Micro-anatomy of primary lymphatics in oral mucosa: a scanning electron microscopic study

Primary or initial lymphatics cannot readily be recognised by conventional histological methods because they have usually collapsed in excised tissues. We have investigated the distribution of 81 initial lymphatics in 24 specimens of normal tissue and specimens from 11 squamous cell carcinomas and their relationship with the invasion of carcinoma. We used indirect injection methods and the distended initial lymphatics were observed by scanning electron microscopy. The lymphatics were arranged in a network consisting of integrated lymph capillaries and precollectors in the subepithelial area. There was a zone of high density 100 μm below the epithelium. The arrangement of initial lymphatics in oral mucosa was similar to that in the skin of head, in contrast to initial lymphatics in the skin at other sites. We saw no carcinoma cells penetrating into initial lymphatics and the route of tumourous infiltration into lymphatics deserves further investigation.