Distant and lymph node metastases of thyroid nodules with no pathological evidence of malignancy: a limitation of pathological examination

Pulmonary Metastatic Follicular Thyroid Carcinoma Without Intrathyroidal Primary Thyroid Cancer

Background/Objective

Follicular thyroid cancer without an intrathyroidal primary cancer is rare. We present a patient with multifocal pulmonary metastatic follicular thyroid cancer without apparent cancer within her thyroid.

Case Report

A 44-year-old woman was referred to the thyroid cancer clinic via telemedicine for evaluation of intrapulmonary thyroid tissue. Her past medical history included Roux-en-Y gastric bypass and hysterectomy with bilateral oophorectomy. Six months prior, abdominal computed tomography (CT) showed incidental bilateral lung nodules. Chest CT demonstrated 4 solid left and 1 solid right lung nodules. Lung nodule core biopsy revealed benign thyroid tissue. Thyroid ultrasound showed bilateral subcentimeter anechoic nodules. Chest CT 6 months after initial CT demonstrated stable lung nodules. The levels of thyroid-stimulating hormone, serum thyroglobulin, and thyroglobulin antibody were 1.63 mIU/L (reference range, 0.3-5.5 mIU/L), 40.9 ng/mL (reference range, 0-35 ng/mL), and <1 IU/mL (reference range, <4), respectively. Positron emission tomography/CT showed fluorodeoxyglucose-avid lung lesions measuring 1.5, 1.1, and 2.2 cm and other subcentimeter pulmonary nodules. Repeat lung core biopsy showed thyroid tissue with microfollicular architecture, favoring metastatic follicular carcinoma with neuroblastoma-RAS gene (NRAS) mutation. Total thyroidectomy performed showed multinodular hyperplasia without thyroid cancer. Her postoperative radioiodine scan demonstrated bilateral iodine-avid pulmonary nodules, a serum thyroglobulin level of 179.8 ng/mL, a thyroid-stimulating hormone level of 151.3 mIU/L, and undetectable serum thyroglobulin antibody. She received 261 mCi of radioactive iodine. Fourteen months later, chest CT revealed decreased lung nodules and a serum thyroglobulin level of 0.7 ng/mL.

Discussion

Approximately 2 cases of multifocal pulmonary follicular thyroid cancer without a primary source and no other site of metastasis have been reported.

Conclusion

Pulmonary follicular thyroid cancer without a primary source and no other site of metastasis is extremely rare.

Role of the Degree of Vascular Invasion in Predicting Prognosis of Follicular Thyroid Carcinoma

OBJECTIVE

The present study investigated the prognostic factors for follicular thyroid carcinoma (FTC) with the incorporation of the histologic subtype and degree of vascular invasion (VI).

PATIENTS

The records of 474 patients with FTC confirmed by surgical specimens at Ito Hospital from January 2005 to December 2014 were reviewed in this retrospective cohort study. The Cox proportional hazard model was used to determine factors associated with disease-free survival (DFS) and distant metastasis-free survival.

RESULTS

Of the 474 patients, 140 (30%) had minimally invasive FTC, 260 (55%) had encapsulated angio-invasive FTC, and 74 (16%) had widely invasive FTC. Among the 428 patients with M0 FTC, the 10-year DFS rates of patients with minimally invasive FTC (n = 133), encapsulated angio-invasive FTC (n = 247), and widely invasive FTC (n = 48) were 97.3%, 84.2%, and 69.9% (P < .001), respectively. A multivariate analysis identified aged ≥55 years (hazard ratio [HR], 2.204; 95% CI, 1.223-3.969; P = .009), histologic subtype (HR, 2.068; 95% CI, 1.064-4.021; P = .032), VI of ≥2 (HR, 6.814; 95% CI, 3.157-14.710; P < .001), and tumor size >40 mm (HR, 2.014; 95% CI, 1.089-3.727; P = .026) as independent negative prognostic factors for DFS.

CONCLUSION

Our study results may enable us to stratify the prognosis of FTC more accurately by combining the histologic subtype with the degree of VI ≥2, aged ≥55 years, and tumor size >40 mm.

Prevalence and diagnostic significance of non-invasive follicular thyroid neoplasm with papillary-like nuclear features in Japan-A multi-institutional study

This multi-institutional study investigated non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) frequency and its diagnostic significance in Japan. We reviewed 4008 thyroid nodules resected in six institutions before NIFTP was proposed. Overall, 26 cases diagnosed as non-invasive encapsulated follicular variant of papillary thyroid carcinoma (PTC) and 145 cases of follicular thyroid adenoma (FTA) were included. Of these nodules, 80.8% and 31.0%, respectively, were NIFTPs. In five institutions, NIFTPs were more commonly found in FTA than in PTC nodules. When NIFTP was included with PTC, the overall prevalence was 2.3%, with rates in five institutions below 5.0% (0.8%-4.4%). One NIFTP case with nuclear score 3 revealed nodal metastasis 2.5 years post-resection, and the carcinoma cells were immunohistochemically positive for BRAF. FTAs or NIFTPs with nuclear score 2 did not metastasize. NIFTP was more common among FTA than among PTC nodules, possibly due to underdiagnosis of PTC on nuclear findings. Considering the clinical findings, molecular pathogenesis, and therapeutic strategy in Japan, NIFTP with nuclear score 2 is not different from FTA, and use of this entity terminology is not meaningful. In contrast, NIFTP with nuclear score 3 has potential for metastasis and BRAFV600E mutation. Therefore, in NIFTP cases, nuclear scores 2 and 3 should be separately reported.

Unexpected Widespread Bone Metastases from a BRAF K601N Mutated Follicular Thyroid Carcinoma within a Previously Resected Multinodular Goiter

Follicular thyroid carcinoma (FTC) represents the second most common malignant thyroid neoplasm after papillary carcinoma (PTC). FTC is characterized by the tendency to metastasize to distant sites such as bone and lung. In the last 20 years, the understanding of the molecular pathology of thyroid tumors has greatly improved. Uncommon BRAF non-V600E mutations have been identified and are generally believed to associate with follicular patterned tumors of low malignant potential, particularly non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTPs) (i.e., non-invasive encapsulated follicular variant PTC). We here report for the first time widespread bone metastases from a BRAF K601N mutated follicular tumor.

The Autoantibodies against Tumor-Associated Antigens as Potential Blood-Based Biomarkers in Thyroid Neoplasia: Rationales, Opportunities and Challenges

The Autoantibodies targeting Tumor-Associated Antigens (TAA-AAbs) emerge as a result of a variety of tumor-related immunogenic stimuli and may be regarded as the eyewitnesses to the anti-tumor immune response. TAA-AAbs may be readily detected in peripheral blood to unveil the presence of a particular TAA-expressing tumor, and a fair number of TAAs eliciting the tumor-associated autoantibody response have been identified. The potential of TAA-AAbs as tumor biomarkers has been extensively studied in many human malignancies with a major influence on public health; however, tumors of the endocrine system, and, in particular, the well-differentiated follicular cell-derived thyroid neoplasms, remain understudied in this context. This review provides a detailed perspective on and legitimate rationales for the potential use of TAA-AAbs in thyroid neoplasia, with particular reference to the already established diagnostic implications of the TAA-AAbs in human cancer, to the windows for improvement and diagnostic niches in the current workup strategies in nodular thyroid disease and differentiated thyroid cancer that TAA-AAbs may successfully occupy, as well as to the proof-of-concept studies demonstrating the usefulness of TAA-AAbs in thyroid oncology, particularly for the pre-surgical discrimination between tumors of different malignant potential in the context of the indeterminate results of the fine-needle aspiration cytology.

Additional Tissue Sampling Trials Did Not Change Our Thyroid Practice

Simple Summary

Some studies have suggested that the use of additional tissue blocks to diagnose follicular thyroid carcinoma (FTC) could increase the accuracy of diagnosis and improve prognosis, and entire capsule sampling was recommended for a definitive diagnosis of borderline thyroid tumors in 2016. We conducted a study in 2016 to examine whether additional tissue sampling of the encapsulated follicular tumor increases the diagnosis of malignant cases in our patient cohort. Furthermore, the diagnosis was reclassified according to the 4th edition of the World Health Organization’s classification system. The additional tissue sampling only had a slight impact on our thyroid practice and resulted in no benefits to the patient; therefore, we decided to cease it.

Abstract

This study aimed to determine whether additional tissue sampling of encapsulated thyroid nodules would increase the frequency of follicular thyroid carcinoma (FTC) diagnoses. We examined thyroid tissue specimens from 86 patients suspected of FTC (84.9% female; mean age, 49.0 ± 17.8 years). The number of tissue blocks created for pathological assessments ranged from 3 to 20 (mean, 9.1 ± 4.1); the numbers in the previous method recommended by the Japanese General Rules for the Description of Thyroid Cancer and additional blocks ranged from 1 to 12 (mean, 6.0 ± 2.8) and from 1 to 8 (mean, 3.1 ± 2.0), respectively. The additional blocks were subsequently examined to determine whether any diagnoses changed from those based on the previous method. Five patients were diagnosed with FTC using the previous method; however, additional tissue blocks led to the diagnosis of FTC in 6 patients, as 1 diagnosis was revised from follicular adenoma to FTC. It has been reported that increasing the number of tissue blocks used for pathological assessments can increase the frequency of FTC diagnoses; however, this was not clinically significant in thyroid carcinoma, which requires completion thyroidectomy and radioactive iodine treatment. It resulted in no benefits to the patient because all minimally invasive FTCs, follicular tumors of uncertain malignant potential (FT-UMP), and follicular adenomas are treated with lobectomy alone in Japan. Additional tissue sampling only had a slight impact on our thyroid practice; therefore, we decided to cease it.

Ectopic intrapulmonary follicular adenoma diagnosed by surgical resection

Ectopic intrapulmonary thyroid tissue is extremely rare and considerably difficult to diagnose without surgery. Ectopic thyroid tissue, described as a mediastinal tumor, and intrapulmonary lesions are infrequent. An abnormal shadow was detected upon chest X-ray in a 60-year old woman with a history of benign thyroid goiter. A computed tomography scan revealed a solitary nodule measuring 27 mm in diameter in the left lower lobe, the diameter of which had increased by 5 mm since initial observation eight years ago. A thoracoscopic wedge resection was performed and the lesion was determined to be a non-invasive, soft-tissue tumor. It was pathologically diagnosed as an ectopic thyroid follicular adenoma. The course of the tumor was uneventful. A diagnosis of ectopic intrapulmonary thyroid should be made cautiously and only after ruling out metastasis of a follicular adenoma or thyroid carcinoma. This diagnosis of ectopic thyroid tissue was made possible by the surgical approach.

Macrofollicular Variant of Follicular Thyroid Carcinoma (MV-FTC) with a Somatic DICER1 Gene Mutation: Case Report and Review of the Literature

Benign thyroid lesions such as multinodular goiter and adenomatoid nodules are well-circumscribed lesions displaying a macrofollicular growth pattern and lack of nuclear atypia. The highly unusual macrofollicular variant of follicular thyroid carcinoma (MV-FTC) mirrors these attributes and is thereby misclassified by cytological examination of fine-needle aspiration biopsies. The MV-FTC diagnosis is instead suggested following histological investigation, in which malignant attributes, most commonly capsular invasion, are noted. The bulk of MV-FTCs described in the literature arise in younger female patients and carry an excellent prognosis. A recent coupling to mutations in the DICER1 tumor suppressor gene has been proposed, possibly indicating aberrancies in micro-RNA (miRNA) patterns as responsible of the tumorigenic process. We describe the cytological, histological and molecular phenotype of a 35 mm large MV-FTC arising in the right thyroid lobe of a 33-year-old female with a family history of multinodular goiter. The tumor was encapsulated and strikingly inconspicuous in terms of cellularity and atypia, but nevertheless displayed multiple foci with capsular invasion. A next-generation molecular screening of tumor DNA revealed missense variants in DICER1 (p. D1709N) and MET (p. T1010I), but no established fusion gene events. After sequencing of germline DNA, the DICER1 mutation was confirmed as somatic, while the MET variant was constitutional. The patient is alive and well, currently awaiting radioiodine treatment. This MV-FTC mirrors previous publications, suggesting that these tumors carry a favorable prognosis and predominantly arise in younger females. Moreover, DICER1 mutations should be considered a common driver event in the development of MV-FTCs.

Distant metastases from pathologically proven benign follicular nodules of the thyroid: clinicopathological features and predictors of long-term survival

OBJECTIVE

Distant metastases are rarely observed in patients with initial pathologically proven benign follicular nodules of the thyroid. This study aimed to evaluate the clinicopathological features and independent variables associated with survival in such patients with distant metastases.

METHODS

In total, 10,992 consecutive differentiated thyroid cancer (DTC) patients treated with ¹³¹I after total or near-total thyroidectomy from 2000 to 2018 were retrospectively reviewed.

RESULTS

Thirty-nine patients with initial pathologically proven benign follicular nodules of the thyroid were enrolled. Among them, 26 were pathologically diagnosed as thyroid adenoma, 8 as benign nodular goiter, 4 as thyroid adenoma combined with benign nodular goiter, and 1 as normal thyroid tissue. Of 26 patients with the initial pathological slides obtained, eight cases were rediagnosed as minimally invasive thyroid carcinoma (MI-FTC), 10 as follicular tumor of uncertain malignant potential (FT-UMP), and five as well-differentiated tumor of UMP (WDT-UMP). Monitoring of thyroglobulin (Tg) changes after initial thyroidectomy and preablation-stimulated Tg (psTg) level were significantly associated with 5-year OS rate (P = 0.007 and P = 0.005, respectively). The presence of radioactive-refractory DTC (RR-DTC), monitoring of Tg changes after initial thyroidectomy, and psTg level had significant effects on 10-year OS rate (P = 0.002, P < 0.001, and P = 0.005, respectively). Lack of monitoring of Tg changes after initial thyroidectomy and RR-DTC were independent factors associated with poor prognosis (P = 0.003 and P = 0.008, respectively).

CONCLUSIONS

MI-FTC, FT-UMP, and WDT-UMP tended to be ignored and/or misdiagnosed as benign follicular lesions. Lack of monitoring of Tg changes after initial thyroidectomy and the presence of RR-DTC were identified as independent factors associated with poor survival.

Macrofollicular Variant of Follicular Thyroid Carcinoma: A Rare Underappreciated Pitfall in the Diagnosis of Thyroid Carcinoma

Background: Follicular-patterned thyroid nodules predominantly composed of macrofollicular structures without nuclear atypia are generally regarded as benign (i.e., hyperplastic nodules or follicular adenomas). In line with this concept, fine-needle aspiration cytology (FNAC) also assigns a benign connotation to the presence of macrofollicular structures, unless thyrocytes present papillary thyroid carcinoma (PTC)-related nuclear features that raise the possibility of a macrofollicular variant of PTC. However, cases showing macrofollicular architecture, capsular invasion, and no PTC features can also be observed. Methods: We describe the clinical, cytological, histological, and molecular genetic features of four cases of encapsulated follicular neoplasms that presented histologically with a predominant (>70%) macrofollicular architecture, but which also showed clear signs of capsular invasion, and thus were classified as macrofollicular variant of follicular thyroid carcinoma (MV-FTC). Results: Cytologically, macrofollicular structures were identified in all cases, leading to a benign FNAC diagnosis in three of the four cases. Due to increasing nodule size, thyroidectomy was performed in all cases. Histology showed focal and limited capsular invasion, without vascular invasion. Next-generation sequencing (custom 394 gene panel) of each tumor compared with matched normal DNA revealed a total of 7 somatic variants, including dual (likely biallelic) mutations in the DICER1 gene in 2 patients. The clinical outcome was excellent in all cases. Conclusions: Similar to the classical minimally invasive follicular thyroid carcinoma, MV-FTC appears to behave indolently. MV-FTC has a high rate of false-negative FNAC results, but MV-FTC is very rare (<0.05% of all thyroidectomies) and apparently has an indolent behavior. Further studies comprising larger series are necessary to better clarify the biology of this diagnostically challenging rare tumor.

Unexpected Lung and Brain Metastases 9 Years After Thyroid Lobectomy for Follicular Adenoma: A Case Report

Background: Benign thyroid follicular tumors without histological evidence of carcinoma can metastasize. However, the pathogenesis of metastasis remains unclear. Here, the new proposed terminology, "non-invasive follicular thyroid neoplasm with papillary-like nuclear features" should be considered. We present a case of an encapsulated type of follicular variant of papillary thyroid carcinoma (FVPTC) that exhibited distant lung and brain metastases and was initially diagnosed as follicular adenoma. Case Report: In December 2006, a 64-year-old woman underwent ultrasonography-guided fine-needle aspiration of the right thyroid nodule at our hospital because of a palpable right neck mass. Right lobectomy was performed, and a follicular adenoma was diagnosed. In October 2015, she visited our hospital owing to dry cough and mild dyspnea and underwent computed tomography-guided transthoracic core needle biopsy for the lung nodule owing to probably multiple lung metastasis on chest X-ray and computed tomography. Based on retrospective analysis of the primary thyroid tumor and lung nodule specimen, an encapsulated follicular variant of papillary thyroid carcinoma with lung metastasis was confirmed. Conclusion: We report a case of an encapsulated follicular variant of papillary thyroid carcinoma with unexpected metastasis to the lung 9 years after thyroid surgery in a patient who was initially diagnosed as follicular adenoma. A careful close follow-up with re-examination of the histopathology specimen may be needed in patients who were diagnosed with benign thyroid follicular tumors.

Benign-Appearing Thyroid Follicles in Cervical Lymph Nodes: A Report of 3 Cases and a Review of the Literature

Thyroid carcinoma tissue is frequently found in cervical lymph nodes following metastasis of thyroid, and particularly, thyroid papillary carcinoma. However, thyroid follicles without any malignant characteristics also are frequently detected in cervical lymph nodes. The reasons for the existence of “benign thyroid tissue” in lymph nodes are presently not understood. We present 3 cases of benign-appearing thyroid follicles in cervical lymph nodes. All patients underwent thyroidectomy and a central neck dissection after discovery of thyroid nodules by ultrasonography. The intraoperative frozen pathology and postoperative pathology of the 3 cases demonstrated that the lymph nodes contained thyroid follicles without any malignant features, and that the thyroid glands only displayed benign diseases, such as nodular goiter and thyroiditis. The patients remained disease-free for 1 to 6 months without evidence of abnormal cervical lymph nodes at the latest follow-up. The incidence of benign-appearing thyroid follicles in cervical lymph nodes is high.

Noninvasive follicular thyroid neoplasm with papillary-like nuclear features: a review for pathologists

The rising incidence of papillary thyroid carcinoma is linked in part to inclusion of noninvasive follicular variant of papillary thyroid carcinoma. Despite its designation as carcinoma, noninvasive follicular variant of papillary thyroid carcinoma appears to be exceptionally indolent, often over treated by current treatment practices. Additionally, criteria for diagnosis have historically been subjective and challenging. Recently, an international multidisciplinary collaborative group performed a clinicopathologic survey of such cases with extended follow-up and concluded based on the outcome data that a revision in nomenclature was warranted, proposing 'Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features (NIFTP).' This monograph is a synopsis and guide for pathologists on NIFTP and focuses on histologic features, including inclusion and exclusion criteria used to define NIFTP, as well as grossing guidelines, reporting practices, and potential diagnostic limitations.

Multiple thyroid nodules in the lung: metastasis or ectopia?

Background

Intrapulmonary thyroid tissue with no malignant history of the thyroid gland is extremely rare. Usually, it is interpreted as ectopic thyroid tissue. Here we describe a case of bilateral pulmonary thyroid nodules with a history of multinodular thyroid goiter.

History

A 37-year-old female had recurrent multinodular thyroid goiter and showed bilateral pulmonary nodules on CT scan. Video-assisted thoracic surgery (VATS) was performed for the largest nodule biopsy. Pathological and molecular examinations were done after biopsy, and both were shown the characters of benign thyroid tissues. To eliminate the possibility of thyroid carcinoma metastases, total thyroidectomy with modified radical neck dissection was performed, and there were no malignant pathological findings. After surgery, this patient accepted adjuvant radiometabolic treatment for ablation of the remaining intrapulmonary nodules. Her thyroglobulin level decreased to an undetectable level, and she has currently survived for 24 months after surgery.

Clinical significance

In this case, pulmonary ectopic thyroid and metastasizing thyroid carcinoma should both be considered, but the metastatic pattern and benign pathological characters were inconsistent with any of the corresponding diagnosis. Ultimately, this patient accepted postoperative treatment of thyroid carcinoma metastasis.

Conclusions

This is a rare thyroid disease with malignant behavior but no pathological evidence. Careful diagnosis and postoprative follow-up should be carried out whenever such nodules are encountered in clinical practice.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1255194331453728.

Classification of thyroid follicular cell tumors: with special reference to borderline lesions

We propose a new classification of thyroid follicular cell tumors which is correlated with patient's prognosis. It is unique as to two new categories: borderline malignancy between benign and malignant, and moderately differentiated adenocarcinoma (MDA) as a differentiation classification to stratify tumor aggressiveness. As to diagnostic criteria, we recommend invasiveness (capsular and vascular invasion) to separate benign and malignant and it should not be based on presence or absence of papillary thyroid carcinoma (PTC) type nuclear features (PTC-N). Thus borderline malignancy in our new classification includes some of the formerly malignant tumors and they are 1) papillary microcarcinoma, 2) encapsulated conventional PTC (EncPTC), 3) encapsulated follicular variant PTC (EnFVPTC), 4) well differentiated tumor of uncertain malignant potential (WDT-UMP), 5) follicular tumors of uncertain malignant potential (FT-UMP), and 6) capsular invasion only follicular thyroid carcinoma (FTC). Review of the literature revealed that those thyroid tumors have consistently excellent outcome. Well differentiated follicular cell adenocarcinoma (WDA) in our classification includes common type PTC and low-risk follicular carcinoma (FTC). They are invasive (diffuse infiltrative) common type PTC and minimally invasive type FTC with less than 4 foci of angioinvasion. Moderately differentiated follicular cell adenocarcinoma (MDA) includes FTC with angioinvasion (more than 4), aggressive variants of PTC, such as tall cell, columnar cell, solid, loss of cellular polarity/cohesiveness (hobnail) variants and encapsulated carcinoma with high grade histology. Poorly differentiated carcinoma (PDC) includes PDC of WHO definition, insular carcinoma, tumors with minor anaplastic transformation and tumors with distant metastasis at presentation.

Measurement of TFF3 mRNA in aspirates from thyroid nodules using mesh filtration: the first clinical trial in 130 cases

Measurement of gene expression levels in thyroid tumor cells in aspirates was difficult because it is interfered with peripheral blood cells or infiltrating lymphocytes. In this study, we established a novel method to separate thyroid tumor cells from blood cells efficiently with mesh filtration. The expression level of trefoil factor 3 (TFF3) mRNA was estimated using LGALS3 mRNA as an internal control (T/G ratio) in 148 preoperative thyroid aspirates. Intra-assay coefficients of variation (CV) of T/G ratio for high, moderate, and low samples were 6.5%, 2.5%, and 9.7%, respectively, and inter-assay CV for high, moderate, and low samples were 27.7%, 21.9%, and 38.2%, respectively. Nondiagnostic samples in terms of T/G ratio and cytology were 12.2% and 16.9%, respectively. We observed no interference with the data by contaminating blood cells. Among these patients, 12 patients received more than two repeated aspirations. We did not observe a marked day-to-day variation except in two cases. All 13 preoperative aspirates diagnosed as malignant by cytology showed an extremely low T/G ratio, whereas 93 aspirates diagnosed as benign by cytology showed extremely varied T/G ratios and 21.5% of them showed a T/G ratio below the cut-off value. Eleven cases underwent surgery. All nodules showing a low T/G ratio were diagnosed as papillary carcinoma by pathological diagnosis. However, one nodule diagnosed as follicular adenoma after surgery showed a high T/G ratio. Our present method may be a promising preoperative test for measuring mRNAs in thyroid aspirates.

Brain metastasis from thyroid adenomatous nodules or an encapsulated thyroid follicular tumor without capsular and vascular invasion: a case report

Because benign-appearing thyroid nodules with metastasis are very rare, the author reports herein four thyroid nodules (one follicular adenoma and three adenomatous nodules) with brain metastasis. A 75-year-old Japanese woman was admitted to our hospital because of thyroid mass. Imaging modalities revealed four distinct nodules in the thyroid, and tumorectomies of all nodules were performed under the clinical diagnosis of benign thyroid nodules. Grossly, one of them was a completely encapsulated tumor (35 mm in diameter). Other three nodules were non-encapsulated nodules (10 mm, 8 mm, and 7 mm in diameters). Multiple sections were obtained from the largest nodule. One section was obtained from each of the smaller three nodules. Microscopically, the largest tumor was an encapsulated follicular adenoma. The tumor consisted of normofollicles and microfollicles surrounded by a fibrous capsule. Neither capsular invasion nor vascular permeation was recognized. The parenchyma lacked nuclear atypia, mitotic figures, degenerative changes, papillary structures, nuclear inclusions, nuclear ground-glass features, and nuclear grooves. Thus, the largest tumor was diagnosed as follicular thyroid adenoma. The remaining three small nodules were typical adenomatous nodules composed of normofollicles and macrofollicles without nuclear atypia, mitotic figures, degenerative changes, papillary structures, nuclear inclusions, nuclear ground-glass features, and nuclear grooves. Therefore, a diagnosis of adenomatous nodules (goiters) was made. However, six years later, the patient showed a brain metastasis of thyroid tumor composed of macrofollicles without cellular and nuclear atypia. A diagnosis of metastatic follicular thyroid carcinoma was made. The present case suggests that benign thyroid nodules can metastasize.

Macrofollicular variant of papillary thyroid carcinoma: its clinicopathological features and long-term prognosis

Macrofollicular variant is a rare entity of papillary carcinoma. We previously demonstrated that this variant accounts for 0.3% of papillary carcinoma in Japan. In this study, we investigated the biological characteristics of 5 cases of macrofollicular variant. We reviewed the diagnosis and clinical course of 5 patients with macrofollicular variant. On preoperative ultrasonographic study, 2 cases were diagnosed as having benign nodule and the remaining 3 suspected of having papillary carcinoma, although they lacked typical ultrasonographic findings of papillary carcinoma. Cytological findings suggested papillary carcinoma for 3 cases and the remaining 2 were diagnosed as indeterminate. Based on both examinations, 4 of 5 patients were diagnosed as having or suspected of having papillary carcinoma. All patients underwent thyroidectomy with lymph node dissection. Three patients underwent central node dissection and the remaining 2 underwent modified radical neck dissection. None of these patients showed clinically apparent node metastasis or massive extrathyroid extension, although 3 of these patients had latent node metastasis confirmed by pathological examination. All patients survived with no evidence of carcinoma recurrence during follow-up (145-235 months). It is therefore suggested that patients with macrofollicular variant can be diagnosed as having or suspected of having papillary carcinoma if ultrasonographic and cytological examinations are appropriately performed and show an excellent prognosis possibly because this variant lacks the aggressive characteristics of papillary carcinoma.