+4 when they were much smaller than nodules usuaily encountered in general clinica! 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 were not ofsufficient size to cause very significant enlargement or to distort the symmetry ofthe gland.?* Most of the glands 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 many tortuous hair-like vessels on the surface, reminiscent of thy- 2. Microscopic Appearance On microscopic examination all the thvroids 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 tvpes. Unex- pectedly many of the adenomas werepapillary (Figure 31), but all except two of those that were papillary were considered benign. Mostofthe in- dividuals operated on later in the series were given a small tracer dose of !31I so that the functional nature of the adenomatousareas could be studied for radioiodine uptake.83.84 Multiple autoradio- roids 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- graphs prepared from tissues from the last 15 patients have shown thatessentially all the discrete were very firm, pale brown or whitish. In some vidual single lesion, which was papillary in character, took up more radioiodine thanthe surrouinding normalthyroid tissue. Although reducedradioiodine uptake does not necessarily indicate a malignantlesion, it is commonly observed that lesions ure 30). In some instances these discrete lesions 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 mannerthat the en- ure 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. lesions took up significantly less radioiodine than the non-nodular thyroid tissue and in many cases took up noneat all (Figure 32). Only in oneindi- having a capacity to metastasize take up far less radioiodine than the extranodulartissue (usually the ratio is < Yoo). Mostof the thyroids have been found to contain an unusual numberof minute encapsulatedlesions, some of them composed ofsolid cellular masses of cells (Figure 334, B, and D), in contrast tolesions 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 (pinhead size). 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 Figure 30. Gross serial sections of an irradiated Marshallese thyroid, showing multiple discrete adenomata developing throughout both lobes of the thyroid. Scarring is evident between these nodules. 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, which was found in a thyroid that also had a highly malignantlesion in a distantpart. Ofthe four malignantlesions found (Figure 35), two were papillary adenocarcinomasdisplaving someareas that wereless well differentiated, con-