Flexner-Wintersteiner rosette is a spoke and wheel shaped cell formation seen in retinoblastoma and certain other ophthalmic tumors.[1] A rosette is a structure or formation resembling a rose, such as the clusters of polymorphonuclear leukocytes around a globule of lipid nuclear material, as observed in the test for disseminated lupus erythematosus.[1]
Flexner-Wintersteiner rosettes were first described by Simon Flexner (1863–1946), a physician, scientist, administrator, and professor of experimental pathology at the University of Pennsylvania (1899–1903). Flexner noted characteristic clusters of cells in an infantile eye tumor which he called retinoepithelioma.[2][3][4] A few years later, in 1897, Austrian ophthalmologist Hugo Wintersteiner (1865–1946) confirmed Flexner’s observations and noted that the cell clusters resembled rods and cones.[5] These characteristic rosette formations were subsequently recognized as important features of retinoblastomas.
The tumor cells that form the Flexner-Wintersteiner rosette surround a central lumen containing small cytoplasmic extensions of the encircling cells. Unlike the center of the Homer Wright rosette, the central lumen is devoid of fiber-rich neuropil. Like the Homer Wright rosette, the Flexner-Wintersteiner rosette represents a specific form of tumor differentiation.[6][7][8][9] Electron microscopy reveals that the tumor cells forming the Flexner-Wintersteiner rosette have ultrastructural features of primitive photoreceptor cells.[10] Furthermore, the rosette lumen shows similar staining patterns as in rods and cones,[11] suggesting that Flexner-Wintersteiner rosettes represent a specific form of retinal differentiation. In addition to being a characteristic finding in retinoblastomas, Flexner-Wintersteiner rosettes may also be found in pinealoblastomas and medulloepitheliomas.[6]