Pseudomyxoma peritonei: cytomorphologic findings and clinicopathologic correlates

Introduction To analyze the cytomorphology and clinical correlates of pseudomyxoma peritonei (PP), a frequently fatal pathological entity defined by gelatinous ascites caused by slow but relentless accumulation of mucin produced by neoplastic glandular epithelium. Materials and methods A retrospective search of the electronic pathology data systems of three large tertiary care medical institutions revealed 41 cases from 32 patients with PP and corresponding abdominal fluid cytologic specimens. Cytologic material was available for review in 15 cases. Results The primary tumor site was appendix in 25 (78.1%) of the 32 patients, other regions of the gastrointestinal tract in 2 (6.3%) patients, and in 5 (15.6%) patients, the primary could not be entirely identified. Of the 41 cases, only 15 had available cytologic slides to review. Extracellular mucin was a constant feature in all 15 (100%) cases, being abundant in 13 cases and focal in 2 cases. Predominance of mucin-secreting neoplastic epithelial cells were observed in 10 (66.7%) and muciphages in 11 (73.4%) cases. Cytopathologic interpretations were consistent with the subsequent histopathologic diagnosis in 30 of 32 cases (93.8%). There were two false negative cases, both of which showed scant mucinous material on second review. Conclusions PP is uncommonly encountered in routine cytopathology practice. The common denominator is the presence of an often-abundant extracellular mucin. Epithelial (glandular) component is usually scant. An accurate diagnosis in a fluid specimen requires proper identification of free/extracellular mucin as well as distinguishing the often “benign-appearing” epithelial cells from reactive mesothelial cells and histiocytes.