44 when they were much smaller than nodules usually encountered in generalclinical practice. Few of the lesions were visible from the exterior, and none was accompanied by symptoms. At the timeof surgical exploration most of the thyroids in the exposed Rongelap people were lobulated and contained small discrete masses which were notofsufficient size to cause very significant enlargement or to distort the symmetry of the gland.22 Most of the glands in the exposed Rongelap people with only one palpable nodule proved to have multiple nodules. Often the palpated nodule was Notthe lesion that ultimately prompted the most concern onhistological examination. The gland in some cases showed manytortuous hair-like vessels on the surface, reminiscent of thyroids that had previously been treated with radioactive iodine for hyperthyroidism. The cut surface of the thyroids revealed some nodules which appeared to be discrete with distinct capsules (Fig- ure 30). In some instances these discrete lesions were very firm, pale brown or whitish. In some there were hemorrhagic or degenerative cysts. The margins of some other nodules were indistinct, producing a lobular character which comprised most of the thyroid in such a mannerthatthe entire gland appeared to be responding to a diffuse pathologic process, not unlike the type of gland observed in chronic iodine deficiency but in miniature proportions. 2. Microscopic Appearance On microscopic examinationall the thyroids of exposed Rongelap people showed varying degrees of adenomatous change. Manyofthelesions were completely surrounded ‘by a distinct capsule and, unlike the remainderof the thyroid, had a distinct histological pattern which ranged from microfollicularto fetal, solid, or embryonal types. Unexpectedly many of the adenomas were papillary (Figure 31), but all except two of those that were papillary were considered benign. Mostoftheindividuals operated onlater in the series were given a small tracer dose of 1311 so that the functional nature of the adenomatous areas could be studied for radioiodine uptake.83.84 Multiple autoradiographs preparedfrom tissues from the last 15 patients have shownthatessentially all the discrete lesions took up significantly less radioiodine than the non-nodular thyroid tissue and in manycases took up noneatall (Figure 32). Only in oneindividual a single lesion, which was papillary in character, took up more radioiodine than the surrounding normalthyroid tissue. Although reduced radioiodine uptake does not necessarily indicate a maiignantlesion, it is commonly observedthatlesions having a capacity to metastasize take up far less radioiodine than the extranodular tissue (usually the ratio is < Yoo), Mostof the thyroids have been foundto contain an unusual numberof minute encapsulated lesions, some of them composedofsolid cellular masses of cells (Figure 33A, B, and D), in contrastto lesions found in most adenomatous goiters, which are composed offollicular structures similar to but not identical to normal or hyperplastic glands. On careful gross examination of the glands, these minute lesions appeared as tiny whitish dots ~! mm in diameter (pinheadsize). The atypicality of these lesions and the presence of mitoses in the cells of some of them give nse to speculation regarding their ultimate malignant potential (Figure 34A and B and Figure 33D), especially since several obviously malignantlesions have been found in this exposed population. The lesions shown are from thyroids not harboring frankly malignant lesions elsewhere, except the lesion in Figure 338, Figure 30. Gross serial sections of an irradiated Marshallese thyroid, showing multiple discrete adenomata developing throughout both lobes of the thyroid. Scarringis evident between these nodules. which was found in a thyroid that also had a highly malignantlesion in a distant part. Of the four malignantlesions found (Figure 35), two were papillary adenocarcinomas displaying some areas that wereless well differentiated, con-