Definition/General
Introduction:
Pseudomyxoma peritonei is mucinous tumor implants throughout peritoneal cavity
Characterized by abundant mucin production
Results from appendiceal mucinous neoplasms (90% cases)
Creates "jelly belly" appearance
Indolent growth pattern with local spread.
Origin:
Originates from appendiceal mucinous tumors (90%)
Ovarian mucinous tumors (10%)
Perforation of mucinous cystadenoma
Peritoneal seeding of mucin-producing cells
Redistribution phenomenon guides tumor spread.
Classification:
WHO classification: Low-grade mucinous carcinoma peritonei (LMCP)
High-grade mucinous carcinoma peritonei (HMCP)
Older terms: Disseminated peritoneal adenomucinosis (DPAM)
Peritoneal mucinous carcinomatosis (PMCA).
Epidemiology:
Rare condition: 1-2 per million population
Peak incidence 50-60 years
Slight female predominance
Appendiceal origin in 90% cases
Better prognosis than conventional peritoneal carcinomatosis.
Clinical Features
Presentation:
Progressive abdominal distention
Palpable abdominal mass
New-onset hernia
Change in bowel habits
Early satiety
Weight gain due to mucin accumulation.
Symptoms:
Abdominal distention (95% cases)
Abdominal discomfort (70% cases)
Change in bowel habits (50% cases)
New hernias (30% cases)
Urinary frequency (25% cases)
Weight gain paradoxically.
Risk Factors:
Appendiceal mucinous neoplasms
Previous appendiceal perforation
Family history of colorectal cancer
Inflammatory bowel disease
Previous abdominal surgery.
Screening:
CT abdomen shows mucinous ascites
Tumor markers: CEA, CA 19-9, CA-125
Colonoscopy to exclude colorectal primary
Appendiceal imaging
Diagnostic laparoscopy if indicated.
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Gross Description
Appearance:
Ascitic fluid has thick, gelatinous consistency
Mucoid and viscous
Clear to slightly turbid
Stringy appearance
High viscosity - may not flow easily.
Characteristics:
High protein content due to mucin
Elevated CEA levels
CA 19-9 elevated
Mucin stains positive
Low cellular content
Specific gravity >1.015.
Size Location:
Massive ascites often present
Loculated in dependent areas
Omental involvement common
Right lower quadrant predominance
Pelvis frequently involved.
Multifocality:
Widespread peritoneal involvement
Omental caking
Mucinous implants on peritoneal surfaces
Diaphragmatic involvement
Liver surface deposits.
Microscopic Description
Histological Features:
Low cellularity in abundant mucin background
Mucinous epithelial cells in strips or clusters
Goblet-like cells
Signet ring cells may be present
Acellular mucin pools.
Cellular Characteristics:
Columnar epithelial cells with mucin-filled cytoplasm
Basal nuclei displaced by mucin
Mild to moderate nuclear atypia
Goblet cell morphology
Signet ring appearance when mucin abundant.
Architectural Patterns:
Single cells and small clusters
Strips of epithelial cells
Acellular mucin background
No complex architectural patterns
Sparse cellularity overall.
Grading Criteria:
Low-grade: minimal atypia, abundant mucin
High-grade: significant atypia, destructive growth
Ki-67 proliferation index
Nuclear grading important for prognosis.
Immunohistochemistry
Positive Markers:
CK20 positive in epithelial cells
CDX2 positive (intestinal differentiation)
CEA positive
CA 19-9 may be positive
MUC2 positive (intestinal mucin)
Mucin stains: PAS, mucicarmine positive.
Negative Markers:
CK7 usually negative
TTF-1 negative
PAX8 negative (excludes ovarian)
WT1 negative
Calretinin negative (excludes mesothelioma).
Diagnostic Utility:
CK20+/CK7- pattern supports GI origin
CDX2 positivity confirms intestinal differentiation
Mucin stains highlight extracellular mucin
Distinguishes from ovarian mucinous tumors.
Molecular Subtypes:
KRAS mutations common
GNAS mutations in appendiceal tumors
TP53 mutations in high-grade cases
Microsatellite stability typical.
Molecular/Genetic
Genetic Mutations:
KRAS mutations (70-80% cases)
GNAS mutations (appendiceal origin)
TP53 mutations (high-grade cases)
PIK3CA mutations
APC mutations less common.
Molecular Markers:
CEA markedly elevated
CA 19-9 elevated
CA-125 may be elevated
Mucin markers: MUC1, MUC2, MUC5AC
Peritoneal cancer index (PCI) for staging.
Prognostic Significance:
Grade most important prognostic factor
Low-grade: 5-year survival 75-85%
High-grade: 5-year survival 15-20%
Completeness of cytoreduction affects outcome
Ki-67 index correlates with survival.
Therapeutic Targets:
Cytoreductive surgery (CRS) with heated intraperitoneal chemotherapy (HIPEC)
Mitomycin C commonly used
Systemic chemotherapy for unresectable disease
5-FU based regimens.
Differential Diagnosis
Similar Entities:
Ovarian mucinous carcinoma
Gastric signet ring carcinoma
Colorectal adenocarcinoma
Mesothelioma (epithelioid type)
Adenocarcinoma of unknown primary.
Distinguishing Features:
Pseudomyxoma: Abundant extracellular mucin
Pseudomyxoma: CK20+/CK7-
Ovarian: PAX8 positive
Gastric: More cellular, CK7+
Mesothelioma: Calretinin positive.
Diagnostic Challenges:
Low cellularity may limit diagnosis
Primary site identification
Grade assessment in sparse material
Distinguishing reactive mesothelial cells
Sampling adequacy.
Rare Variants:
Ovarian origin pseudomyxoma
Colonic origin
Pancreatic origin
Pseudomyxoma with sarcomatous elements
Hybrid low/high-grade patterns.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Peritoneal fluid, volume [X] mL, thick, gelatinous, mucinous consistency
Adequacy
Adequate for cytological evaluation despite low cellularity
Cellularity
Low to moderate cellularity with [X] cells/μL
Mucin Characterization
Abundant extracellular mucin present. Mucin stains: [Positive results]
Malignant Cells
POSITIVE for malignant mucinous epithelial cells
Morphological Features
Mucinous epithelial cells in small clusters and single cells. Abundant mucin background. [Grade assessment based on atypia].
Immunohistochemistry
CK20: [Result], CK7: [Result], CDX2: [Result], CEA: [Result]
Grade Assessment
[Low-grade/High-grade] mucinous carcinoma peritonei
Final Diagnosis
Malignant peritoneal effusion consistent with pseudomyxoma peritonei - [Low-grade/High-grade] mucinous carcinoma peritonei
Comment
Findings consistent with pseudomyxoma peritonei. Recommend correlation with imaging and primary site evaluation. Oncology consultation for staging and treatment planning.