The lining of branchial cysts studied by electron microscopy and enzyme histochemistry.

The lining of five branchial cysts from patients aged from 17 to 51 was studied by histochemical methods for non-specific acid esterase and acid phosphatase and by scanning and transmission electron microscopy. The stratified squamous epithelium was shown to be a specialised structure, with a few microvillous cells on the surface and an intra-epithelial network of channels containing lymphocytes, notable T cells, and mononuclear phagocytic cells. The appearance of the cyst lining was similar to that of the epithelium lining the crypts of palatine tonsils. The demonstration of a complex lympho-epithelial lining of the cysts does not settle the controversial question of their origin, but it must be taken into account by hypotheses explaining the development of branchial cysts.