Cytology is most useful for detecting flat CIS, which may be difficult to identify grossly.
Neoplastic cells usually exfoliate in large numbers and are poorly cohesive (shed singly or in small clusters).
High N:C ratio.
Nuclei are large, hyperchromatic, pleomorphic, with prominent red nucleoli (image A).
Chromatin is coarsely clumped.
Distinction between CIS and invasive TCC is tricky, but as a rule of thumb, the presence of necrotic debris (cell parts and lots of neutrophils) favors invasion (image B); CIS typically has a much cleaner background.