FIG 4. Patient 5.

A and B, Axial T2-weighted (3400/119/1) (A) and contrast-enhanced T1-weighted (600/14/2) (B) MR images show a nonenhancing left parietal focus of PML.

C, Accompanying contrast-enhanced CT scan shows a nonenhancing hypodensity in the white matter of the left parietal lobe.

D and E, Anteroposterior (D) and lateral (E) arterial phase DSA images from the left ICA stereo angiogram fail to show any abnormal parenchymal blush or evidence of arteriovenous shunting.

F, A vascular channel (v) devoid of perivascular inflammation is outlined by azocarmine, illustrating the ordinary histologic appearance in this patient with an angiographically occult lesion (azocarmine stain, original magnification x100).