Evaluation of Thyroid Lesions by Fine-Needle Aspiration Cytology: A Cross-sectional Study

1. Assistant Professor, Department of Pathology, Gulbarga Institute of Medical Sciences, Kalaburagi, Karnataka, India. 2. Professor and Head, Department of Pathology, Gulbarga Institute of Medical Sciences, Kalaburagi, Karnataka, India. 3. Assistant Professor, Department of Pathology, Khaja Banda Nawaz Institute of Medical Sciences, Kalaburagi, Karnataka, India.

Abstract

Introduction: Thyroid diseases are the most common endocrine disorders treated by physicians in their routine practice. Fine Needle Aspiration Cytology (FNAC) plays a dominant role in managing thyroid lesions.

Aim: To determine the utility of FNAC in diagnosing various thyroid lesions and to categorise them according to the Bethesda system of reporting.

Materials and Methods: This retrospective cross-sectional study was conducted in the pathology department of a tertiary care hospital from July 1, 2016, to June 30, 2021. FNA specimens obtained from 540 patients presenting with thyroid swelling were analysed, classified using the Bethesda system, and the distribution of cases in each category was studied.

Results: The age of the patients ranged from 8 years to 74 years, with a mean age of 41 years. The majority of patients were in their third and fourth decades. There was a female preponderance, with a female-to-male ratio of 11:1. Out of 540 cases, 476 (88.15%) were benign lesions, six (1.11%) were Follicular Lesion of Undetermined Significance (FLUS), 22 (4.07%) were Follicular Neoplasm (FN)/Suspicious for FN, three (0.56%) were suspicious of malignancy, 14 (2.59%) were malignant, and 19 (3.52%) were non-diagnostic/unsatisfactory. Cytohistopathological correlation was performed in 52 benign and nine malignant lesions in this study. The sensitivity of FNAC was 94.7%, specificity was 97.6%, and diagnostic accuracy was 96.7%.

Conclusion: FNAC is a rapid and minimally invasive procedure used in preoperative screening to distinguish between benign and malignant thyroid lesions. It has high sensitivity and specificity. The Bethesda system allows for precise cytological diagnosis, standardisation in reporting, improved clinical significance, and leads to the best management approaches.

Bethesda system, Colloid goiter, Papillary carcinoma thyroid

Thyroid diseases are the most common endocrine disorders treated by physicians in their routine practice. Thyroid lesions are easy to diagnose, as even a small swelling of the thyroid is easily visible and can be treated by the physician. It is necessary to differentiate between benign and malignant lesions because malignancy requires immediate surgery (1).

Fine-needle aspiration cytology (FNAC) is an effective tool in evaluating diffuse thyroid lesions, although there are various tests to assess thyroid gland function (2). It is a simple, rapid, cost-effective, and minimally invasive procedure used in preoperative screening to distinguish between benign and malignant lesions. The use of FNAC has significantly reduced the number of surgeries performed for thyroid lesions (3). However, it has a few drawbacks, such as incomplete aspiration, a risk of false positives and false negatives, and the inability to distinguish between follicular adenoma and follicular carcinoma (4). The success of FNA depends on the experience of the aspirator, skillful cytological interpretation, along with relevant clinical and radiological details (5).

However, due to a lack of standardised terminology for the cytologic diagnosis of the thyroid, FNA diagnoses, and diagnostic categories are defined differently among institutions. The Bethesda System was introduced in 2007 to standardise the reporting system for thyroid FNA specimens and was revised in the year 2017 (6),(7). The new recommendations included six diagnostic categories: i) non-diagnostic or unsatisfactory (ND/UNS); ii) benign; iii) Atypia of Undetermined Significance (AUS) or FLUS; iv) FN or SFN; v) Suspicious for Malignancy (SM); and vi) malignant (6),(7).

The study is undertaken to evaluate the advantage of FNAC as an initial investigative procedure for the diagnosis of thyroid lesions and to categorise them according to the Bethesda System, which has improved clinical significance and high predictive value. It helps differentiate benign from malignant lesions and triage patients who need surgery. Hence, appropriate therapy necessary for the patient can be planned by the clinicians.

Material and Methods

In this cross-sectional study, thyroid FNAC slides reported in Gulbarga Institute of Medical Sciences, Kalaburagi, Karnataka, India, were collected retrospectively from July 2016 to June 2021 and reviewed as per the current recommended Bethesda nomenclature (7), with approval from the ethical committee of our institute (IEC No- 95/2021-22). All patients presenting with diffuse or nodular thyroid enlargement, who were subjected to FNAC (either direct or ultrasound-guided), were included in the study, while patients with neck swellings unrelated to the thyroid were excluded.

Procedure

FNAC was performed on five hundred and forty patients using a sterile 24-gauge disposable needle under all aseptic precautions. Patient details such as age, sex, and investigations like thyroid profile and Ultrasonography (USG) were noted. Dry smears were prepared and stained with Giemsa stain, while wet smears were stained with Papanicolaou stain. Cytodiagnosis was provided after the smears were examined by two experienced cytologists. The inter-observer variability of the Kappa statistic value was 0.92, indicating perfect agreement between the two cytologists. The results were classified as per the current recommended Bethesda nomenclature into six groups (6). The results were analysed using descriptive statistics.

Results

In this study, a total of 540 cases of thyroid swelling were included, with 497 females and 43 males. The female-to-male ratio is 11:1, indicating a female preponderance. The age of presentation ranged from 8 years to 74 years, with a mean age of 41 years. The most common age group affected was 21-30 years, with 193 cases (35.74%), followed by the 31-40 years age group with 159 cases (29.44%), and the 41-50 years age group with 80 cases (14.82%). The least affected age groups were below 10 years, with five cases (0.92%), and above 70 years, with two cases (0.37%), as shown in (Table/Fig 1).

The majority of patients, 440 (81.48%), presented with painless, slow-growing thyroid swelling. A few patients, 49 (9.07%), complained of pain and discomfort, 22 patients (4.08%) presented with difficulty in swallowing, 17 (3.15%) with hoarseness of voice, 10 (1.85%) with rapid growth, and two (0.37%) presented with thyromegaly and cervical lymphadenopathy. The thyroid swelling was diffuse in 63% of cases and nodular in 37% of cases. The swelling was mobile and soft in most cases (42.59%) and firm in 39.63% of cases.

Thyroid profile status was available for 280 patients, among whom most (38%) were euthyroid (n=210), and 11.86% were hypothyroid (n=64). The majority of thyroid aspirates were haemorrhagic (62%), followed by colloid-like aspirate (35%), and cystic fluid (3%).

On cytology, out of 540 cases, 476 (88.15%) were benign lesions, six (1.11%) were reported as FLUS, 22 (4.07%) were FN/SFN, three (0.56%) were suspicious of malignancy, 14 (2.59%) were malignant, and 19 (3.52%) were non-diagnostic/unsatisfactory, as shown in (Table/Fig 2).

The cytological spectrum of 476 benign lesions revealed 216 (45.38%) cases of colloid goitre, 134 (28.15%) cases of nodular goitre, three (0.63%) cases of thyroglossal cyst, two (0.42%) cases of toxic goitre, six (1.26%) cases of a cystic nodule, and 115 (24.16%) cases of thyroiditis (69 Hashimoto’s thyroiditis, 43 lymphocytic thyroiditis, and three granulomatous thyroiditis). Out of 14 malignant cases, 12 (85.71%) were reported as papillary carcinoma, one (7.14%) was poorly differentiated carcinoma, and one (7.14%) was anaplastic carcinoma (Table/Fig 2).

In the benign category (category II), the most common lesion diagnosed was colloid goitre (Table/Fig 3). The cytological features seen were follicular epithelial cells arranged in monolayered sheets or in clusters, cyst macrophages, and lymphocytic infiltrate in a few cases. Cellularity was low to moderate in a blood-mixed colloid background.

A diagnosis of thyroiditis was made in 115 patients. A total of 12.78% of cases were of Hashimoto’s thyroiditis and showed lymphocytic infiltrate destroying follicular epithelial cells with Hurthle cell change (Table/Fig 4). Clusters of epithelioid histiocytes and multinucleated giant cells were seen in granulomatous thyroiditis.

There were three (0.63%) cases of thyroglossal cysts. Aspirated fluid showed scant cellularity. Squamous cells and macrophages were seen in the smear.

In this study, AUS/FLUS (category III) constituted 1.11% of cases. Few aspirates which had some features of atypia but could not be categorised definitely into either of the benign, SFN, SM, or malignancy categories were grouped under this category. Smears showed cytological features of high cellularity, follicular cells with cytological and architectural atypia at places with an occasional occurrence of Hurthle cells.

Around 4.07% of cases were of FN or SFN (Category IV). Aspirates showing moderate to high cellularity, predominantly microfollicular pattern of follicular cells in a repetitive pattern, with scant colloid, were grouped under this category.

Three (0.56%) cases were of SM (Category V). All three cases were reported as suspicious for papillary carcinoma. Smears were highly cellular with follicular cells showing a papillary pattern of arrangement. The nuclei were enlarged with an irregular nuclear membrane. Nuclear grooving and intranuclear inclusions were absent.

Papillary carcinoma is the most common malignant lesion in the present study. The aspirated smears showed the cells with round to oval pale nuclei with powdery chromatin and intranuclear cytoplasmic inclusions, irregular nuclear outlines, and nuclear grooves (Table/Fig 5),(Table/Fig 6),(Table/Fig 7). Hurthle cell changes were noted in three cases. Two patients had cervical lymphadenopathy along with thyroid enlargement, where the smears from the cervical lymph nodes showed metastatic deposits of papillary carcinoma.

One case of anaplastic carcinoma was diagnosed, showing high cellularity. The tumour cells were large and arranged in sheets. These cells had pleomorphic nuclei with prominent nucleoli. A few mitotic figures were seen. Tumour giant cells were also observed in some areas (Table/Fig 8).

A specimen was considered adequate if it contained atleast six groups of benign follicular cells, with each group containing atleast ten cells. In this study, 19 cases were placed in the non-diagnostic or unsatisfactory category due to repeated haemorrhagic aspirate, thick smears, and poorly preserved cell morphology.

Out of 540 cases of FNAC, histopathological diagnosis was available in only 61 cases, who underwent subtotal thyroidectomy/total thyroidectomy. Of the 61 cases, 52 (85.25%) were reported as benign, while nine (14.75%) were reported as malignant. The benign lesions (52) comprised nodular goitre (32), follicular adenoma (10), Hashimoto’s thyroiditis (8), thyroglossal cyst (1), and multinodular goitre (1). Among the malignant lesions, eight were diagnosed as papillary carcinoma and one as follicular carcinoma (Table/Fig 9).

The results of FNAC were compared with the corresponding histopathological diagnosis in 61 cases. Cytohistological concordance was found in 59 cases (96.77%), and two cases were discordant. Among the two discordant cases, one false positive case that was reported as FN turned out to be multinodular goitre on Histopathological Examination (HPE), and one false negative case of nodular goitre on cytology was found to be papillary carcinoma on HPE (Table/Fig 10). The results of the present study showed a sensitivity of 94.73%, specificity of 97.61%, and diagnostic accuracy of 96.72%.

Discussion

In thyroid disease, the early diagnosis of lesions is established by FNAC, which is an accurate and relatively precise tool. In this study, thyroid lesions are categorised according to the Bethesda system of reporting and compared with the histopathological report, wherever available, to evaluate the efficacy of this reporting system in interpreting the FNA results. In the present study, the age of the patients ranged from eight years to 74 years, with a mean age of 41 years. The peak incidence was between 20 and 40 years of age, similar to a study conducted by Handa U et al., (8).

Males constituted 8%, whereas females outnumbered males at 92% in the present study. The female-to-male ratio was 11:1, which can be compared to the study by Handa U et al., where the ratio was 6.35:1 (8). Sinna EA and Ezzat N in Egypt revealed that 16.2% of patients in their study were male and 83.8% were female, with a female-to-male ratio of 5.2:1 (9).

A good correlation was found between the occurrence of benign thyroid lesions in the present study and that of Mondal SK et al., They found 87.5% as benign, 1% as atypical FLUS (AFLUS), 4.2% as SFN, 1.4% as SM, 4.7% as malignant, and 1.2% as ND/UNS (1). In the study by Mehra P and Verma AK in New Delhi, 80.0% were diagnosed as benign, 4.9% AUS/FLUS, 2.2% FN, 3.5% SFM, 2.2% malignant, and 7.2% ND/UNS (10). Another study by Theoharis CG et al., demonstrated that 11.1% were unsatisfactory, 73.8% benign, 3% indeterminate, 5.5% FN, 1.3% SM, and 5.2% malignant (11). However, compared to the present study, Jo VY et al., (59%) and Yassa L et al., (66%) have reported fewer benign thyroid lesions (12),(13).

In the present study, benign lesions are high as the institution treats patients who are referred and those who come directly without a referral. A second reason is the fact that FNAC is performed free of cost for the economically backward sections of society.

The benign diagnosis in the study included 216 cases (45.38%) of colloid goitre and 69 cases (14.49%) of Hashimoto’s thyroiditis. The malignant diagnosis included 12 cases (85.71%) of papillary carcinoma, one case (7.14%) of poorly differentiated carcinoma, and one case (7.14%) of anaplastic carcinoma. Whereas in the study done by Mondal SK et al., the benign diagnosis were 81.18% colloid/adenomatoid nodule and 17.69% Hashimoto’s thyroiditis, and the malignant diagnosis were 87.5% papillary carcinoma, 2.08% follicular variant of papillary carcinoma, 4.16% medullary carcinoma thyroid, 4.16% poorly differentiated carcinoma, and 2.08% anaplastic carcinoma (1).

In the study conducted by Mehra P and Verma AK, 76.7% of total benign cases were reported as benign follicular nodules, and 20% of cases as lymphocytic thyroiditis (10). The malignant category included 80% of cases of papillary carcinoma and 20% of cases of medullary thyroid carcinoma. The number of cases diagnosed was lower in the non-diagnostic and FLUS categories in the present study because the experienced cytopathologist himself performed the FNAC with all the standard procedures. Sample adequacy is contributed by factors like cellularity and the experience of the aspirator. Ultrasound-guided FNA plays an important role in extracting samples from small thyroid nodules. A lower number of cases were diagnosed under the FLUS category due to the cytopathologist’s efforts to avoid ambiguity and minimise the use of AUS/FLUS. A lower percentage of non-diagnostic and AUS/FLUS cases were also reported by Mondal SK et al., and Likhar KS et al., (1),(14).

Thyroid lesions diagnosed as “SM” in the present study accounted for only 0.56% of total cases, similar to the studies by Mondal SK et al., and Sarkis LM et al., who reported 1.4% and 0.8% of cases as SM, respectively (1),(15). A higher number (9%) of cases were reported as suspicious of malignancy in the study by Yassa L et al., (13). It was found that 4.07% of cases were classified as FN, which is consistent with the studies by Mondal SK et al., (4.2%), Theoharis CG et al., (5.5%), and Sarkis LM et al., (4.7%) (1),(11),(15).

False positive and false negative results can be calculated based on the comparison of cytological and histopathological diagnosis. A comparison was done for only 61 cases, where a discrepancy was found in two cases. In the first case, the cytological findings suggested nodular goitre, while the histopathology revealed a focus of papillary carcinoma in a multinodular goitre, resulting in a false negative diagnosis. The reason for this discrepancy was that the aspirate was taken from the cystic area rather than the cellular area, and the smear showed few follicular cells and cystic macrophages with more colloid material, leading to misinterpretation as nodular goitre. In the second case, FNAC findings suggested FN, but histopathology diagnosed it as multinodular goitre. In this case, the aspirate might have been taken from the hypercellular areas of colloid nodule, resulting in an overdiagnosis as FN.

One case of FN, which was diagnosed cytologically, turned out to be follicular carcinoma on histopathology. Follicular adenoma cannot be differentiated from carcinoma based only on the cytological findings because vascular or capsular invasion or intrathyroid spread cannot be evaluated on cytology. Hence, this is considered a true positive case without any discordance. FNAC sensitivity ranges from 80% to 98%, and specificity ranges from 58% to 100% (8). The overall sensitivity, specificity, and accuracy in our study were 94.73%, 97.61%, and 96.72%, respectively, which were comparable to other studies (Table/Fig 11),(Table/Fig 12) (8),(16),(17),(18),(19),(20),(21),(22),(23).

The results of the present study were comparable with other past and recently published data, and FNAC is now considered a good screening test in diagnosing various lesions of the thyroid.

The limitations of FNAC include obtaining inadequate specimens, the skill and experience of the pathologist in aspirating the sample, and the inability to distinguish between benign and malignant follicular lesions. In cytology, cystic changes in thyroid lesions can lead to diagnostic errors. All these factors can result in false positive and false negative results; thus, pathologists should be aware of the diagnostic pitfalls to make an accurate diagnosis. Sample yield is improved with the help of USG-guided FNAC, minimising diagnostic errors.

Limitation(s)

Clinical and radiological details were not available for a few cases, leading to slight difficulty in categorising the aspirates.

Conclusion

The FNAC is a reliable and powerful diagnostic tool used in preoperative screening to distinguish between benign and malignant thyroid lesions. It is a cost-effective test with improved clinical significance and high sensitivity and specificity for diagnosing the nature of the lesion. The Bethesda system provides standard guidelines for reporting thyroid cytopathology, leading to more efficient management of patients with thyroid lesions. More studies on a larger number of cases are needed to validate this reporting system. Ultrasound-guided FNA procedures, expert cytopathologists to interpret the smears, and immunohistochemical and molecular markers are needed to overcome diagnostic errors.

DOI and Others

DOI: 10.7860/JCDR/2024/61390.19784

Date of Submission: Nov 12, 2022
Date of Peer Review: Jan 04, 2023
Date of Acceptance: May 28, 2024
Date of Publishing: Aug 01, 2024

AUTHOR DECLARATION:
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? Yes
• Was informed consent obtained from the subjects involved in the study? Yes
• For any images presented appropriate consent has been obtained from the subjects. Yes

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ETYMOLOGY: Author Origin

EMENDATIONS: 10