Retinal hemangioblastoma in Von Hippel-Lindau syndrome. A, Low-power photomicrograph (PAS stain) showing a retinal tumor with a thick-walled feeder vessel (arrow) and a cystic area filled with proteinaceous material (asterisk). Note the prominent vascularity and areas of denser cellularity. B, Higher power magnification (PAS stain), note the numerous small capillarylike vascular channels (arrows). The vacuolated, foamy stromal cells (arrowheads) are tumor cells which express the VHL gene mutation.