FIG 4. Photomicrographs of PNETs.

A, Hematoxylin and eosin stain shows a hypercellular neoplasm. Poorly differentiated, primitive small cells growing in compact sheets, forming a characteristic Homer-Wright rosette (R), can be seen. Tumor cells have round to oval hyperchromatic nuclei with scant cytoplasm. Mitotic figures are also identified (arrow). The increased cellularity explains iso- or hypointensity of many of the lesions on T2-weighted images (original magnification, x200).

B, Hematoxylin and eosin stain shows increased vascular channels (arrows) in PNET (original magnification, x50).

C, Hematoxylin and eosin stain at higher power shows endothelial hyperplasia (arrows) (original magnification, x400).

D, Azocarmine stain highlights the vascular channels and shows proliferation and thickening of the vascular endothelium within the PNET (original magnification, x100).