pseudorosettes

Pseudorosettes are a histopathologic pattern seen in some tumors, characterized by tumor cells arranged in a rosette-like fashion around a central structure, but without a true lumen. The term distinguishes these arrangements from true rosettes that contain a central lumen or neuropil.

The most common and characteristic form is the perivascular pseudorosette, in which tumor cells are radially oriented around a central blood vessel with an intervening zone of cytoplasmic processes. This pattern is especially associated with ependymomas and can aid in diagnosis, though it is not exclusive to them. Other, less defined pseudorosette patterns can involve tumor cells organizing around fibrous or neuropil-like centers, but the defining feature remains the absence of a true lumen and the central structural focus around which cells crowd.

In practice, pseudorosettes are used to support, but not confirm, a diagnosis of ependymoma. They are typically evaluated alongside architectural features and immunohistochemical findings, such as GFAP positivity in tumor cells and characteristic EMA staining patterns. It is important to distinguish pseudorosettes from true rosettes, such as Homer Wright rosettes (around neurofibrillary material) and Flexner-Wintersteiner rosettes (around a central lumen), which reflect different tumor lineages.

Overall, pseudorosettes describe a rosette-like cellular arrangement with a central structure but no true lumen, most notably seen in ependymal tumors, and they contribute to the histologic characterization used in neuropathology.