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Peritoneal metastases

Peritoneal metastases (also known as peritoneal carcinomatosis when extensive) are relatively common particularly in tumours of the abdomen and pelvis and generally imply a poor prognosis, often with a significant impact on palliation. 

Epidemiology

The epidemiology of patients with peritoneal metastases mirrors that of affected patients. Common primaries include 1-2

Clinical presentation

Isolated peritoneal metastases are usually asymptomatic. Peritoneal carcinomatosis may also be asymptomatic, but eventually most patients begin to report symptoms which can vary from uncomfortable to debilitating. Symptoms include 1:

  • abdominal distention due to malignant ascities
  • abnormal bowel motility, resulting
    • nausea / bloating
    • intermittent pains
    • bowel obstruction (most common from colorectal cancer metastases)

Pathology

Malignant involvement of the peritoneal lining occurs via a number of routes, including 1

  • intraperitoneal seeding & direct invasion: most common
  • haematogenous dissemination
  • lymphatic dissemination: rare

Radiographic features

Although peritoneal metastases are visible on ultrasound, MRI and sometimes are implied on barium studies, CT is the most frequently used modality to investigate patients with suspected peritoneal metastases, or assess the resultant complications. 

CT

Peritoneal metastases can range in appearance from invisible to multiple large masses, and historically CT can only detects 60-80% of peritoneal metastases later shown to be present at surgery, although more recent studies reported detection rates of 85-93% 1,3. Appearances include 1:

  • thickening and enhancement of peritoneal reflections (especially if nodular) 
  • soft tissue nodules
  • stranding and thickening of the omentum (omental cake
  • stranding an distortion of the small bowel mesentery 
  • ascites, especially if loculated 
  • calcifications 2 (particularly in cystadenocarcinoma of the ovary)
    • nodular with non-calcified component are typical
    • nodal calcification

Intraperitoneal contrast has been investigated as a way of improving sensitivity to the presence of small deposits, and may improve detection but has not been widely adopted 3

Ultrasound

Malignant ascites may be anechoic or have low level echoes, and aids in the identification of deposits 1. Nodules are of intermediate echogenicity, hypo-echoic compared to peritoneum, whereas infiltration of the omentum results in hyperechogenicity 1.  

MRI

MRI can be very sensitive, probably more so than CT (85-90%) 1. Peritoneal metastases show up as increased enhancement (greater than liver), best seen after 5-10 minutes 1

Treatment and prognosis

Peritoneal metastases per se are not locally treated, although systemic treatment may have some effect. Complications do however frequently require treatment for palliation: 

Differential diagnosis

Differential diagnosis depends on the dominant pattern. Peritoneal mesothelioma is very similar to peritoneal carcinomatosis, but usually no primary neoplasm is known.

Smooth thickening and enhancement of the peritoneum, with stranding of the omentum and mesentery may be seen in intra-abdominal sepsis. 

Benign calcifications tend to be sheetlike, and nodal calcifications in these patients less common 2. A history of peritoneal dialysis or recent abdominal sepsis is usually easily obtained. 

Another uncommon consideration would include peritoneal tuberculosis.

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