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Pseudomyxoma peritonei

Reviewer: Jaleh Mansouri, M.D. (see Reviewers page)
Revised: 21 October 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Clinical syndrome of extravasation of mucin into abdomen outside of right lower quadrant
● Not a histologic diagnosis

Clinical features

● Poor prognosis due to infection, intestinal obstruction, peritonitis
● Appears to be clonally derived from associated mucinous tumor, usually of appendix (Am J Surg Pathol 2001;25:1095)
● Also associated with ovarian mucinous tumors, although these are probably metastatic from appendix or other GI sites (Am J Surg Pathol 2000;24:1447, Am J Surg Pathol 1996;20:739, Am J Surg Pathol 1994;18:591, Am J Surg Pathol 1991;15:415)


Table of various classification systems

● WHO 2010 two-tiered system divides pseudomyxoma peritonei (PMP) into low and high grades based on cellularity of mucin pools, cytologic features, and architectural complexity (Arch Pathol Lab Med 2011;135:1261)
● High concordance between grades of primary neoplasm and PMP (J Clin Pathol 2012;65:919)

Low grade PMP
● Mucin pools with low cellularity (<10%), bland cytology, and nonstratified simple cuboidal epithelium

High grade PMP
● Mucin pools with high cellularity, moderate/severe cytologic atypia, and cribriform/signet ring morphology with desmoplastic stroma

Other classifications:
● Disseminated peritoneal adenomucinosis (associated with cystadenoma), and two types of peritoneal mucinous carcinomatosis (an aggressive type and an intermediate type, both associated with carcinoma, Am J Surg Pathol 1995;19:1390, Am J Surg Pathol 2003;27:650)

Peritoneal adenomucinosis:
● Multifocal mucinous tumors adherent to but not invading into visceral and parietal peritoneal surfaces
● Peritoneal lesions contain scant histologically benign mucinous epithelium within abundant extracellular mucin
● Intense hyalinizing fibrotic reaction separates pools of mucin
● Noninvasive involvement of the parietal peritoneal surfaces with sparing of peritoneal surfaces of bowel and its mesentery

Mucinous adenocarcinoma:
● Invasive peritoneal lesions composed of abundant epithelium with glandular or signet-ring cell morphology with malignant architectural complexity or cytological atypia
● Separated into well-differentiated (composed predominantly of single tubular glands
● Tumor cells well polarized similar to adenomatous epithelium, prominent atypia, invasive component present)
● Moderately differentiated (characteristics between well- and poorly differentiated adenocarcinoma; composed of solid sheets of malignant cells mixed with glandular formations, minimal/absent polarity of tumor cells) and poorly differentiated (composed of highly irregular glandular structures or no glandular differentiation, no tumor cell polarity, variable signet-ring cells)

Hybrid appendiceal mucinous tumors:
● Foci of diffuse peritoneal adenomucinosis and mucinous adenocarcinoma
● Mucinous appendiceal tumors with pseudomyxoma peritonei over time and with repeated surgical and intraperitoneal chemotherapy interventions may change to a more invasive process

● Some authors oppose use of “adenomucinosis” and “borderline” as misleading, because lesions may have aggressive biologic behavior
Poorer prognosis

● Presence of any epithelium within mucin (low grade or high grade, although high grade may be worse), invasive adenocarcinoma, bulky peritoneal disease, mucinous carcinomas of colonic origin

Gross images

Various images

Micro description

● Viable but bland epithelial glandular cells within large pools of mucus, also hyperemic vessels and chronic inflammatory cells
● Low grade: mucin pools with low cellularity (<10%), bland cytology, and nonstratified simple cuboidal epithelium
● High grade: mucin pools with high cellularity, moderate/severe cytologic atypia, and cribriform/signet ring morphology with desmoplastic stroma

Micro images

Various images

Disseminated peritoneal adenomucinosis (simple mucinous epithelial strips without atypia)

Ruptured appendiceal diverticulum with adenomatous epithelium

Low grade mucinous tumor with peritoneal involvement

Positive stains

● MUC2

Differential diagnosis

● Ruptured mucinous cystadenomas of appendix or ovary
● Soft tissue neoplasms with myxoid changes
● Endometriosis with myxoid change
● Ruptured viscus with mucus extravasation

Additional references

Arch Pathol Lab Med 2010;134:864, Am J Surg Pathol 2009;33:248

End of Appendix > Carcinoma > Pseudomyxoma peritonei

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