A "pseudorosette" is a histological term used to describe a pattern of cellular arrangement often observed in certain types of tumors, particularly in neuroepithelial tumors such as ependymomas and medulloblastomas.

In a pseudorosette, tumor cells are arranged around a central structure, but unlike true rosettes where cells surround a lumen or empty space, in pseudorosettes, the central structure is typically a blood vessel, neuropil, or fibrillary material.

These formations can be seen under a microscope during the examination of tissue samples obtained from biopsies or surgical resections. Pseudorosettes can vary in appearance depending on the tumor type and other factors, and their presence can aid in the diagnosis and classification of certain types of tumors.