[The significance of the 5th gland as a cause of primary hyperparathyroidism. Case report and review of the literature].

Of 140 patients surgically treated for primary hyperparathyroidism one patient had persistent hypercalcemia due to an abnormal and ectopic fifth parathyroid gland (0.7%). The possibility of an abnormal fifth gland as the cause of primary hyperparathyroidism should be considered when four glands of normal size and histology have been found in the neck, and of such a gland should be thought in all patients with diffuse hyperplasia after subtotal parathyroidectomy suffering from persistent hyperparathyroidism. The fifth gland is usually found in the lower neck or upper mediastinum, frequently within the thymus. If present, it should be excised by transcervical thymectomy during first operation. In reoperations sternal splitting should be performed.