Pathologic findings of silent hyperintense white matter lesions on MRI

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Abstract

The pathologic features of silent hyperintense white matter lesions in T2-weighted images on MRI were studied in patients with no neurologic signs or symptoms. The small patchy hyperintense white matter lesions represented myelin pallor associated with vessels showing hypertension and arteriosclerotic changes. ‘Caps’ also showed myelin pallor with dilated perivascular spaces. There were no lacunar infarcts in these lesions. Some of ‘caps’ was shown to be elongated normal lateral ventricle. ‘Rims’ of early stage revealed subependymal gliosis that was a part of normal aging processes.

Introduction

We have reported the histopathologic findings of silent hyperintense foci in the basal ganglia and thalamus noted on MRI [1]. Similarly, silent hyperintense white matter lesions are frequently noted on T2-weighted images (T2WI) and proton density weighted images (PDWI) of MRI in apparently normal individuals. These lesions are usually small patchy and multiple, and sometimes diffuse in the white matter [2]. Although patients with these hyperintense lesions are clinically diagnosed as having silent cerebral infarction, their pathologic features remain unclear. Kirkpatrick and Hayman studied the pathologic features of white matter lesions at autopsy and reported that small white matter lesions often revealed perivascular demyelination [3]. However, we consider that the lesions possibly reflect various pathologic conditions, such as lacunar infarcts, dilated perivascular spaces and myelin pallor. Since most previous studies used postmortem MRI, very little information is available on the pathology of the lesions noted on MRI performed during life. The purpose of the present study was to elucidate the pathologic features of silent hyperintense white matter lesions with the employment of in vivo MRI.

Section snippets

Patients

We studied silent hyperintense white matter lesions on T2WI of MRI from six patients who ranged from 59 to 84 years old (mean, 71). The patients presented with malignant neoplasm of the lung (two patients), stomach (one patient), urinary bladder (one patient), cervix (one patient) and SIADH (one patient). MRI was carried out to rule out brain metastases or a pituitary lesion. As to the relevant risk factors, three patients had hypertension and two patients each had hypercholesterolemia and

Small patchy hyperintense lesions (Fig. 1)

On T2WI of MRI, six patients showed small patchy hyperintense white matter lesions. In all of these cases, no gross abnormalities were apparent at the time of brain cutting. However, all cases showed myelin pallor with indistinct margins with Luxol fast blue staining. Furthermore, on microscopic examination, we detected a decreased number of myelinated fibers and an increased number of reactive glial cells. Small vessels in these lesions often revealed marked thickening of the wall, with

Discussion

Silent hyperintense white matter lesions are frequently noted on T2WI. Except in a few cases [6], [7], [8], most studies that correlated the images and pathologic features were performed using postmortem MRI. However, we consider that postmortem MRI findings are affected by formalin fixation, brain shrinkage and parenchymal changes following death. Fazekas et al. [7] reported that postmortem MRI has less ability to identify small hyperintense white matter lesions compared with in vivo MRI. Our

Acknowledgements

This study was supported in part by a grant-in-aid for Cardiovascular Disease and Comprehensive Research on Aging and Health from the Ministry of Health and Welfare of Japan.

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