Pseudomyxoma Peritonei: Pathology, a Historical Overview, and Proposal for Unified Nomenclature and Updated Grading

Abstract

Abstract Pseudomyxoma peritonei (PMP) is a clinically distinctive form of malignancy that typically arises from the appendix and is characterized by bulky accumulation of mucinous tumor deposits in the peritoneal cavity. It has defied stable pathologic categorization ever since first being described in the late 19th century. Since the early 20th century, many accounts have emphasized the bland histology of those cases arising from appendiceal precursors that had been considered benign, in contrast to higher-grade cases with more conventionally malignant histology. Beginning in the late 20th century, this was exemplified by divided nomenclature, with “carcinoma” phraseology being reserved for cases with clear-cut high-grade morphology. Such a divided approach is rendered problematic by the spectrum of atypia in many cases, including a significant subset with “intermediate” features. More recently, unified nomenclature has been favored for PMP of appendiceal origin, with an emphasis on tiers of grading. The goal is a clinically relevant and objectively reproducible grading scheme for what appears to be the spectrum of one clinicopathological entity (except perhaps for cases purely composed of signet-ring cells). Currently proposed consensus criteria focus on the distinction of cases of PMP as low grade, high grade, or high grade with signet-ring cells.