Diagnosis Of Follicular Neoplasm Research Articles

Fine needle aspiration of follicular lesions of the thyroid

Background: Fine needle aspiration (FNA) is a reliable method in the initial assessment of thyroid nodules. This study evaluated the accuracy of fine needle aspiration cytology (FNAC) in cases of follicular neoplasm (FN) on the basis of histologic diagnosis, and reviewed the cytologic findings of FN according to the FNAC.Method: Among the 100 cases diagnosed with thyroid Follicular Neoplasm by FNAC during the 3 year period from October 2020 to September 2022, 54 cases that had undergone thyroid surgery were available for review. Cytologic diagnosis was compared with the histologic diagnosis of each case.Results: Among the 54 cases with a cytologic diagnosis of thyroid FN, histologic diagnosis was as follows: 32 follicular adenomas (59.3%), 4 Hurthle cell adenomas (7.4%), 2 follicularcarcinomas (3.7%),10 nodular goitres (18.5%), 2 papillary carcinomas (3.7%), and 1 Hashimoto'sthyroiditis (3.7%), resulting in a diagnostic accuracy of FNAC for thyroid FN of 70.4%.Conclusion: This study shows that FNAC for thyroid FN is a useful primary screening method because when FN is diagnosed by FNAC, the rate of FN histological diagnosis is relatively high and however, adequate sampling and experience is a prerequisite for this procedure.

Criteria for follow-up of thyroid nodules diagnosed as follicular neoplasm without molecular testing - The experience of a high-volume thyroid centre in Japan.

BackgroundClinical management of follicular neoplasms (FNs) using molecular testing of thyroid‐aspirated materials is not routinely performed in Japan. This article aims to identify low‐risk FN nodules that can be followed up without molecular testing.MethodsThe relationship between preoperative findings, factors influencing surgical decision, and the risk of malignancy (ROM) was examined in 356 thyroid nodules with cytological diagnosis of FN at Kuma Hospital from January to December 2020.ResultsROMs of FN with cytology results favouring malignancy (41.2%) were significantly higher than those favouring benign (7.7%) or borderline (8.2%) (p < .001). Moreover, ROMs of FN with ultrasonography results of high suspicion (54.5%) were significantly higher than those with low (4.5%) or intermediate suspicion (0%) (p < .0001). There was a large difference in overall ROM in tumours bordering 30 mm in size (<30 mm; 3.6%, ≥30 mm; 20.0%). ROMs of FNs with a tumour volume doubling rate (TVDR) of 1.0/year or more (28.6%) were higher than those of FNs with a lower TVDR (9.9%) (p < .05). The ROMs of FNs with or without one or more of the following four findings suggestive of malignancy: cytological findings favouring malignancy, ultrasonography findings of high suspicion, tumour size ≥30 mm, and TV‐DR ≥1.0/year, were 14.6% and 1.0%, respectively.ConclusionFNs with no cytological findings favouring malignancy, no ultrasonography findings of high suspicion, tumour size <30 mm and TV‐DR <1.0/year, are considered low risk and can be followed up without the need for molecular testing.

Follicular neoplasm of the thyroid: can clinical, ultrasonographical and cytological factors be used to predict carcinoma and determine extent of surgery

Background: The optimal management of cytologically indeterminate thyroid nodules in follicular neoplasm is controversial. We examined the prevalence of malignancy within cytologically indeterminate follicular thyroid lesions in an attempt to predict malignancy based on clinical, sonographic and cytologic features.Methods: Retrospective study was done in between April 2017 to July 2019 of 46 patients having a diagnosis of follicular neoplasm on fine needle aspiration cytology.Results: A total of 46 patients (8 men, 38 women; mean age 47 year) with indeterminate cytology underwent thyroidectomy and had histopathological diagnoses. The prevalence of malignancy in patients was 34.7%. The size of nodules and ultrasonographic feature were significant predictor of malignancy with p value &lt;0.05.Conclusions: Author can predict malignancy in follicular neoplasm of thyroid with indeterminate nodule by using clinical and sonographic feature for the best compromise between the risk of missing carcinomas and the need for reducing unnecessary surgical procedures and cost benefit of the patients.

Morphology combined with ancillary techniques: An algorithm approach for thyroid nodules.

Several authors have underlined the limits of morphological analysis mostly in the diagnosis of follicular neoplasms (FN). The application of ancillary techniques, including immunocytochemistry (ICC) and molecular testing, contributes to a better definition of the risk of malignancy (ROM) and management of FN. According to literature, the application of models, including the evaluation of ICC, somatic mutations (ie, BRAFV600E ), micro RNA analysis is proposed for FNs. This study discusses the validation of a diagnostic algorithm in FN with a special focus on the role of morphology then followed by ancillary techniques. From June 2014 to January 2016, we enrolled 37 FNs with histological follow-up. In the same reference period, 20 benign nodules and 20 positive for malignancy were selected as control. ICC, BRAFV600E mutation and miR-375 were carried out on LBC. The 37 FNs included 14 atypia of undetermined significance/follicular lesion of undetermined significance and 23 FN. Specifically, atypia of undetermined significance/follicular lesion of undetermined significance resulted in three goitres, 10 follicular adenomas and one NIFTP whereas FN/suspicious for FN by seven follicular adenomas and 16 malignancies (nine non-invasive follicular thyroid neoplasms with papillary-like nuclear features, two invasive follicular variant of papillary thyroid carcinoma [PTC] and five PTC). The 20 positive for malignancy samples included two invasive follicular variant of PTC, 16 PTCs and two medullary carcinomas. The morphological features of BRAFV600E mutation (nuclear features of PTC and moderate/abundant eosinophilic cytoplasms) were associated with 100% ROM. In the wild type cases, ROM was 83.3% in presence of a concordant positive ICC panel whilst significantly lower (10.5%) in a negative concordant ICC. High expression values of MirR-375 provided 100% ROM. The adoption of an algorithm might represent the best choice for the correct diagnosis of FNs. The morphological detection of BRAFV600E represents the first step for the identification of malignant FNs. A significant reduction of unnecessary thyroidectomies is the goal of this application.

Predictive Factors of Malignancy in Cytology of Indeterminate Follicular and Hürthle Cell Neoplasms of the Thyroid Gland

The objective of the current study was to determine the risk of malignancy in patients with thyroid nodules with cytology of indeterminate follicular and indeterminate Hürthle cell neoplasm (HN). The cytologic diagnosis of follicular neoplasm (FN) or HN remains a diagnostic challenge. Often, surgery is recommended for such lesions. A retrospective analysis was performed on 80 patients who underwent thyroid surgery following a diagnosis of indeterminate FN and indeterminate HN in thyroid fine-needle aspiration biopsy. Sex; age; family history of thyroid cancer and radiation exposure; coexisting thyroid conditions, such as solitary nodule; multinodularity; cytologic diagnosis; sonographic features; type of surgical treatment; and histopathologic results were recorded. Of the 80 patients, 52 (65%) had FN on fine-needle aspiration biopsy cytology and 28 (35%) had HN. A total of 23 patients (28.7%) had primary thyroid cancers on surgical pathology, and 57 (71.3%) had benign diagnoses. Univariate analysis showed no differences between the benign and malignant groups by sex, nodule size, family history of thyroid cancer, history of radiation exposure, presence of solitary nodule or multinodularity in the nodular features. In multivariate binary logistic regression analysis, the factors that were statistically significant predictors of malignancy were microcalcification [odds ratio (OR), 10.9; 95% confidence interval (CI), 2.18–54.7; P = 0.004], being older than 45 years (OR, 4.2; 95% CI, 1.25–14.63; P = 0.02]. The independent predictors of malignancy in FN and HN are micorcalcification and being older than 45 years, the use of which may predict the risk of thyroid cancer.

Cytological Features That Differentiate Follicular Neoplasm from Mimicking Lesions.

BackgroundIt is difficult to correctly diagnose follicular neoplasms (FNs) on fine-needle aspiration cytology (FNAC) because it shares many cytological features with other mimicking lesions. The aim of this study was to identify the cytological features that differentiate FNs from mimicking lesions. MethodsWe included the cytological slides from 116 cases of thyroid FN diagnosed on FNAC, and included their subsequent histological diagnoses. We evaluated the cytological architectural pattern and nuclear features of the lesions according to their histological groups. ResultsThe final histological diagnoses of the 116 cases varied, and included 51 FNs (44%), 47 papillary thyroid carcinomas (40%) including follicular variant, and seventeen cellular nodular hyperplasias (15%). Regardless of the final histological diagnosis, microfollicular pattern was observed in most cases. On the other hand, trabecular pattern was identified in 34% of FNs, but not in any other lesions. Additionally, elongated nuclei and ground glass chromatin were found in only some papillary thyroid carcinomas. ConclusionsThis study shows that the trabecular pattern is a representative cytological feature of FNs that can be used to distinguish FNs from mimicking lesions. In addition, nuclear shape and chromatin pattern can be used to further confirm the diagnosis of FNs from mimicking lesions through FNAC.

How to solve problems in diagnosis of follicular neoplasms

How to solve problems in diagnosis of follicular neoplasms

Handling of resected thyroid specimens and diagnosis of follicular tumors

Handling of resected thyroid specimens and diagnosis of follicular tumors

Intraoperative Frozen Section May Reduce the Need for Reoperative Thyroid Surgery in Patients with Follicular Neoplasm

Background: Follicular neoplasm (Bethesda IV cytology) requires thyroid lobectomy for diagnosis. Approximately 15-30% of cases are ultimately malignant, requiring reoperative completion thyroidectomy. We sought to reassess whether intraoperative frozen section (FS) reduces the need for reoperative thyroidectomy in these cases. Methods: A retrospective chart review of fine needle aspiration (FNA) results showing follicular neoplasm from 2003 to 2012 was performed. Our practice is to offer thyroid lobectomy with FS for these patients; with suspicious FS, surgery proceeded to total thyroidectomy. FS suspicious for papillary thyroid carcinoma (PTC) was based on nuclear features (nuclear grooves/atypia, pseudo-nuclear inclusions) and for follicular thyroid carcinoma (FTC) was based on capsular/vascular invasion. Results: A total of 148 patients with follicular neoplasm on FNA were identified, of which 79 underwent FS. Fifteen had suspicious FS with 12 having malignancy on final pathology, for a positive predictive value of 80%. Nine showed features suspicious for PTC, of which eight had PTC. Six showed features suspicious for FTC, of which four had malignancy on final pathology. Of the 64 patients with unremarkable FS, 49 had benign final pathology, for a negative predictive value of 77%. Twelve (19%) patients required reoperation. Seven of 19 patients (37%) with malignancy avoided reoperation due to FS. Risk of malignancy with follicular neoplasm diagnosis was 34% (51/148), while risk of malignancy with follicular neoplasm and suspicious FS was 80%. Conclusions: Risk of malignancy with follicular neoplasm and suspicious FS is 80%. FS may avoid reoperative completion thyroidectomy in up to a third of patients. J Curr Surg. 2016;6(1):1-5 doi: http://dx.doi.org/10.14740/jcs286w

Efficacy of fine needle aspiration-yielded cell block combined with molecular markers in the diagnosis of thyroid nodules

Objective To study the clinical efficacy of cell block yielded by ultrasound-guided fine needle aspiration in the early diagnosis of thyroid cancer and differential diagnosis of thyroid follicular tumor. Methods Cytological smears were performed in 864 thyroid nodules by ultrasound-guided fine needle aspiration. Then the residual specimens were made as cell blocks. Diagnosis was made by observation of the organization structure of the cell block. Cell block sections from 78 nodules with diagnosis of follicular tumors were applied to the detection of immunocytochemical staining for minichromosome maintenance protein(MCM2), growth arrest and DNA damage-induced nuclear protein 153(GADD153), and Ki-67. Results Satisfaction rate of cytological smear combined with cell block specimen was 94.3%(815/864)and accuracy rate of the diagnosis was 94.0%(766/815), which were higher than in cytological smear group(P 0.05). Conclusions The combination of ultrasound-guided fine needle aspiration-yielded cell block and molecular markers has great significance in early diagnosis of thyroid cancer and differentially diagnosis of thyroid follicular tumor. (Chin J Endocrinol Metab, 2015, 31: 932-936) Key words: Thyroid; Fine needle aspiration; Cell block; Molecular marker; Follicular tumor

Core-needle biopsy for the preoperative diagnosis of follicular neoplasm in thyroid nodule screening: A validation study

The role of ultrasound-guided core-needle biopsy (CNB) for the diagnosis of follicular neoplasm (FN) in the screening of thyroid nodules is controversial. We developed a diagnostic system for FN in CNB specimens and aimed to validate the clinical usefulness of the method compared with fine-needle aspiration cytology (FNAC). We reviewed 5993 FNACs and 1303 CNBs from the pathology database at Seoul St. Mary's Hospital between August 2012 and December 2014. The diagnostic rate of FN was significantly higher in CNB than in FNAC (15.7% vs. 2.4%, respectively; P<0.001). A total of 289 cases (117 FNACs and 172 CNBs) were confirmed histologically after surgical resection. NRAS mutation testing was performed with pyrosequencing. Comparing the FNAC and CNB groups, there were no differences in the positive predictive values for neoplasm (84.6% vs. 89.0%, respectively; P=0.200) and malignancy (48.7% vs. 43.0%, respectively; P=0.340). When we excluded the noninvasive encapsulated follicular variant of papillary carcinoma from the malignancy group, there was also no significant difference in the malignancy risk between the two groups (22.7% and 27.4% in the CNB and FNAC groups, respectively; P=0.365). The NRAS mutation rate was 26.5% (57/215) in all FNs and occurred with similar frequency in both groups. The sensitivity, specificity, positive predictive value, and negative predictive value of a NRAS testing to predict malignancy were 40.6%, 84.9%, 68.4%, and 63.9%. In conclusion, FN was more frequently diagnosed in the CNB group than in the FNAC group, but the rates of malignancy, neoplasm, and NRAS mutation were equivalent in both groups. Therefore, CNB is a good method for the diagnosis of FN in thyroid nodule screening.

Skin adnexal tumors with follicular differentiation

Skin adnexal tumors with predominantly follicular differentiation represent a clinicopathological heterogeneous group of neoplasms and are classified according to the cytologically achieved differentiation of the follicular compartment. Given the complex structure of non-neoplastic hair follicles it is not surprising to find varying differentiations in neoplasms and there are overlapping clinicopathological features between the established entities. The use of immunohistochemical staining has only a limited value in the diagnosis of follicular neoplasms.

Risk stratification in follicular neoplasm: a cytological assessment using the modified Bethesda classification.

The 2007 Bethesda classification for thyroid cytology defines follicular neoplasm as a category of cases with cellular specimens demonstrating abundant follicular cells arranged in a microfollicular pattern with little or no colloid. The current recommendation for the management of these cases is diagnostic lobectomy. There has been great difficulty and variability in triaging and reporting follicular neoplasm. To increase diagnostic accuracy, at the study institution, this category is subclassified further into 3 categories: 1) microfollicular-patterned neoplasm (MN); 2) Hürthle cell neoplasm (HN); and 3) follicular lesion with some features suggestive of but not diagnostic of the follicular variant of papillary thyroid carcinoma (FL). The authors reviewed the cases of follicular neoplasm observed over a period of 5 years to document the follow-up trend using this modified classification. A search of the cytology records was performed for the period between January 2008 and December 2012. All thyroid fine-needle aspiration cases were reviewed and those with a diagnosis of follicular neoplasm (including Hürthle cell neoplasm) were identified. Correlating follow-up surgical pathology reports were reviewed. A total of 399 cases of follicular neoplasm with surgical follow-up were identified. Malignancy was identified in 32% of all cases of follicular neoplasm and was found to be disproportionately higher in the FL category (73%). A cytological diagnosis of FL is more likely to be called malignant (73%) than benign neoplastic (9%) or benign nonneoplastic (18%). A cytological diagnosis of MN or HN is more likely to be benign neoplastic (46% and 46%, respectively) than malignant (29% and 26%, respectively) or benign nonneoplastic (25% and 28%, respectively). Of the cytological features examined, 2 (nuclear enlargement and nuclear grooves) were significantly associated with the follicular variant of papillary thyroid carcinoma. The results of the current study clearly indicate that follicular lesions with even subtle nuclear atypia have a high positive predictive value for malignancy and therefore should be distinguished from other follicular lesions because these cases require more aggressive surgical management. The current study also raises an important issue concerning the current thyroid classification based on the 2007 Bethesda classification for thyroid cytology. Future thyroid fine-needle aspiration classification schemes should consider subclassifying follicular neoplasms for the purpose of risk stratification.

Unexpected conversion from hypothyroidism to an euthyroid state due to Graves’ disease in a patient with an ectopic thyroid

A 15-year-old woman was diagnosed with hypothyroidism and unilateral ectopic thyroid. Levothyroxine treatment was introduced; however, the patient was non-compliant and took the medication irregularly. When she presented to an endocrinologist at the age of 30, she had not been using levothyroxine for at least 6 months. Surprisingly, she was clinically and biochemically euthyroid. Due to decreased echogenicity on ultrasound examination, enhanced vascularization on Color Doppler examination and increased concentration of anti-TSH receptor autoantibodies, she was diagnosed with Graves’ disease. Eventually, she underwent total thyroidectomy due to diagnosis of follicular neoplasm in fine-needle aspiration biopsy of the focal lesion found in the thyroid gland. To our knowledge, our patient is the first described with ectopic thyroid, presenting a nodular variant of Graves’ disease and no signs of orbitopathy, who was initially hypothyroid and became euthyroid in the course of autoimmune thyroid disease.Electronic supplementary materialThe online version of this article (doi:10.1007/s12020-013-0117-6) contains supplementary material, which is available to authorized users.

Malignant Lesions in Follow-up Surgery after a Diagnosis of Follicular Neoplasm on Thyroid Fine Needle Aspiration

s S51 Conclusions: Incidental thyroid “non-microcarcinomas” (>1 cm) are rare and found in approximately 0.5% of resection specimens. The majority of these represent low-grade carcinomas and the incidenceoffindingoneof the common mutations (40%) is less than that for thyroid carcinomas in general (70%).

Impact of the Gene Expression Classifier on Surgeon‐Patient Decision Making in Indeterminate Thyroid Nodules

Objectives: 1) Describe the impact the gene expression classifier has on management of indeterminate thyroid nodules. 2) Define patient and nodule characteristics which influence further testing with the gene expression classifier (GEC) versus diagnostic thyroidectomy (DT). Methods: A retrospective chart review was performed on 273 patients who underwent fine-needle aspiration (FNA) for thyroid nodules from November 2011 to January 2013. We further analyzed 68 patients with cytological indeterminate aspirates. These patients were offered serial observation with repeat FNA, GEC testing, or DT. Demographic data, cytologic and histologic findings, and management outcomes will be discussed. Results: In 68 patients with indeterminate cytology, 47% underwent GEC testing, 52% chose DT, and 1% elected for continued observation. The mean age in patients who underwent GEC testing was 57 years and 49 years in those who elected DT (p&lt;0.05). Patients with a Bethesda classification of suspicious for malignancy were more likely to undergo DT, whereas those with a diagnosis of atypical of undetermined significance (AUS) or follicular neoplasm (FN) were more likely to obtain the GEC test (p&lt;0.05). Those factors not found to be statistically significant were gender and size of the nodule (p&gt;0.05). Thirty-seven percent of patients with an AUS or FN diagnosis who obtained the GEC test underwent a DT. However, of those patients with an AUS or FN diagnosis who did not obtain the GEC test, 97% underwent a DT (p&lt;0.0001). Conclusions: Use of the GEC significantly reduced the surgical rate among patients with a Bethesda classification of AUS or FN.

Diagnostic accuracy of fine needle aspiration biopsy cytology and ultrasonography in patients with thyroid nodules diagnosed as benign or indeterminate before thyroidectomy

Fine-needle aspiration biopsy cytology (FNABC) and ultrasonography (US) play an important role in differentiating benign thyroid nodules from malignant nodules. We retrospectively investigated the prevalence of follicular thyroid carcinoma (FTC) in patients with thyroid nodules whose FNABC and US readings were not malignant before thyroidectomy. Between 2007 and 2008, 3333 patients underwent thyroidectomy at our institution, and the 737 of them who had thyroid nodule that had been diagnosed as hyperplastic nodule or follicular tumor by FNABC and US preoperatively were the subjects in this study. Postoperative histopathology showed hyperplastic nodule in 416 patients, follicular adenoma in 200 patients, FTC in 99 patients, and other disease in 22 patients. By FNABC, 34 (6.7%) of the 505 patients with diagnosis as benign and 65 (28%) of the 232 patients with diagnosis as indeterminate, were diagnosed as having FTC. The diagnosis was FTC in 56 (9.6%) of the 582 patients with a preoperative diagnosis of hyperplastic nodule by US and 43 (27.7%) of the 155 patients with a diagnosis of follicular tumor by US. The diagnosis of FTC was made in 21 (4.8%) of 438 patients who were concurrently diagnosed as benign by FNABC and as hyperplastic nodule by US, and in 30 (34.1%) of 88 patients who were diagnosed as indeterminate by FNABC and follicular tumor by US. FNABC has been the mainstay for the preoperative evaluation of thyroid nodule. The results of this study showed that US can also be a useful tool for diagnosing FTC.

Fine needle aspiration cytology of thyroid follicular neoplasm: cytohistologic correlation and accuracy.

BackgroundThis study evaluated the accuracy of fine needle aspiration cytology (FNAC) in cases of follicular neoplasm (FN) on the basis of histologic diagnosis, and reviewed the cytologic findings of FN according to the FNAC.MethodsAmong the 66 cases diagnosed with thyroid FN by FNAC during the 7-year period from 2003 to 2009, 36 cases that had undergone thyroid surgery were available for review. Cytologic diagnosis was compared with the histologic diagnosis of each case.ResultsAmong the 36 cases with a cytologic diagnosis of thyroid FN, histologic diagnosis was as follows: 20 follicular adenomas (55.6%), 3 Hurthle cell adenomas (8.3%), 2 follicular carcinomas (5.6%), 8 nodular goiters (22.2%), 2 papillary carcinomas (5.6%), and 1 Hashimoto's thyroiditis (2.8%), resulting in a diagnostic accuracy of FNAC for thyroid FN of 69.5%.ConclusionsThis study shows that FNAC for thyroid FN is a useful primary screening method because when FN is diagnosed by FNAC, the rate of FN histologic diagnosis is relatively high, however, adequate sampling and experience is a prerequisite for this procedure.

Follicular carcinoma in a 9-year-old child: A case report and review of literature

Thyroid cancer is rare in children and is mostly of the papillary carcinoma histologically. Follicular carcinoma constitutes 10-20% of all primary thyroid cancers with the age peak at the fourth and fifth decades. Iodine deficiency appears to be the main contributing factor for follicular carcinoma because iodine supplementation to the diet has been associated with a decline in the incidence of this tumor in iodine-deficient areas. A 9-year-old female patient who was under treatment for hypothyroidism presented with a single thyroid nodule, which on fine needle aspiration cytology, a cytologic diagnosis of follicular neoplasm was made. A histological diagnosis of minimally invasive follicular carcinoma was done after subtotal thyroidectomy. This case was presented with review of the literature.

Risk of malignancy in follicular thyroid neoplasm

SummaryThe cytological diagnosis of follicular neoplasm is a common finding in fine needle aspiration cytology (FNAC) of thyroid nodules and includes benign disease as well as differentiated thyroid cancer. The aim of the study is to determine if thyrotropin is a predictive factor for a malignant nature of follicular neoplasm. Patients, methods: The records of 119 patients with follicular neoplasm on FNAC, who underwent surgery for final diagnosis, were reviewed retrospectively. The predictive value of serum parameters including thyrotropin, thyroglobulin, and anti-thyroid antibodies, ultrasonographic criteria and clinical variables was evaluated by univariate analysis and logistic regression analysis. Results, discussion: Patients with malignant nodules showed a higher thyrotropin concentration compared to patients with benign nodules (median 1.6 mU/l, interquartile range 1.4–3.0 mU/l vs. median 1.2 mU/l, interquartile range 0.8–1.6 mU/l, p &lt; 0.01). ROC-analysis of thyrotropin revealed an optimal cut off value to differentiate benign and malignant nodules of 1.34 mU/l. The incidence of malignancy was 30.3% for a thyrotropin concentration higher than 1.34 mU/l compared to 6.4% for a thyrotropin concentration lower than or equal to 1.34 mU/l. On univariate analysis thyroglobulin higher than 300 ng/ml, positive anti-thyroid antibodies, hypoechogenicity, and ill-defined margins, respectively, were also significantly associated with malignancy. On logistic regression analysis higher thyrotropin concentrations, ill-defined margins, and thyroglobulin higher than 300 ng/ml, respectively, were independent predictive factors for malignancy (OR 20.0, 10.7, and 22.7, respectively). Conclusion: Higher thyrotropin concentrations are predictive for a malignant nature of follicular neoplasm.