The etiology of cysts of the breast furnishes a field for interesting speculation, and many theories have been advanced to explain their origin and development.1 Cheatle's2 study of sections of the entire breast shows the relation of cysts to the epithelium of the ducts and acini.
Two varieties of cysts may be separated according to the character of the cyst wall. In the first, the wall is lined by one or more layers of epithelial cells, and either is smooth or shows papillary ingrowths. In the second, the epithelial lining is absent or fragmentary and degenerative.
In the first variety the cysts are small, mutliple tumors which contain clear, cloudy, milky or bloody fluid. The epithelial lining of these cysts is derived more often from the duct than from the acinus, and the cysts are due not to mechanical obstruction from the outside, but to epithelial proliferation in