Cytological examinations of ascitic fluid

A case report of malignant melanoma with peritoneal dissemination

Abstract

Background: Since peritoneal dissemination of malignant melanoma is rare, most cytopathologists and cytotechnologists are not so familiar with ascitic fluid cytology. We discuss cytological and immunocytochemical features from a case of malignant melanoma with peritoneal dissemination.
Case: An 81-year-old woman operated on for malignant melanoma arising from the right maxillary sinus in Nov. 2000 reported abdominal distention with ascites one month later. Ascitic fluid was yellowish. Cytologically, round tumor cells with irregular nuclei, prominent nucleoli, intranuclear cytoplasmic inclusion, and intracytoplasmic fine melanin pigments were found by Papanicolaou-staining, as was “bleb” formation of cytoplasm similar to mesothelial cells. Immmunocytochemically, tumor cells were positive for HMB-45 and S-100 protein. The patient died, and autopsy showed peritoneal dissemination of malignant melanoma in Feb. 2001.
Conclusion: We report a case of malignant melanoma with peritoneal dissemination. Typical cytological features described in the literature were recognized except for “bleb” formation of cytoplasm mimicking mesothelial cells. Immunocytochemical staining was useful for differentialy diagnosing malignant melanoma from mesothelial cells.