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

Area of Science:

• Neuroradiology
• Neuroimaging
• Magnetic Resonance Imaging (MRI)

Background:

• Low-signal-intensity (LSI) rim on susceptibility-weighted imaging (SWI) is a known finding in progressive multifocal leukoencephalopathy (PML).
• The specificity of this LSI rim finding for PML has not been extensively evaluated in other neurological conditions.

Purpose of the Study:

• To investigate the presence of LSI rim on SWI in patients with conditions other than PML.
• To determine if the LSI rim finding is specific to PML or if it can be observed in other pathologies.

Main Methods:

• Retrospective review of brain MRI scans from 5605 patients who underwent 3T SWI.
• Analysis of 370 patients with cortical and subcortical FLAIR hyperintense lesions, focusing on the presence of LSI rim on thin-slice SWI.
• Correlation of LSI rim with adjacent hyperintense cortical signal (HCS) on T1-weighted images and assessment of signal changes on serial SWI.

Main Results:

• A SWI LSI rim was identified in 25 out of 370 patients (6.8%), specifically in cases of infarct (n=22) and encephalitis (n=3).
• Adjacent HCS was observed in 17 patients (15 infarct, 2 encephalitis).
• Serial SWI in 17 patients showed that the LSI rim appeared later than 45 days after onset in 10 patients (8 infarct, 2 encephalitis).

Conclusions:

• The LSI rim finding on SWI is not specific to PML and can be observed in infarct and encephalitis.
• The presence of LSI rim appears to be associated with HCS.
• This finding broadens the differential diagnosis for LSI rim on SWI in neuroimaging.