What is Pseudomyxoma Peritonei?

What is Pseudomyxoma Peritonei?

Pseudomyxoma peritonei (PMP) is a rare clinical syndrome characterized by progressive dissemination of mucinous tumors and mucinous ascites throughout the abdomen and pelvis, most commonly originating from a ruptured low-grade mucinous neoplasm of the appendix. 1, 2

Epidemiology and Clinical Presentation

• PMP has an estimated incidence of 1-2 cases per million population, making it an orphan disease 1
• Patients typically present with nonspecific symptoms including abdominal pain, abdominal distention, ascites, or bowel obstruction 1
• The disease is frequently diagnosed incidentally during surgical or imaging investigations of the abdominopelvic region 1
• Some cases present as suspected acute appendicitis, ovarian mass, or ventral hernia 3

Pathophysiology and Natural History

The disease follows a unique "redistribution phenomenon" where mucinous tumor cells accumulate at specific anatomic sites based on gravity and peritoneal fluid absorption patterns. 2

• Tumor preferentially accumulates in the greater and lesser omentum and the undersurface of the diaphragm (particularly on the right side) 2
• The motile small bowel and other parts of the gastrointestinal tract are relatively spared 2
• The primary tumor originates from the appendix in the vast majority of cases, with a distinctive pattern of peritoneal spread 1

Pathologic Classification

PMP is divided into two main histopathologic categories with dramatically different prognoses: 4

Disseminated Peritoneal Adenomucinosis (DPAM):

• Represents 59.6% of cases and is the benign variant 4
• Characterized by abundant extracellular mucin containing scant simple to focally proliferative mucinous epithelium with minimal cytologic atypia or mitotic activity 4
• Associated with appendiceal mucinous adenoma 4
• Age-adjusted 5-year survival rate of 84% 4

Peritoneal Mucinous Carcinomatosis (PMCA):

• Represents 27.5% of cases and is the malignant variant 4
• Characterized by abundant mucinous epithelium with architectural and cytologic features of carcinoma 4
• Associated with appendiceal or intestinal mucinous adenocarcinoma 4
• Age-adjusted 5-year survival rate of only 6.7% 4

Intermediate/Discordant Features:

• Represents 12.8% of cases with features between DPAM and PMCA 4
• Age-adjusted 5-year survival rate of 37.6% 4

Key Molecular Features

• MUC2, MUC5AC, and MUC5B are the predominant secreted mucins found in PMP 1
• These mucins are responsible for the characteristic mucinous ascites and peritoneal implants that define the disease 1

Diagnostic Approach

• Computed tomography is the most reliable imaging modality for diagnosis 1
• Histopathology provides definitive diagnosis and prognostic classification 1
• The disease must be differentiated from secondary peritoneal carcinomatoses from other primary sites (gastric, ovarian, colon) and other rare peritoneal conditions 1

Clinical Course and Prognosis

PMP is characterized by slow disease progression that may remain asymptomatic until advanced stages, distinguishing it from other peritoneal malignancies. 2

• The disease follows a chronic, relapsing course with multiple recurrences despite aggressive treatment 5
• Even very extensive disease with high Peritoneal Carcinomatosis Index may still be amenable to complete excision and potential cure in low-grade PMP 2
• The disease severely impacts quality of life despite its indolent nature 1
• Median survival with optimal treatment is 16.3 years, with median progression-free survival of 8.2 years 1
• 10-year and 15-year survival rates are 63% and 59%, respectively, with modern treatment approaches 1

Standard of Care Treatment

The current standard of care is complete macroscopic tumor excision (cytoreductive surgery) combined with hyperthermic intraperitoneal chemotherapy (HIPEC), offered in specialized centers. 1, 2

• Complete cytoreductive surgery typically requires 10 hours of operating time for extensive disease 2
• Surgery generally involves bilateral parietal and diaphragmatic peritonectomies, right hemicolectomy, radical greater omentectomy with splenectomy, cholecystectomy, liver capsulectomy, pelvic peritonectomy with or without rectosigmoid resection, and bilateral salpingo-oophorectomy with hysterectomy in females 2
• Even when complete tumor removal is not feasible, maximum tumor debulking can result in long-term survival in PMP 2

Critical Clinical Pitfall

Surgeons must exercise extreme vigilance when treating mucinous neoplasms of the appendix, as PMP can develop as a delayed consequence years after initial diagnosis if adequate excision and thorough debridement are not performed at the initial surgery. 5