Retinal hemangioblastoma in von Hippel–Lindau syndrome. A, Low-magnification 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 magnification (PAS stain) shows the numerous small, capillary-like vascular channels (arrows). The vacuolated, foamy stromal cells (arrowheads) are tumor cells that express the VHL gene mutation.