+4 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 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 Mostof the giands in the exposed Rongelap people with only one palpable nodule proved to have multiple nodules. Often the palpated nodule was not the lesion that ultimately prompted the most concern on histological examination. The gland in some cases showed manytortuous hair-like vessels on the surface, reminiscent of thyroids that had previously been treated with radio- active 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 en- tire gland appeared to be respondingto a diffuse pathologic process, not unlike the type of gland observed in chronic iodine deficiency but in mini- ature proportions. 2. Microscopic Appearance On microscopic examinationall the thvroids 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 microfollicular to fetal, solid, or embryonal types. Unex- pectedly many of the adenomas were papillary (Figure 31), but all except two of those that were papillary were considered benign. Most ofthe individuals operated on iater in the series were given a small tracer dose of 131] so that the functional nature of the adenomatous areas could be studied for radioiodine uptake.3.84 Multiple autoradio- graphs prepared from tissues from the last 15 patients have shown thatessentially all the discrete lesions took up significantly less radioiodine than the non-nodular thyroid tissue and in manycases took up noneat all (Figure 32). Only in one indi- viduai a single lesion, which was papillaryin character, took up more radioiodine than the surrounding normal thyroid tissue. Although reduced radioiodine uptake does not necessarily indicate a malignantlesion,it is commonly observed thatlesions having a capacity to metastasize take up far less radioiodine than the extranodular tissue (usually the ratio is < Yioo). Mostof the thyroids have been found to contain an unusual numberof minute encapsulatedlesions, some of them composedofsolid cellular masses of cells (Figure 33A, 8, 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 mi- nute lesions appeared as tiny whitish dots ~ 1 mm in diameter(pinheadsize). The atypicality of these lesions and the presence of mitoses in the cells 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 found in this exposed population. The lesions shown are from thyroids not harboring frankly malignant lesions elsewhere, except the lesion in Figure 338, which was found in a thyroid that also had a Figure 30. Gross serial sections of an irradiated Marshall- ese thyroid, showing multiple discrete adenomata developing throughoutboth lobes of the thyroid. Scarringis evident between these nodules. 200bTuI highly malignant lesion in a distant part. Ofthe four malignantlesions found (Figure 35), two were papillary adenocarcinomas displaving some areas that were less well differentiated, con-