P‐24 MUCINOUS ASCITES ‐ AN APPROACH TO CYTOLOGICAL CLASSIFICATION

Abstract

Pseudomyxoma peritonei (PMP) is the name given to the clinical syndrome and the heterogeneous group of conditions characterised by mucinous ascites and mucinous implants. Patients with PMP are treated with a combination of cytoreductive surgery, peritonectomy and hyperthermic intraperitoneal chemotherapy (HIPEC). A dedicated PMP outpatient clinic refers samples of mucinous ascites to our laboratory. Peritoneal fluid samples in disseminated peritoneal adenomucinosis (DPAM) contain abundant extracellular mucin together with epithelium showing mild to moderate (low grade) cytological atypia. DPAM is associated with the presence of an appendiceal mucinous adenoma. Peritoneal mucinous carcinomatosis (PMCA) is associated with the presence of an appendiceal or intestinal mucinous adenocarcinoma and mucinous ascites containing mucinous epithelium with the cytological features of a carcinoma. PMCA –I (intermediate) cases are those with peritoneal lesions demonstrating predominantly features of DPAM but with foci of well differentiated mucinous adenocarcinoma. Cases classified as PMCA‐D (discordant) are characterised by an atypical adenoma of the appendix and associated peritoneal mucinous adenocarcinoma. There is a recognised statistically significant difference in survival in cases reported as DPAM, cases with intermediate features and PMCA. Therefore we advocate reporting cases of mucinous ascites in conjunction with histology according to the following diagnostic categories: (1) Mucin without the presence of any epithelial cells (2) Disseminated peritoneal adenomucinosis (DPAM) (3) PMCA‐I/D (4) Peritoneal mucinous carcinomatosis (PMCA). Cases histologically diagnosed initially as DPAM may after a period of time undergo dedifferentiation and re‐present as PMCA. It is important that the cytopathologist recognise and classify the features of the cells present within the peritoneal fluid. It is essential that the histological features are correlated with the cytological diagnosis and that any differences in morphology are documented for accurate survival prediction and appropriate clinical management. We present the clinicopathological and cytological features in the cases of PMP which we have encountered in our department and describe our cytological approach to classification.