Microscopic thymoma and parathyroid adenoma: rare combination of two distinct pathologies.

While there is an intimate anatomical and embryological relationship between the inferior parathyroid gland and thymus, concurrent pathology is rare. Three cases have been reported in the literature of a parathyroid adenoma in conjunction with a thymoma. We present a case report of a 60-year-old female with a past medical history of hypercalcemia subsequently found to have primary hyperparathyroidism. Sestamibi scan of the parathyroid revealed increased uptake in the lower left neck consistent with a parathyroid adenoma. A standard transverse neck incision was performed with exploration of the lower left thyroid pole. Further dissection was required to identify the parathyroid gland which was intimately associated with thymic tissue in the superior mediastinum. Both thymic tissue and the parathyroid gland were sent for pathology. Permanent pathology subsequently revealed a parathyroid adenoma with an incidental spindle cell thymoma. The embryological relationship of the inferior parathyroid glands and the thymus is well known as both are derived from the third branchial pouch. However, there are only 3 other previous reports of parathyroid adenoma associated with a thymoma in the current literature. Interestingly, up to 16% of parathyroid adenomas are found in the mediastinum, and the current literature states the incidence of thymoma varies from 10-42%.