Appendix
Carcinoma
Pseudomyxoma peritonei

Reviewer: Jaleh Mansouri, M.D. (see Authors page)

Revised: 29 February 2016, last major update August 2012

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Pseudomyxoma peritonei appendix
Definition / General
  • Clinical syndrome of extravasation of mucin into abdomen outside of right lower quadrant
  • Not a histologic diagnosis
  • Diagrams / Tables

    Images hosted on other servers:

    Table of various classification systems

    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)
  • Classification
  • 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:
    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

    Images hosted on other servers:

    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

    Images hosted on other servers:

    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