Susceptibility-Weighted MR Imaging Hypointense Rim in Progressive Multifocal Leukoencephalopathy: The End Point of Neuroinflammation and a Potential Outcome Predictor

Abstract

Background and purpose: Progressive multifocal leukoencephalopathy (PML) represents a life-threatening demyelinating disorder of the brain caused by reactivation of a rare opportunistic infection with JC Polyomavirus. The aims of this study were to describe the incidence of a susceptibility-weighted imaging hypointense rim in patients with multifocal leukoencephalopathy and to explore the histologic correlates and prognostic value of the rim with regard to the clinical outcome.

Materials and methods: This retrospective study included 18 patients with a definite diagnosis of progressive multifocal leukoencephalopathy. Ten patients were HIV-positive, 3 patients had natalizumab-associated progressive multifocal leukoencephalopathy, 1 patient had multiple myeloma, 3 patients had a history of lymphoma, and 1 was diagnosed with acute myeloid leukemia. Patients were divided into short- (up to 12 months) and long-term (>12 months) survivors. A total of 93 initial and follow-up MR imaging examinations were reviewed. On SWI, the presence and development of a hypointense rim at the periphery of the progressive multifocal leukoencephalopathy lesions were noted. A postmortem histologic examination was performed in 2 patients: A rim formed in one, and in one, there was no rim.

Results: A total of 73 progressive multifocal leukoencephalopathy lesions were observed. In 13 (72.2%) patients, a well-defined thin, linear, hypointense rim at the periphery of the lesion toward the cortical side was present, while in 5 (27.8%) patients, it was completely absent. All 11 long-term survivors and 2 short-term survivors presented with a prominent SWI-hypointense rim, while 5/7 short-term survivors did not have this rim.

Conclusions: The thin, uniformly linear, gyriform SWI-hypointense rim in the paralesional U-fibers in patients with definite progressive multifocal leukoencephalopathy might represent an end-point stage of the neuroinflammatory process in long-term survivors.

Fig 1.

Kaplan-Meier survival analysis, with differences in survival and outcome between patients with (in purple) and without (in orange) an SWI-hypointense rim.

Fig 2.

On axial FLAIR images (A–C), multifocal PML lesions are observed in both frontal lobes, the capsula interna and externa, and the right parietal lobe. A linear, relatively thin hypointense rim is observed on the cortical side of the lesions on axial SWI (D–F) in a long-term survivor (9 years, still alive).

Fig 3.

A typical T2-weighted (A) and FLAIR (B) hyperintense PML lesion is observed in the frontoparietal corona radiata on the right side. On the postcontrast T1-weighted axial image (C), only a faint enhancement pattern is observed. On the axial SWI (D), there are no signs of a gyriform hypointense rim. The patient was classified as a short-term survivor (11 weeks).

Fig 4.

On an axial FLAIR image (A), bilateral high-signal-intensity lesions are detected. DWI clearly demonstrates a high-signal-intensity rim at the periphery of the lesion in the right frontal lobe on trace DWI (B), with low ADC values (C) indicating restricted diffusion. On SWI (D), no abnormalities are seen. On follow-up MR imaging (3 months later), atrophic changes with dilation of the ventricles are observed in both hemispheres (more prominent in the right) (E). On DWI/ADC (F and G), no hyperintense rim is present. On SWI (H), a dark rim is clearly visible.