The distribution of cancer cells in the abdominal cavity is partly influenced by gravity and partly follows the current of the peritoneal fluid.
- Gravity creates an accumulation of cells in the pelvis with growth on the peritoneum in the transition fold in colon/uterus/ovaries/bladder. Additionally the gravity brings tumorcells to both flanks which is the lowest point in lying position.
- The peritoneal fluid is reabsorbed at the diaphragm and the large and small omentums . The accumulated cells under the diaphragm attach easily to the liver, gallbladder, and surface of the spleen . Tumor in the small omentum often grows on the gastric antrum.
Malignant cells of high and moderate differentiation attach themselves to the mobile small intestine usually only in an advanced stage . In more malignant cases, larger parts of the small intestine are affected. The same occurs if adhesions of intestinal loops (for instance after previous surgery) causes less possibility of movement for the intestine.
The thickness of the peritoneum may in different areas vary from microscopic to thick layers of several centimeters.
- In DPAM (disseminated peritoneal adenomucinosis), the tumor grows on the peritoneum without infiltrating the underlying tissue and the peritoneum is separated relatively easily when there is no pre-tumoral inflammation.
- For diseases with infiltrating growth, (PMCA variant of pseudomyxoma, peritoneal carcinomatosis from colon and rectum and mesothelioma) the tumor along with the peritoneum attaches to underlying tissue, which must be resected together with the tumor.
Lymph nodes and distant metastases
- Pseudomyxoma of an adenomatous type does not spread to lymph nodes or hematogenously.
- Apparent benign mesothelioma may to some degree spread to lymph nodes or hematogenously. In more malignant types, lymph node involvement in the thorax (cardiophrenic angle) is common.
- The more malignant a tumor appears to be, the larger the tendency for spreading to lymph nodes and other organs. Synchronous metastases to liver or lungs are more common in peritoneal colorectal cancer.