Appendix
Carcinoma
Pseudomyxoma peritonei


Topic Completed: 1 August 2012

Minor changes: 19 November 2020

Copyright: 2003-2020, PathologyOutlines.com, Inc.

PubMed Search: Pseudomyxoma peritonei appendix

Page views in 2019: 8,235
Page views in 2020 to date: 7,464
Cite this page: Mansouri J. Pseudomyxoma peritonei. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/appendixpseudomyxoma.html. Accessed November 23rd, 2020.
Definition / general
  • Clinical syndrome of extravasation of mucin into abdomen outside of right lower quadrant
  • Not a histologic diagnosis
Clinical features
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
Microscopic (histologic) 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
Positive stains
Differential diagnosis
  • Ruptured mucinous cystadenomas of appendix or ovary
  • Soft tissue neoplasms with myxoid changes
  • Endometriosis with myxoid change
  • Ruptured viscus with mucus extravasation
Back to top
Image 01 Image 02