Trans-Lymphatic Metastasis in Peritoneal Dissemination

Mechanism of the formation of peritoneal metastasis (PM) through lymphatic vessels was studied. Materials and methods: Parietal peritoneum was divided into 8 regions, and specimens of each zone were removed from patients with PM. The specimens were stained with enzyme histochemical staining for alkaline phoshatase (ALPase) and 5-Nase activity, and with immunohistochemical staining with D2-40. Surface of the peritoneum and subperitoneal tissue were observed by a scanning electron mcirosopy. Results: Well-developed lymphatic lacunae were found in the shallow submesothelial layer of 7 regions except for the anterior abdominal wall. Lymphatic vessels were found in the deep submesothelial layer up to 200 micrometer from the peritoneal surface. The mesothelial stomata directly connect with the submesothelial lymphatic vessels through holes of the macula cribrifolmis. Migration of cancer cells through stoma was found, and cancer cells were detected in the submesothelial lymphatic lacunae. Lymphatic vessels are not found in the center of established PM, but were found in the adjacent normal tissue. In the subperitoneal tissue outside the PM, morphological findings suggesting lymphangiogenesis designated as cystic Lymphatic Island, ladder formation, budding, and extension of lymphatic vessels were found. Conclusion: The triplet structure consisting of mesothelial stomata, holes on macula cribriformis and submesothelial lymphatic lacunae is essential for the migration of peritoneal free cancer cells into the submesothelial lymphatic lacunae. The rout of the formation of PM through peritoneal lymphatic vessels was named as translymphatic metastasis.