Incidental acute infarcts identified on diffusion-weighted images: a university hospital-based study

Abstract

Background and purpose: Pathogenesis of leukoaraiosis is incompletely understood and accumulation of small infarctions may be one of the possible sources of such white matter lesions. Thus, the purpose of this study was to identify the rate of incident infarction as depicted on diffusion-weighted images (DWIs) obtained from a general patient population.

Materials and methods: During the 4-year study period, a total of 60 patients (36 men and 24 women) had an incidental DWI-defined infarction without overt clinical symptoms suggestive of a stroke or a transient ischemic attack. All of the MR images were obtained by using a similar protocol on 2 identical 1.5T whole-body scanners. The patient's vascular risk factors, as well as the presence of white matter lesions (WMLs) on MR imaging and atheromatous changes on MR angiography, were assessed retrospectively. The incidental DWI-defined infarcts were also characterized in terms of their lateralization, lobe, and specific location.

Results: A total of 16,206 consecutive brain MR images were done during the study period; the overall incidence of incidental infarcts was 0.37%. Most of these patients with an incidental infarct had vascular risk factors and WMLs on MR images. Most of these patients (80%) had a single lesion on DWI. A total of 88 lesions were identified; most were located in the white matter of the supratentorial brain, primarily in the frontoparietal lobes. There were also lesions involving the brain stem (n = 2). The lesions involving cerebrum were more commonly located in the right side (right to left = 52:34).

Conclusion: Small, DWI-defined acute brain infarctions can be found incidentally in an asymptomatic population; this finding may account, at least in part, for the pathogenesis of WMLs identified on MR imaging.

Fig 1.

A 75-year-old woman, who was being regularly seen by her neurologist for a gradual decline in cognitive function over a few years, was referred to the department of radiology for MR examination to rule out temporal lobe atrophy, which could indicate Alzheimer disease. On FLAIR, multiple WMLs are seen, and on DWIs, there is a single focus of hyperintensity among these multiple WMLs at the left centrum semiovale (black arrows). The lesion also has a reduced ADC (white arrows), which suggests that this is a relatively acute lesion. The presence of minimal temporal lobe atrophy (not shown) does not support a diagnosis of Alzheimer disease.