44 whenthey were much smaller than nodules usually encountered in general clinical practice. Few of the lesions were visible from the exterior, and none was accompanied by symptoms. At the time of surgical exploration mostof the thyroids in the exposed Rongelap people were lobulated and contained small discrete masses which werenotofsufficient size to cause very significant enlargement or to distort the symmetry ofthe gland.?2 Most of the glands in the exposed Rongelap people with only one palpable nodule proved to have multiple nodules. Often the palpated nodule wasnot the lesion that ultimately prompted the most concern on histological examination. The gland in some cases showed manytortuous hair-like vessels on the surface, reminiscentof thy- roids that had previously been treated with radioactive iodine for hyperthyroidism. The cut surface of the thyroids revealed some nodules which appearedto be discrete with distinct capsules (Figure 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 compnsed most of the thyroid in such a mannerthat the entire gland appeared to be respondingto a diffuse pathologic process, not unlike the type of gland observed in chronic iodine deficiency but in miniature proportions. 2. Microscopic Appearance On microscopic examination all the thyroids of exposed Rongelap people showed varying degrees of adenomatous change. Manyofthe lesions were completely surrounded by a distinct capsule and, unlike the remainderof the thyroid, had a distinct histological pattern which ranged from microfollicular to fetal, solid, or embryonal types. Unexpectediy many of the adenomas werepapillary (Figure 31), but all except two of those that were papillary were considered benign. Mostofthe individuals operated onlater in the series were given a small tracer dose of 131] so that the functional nature of the adenomatousareas could be studied for radioiodine uptake.83-84 Multiple autoradiographs prepared from tissues from thelast 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 malignantlesion,it is commonly observed that lesions having a capacity to metastasize take upfarless radioiodine than the extranodulartissue (usually the ratio is < Yoo). Most of the thyroids have been found to contain an unusual numberof minute encapsulatedlesions, some of them composed of solid cellular masses of cells (Figure 334, B, and D), in contrastto lesions found in most adenomatous goiters, which are composedoffollicular 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 thecells of some of them give rise to speculation regarding their ultimate malignant potential (Figure 344 and B and Figure 33D), especially since several obviously malignant lesions have been foundin this exposed population. The lesions shownare from thyroids not harboring frankly malignant lesions elsewhere, except the lesion in Figure 338, Figure 30. Gross serial sections of an irradiated Marshall- ese thyroid, showing multiple discrete adenomata developing throughout both lobesof the thyroid. Scarringis evident between these nodules. which was found in a thyroid that also had a highly malignantlesion in a distant part. Ofthe four malignantlesions found (Figure 35), two were papillary adenocarcinomasdisplaving some areas that wereless well differentiated, con-