The morphologic correlate of incidental punctate white matter hyperintensities on MR images.

Postmortem examinations were made of the brains of six patients, 52-63 years old, who exhibited incidental punctate white matter hyperintensities on MR images before death. Our aim was to unravel the morphologic correlate of such lesions. By repeating the MR study after fixation on four specimens, cutting the brain parallel to the MR imaging plane, and examining whole-hemisphere microscopic sections, we optimized lesion identification. The white matter signal abnormalities were better delineated on pre- than postmortem scans, and visual inspection of the brain slices was normal in all but one location. Histologically, we found areas of reduced myelination with atrophy of the neuropil around fibrohyalinotic arteries as well as different stages of perivenous damage. The latter ranged from spongiform transformation of the neuropil and scattered foci of demyelination to large perivenous areas with marked rarefaction of myelinated fibers. Edematous glial swelling in foci of ganglion cell heterotopia caused subcortical white matter hyperintensities in one case. Our results suggest minor perivascular damage but not infarction as the most likely substrate of punctate MR white matter hyperintensities in elderly brains. Histologic correlations with MR images obtained during life or with studies of unfixed material are necessary to analyze such small lesions.