Peritoneal malignancy

Mostly metastatic - primary peritoneal malignancy is rare

• Carcinomatosis - the diffuse coating of the visceral and parietal peritoneum by peritoneal metastases from an intra-abdominal or pelvic malignancy.

Pseudomyxoma peritonei

• Epidemiology
  • Rare
  • Usually 40-50yo
• Pathophysiology
  • Characterised by mucinous ascites and peritoneal implants - typically most prominent in the pelvis, paracolic gutters, omentum, and subdiaphragmatic spaces
  • Most common primary tumour is a perforated mucinous tumour of appendix, but can come from mucinous ovarian, colonic or pancreatic tumours
• Presentation
  • Usually asymptomatic until late in disease course
  • Often slow global deterioration in health
  • Check for new hernia, ascites, abdominal distension with non-shifting dullness, and sometimes a palpable mass
• Grading - WHO
  • Acellular mucin
  • Low-grade mucinous carcinoma peritonei - low cellularity
  • High-grade mucinous carcinoma peritonei - high cellularity, infiltrative invasion
  • High-grade mucinous carcinoma peritonei with signed ring cells - signed ring cells
• Imaging
  • Ct may show ascites, loculated pools of fluid, peritoneal-based tumour nodules, thickened omentum, scalloping of liver margins, and evidence of invasion of the mesentery, porta hepatis and small bowel
  • 'Redistribution phenomenon' - peripheral location of the tumour, and relative sparing of the central small bowel and mesentery
• Management (see separate topic with technical description under 'oncology')
  • Cytoreduction (resection of as much of the tumour as possible)
    • Often limited by diffuse small bowel involvement or porta hepatis involvement
    • Could include omentectomy, stripping of involved parietal peritoneum, resection of involved organs, and appendicectomy or ileocolectomy - leave no visible disease, or at least no nodules >2mm
  • HIPEC (hyperthermic intra-peritoneal chemotherapy)
    • Commonly mitomycin C or oxaliplatin
• Prognosis
  • A low-grade tumour with successful cytoreduction and HIPEC has a 5-year survival rate of 60-90%
  • Even patients with high-grade tumours can have 5-year survival rates of 50%

Carcinomatosis from colorectal cancer

• Can be considered for CRS/HIPEC in select cases

Peritoneal cancer index (PCI)

• Sum of scores in 13 abdominal regions, each region scored 0-3 based on the largest tumour size

Peritoneal mesothelioma

• Epidemiology
  • Most common primary malignant neoplasm of peritoneum
  • Asbestos exposure is a risk factor, but less so than pleural mesothelioma
• Pathophysiology
  • Malignant transformation of the simple squamoid epithelium covering the peritoneal cavity
  • Tends to involve all peritoneal surfaces - hard, white masses and plaques of tumour
  • Can invade intra-abdominal organs including small bowel - can encase and obstruct small bowel
  • Direct extension to pleural cavities is more likely than dissemination
  • Subtypes
    • Epithelioid - most common and best prognosis
    • Sarcomatoid
    • Biphasic
• Presentation
  • Abdominal pain and weight loss
  • Ascites - often intractable
• Workup
  • Paracentesis has a low diagnostic yield
  • Diagnostic laparoscopy or image-guided core biopsy of a visible implant is generally needed
• Management
  • CRS/HIPEC if favourable factors
• Prognosis
  • Variable rate of progression, tends to remain intra-peritoneal until very late in the disease
  • If able to undergo complete cytoreduction, 5-year survival is 42%