Rossets are not seen in: a) Retinoblastoma b) Medulloblastoma c) PNET d) Neuro-cysticercosis Answer: Neuro-cysticercosis Explanation: Rosettes are little round groupings of cells found in tumors. They usually consist of cells in a spoke-wheel or halo arrangement surrounding a central, acellular region. Homer Wright rosette: 1. This rosette is typically seen in neuroblastoma, Medulloblastoma, and primitive neuroectodermal tumors (PNETs). 2. It consists of a halo of tumor cells surrounding a central region containing neuropil (hence its association with tumors of neuronal origin). Flexner-Wintersteiner Rosette: 1. This rosette is characteristic of retinoblastomas. It consists of tumor cells surrounding a central lumen that contains cytoplasmic extensions from the tumor cells. True Ependymal Rosette: 1. This rosette is seen in ependymoma and consists of tumor cells surrounding an empty lumen. Peri-vascular Pseudo-rosette: 1. This rosette consists of tumor cells collected around a blood vessel. It’s called a pseudo- rosette because the central structure isn’t part of the tumor. 2. These rosettes are common in ependymomas, but also see in medulloblastoma, PNET, central neurocytomas, and glioblastomas.