Progressive multifocal leukoencephalopathy: diffusion-weighted imaging and pathological correlations

Abstract

We examined MRI of two patients with progressive multifocal leukoencephalopathy (PML), including diffusion-weighted imaging (DWI), with calculation of apparent diffusion coefficients (ADC). The pathology findings of one patient were compared with those of MRI. The lesions had different ADC and DWI appearances, depending on the stage of the disease. Newer lesions and the advancing edge of large lesions had normal-to-low ADC and gave high signal on DWI. Older lesions and the centre of large lesions had increased ADC and gave low signal. High signal on DWI and low ADC mark the regions of active infection and cell swelling, distinguishing them from areas of reparative gliosis.

JC Virus Infection of the Brain

“…101 In new active lesions, there is a rim of diffusion restriction at the advancing edge and a central core of facilitated diffusion (Fig 1A, -B). 101,102 The rim is usually incomplete and signifies active infection.…”

“…101 In new active lesions, there is a rim of diffusion restriction at the advancing edge and a central core of facilitated diffusion (Fig 1A, -B). 101,102 The rim is usually incomplete and signifies active infection. 38 Histopathologically, this advancing edge correlates with large swollen oligodendrocytes, enlarged "bizarre astrocytes" with numerous large processes, and infiltration of foamy macrophages.…”

“…38 Histopathologically, this advancing edge correlates with large swollen oligodendrocytes, enlarged "bizarre astrocytes" with numerous large processes, and infiltration of foamy macrophages. 38,49,101 This cellular enlargement constricts the extracellular space, the space of maximum Brownian motion of water. Diffusion restriction at the margin can be either due to constricted extracellular space [103][104][105] or enlarged cells per se due to entrapment of water in motion-restricted intracellular space.…”

“…106 In old "burnt out" lesions after therapy or at the center of a large lesion, there is facilitated diffusion due to disorganized cellular architecture, increased extracellular space secondary to dead oligodendrocytes, macrophage action, and astrocytic reparative responses. 101,107 Diffusion tensor imaging also has an important role in the evaluation of PML. Fractional anisotropy, which reflects the organized architecture of the white matter, decreases in PML, suggesting disorganization of the white matter structure.…”

Use of Diffusion-Weighted Imaging to Evaluate the Initial Response of Progressive Multifocal Leukoencephalopathy to Highly Active Antiretroviral Therapy: Early Experience

“…2 Untreated, the disease has a rapid and fatal course, with an average life expectancy of 4 months. 3 The use of HAART in the treatment of PML has increased the 1-year survival rate by 10%-50%. 4 However, even when HAART successfully restores immune function, 50% of patients with PML die.…”