Appendix - Pseudomyxoma peritonei

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Appendix

Carcinoma

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.

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

Clinical features
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● 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)

Classification
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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
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Various images

Micro description
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● 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
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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
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● MUC2

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

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

End of Appendix > Carcinoma > Pseudomyxoma peritonei

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