A Consensus for Classification and Pathologic Reporting of Pseudomyxoma Peritonei and Associated Appendiceal Neoplasia

Abstract

Pseudomyxoma peritonei (PMP) is a complex disease with unique biological behavior that usually arises from appendiceal mucinous neoplasia. The classification of PMP and its primary appendiceal neoplasia is contentious, and an international modified Delphi consensus process was instigated to address terminology and definitions. A classification of mucinous appendiceal neoplasia was developed, and it was agreed that "mucinous adenocarcinoma" should be reserved for lesions with infiltrative invasion. The term "low-grade appendiceal mucinous neoplasm" was supported and it was agreed that "cystadenoma" should no longer be recommended. A new term of "high-grade appendiceal mucinous neoplasm" was proposed for lesions without infiltrative invasion but with high-grade cytologic atypia. Serrated polyp with or without dysplasia was preferred for tumors with serrated features confined to the mucosa with an intact muscularis mucosae. Consensus was achieved on the pathologic classification of PMP, defined as the intraperitoneal accumulation of mucus due to mucinous neoplasia characterized by the redistribution phenomenon. Three categories of PMP were agreed-low grade, high grade, and high grade with signet ring cells. Acellular mucin should be classified separately. It was agreed that low-grade and high-grade mucinous carcinoma peritonei should be considered synonymous with disseminated peritoneal adenomucinosis and peritoneal mucinous carcinomatosis, respectively. A checklist for the pathologic reporting of PMP and appendiceal mucinous neoplasms was also developed. By adopting the classifications and definitions that were agreed, different centers will be able to use uniform terminology that will allow meaningful comparison of their results.

Mucinous neoplasm of the appendix: management according to reviewed histologic spectral aspects

“…The survival rates for appendiceal adenocarcinoma after 5 years varies (18.7-55%), and patients with mucinous adenocarcinomas have better prognosis. 8,14 The issue is much more complex and other elements can be added to achieve consensual disease report avoiding misinterpretation. Valasek et al (2017) reviewed 46 appendiceal specimens with diagnosis of primary neoplasia.…”

“…Both benign and malignant hyperplasia may obstruct the appendiceal ostium and cause symptoms, although benign hyperplasia is more common, representing 63-84% of cases. 1,6,8,9 The disease may manifest as acute appendicitis in 8-14% of cases. Other rare complications include intussusception, bleeding, and peritonitis.…”

“…Experts postulate that the term mucocele is inadequate and should be replaced by terms that address the degrees of invasion and cellular atypia while unifying the terminology and contributing to decreased dubious interpretations and the possibility of conflicting reports. 8 The term mucinous adenocarcinoma should be reserved for infiltrative lesions with severe cellular atypia. In addition, the term cystadenoma is no longer recommended, and the following classi- fication is proposed: adenomas, low-grade mucinous neoplasm (LAMN), high-grade mucinous neoplasm (HANM), and adenocarcinomas.…”

“…The same lesion can, therefore, be diagnosed as malignant, having uncertain biological behavior, or benign, the differences among which have significant treatment implications. 8 The present study aims to report a case of mucinous neoplasm of the appendix, that manifested as a recurrent partial obstruction of the intestines due to repeated cecal-appendiceal intussusception; and at same time, revises the current uniform nomenclature that allow subsequent propose a standard of care for operative management of mucinous neoplasm of appendix.…”

Differing expression profiles ofNotch/enterocyte andWnt/secretory lineage signallings are associated with morphological diversity of appendiceal tumours

“…Histologically, they vary across a wide spectrum, and their different morphological features are linked to different clinical behaviour. They are commonly classified into five groups based on their histology:1 (a) low-grade appendiceal mucinous neoplasm (LAMN)— tumour showing prominent mucin production with bland cytology or mild/low-grade cytological atypia, (b) mucinous adenocarcinoma (MCA) or high-grade appendiceal mucinous neoplasm (HAMN) —tumour showing mucin production and malignant-appearing/high-grade cytological features, with or without invasion, (c) non-mucinous adenocarcinoma (NMA) —conventional colonic-type invasive adenocarcinoma with no mucin production, (d) classic carcinoid tumour (CCT)— well-differentiated neuroendocrine tumour, and (e) goblet cell carcinoid (GCC)— tumour showing biphasic neuroendocrine and glandular features with prominent goblet cell phenotype. Moreover, it is not unusual to see a mixture of various morphological components within a single tumour.…”