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. Rosettes are so named for their resemblance to the rose windows found in gothic cathedrals (check out the beautiful rose window in the Cathedral of Notre-Dame in Strasbourg).

There are a bunch of different kinds of rosettes, each with different types of cells and different names. Most of them are found in tumors of the nervous system. It’s useful to be able to recognize these, because they help with the diagnoses of difficult tumors. Plus, somebody will definitely ask you about them on some pathology exam somewhere.

Let’s take a look at the four main kinds of rosettes. You’ll want to remember what each type of rosette looks like, what’s in the lumen (if anything), and which tumors it is found in.

Homer Wright rosette

This rosette, named for James Homer Wright, the first director of the Massachusetts General Hospital, is typically seen in neuroblastomas, medulloblastomas, and primitive neuroectodermal tumors (PNETs). 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

This rosette (named for pathologist Simon Flexner and ophthalmologist Hugo Wintersteiner) is characteristic of retinoblastomas. It consists of tumor cells surrounding a central lumen that contains cytoplasmic extensions from the tumor cells. If you look at the tumor cells under electron microscopy, they have features of primitive photoreceptor cells.

True Ependymal Rosette

This rosette (seen in – you guessed it – ependymoma) consists of tumor cells surrounding an empty lumen. It is thought that these structures represent attempts by the tumor cells to recreate little ventricles with ependymal lining. One thing to note: although these guys are characteristic of ependymoma, they’re not seen in every case. In fact, it’s fairly uncommon to find them at all (they’re only present in a small percentage of well-differentiated ependymoma).

Perivascular Pseudorosette

This rosette consists of tumor cells collected around a blood vessel. It’s called a pseudorosette because the central structure isn’t part of the tumor. In the past, the term pseudorosette meant any rosette that didn’t have a truly empty lumen…but it seems that designation is kind of outdated. These rosettes are common in ependymomas, but you also see them in medulloblastoma, PNET, central neurocytomas, and glioblastomas.