset and one day after mental change revealed progression of edema in right temporooccipital lobe and newly appearing thalamic lesion (arrowhead). C. Affected areas are seen as having high signal intensity (arrowhead) on diffusion-weighted MR imaging. D. Apparent diffusion coefficient decline is prominent at white matter, whereas swollen cortex and right thalamic lesion (arrowhead) show relatively increased or iso-signal intensity on apparent diffusion coefficient map. E. T1-weighted image shows high signal rim (arrows) along cortex of swollen right temporooccipital lobe, suggesting cortical laminar necrosis.

Fig. 2

Serial MR images in 50-year-old woman with four stroke-like episodes. A, B. T2-weighted image (A) and cerebral blood flow map (B) obtained on same day as first attack show subtle hyperintensity (arrows in A) and hyperperfusion (arrows in B) in both temporal lobes. C. Five days later, swelling worsened in both temporooccipital lobes as noted on T2-weighted image. D. Diffusion-weighted MR imaging shows cortical bright signal intensity that corresponds to iso or slightly dark cortical area on apparent diffusion coefficient map (E), while white matter of affected areas shows increase in apparent diffusion coefficient. F. Follow-up fluid attenuated inversion recovery image obtained 20 months later shows localized atrophy of both temporooccipital lobes associated with residual high signal intensity.

Fig. 3

57-year-old man with two stroke-like episodes. A. Fluid attenuated inversion recovery image obtained 18 days after first symptom onset shows infract-like lesion at left temporal lobe (arrow). B. T2-weighted image obtained on day of second attack and 17 months after prior episode shows high signal intensity in left temporooccipital lobe, including prior lesion. C. Apparent diffusion coefficient map shows diffusion restriction in posterior region of lesion (arrow), while anterior old lesion shows increased apparent diffusion coefficient (arrowhead). D. Perfusion curves (relaxivity on vertical axis and time on horizontal axis) show increased blood volume (which is proportional to signal loss) in left occipital lesion (green curve) compared to that of contralateral normal tissue (purple curve). E. Cerebral blood flow map demonstrates hyper-perfusion at newly appearing left occipital lesion (arrow), while anterior chronic lesion shows decreased perfusion (arrowheads).

Fig. 4

Scatter plots of the % apparent diffusion coefficient (vertical axis) according to elapsed time (days) after symptom onset (horizontal axis) in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode lesions (A) and lesions of ischemic infarcts (B).