In general, the diagnosis of low-grade TCC is difficult, if not impossible, to make on urine cytology. This is because many of the features that are used to diagnose cancer are quite similar to the changes seen in reactive urothelium. Histologically, the architecture of the tumor helps make the distinction, but when dealing with a cytology specimen, the architecture (i.e., papillary or non-papillary) can generally not be assessed. Therefore, be very hesitant to render a diagnosis of "low-grade TCC" unless you see good papillary structures with cytologic atypia... preferably in voided urine!
Nuclei vary in size and shape, but often have indented or grooved appearance (image A).
Nucleoli are absent or small.
Cells are generally larger than normal transitional cells, with a higher N:C ratio.
Clusters have a truly "papillary" appearance (image B) with fibrovascular cores.
Findings are most significant on a voided urine
Remember, in order to make a diagnosis of low grade TCC based on the presence of papillary clusters, the specimen should be a voided urine, preferably without a recent history of instrumentation. Otherwise, the presence of papillary clusters may be deceptive.