Fig 4.

Histologic specimens confirming ALCL.

A, Immunostaining with L26, a monoclonal antibody B cell marker, reveals large, atypical intravascular tumor cells occluding the lumen of a small cerebral blood vessel. Note the large ratio of vessel diameter to wall thickness, indicative of neoplastic lymphocytes occluding and distending the vessel lumen. In contrast to a true vasculitic process, the vessel wall itself does not show inflammatory damage.

B, Hematoxylin and eosin staining shows gray (black arrow) and white (white arrows) matter infarctions resulting from blood flow compromised by intravascular lymphoma.