Lymphoepithelial cyst of the parotid gland: its possible histopathogenesis based on clinicopathologic analysis of 64 cases.

Sixty-four cases of lymphoepithelial cysts of the parotid gland, the largest scale collection in the literature, were clinicopathologically analyzed for their possible pathogenesis. All 64 cases were unilateral, 27 left and 37 right. There were 28 male and 36 female patients with a ratio of 1:1.3. The mean age of the patients was 52.0 years, and their average duration of symptoms was 29.3 months. The mean longest diameter of the cysts was 3.0 cm. Histologically, lymphoepithelial cysts were classified into 3 subtypes: type I, a cystic dilation of ducts within parotid glands (9 cases, 14.1%); type II, partially demarcated cystic lesions with lymphoid stroma (27, 42.2%); type III, well-encapsulated cystic lesions with lymphoid stroma containing lymph follicular structures (28, 43.8%). Based on immunohistochemical results for lymphocyte/macrophage (CD20/CD45RO/IgG4), cell cycle (Ki-67), and lymphatic (D2-40) markers, the lymphoid stroma was shown to have neither the usual lymph follicular distributions of T/B cells nor lymph sinus structures. No viral infection was confirmed. The results seemed to indicate that the lymphoid stroma were induced along with the growth of the cystic dilatation of ducts within sialadenitis, which were neither induced by Epstein-Barr virus nor HIV infections, and that the formation of lymphoepithelial cysts was completed by demarcation, which should have been a kind of granulation tissue reaction, from the parotid parenchyma but did not arise from intraparotid lymph nodes.