Metastatic urothelial carcinoma with signet ring features: cytomorphologic findings in abdominal paracentesis.

Signet ring cells, characterized by large clear cytoplasmic vacuoles eccentrically displacing and indenting the nuclei, seen in cytopathology effusion specimens are most commonly due to metastatic adenocarcinoma of gastric, esophageal, and breast origin. Urothelial carcinoma can display a wide range of differentiation and is an extremely rare cause of metastatic signet ring cells. Here, we report the case of a 75-year-old male with high-grade urothelial carcinoma with signet ring features, who was status-post chemoradiation and radical cystoprostatectomy. The patient subsequently developed an abdominal mass and ascites. The paracentesis cytology revealed a hypercellular specimen with malignant cells dispersed singly as well as in small fragments displaying pleomorphism, nuclear irregularity, hyperchromasia, and binucleation. Numerous malignant cells displayed well-formed signet ring morphology, identical to adenocarcinoma. This is the first report of metastatic high-grade urothelial carcinoma manifesting as signet ring cells in peritoneal fluid.