[Clinical study of bilateral parotid tumors]

We studied retrospectively 212 patients with parotid tumors who were treated in our hospital between October 1981 and March 1998. One hundred seventy-two of the tumors were benign, and 40 of them were malignant. The tumors were bilateral in 13 patients. Since 1992, we have treated at least 1 bilateral parotid tumor patient per year, and the number of patients with bilateral parotid tumors has tended to increase. Histologically, adenolymphomas occurred in 11 patients, and there was one occurrence of pleomorphic adenoma and one occurrence of basal cell adenoma. Eighty-five percent of all bilateral parotid tumors were adenolymphomas, and the bilateral parotid tumors comprised twenty percent (11 of 53 patients) of all adenolymphomas that we encountered. Among the 13 patients with bilateral parotid tumors, 1 patient experienced them heterochronously. In 7 of the 13 patients the tumor on the opposite side was found by diagnostic imaging. One patient showed recurrence in both parotid glands 4 years after initial surgery. Comparing bilareral adenolymphomas with unilateral adenolymphomas, there was no significant difference in the age or sex of the patients. Regarding bilateral adenolymphoma, 4 patients showed a solitary tumor on either side, 4 patients showed a solitary tumor on one side and multiple tumors on the other side, and 4 patients showed multiple bilateral tumors. Regarding unilateral adenolymphoma, 38 patients showed solitary tumors and 4 patients showed multiple tumors. Bilateral adenolymphomas were more multicentric than unilateral adenolymphomas. Epstein-Barr virus-encoded RNA (EBER) was detected in 11 of the 12 bilateral adenolymphomas and in 18 of 35 patients with unilateral adenolymphoma, by in situ hybridization. EBER was detected more frequently in the multiple unilateral adenolymphomas than in the solitary unilateral adenolymphomas. Based on our experience, the bilateral parotid tumor is not rare. Care should be taken to observe the other side of the parotid gland with parotid tumors that are suspected adenolymphomas. Imaging may be helpful for the detection of bilateral tumors. A relationship may exist between Epstein-Barr virus and adenolymphoma multicentricity.