Low-signal-intensity rim on susceptibility-weighted imaging is not a specific finding to progressive multifocal leukoencephalopathy

• We previously reported two PML cases showing low-signal-intensity rim along deep layers of the cerebral cortex on SWI.
• This finding could be seen in infarct and encephalitis, indicating it is not a specific finding to PML.
• Low-signal-intensity rim appeared to be associated with hyperintense cortical signal on T1-weighted images.

BackgroundLow-signal-intensity (LSI) rim along deep layers of the cerebral cortex is reportedly a susceptibility-weighted imaging (SWI) finding in progressive multifocal leukoencephalopathy (PML). We aimed to evaluate whether this finding can be identified in diseases other than PML.MethodsWe retrospectively reviewed brain MR images from 5605 patients who underwent SWI at 3T; 370 patients with various diseases, who showed cortical and subcortical FLAIR high-signal lesions including U-fiber, were enrolled. The presence or absence of LSI rim on thin-slice SWI and hyperintense cortical signal (HCS) on T1-weighted images adjacent to LSI rim was analyzed. Signal changes of the LSI rim were assessed on serial SWI, if available.ResultsTwenty-five of the 370 patients (6.8%) showed SWI LSI rim, in infarct (n = 22) and encephalitis (n = 3). HCS was apparent adjacent to SWI LSI rim in 17 patients (15 infarct, 2 encephalitis). Serial SWI was available for 17 patients, of whom 10 patients (8 infarct, 2 encephalitis) presented LSI rim later than 45 days after onset.ConclusionLSI rim can be observed in infarct and encephalitis. Therefore, this finding is not specific to PML. LSI rim appears to be associated with HCS.