Palpation thyroiditis (multifocal granulomatour folliculitis)

Unifocal Conventional Papillary Thyroid Carcinoma with Coexisting Caseating Granulomatous Inflammation in India

Thyroid cancer remains one of the leading endocrine malignancies with Conventional Papillary Thyroid Carcinoma (CVPTC) being the most commonly reported cancer. Caseating granulomatous inflammation is an unusual presentation in the thyroid even in places with high incidence of tuberculosis. The association of CVPTC with caseating granulomatous inflammation is infrequent. It can occur as a result of chronic inflammation which subsequently leads to DNA damage by producing nitric oxide and reactive oxygen species resulting in carcinogenesis. Other than tuberculosis, necrotizing granulomas in the thyroid can also be found in association with fungal diseases, plasma cell granulomas and palpation thyroiditis. We report a case of a 46-year-old lady who presented with neck swelling and dysphagia. Examination of the neck showed a firm, non-tender swelling involving the right lobe of the thyroid that moved with deglutination. The thyroid profile was normal. Ultrasound neck revealed a solitary nodule in the right lobe of the thyroid with heterogeneous architecture and increased vascularity. Fine needle aspiration (FNA) suggested Nodular colloid goitre (Bethesda Category II). Intraoperatively, the gland was stony hard and was found adherent to the underlying muscles with no obvious lymphadenopathy. A gross examination of the right hemithyroidectomy specimen revealed a single nodule with the cavity filled with multiple grey-white papillary excrescences along with an adjacent cystic cavity filled with colloid. Histopathological examination was suggestive of unifocal conventional papillary thyroid carcinoma with surrounding caseating granulomatous inflammation involving the right lobe of the thyroid (pT2 Nx Mx). CVPTC with coexisting caseating granulomatous inflammation is a rare presentation. The exact pathology of caseating granulomatous inflammation in our case is unknown. However, chronic inflammation might have played a role in tumorigenesis.

Retracting the thyroid matters: Who develops asymptomatic transient thyrotoxicosis after parathyroidectomy

BACKGROUND

Hyperthyroidism after parathyroidectomy is not a well-understood complication. We sought to determine the incidence and risk factors of hyperthyroidism after parathyroidectomy.

MATERIALS AND METHODS

This is a prospective study of 91 patients undergoing parathyroidectomy. Pre- and post-operative thyroid-stimulating hormone(TSH) and free thyroxine(T4) levels at two-week follow-ups were collected. Bivariate analyses were conducted to compare demographics, laboratory results, and intraoperative findings between patients with normal and suppressed post-parathyroidectomy TSH.

RESULTS

Twenty-two(24.2 ​%) patients had suppressed TSH after parathyroidectomy and 2(2.2 ​%) reported symptoms of hyperthyroidism. All hyperthyroidism resolved within 6 weeks. No patients required medical treatment. Compared to the normal TSH group, the suppressed TSH group had significantly more bilateral explorations(91.0 ​% vs. 58.0 ​%, p ​= ​0.006), and superior parathyroid resections(95.5 ​% vs. 65.2 ​%, p ​= ​0.006).

CONCLUSION

Transient hyperthyroidism is common following parathyroidectomy, which is likely associated with intraoperative thyroid manipulation. Gentle retraction of thyroid glands in parathyroidectomy is warranted, especially during superior parathyroid gland resection.

The Spectrum of Endocrine Pathology

Endocrine pathology comprises a spectrum of disorders originating in various sites throughout the body. Some disorders affect endocrine glands, and others arise from endocrine cells that are dispersed in non-endocrine tissues. Endocrine cells can broadly be classified as neuroendocrine, steroidogenic, or thyroid follicular cells; these three families have distinct embryologic origins, morphologic structure, and biochemical hormone synthetic pathways. Lesions affecting the endocrine system include developmental abnormalities, inflammatory processes that can be infectious or autoimmune, hypofunction with atrophy or hyperfunction caused by hyperplasia secondary to pathology in other sites, and neoplasia of many types. Understanding endocrine pathology requires knowledge of both structure and function, including the biochemical signaling pathways that regulate hormone synthesis and secretion. Molecular genetics has clarified sporadic and hereditary disease that is common in this field.

Inflammatory and Infectious Disorders in Endocrine Pathology

A variety of inflammatory conditions may directly involve the endocrine glands, leading to endocrine dysfunction that can cause severe consequences on patients' health, if left untreated. Inflammation of the endocrine system may be caused by either infectious agents or other mechanisms, including autoimmune and other immune-mediated processes. Not infrequently, inflammatory and infectious diseases may appear as tumor-like lesions of endocrine organs and simulate neoplastic processes. These diseases may be clinically under-recognized and not infrequently the diagnosis is suggested on pathological samples. Thus, the pathologist should be aware of the basic principles of their pathogenesis, as well as of their morphological features, clinicopathological correlates, and differential diagnosis. Interestingly, several systemic inflammatory conditions show a peculiar tropism to the endocrine system as a whole. In turn, organ-specific inflammatory disorders are observed in endocrine glands. This review will focus on the morphological aspects and clinicopathological features of infectious diseases, autoimmune disorders, drug-induced inflammatory reactions, IgG4-related disease, and other inflammatory disorders involving the endocrine system. A mixed entity-based and organ-based approach will be used, with the aim to provide the practicing pathologist with a comprehensive and practical guide to the diagnosis of infectious and inflammatory disorders of the endocrine system.

Acute Thyroiditis in a Patient with Neck Trauma

The management of patients with major depressive disorder who present with self-injurious behavior is best optimized through a collaborative interprofessional approach. We describe a case of a 27-year-old woman without personal or family history of thyroid pathology who presented at the emergency department due to a suicide attempt by hanging. On examination, she was tachycardic with palpitations which persisted despite administration of analgesics and anxiolytics. Left temporal area swelling, left otorrhagia, and neck contusion were noted, involving consults with the Trauma, Neurosurgery, and Otorhinolaryngology teams. She was admitted to the psychiatric ward on account of persistent suicidal ideations. As part of the workup, thyroid function tests were done to rule out hypothyroidism as a cause of depressive symptoms. Results instead showed suppressed thyroid stimulating hormone and elevated free T4. Endocrinology service was consulted, and further workup showed absence of avid uptake of both thyroid glands on thyroid scan and undetectable thyrotropin receptor antibody level, supportive of a diagnosis of trauma-induced thyroiditis. This case increases awareness that trauma-induced thyroid dysfunction should be considered in patients with symptoms including, but not limited to, tachycardia and palpitations after a traumatic neck injury such as hanging.

Transient Hyperthyroidism Induced by Thyroid Ultrasound

OBJECTIVES

Transient hyperthyroidism has been documented following surgical manipulation or direct trauma to the normal thyroid gland. This has best been studied in patients following parathyroidectomy and also reported following trauma to the neck, strangulation, and vigorous palpation of the thyroid gland. It has not previously been reported following a thyroid ultrasound.

METHODS

We report the case of a 58-year-old euthyroid woman with a large nontoxic multinodular goiter who developed transient hyperthyroidism following an ultrasound of the thyroid gland. She was not treated with anti-thyroid medications.

RESULTS

Two weeks later, her free T3 and free T4 were normal, and 11 weeks after the ultrasound, all thyroid tests, including her TSH, were within the reference range.

CONCLUSIONS

We believe this is the first report of a euthyroid individual who developed hyperthyroidism caused by thyroid ultrasonography. We hypothesize that pressure from the ultrasound probe during the examination compressed her large nodules, releasing stored hormone.

2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis

BACKGROUND

Thyrotoxicosis has multiple etiologies, manifestations, and potential therapies. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions and patient preference. This document describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspecialty physicians and others providing care for patients with this condition.

METHODS

The American Thyroid Association (ATA) previously cosponsored guidelines for the management of thyrotoxicosis that were published in 2011. Considerable new literature has been published since then, and the ATA felt updated evidence-based guidelines were needed. The association assembled a task force of expert clinicians who authored this report. They examined relevant literature using a systematic PubMed search supplemented with additional published materials. An evidence-based medicine approach that incorporated the knowledge and experience of the panel was used to update the 2011 text and recommendations. The strength of the recommendations and the quality of evidence supporting them were rated according to the approach recommended by the Grading of Recommendations, Assessment, Development, and Evaluation Group.

RESULTS

Clinical topics addressed include the initial evaluation and management of thyrotoxicosis; management of Graves' hyperthyroidism using radioactive iodine, antithyroid drugs, or surgery; management of toxic multinodular goiter or toxic adenoma using radioactive iodine or surgery; Graves' disease in children, adolescents, or pregnant patients; subclinical hyperthyroidism; hyperthyroidism in patients with Graves' orbitopathy; and management of other miscellaneous causes of thyrotoxicosis. New paradigms since publication of the 2011 guidelines are presented for the evaluation of the etiology of thyrotoxicosis, the management of Graves' hyperthyroidism with antithyroid drugs, the management of pregnant hyperthyroid patients, and the preparation of patients for thyroid surgery. The sections on less common causes of thyrotoxicosis have been expanded.

CONCLUSIONS

One hundred twenty-four evidence-based recommendations were developed to aid in the care of patients with thyrotoxicosis and to share what the task force believes is current, rational, and optimal medical practice.

Palpation thyroiditis following subtotal parathyroidectomy for hyperparathyroidism

Thyrotoxicosis is an under-recognised but clinically important complication of parathyroidectomy. We report a case of a 37-year-old man with tertiary hyperparathyroidism who initially developed unexplained anxiety, diaphoresis, tachycardia, tremor and hyperreflexia one day after subtotal parathyroidectomy. Thyroid biochemistry revealed suppressed thyroid stimulating hormone and elevated serum free T₄ and free T₃ levels. Technetium-99m scintigraphy scan confirmed diffusely decreased radiotracer uptake consistent with thyroiditis. The patient was diagnosed with thyrotoxicosis resulting from palpation thyroiditis. Administration of oral beta-adrenergic antagonists alleviated his symptoms and there was biochemical evidence of resolution fourteen days later. This case illustrates the need to counsel patients about thyroiditis as one of the potential risks of parathyroid surgery. It also emphasises the need for biochemical surveillance in patients with unexplained symptoms in the post-operative period and may help to minimise further invasive investigations for diagnostic clarification.

Multifocal fibrosing thyroiditis: report of 55 cases of a poorly recognized entity

During the course of our consultation activity, we have recognized a peculiar form of thyroiditis in which multiple foci of fibrosis, most of which were associated with reactive atypia of the surrounding follicles, are present. We have referred to this condition, both in our consultation reports and in the third series of A.F.I.P. Fascicle on Tumors of the Thyroid Gland, as "multifocal fibrosing thyroiditis" or (less frequently) "multifocal sclerosing thyroiditis," which are descriptive terms that highlight the benign/inflammatory nature of the process, its multiplicity, and its unknown pathogenesis. The aim of this study is to better define the morphologic features of this process and correlate it with some clinical data. With this purpose, the consultation files of one of the authors (J.R.) were searched for cases coded as multifocal fibrosing thyroiditis or multifocal sclerosing thyroiditis in a 20-year period ranging from January 1989 to December 2009. A total of 55 cases were identified that displayed the above-listed features. There were 51 (93%) female and 4 (7%) male patients (F/M=12.75), with ages ranging between 15 and 71 years (mean age, 47.03 y; median age, 44.5 y). Microscopically, multiple foci of fibrosis were identified in all cases, their number ranging from 2 to 51 per case (mean number, 16), with a mean diameter of 3 mm (range: 0.36 to 15.1 mm). Although heterogenous in shape and size, the individual foci were rather similar to each other in composition, being characterized by a fibrotic poorly cellular center that merged with a cellular peripheral zone. Some of the follicular structures present at the periphery of the scar and-to a lesser extent-those entrapped inside it underwent complex reactive and regenerative (atypical) changes that simulated malignancy. We discuss the differential diagnosis with other benign and malignant thyroid conditions and speculate about its pathogenesis and possible relationship with papillary thyroid microcarcinoma.

Transient Thyroiditis after Surgery for Tertiary Hyperparathyroidism: A Case Report

Parathyroid (PTH) exploration surgery carries the risk of developing post-operative thyroiditis due to vigorous manual manipulation of the thyroid gland during surgery. Post-operative thyroiditis has a wide spectrum of clinical manifestations. However, it remains underreported. Here, we describe a case of post-operative transient thyroiditis in a 33-year-old male who developed 3 days after parathyroidectomy for PTH hyperplasia. We review the limited literature regarding this interesting entity.

Dietary hyperthyroidism in dogs

OBJECTIVES

Evaluation of dogs with elevated plasma thyroxine concentration fed raw food before and after changing the diet.

METHOD

Between 2006 and 2011 all dogs presented with an elevated plasma thyroxine concentration and a dietary history of feeding raw food were included. Thyroxine (reference interval: 19·3 to 51·5 nmol/L) and in many cases also thyroid-stimulating hormone concentrations (reference interval: <0·30 ng/mL) were measured initially and after changing the diet.

RESULTS

Twelve dogs were presented with a median age of five years. The median plasma thyroxine concentration was 156·1 (range of 79·7 to 391·9) nmol/L; in six dogs, thyroid-stimulating hormone concentration was measured and was <0·03 ng/mL in five dogs and 0·05 ng/mL in one dog. Six dogs showed clinical signs such as weight loss, aggressiveness, tachycardia, panting and restlessness while six dogs had no clinical signs. After changing the diet eight dogs were examined: thyroxine concentration normalised in all dogs and clinical signs resolved.

CLINICAL SIGNIFICANCE

Dietary hyperthyroidism can be seen in dogs on a raw meat diet or fed fresh or dried gullets. Increased plasma thyroxine concentration in a dog, either with or without signs of hyperthyroidism, should prompt the veterinarian to obtain a thorough dietary history.

Palpation thyroiditis causing new-onset atrial fibrillation

OBJECTIVE

Surgery-induced thyroiditis can pose a significant clinical problem that is underappreciated. We present a case of new-onset atrial fibrillation as a consequence of palpation thyroiditis in a 70-year-old man who underwent radical right neck dissection for malignant melanoma and review the limited literature on this topic.

DESIGN

Biochemical parameters including thyrotropin, free thyroxine, triiodothyronine, erythrocyte sedimentation rate, C-reactive protein, thyroglobulin, thyroid stimulating immunoglobulins, thyroid binding inhibitory immunoglobulins, thyroid peroxidase, thyroglobulin antibodies, and 24-hour urine iodine were measured. Thyroid ultrasound and technetium-99m pertechnetate scintigraphy with radioactive iodine 131 uptake were employed for diagnostic purposes.

MAIN OUTCOME

Following right neck exploratory dissection, the patient developed hyperthyroidism and atrial fibrillation. Imaging studies were compatible with right lobar thyroiditis. Other etiologies of thyroiditis were excluded. Despite normalization of thyroid function after 2 weeks, atrial fibrillation persisted and required cardioversion.

CONCLUSIONS

Manipulation of the thyroid gland during neck exploratory surgery can result in hyperthyroidism with atrial fibrillation as a consequence. To avoid this complication, careful attention should be paid during surgical procedures or other clinical situations in which the thyroid gland is manipulated.

Role of fine needle aspiration cytology in thyroiditis

Fine needle aspiration (FNA) of thyroid is a cost-effective, simple, diagnostic tool in the initial screening of patients with thyroid lesions. Its role in a minimally enlarged thyroid in a symptomatic patient suspected of thyroid dysfunction is now well known. It plays an important role in the medical management of all nonpalpable/minimally enlarged thyroid (goiter) in patients suspect for thyroid pathology and/or in combination with thyroid-stimulating hormone, T3 and T4 levels by diagnosing early cases of thyroiditis. FNA may be of assistance in the early detection of subclinical hypothyroidism, which is of utmost importance in pregnant women, and further makes possible the availability of baseline values for future reference. With the implementation of this protocol of FNA thyroid with/without imaging, we affirm that the practice of cytology has differed in different geographic areas and from country to country, depending on economy and availability of infrastructure.

[Inflammatory diseases of the thyroid gland. Epidemiology, symptoms and morphology]

Inflammation of the thyroid gland makes up approximately 20% of all thyroid diseases. According to the clinical course, thyroiditis has been subdivided into acute, subacute, and chronic forms. Recent classifications are based on the fact that the majority of thyroiditis cases have an autoimmune background. The most common form of this disease is autoimmune thyroiditis (AIT), with or without subclinical/manifest hypothyroidism; less common forms of autoimmune thyroiditis comprise subacute granulomatous (de Quervain's) thyroiditis, postpartum thyroiditis, silent ("painless") thyroiditis, and invasive-sclerosing thyroiditis (Riedel's thyroiditis). Non-autoimmune thyroiditis is very rare (acute suppurative thyroiditis, radiation thyroiditis). Thyroiditis is both clinically and morphologically an important differential diagnosis of thyroid tumours. The present paper deals with the epidemiology, clinical course, and morphology of thyroiditis, knowledge of which is essential for the examination of cytological and histological thyroid specimens.

[Diagnostic relevance of multinucleated giant cells in papillary thyroid cancer. A cytological and histological study]

Cytological smears of 17 papillary carcinomas (PC) of the thyroid as well as histological slides of 58 PC and 50 follicular adenomas (FA) and 50 follicular carcinomas (FC) were reviewed to assess the presence of intrafollicularly located multinucleated giant cells. In accordance with the data published, such giant cells were found in 70% of PC but in only 8% of FA and FC. The presence of giant cells, which probably represents a foreign body reaction to, in case of PC, physicochemically altered colloid, is a useful additional criteria for the cytological and histological diagnosis of PC.

Focal sarcoid-like change of the thyroid gland. A possible consequence of aspiration cytology?

An unusual case of focal accumulation of sarcoid-like granulomas occurring within the thyroid gland of a 43-year-old female patient is reported. The granulomas were found solely at the site of previous fine needle aspiration biopsy. The follow-up did not show any symptoms of systemic granulomatous disease. The pathogenesis of this lesion is discussed.

Surgery-induced Thyroiditis: Fact or Fiction?

Neck surgery carries a risk that the patient will develop postoperative thyroiditis as a result of the surgical procedure. Surgery-induced thyroiditis can manifest in a mild form as serum hyperthyroxinemia or in a more severe form as clinical hyperthyroidism. We describe a case of surgery-induced thyroiditis and review the very limited literature on this subject.

Papillary carcinoma in thyroglossal duct cyst

OBJECTIVE

To report the management and outcome of three cases of papillary carcinoma (PC) in thyroglossal duct cysts (TGCs).

METHODS

We present case reports of one female and two male patients between the ages of 22 and 46 years who had TGCs. In addition, we discuss the theories about the pathogenesis of TGC carcinoma (de novo versus metastatic lesions).

RESULTS

In all three patients, we found a TGC that contained a vegetating mass. Subsequent pathologic examination revealed the presence of a PC. All patients underwent total thyroidectomy, and two of them concurrently had PC in the thyroid gland. Besides the PC in the TGC, the first patient had a "cold" scintigraphic thyroid nodule that was also a PC, whereas the second patient had a thyroid microcarcinoma that had not been detected before surgical intervention. The third patient did not have carcinoma of the thyroid, but the histologic pattern of the gland resembled that observed in de Quervain's disease. We interpreted this finding as "palpation thyroiditis." The patients received postoperative 131I and suppressive therapy with levothyroxine. During a follow-up period of 2 to 12 years (mean, 5.8), we found no recurrence of the disease, and serum thyroglobulin remained undetectable in all cases.

CONCLUSION

Although use of total thyroidectomy followed by radioiodine therapy and suppressive treatment with levothyroxine is a matter of debate in patients with PC in TGCs, we conclude that this approach yields a favorable outcome in most cases, especially when the thyroid is also involved by the PC, and allows a better postoperative follow-up.

Atypical subacute thyroiditis: preliminary observations

Nine patients with painless or minimally painful subacute thyroiditis were seen between late June and October 2000. Six had a history of antecedant viral symptoms. Thyroid peroxidase antibodies were negative in eight patients tested; none had a family history of autoimmune thyroid disease. It is possible that these patients represent examples of postviral painless subacute thyroiditis (atypical subacute thyroiditis). In order to establish the nature of the syndrome, cytological examination, HLA typing, and long-term follow-up are necessary.

Multinucleated giant cells in fine-needle aspiration of thyroid nodules: their diagnostic significance

Multinucleated giant cells (MNGCs) are reported in many thyroid lesions. This study examines whether their quantity and quality can help in the differential diagnosis. All fine-needle aspirations (FNAs) of the thyroid with a "significant" number of MNGCs were reviewed from 1995 -1998. There were 23 cases (<1% of thyroid FNAs): 8 papillary carcinomas (PC), 4 subacute thyroiditis (ST), 3 granulomas, 7 adenomatous goiters (AG), and one Hurthle-cell adenoma (HA). MNGCs with dense cytoplasm were seen exclusively in PC, ST, and granulomas. They had angulated shapes. They were most numerous, largest, and with the highest number of nuclei in ST and granulomas. MNGCs with foamy cytoplasm were seen in AG and HA and 80% of the other cases (PC, ST, and granulomas). In PC, rare MNGCs had intranuclear inclusions and grooves. The accompanying cell population was characteristic of each disease. The quantity and quality of MNGCs in thyroid FNA may be helpful in narrowing the differential diagnosis. Diagn. Cytopathol. 1999;21:307-312.

Histological features of the thyroid gland in a patient with lithium induced thyrotoxicosis

A 26 year old woman with lithium induced thyrotoxicosis is reported. The thyrotoxicosis was associated with a non-tender diffuse goitre and a low radioiodine uptake by the gland. The thyrotoxicosis was reversible and remitted on withdrawal of the drug. The histopathological alterations of the thyroid glad were characterised by extensive follicular cell disruption with no lymphocytic infiltration. It is postulated that lithium might directly damage thyroid follicular cells and that subsequent release of thyroglobulin into the circulation might be a cause of transient thyrotoxicosis.

Thyroid multifocal granulomatous folliculitis (palpation thyroiditis): An immunocytochemical study

We analyzed lymphoid cell populations from thyroid multifocal granulomatous folliculitis (palpation thyroiditis) with a panel of antibodies in order to assess the nature of the immunologic process underlying this otherwise clinically insignificant condition as compared with other specific types of thyroiditis. In general, T lymphocytes predominated over B lymphocytes as shown by the extent of the staining with UCHL-1 (CD45RO or CD3 and L26 (CD20) antibodies, respectively. The ratio of kappa-to-lambda-containing plasma cells was 1.4 to 1. Histiocytes, macrophages, and multinucleate giant cells were all found to stain consistently strongly with KPI (CD68) and, when intraluminal, not infrequently also for thyroglobulin, probaby due to colloid phagocytosis. The differing patterns of light chain restriction observed in multifocal granulomatous folliculitis as compared with Riedel's thyroiditis and Graves disease thyroiditis, for instance, may reflect differences in the nature of the underlying immune response.

Silent thyroiditis: a histologic and immunohistochemical study

Twenty-six specimens obtained from 23 patients with clinically and laboratory-proven silent thyroiditis were examined histologically; 11 specimens were obtained during the thyrotoxic phase, and 15 specimens during the early or late recovery phase. All specimens showed chronic thyroiditis, focal or diffuse type; and lymphoid follicles were present in about half of the specimens. Most specimens showed neither stromal fibrosis nor oxyphilic cell changes. The follicular disruptions, which varied from moderate to severe and involved nearly all the visible follicles, were characteristic and common histologic features of this disorder. Giant cells were present in about two thirds of specimens. Six of the 7 specimens taken during the late recovery phase showed no follicular disruption. In 3 patients who had follow-up biopsies, the histologic involvement in the initial biopsy specimens clearly had disappeared in the second biopsy specimens. These histologic features indicate that silent thyroiditis may be a form of chronic thyroiditis, i.e., "chronic thyroiditis with marked follicular destruction." Thyroid biopsy is recommended as a useful tool in differentiating this disease from other thyroid diseases causing hyperthyroidism. In addition to the histologic analysis, intrathyroidal lymphocyte subsets were examined immunohistochemically and compared to those in chronic thyroiditis (Hashimoto's thyroiditis). In both silent and chronic thyroiditis, a great majority of lymphocytes infiltrating between thyroid follicles showed a T-cell phenotype, and no significant differences in T-cell and B-cell distribution between the diseases were observed.

Patterns of human thyroid parenchymal reaction following low-dose childhood irradiation

Microscopic changes in the thyroids of 68 patients who had received low-dose childhood irradiation to the head and neck and who presented with palpable thyroid abnormalities culminating in surgery are compared to 34 control thyroids obtained from age- and sex-matched autopsy cases. Eighty-eight percent of irradiated thyroids showed moderate to severe focal hyperplasia, 51% contained single or multiple adenomas or adenomatous hyperplastic nodules, 68% exhibited chronic lymphocytic thyroiditis, 51% revealed colloid nodules, 42% presented with oxyphile change, 25% had mild fibrosis and 59% contained well-differentiated papillary, follicular or mixed thyroid carcinoma averaging 1.6 cm in diameter. Three small carcinomas were of the sclerosing type. The non irradiated thyroids showed 32% colloid nodule formation, 17% focal hyperplasia, 6% adenomatous hyperplasia and no identifiable carcinomas. Several nonspecific histologic abnormalities are now recognized as following low-dose radiation to the thyroid, the most important being focal hyperplasia, which may represent a pre-malignant change in thyroid parenchyma.