A Case of Plasmacytoid Urothelial Carcinoma Illustrating Diagnostic Pitfalls and Cytologic Diversity in Urine and Ascitic Fluid

초록

Introduction Plasmacytoid Urothelial carcinoma (PUC) is a rare and aggressive subtype. Its unique histologic features can result in underdiagnosis by The Paris System (TPS) for urinary cytology. Case Presentation A 51-year-old man presented with gross hematuria. Initial urine cytology and bladder washing were negative due to low cellularity and severe degeneration. Follow-up voided urine cytology showed atypical urothelial cells, and he subsequently underwent surgery, which revealed PUC. Postoperatively, he received concurrent chemoradiotherapy but later developed malignant ascites, which was confirmed by cytologic findings and supported by immunohistochemical staining. Discussion and conclusion Regardless of site, PUC showed hyperchromasia, coarse chromatin, eccentric nuclei, and a low nuclear-to-cytoplasmic(N/C) ratio. However, due to these features, urinary cytology may be underevaluated when applying TPS, and non-urinary samples may mimic other malignancies such as lymphoma. Awareness of these cytomorphologic features is essential for accurate diagnosis.