INTRATHYROIDAL THYMIC TISSUE - AN AUTOPSY STUDY IN FETUSES WITH SOME EMPHASIS ON PATHOLOGICAL IMPLICATIONS

Fifty-eight human thyroid glands obtained at autopsy from fetuses with proven retrosternal thymus were systematically studied for the presen ce of intrathyroidal thymic tissue. The latter was found in one thyroi d lobe in each of three fetuses (5.1 %). It was located in a subcapsul ar position in two cases (3.4 %) and lying deep in thyroid tissue in o ne (1.7 %). Our findings would support a IV-V pharyngeal pouch origin for some accessory thymic tissue and would provide an explanation of t he histogenesis of intrathyroid thymomas.