HUMAN RETINOBLASTOMA - A MORPHOLOGICAL-STUDY OF APOPTOTIC, LEUKOCYTIC, AND VASCULAR ELEMENTS

Retinoblastoma (Rb), derived from retinal neuroepithelial progenitor c ells, is the most common intraocular malignancy of childhood. This stu dy examined 10 human Rb biopsy specimens with light and electron micro scopy for histopathological features not previously described in detai l, including cell death, leukocytic infiltration, and the tumor vascul ature. Rb is a solid well-vascularized tumor with regions of viable tu mor cells surrounding vessels, interspersed with zones of necrosis; ap optotic cells were seen in all specimens. Mononuclear phagocyte series (MPS) cells and lymphocytes often colocalized, adjacent to tumor vess els, and MPS cells frequently invested the perivascular space. Lymphoc ytes were rarely seen within areas of viable tumor. Tumor vessels at e arly stages of formation resembled normal developing retinal vessels. While junctions were often seen between endothelial cells, disruption of these junctions and endothelial fenestrae was sometimes evident. Mu ller cells and astrocytes extended processes around tumor cells and bl ood vessels, and contributed to the formation of the vascular glia lim itans, which in some mature vessels was disrupted and discontinuous. O verall, this study provides further morphological details of cell deat h within Rb, particularly apoptotic involution, and describes the pres ence of a vascular-associated leukocytic infiltration in Rb. Evidence of compromise of the normal blood-retinal barrier (BRB) within the Rb tumor vessels is presented.