How accurate is fine-needle aspiration cytology (FNAC) for thyroid lesion: A correlation of FNAC with histopathology

ABSTRACT

Introduction:

Indian population have large number of cases with deranged thyroid profile and swelling. Clinically apparent thyroid swelling in general population is 4% to 5%. Excising all the thyroid lesions is impracticable. Thus, final-needle aspiration cytology (FNAC) serves as the initial diagnostic test for the evaluation of thyroid swelling. The main purpose of FNAC is to differentiate the benign lesion from malignant ones, thereby reducing unnecessary surgeries. This study was conducted to establish a cytohistopathological correlation.

Materials and Methods:

FNAC of thyroid swellings was performed using 22G or 23G needle by aspiration or nonaspiration technique, preferable nonaspiration one. A proper correlation of the history, clinical presentation, thyroid profile, and cytopathology report was made, which helped us to make a proper diagnosis. All the cases that required surgery were planned for appropriate surgery and the resected specimen of thyroid was again sent to our department for histopathological examination.

Result:

FNAC was performed on 39 patients (4 males and 35 females). The age group of patients were in the range of 11 to 60 years with a mean age of 38.60 years. Papillary thyroid carcinoma (PTC) and its variants were the most common in our study. Out of 39 surgeries performed, 19 (48.71%) specimens were found to be malignant. Among these 19 malignant cases, the highest number of malignancies were of PTC and its variants (14 cases). Statistical analysis showed sensitivity-90.91%, specificity-94.12%, positive predictive value-95.24%, negative predictive value-88.89%, and accuracy-92.31%.

Discussion:

FNAC being cost-effective, patient-friendly, quick result along with high sensitivity, specificity, and accuracy makes it an initial diagnostic tool for preoperative evaluation of patients with thyroid swelling.

Introduction

Deranged thyroid profile and thyroid swellings are quite common in the Indian population with predominance among females. The incidence of clinically apparent thyroid swelling in general population is 4% to 5%.[1] Major chunk of these swellings are benign, goiter being most common. In India, the prevalence of goiter is more than 40 million.[2] Thyroid lesions may have features suggestive of hyperthyroidism, hypothyroidism or may have malignant potential.[3] Thyroid swelling presents clinically with a lump in the neck and may cause cosmetic deformity, pressure symptoms over trachea, esophagus, and major vessels.[4] Excising all the thyroid lesions is impracticable and is associated with various risks both intraoperatively and postoperatively. Thus, FNAC being reliable, safe, cost-effective, less invasive with high sensitivity and specificity is often used as the initial diagnostic test for the evaluation of thyroid nodule as well as diffuse thyroid lesion with the main purpose of confirming benign lesions and thereby reducing unnecessary surgery.[5,6]

Thyroid cytology serves both therapeutic and diagnostic function. Aspiration of the fluid from thyroid swelling relieves compressive symptoms.[7] FNAC provides a definite diagnosis of thyroid malignancy, with tumor type leading to appropriate surgery. Further, the remaining patients can be segregated into if the patients potentially require surgery and/or medical/endocrinological management.[8]

However, cytological studies have their own limitations; the results of FNAC depend on the aspirator experience and interpretation of the pathologist. Accuracy is lower in suspicious cytology and in follicular neoplasms.[9,10]

The main purpose of FNAC is to decrease the overall thyroidectomy rate in patients with benign thyroid diseases. This study was conducted to establish a cytohistopathological corelation so that unnecessary thyroidectomies in benign pathologies can be avoided.

FNAC being reliable, safe, and cost-effective with high sensitivity and specificity can be used by primary care physicians as an initial diagnostic tool to rule out malignancies in clinically suspected neoplastic thyroid lesions. With the report of FNAC, physicians can refer the patients to surgeons in case the patient requires surgery or may manage the patient with medical management, avoiding unnecessary thyroid surgeries.

Materials and Methods

A cross-sectional study was conducted at the Department of Pathology, RIMS, Ranchi. A retrospective analysis of cases and slide archives in the Department was done including cases from June 2019 to June 2021. Patients of all ages and both sexes were included in the study. All the patients were either sent from the Department of Medicine or Department of ENT for FNAC. Histopathology samples were sent from our surgical department, which was 39 in number. Before performing FNAC, proper history, clinical presentation, thyroid profile, and ultrasound findings of all the patients were taken into account. Most of the patients presented with the complaint of swelling in the neck, which was either solitary, multinodular, or diffuse. Symptoms related to hyperfunctioning and hypofunctioning of the thyroid glands were noted. Cough, pain, dysphagia, hoarseness of voice, and other signs of compression were also mentioned. Thyroid function test was performed for T3, T4, and TSH level, which guided in making a proper diagnosis.

Under available aseptic precaution, slides of FNAC were made by inserting 22G or 23G needle either without aspiration or attached with 10 mL disposable plastic syringe (aspiration method) into the thyroid swelling. Nonaspiration method was preferred as thyroid is highly vascular and was performed by simply inserting the needle in and out multiple times, without exiting the thyroid swelling. Now, this needle with material in its hub was attached to a already developed negative pressure 10 mL syringe and multiple slides were prepared. In case of aspiration method, after developing a negative pressure in the syringe, it was inserted in the thyroid swelling. The needle was passed in and out multiple times, without exiting the thyroid swelling. The aspiration was repeated, if found insufficient. The gross appearance of the aspirate was described, as colloid, or colloid admixed with blood, etc., The aspirates were used to make 5 to 6 smears, one for Leishman and Geimsa (L and G) stain, which was air dried, one for Hematoxylin and Eosin (H and E) stain, which was fixed immediately using alcohol.

A proper correlation of the history, clinical presentation, thyroid profile, and cytopathology report was made, which helped us making a proper diagnosis. All the cases that required surgery were planned for appropriate surgery and the resected specimen of thyroid was again sent to our department for histopathological examination.

After proper fixation of the resected specimen in 10% formalin for 24 hours, detailed grossing of the specimen was done. Further, it underwent different steps of histopathological procedure and paraffin-embedded H and E stained sectioned were obtained for study under light microscope.

A correlation of the cytopathology and histopathology report was made and the efficacy of FNAC was estimated.

Result

FNAC was performed on 39 patients (4 males and 35 females). The age group of patients were in the range of 11–60 years with a mean age of 38.60 years. From the [Table 1], we can make out that papillary thyroid carcinoma (PTC) and its variants are the most common in our study. Out of 39 histopathological studies, 14 (35.90%) were either PTC or its variants. Among these 14 cases of PTC, 10 cases were the follicular variant of PTC and 1 case was of the oxyphilic variant of PTC. From [Table 2], we can make out that maximum number of patients were of the age group of 30 to 39. Following this, 12 patients were of 40 to 49 years of age.

Table 1.

FNAC and histopathological findings and their correlation

Type of thyroid swelling diagnosed by FNAC	No. of cytological diagnosis	Correlation with result of histopathological report		Histopathology finding in case of false cytological diagnosis	Remarks
		Correct cytological diagnosis	False cytological diagnosis
Colloid goiter	13	10	3	Two cases of follicular variant of papillary thyroid carcinoma and 1 case of lymphocytic thyroiditis
Colloid goiter with cystic degeneration	3	3	0
Hashimoto’s thyroiditis	2	2	0
Papillary carcinoma of thyroid (PTC)	11	11	0		Out of 11 cases of PTC, 8 were follicular variant of PTC
Medullary carcinoma of thyroid	2	2
Hurthle cell neoplasm	4	2	2	One case of oxyphilic variant of PTC and 1 case of lymphocytic thyroiditis
Follicular neoplasm	3	2	1	Hurthle cell adenoma	One was found to be follicular adenoma and other being follicular carcinoma
Anaplastic carcinoma of thyroid	1	1

Table 2.

Distribution of subjects by age

Age distribution (years)	Frequency
10-19	2
20-29	6
30-39	13
40-49	12
50-59	4
60-69	2

We can also get to know that out of 39 surgeries performed, 19 (48.71%) specimens were found malignant. Among these 19 malignant cases, the highest number of malignancies were of PTC and its variants (14 cases). The medullary and follicular neoplasm cases were equal in number, having 2 (5.13%) each. On histopathological study of follicular neoplasm, there was one case of follicular adenoma and other being follicular carcinoma. In the whole study, there was only one case (2.57%) of anaplastic carcinoma.

If we look into our study leaving behind the neoplasms, the rest of the cases were of colloid goiter with 13 cases on cytology, but after histopathological confirmation, 2 cases were of follicular variant of PTC and 1 case of lymphocytic thyroiditis. Following this, there were 3 (7.70%) cases of colloid goiter with cystic degeneration and 2 (5.13%) cases of Hashimoto’s thyroiditis.

In this study, we found that 33 out of 39 cases showed the same result in both cytology and histopathology. Out of total FNAC performed, 21 were neoplastic and 18 were nonneoplastic. Among 21 neoplastic cases on FNAC, 20 were true positive and 1 case was false positive as revealed by 2 × 2 contingency table. The table also highlighted that there were 16 true negative and 2 false-negative cases. Statistical analysis showed sensitivity-90.91%, specificity-94.12%, positive predictive value-95.24%, negative predictive value-88.89%, and accuracy-92.31%.

Discussion

In the present study, the age of the patient ranged from 11 to 60 years with a mean of 38.60 years. This age range and mean incidence are comparable with previous studies.[11,12,13] We found that majority of the patients were in their 3^rd decade of life, which is in accordance with the study by Dorairajan and Jayashree.[14]

The total number of thyroid surgeries performed in our institution during the period of our study was only 39 because of the ongoing pandemic of COVID-19.

FNAC has excellent patient acceptance and no morbidity; it is easy, cost-effective test used in the diagnosis of thyroid lesions.[10,15,16]

Figure 1 indicates FNAC of anaplastic carcinoma.

Figure 1.

FNAC-Anaplastic carcinoma

Figure 2 indicates FNAC of benign follicular nodule.

Figure 2.

FNAC-benign follicular nodule

Figure 3 indicates FNAC of colloid cyst.

Figure 3.

FNAC-colloid cyst

Figure 4 indicates FNAC of lymphocytic thyroiditis.

Figure 4.

FNAC-Lymphocytic thyroiditis

Figure 5 indicates H&E of follicular carcinoma.

Figure 5.

H&E-Follicular Carcinoma

Figure 6 indicates H&E of Papillary Carcinoma

Figure 6.

H&E-Papillary carcinoma

Figure 7 indicates Pap - Medullary Carcinoma

Figure 7.

Pap-Medullary carcinoma

The value of any test depends on its ability to detect the presence of disease (sensitivity) and to verify the absence of the disease when it is not present (specificity). The sensitivity of thyroid FNAC ranges from 74% to 92% and specificity ranges from 74% to 100%.[17,18] The sensitivity in our study is 90.91% and specificity is 94.12%, which correlates with other studies.[19,20,21,22,23,24,25] This shows that FNAC is more specific than sensitive.

Table 3 highlights sensitivity, specificity and accuracy of various studies. In this study, the false-negative rate is 9.1% and the false-positive rate is 5.88%, which is in accordance with the study of Chaudhari et al.[26] False-negative FNAC occurred in 2 cases. In both the cases even on repeated aspirations and USG guided aspirations, the FNAC was colloid goiter. But, when the specimens of these thyroid glands were received for histopathological examination, we could grossly make out that the mass was present deep posteriorly in both the cases. That was the reason, why we were not able to aspirate from the mass of the thyroid. On microscopy of histopathology slide, it was clear that the mass, which was present deep posteriorly, was follicular variant of PTC.

Table 3.

Comparison of sensitivity, specificity, and accuracy of various previous studies with the present study

	Year of publication	Sensitivity (%)	Specificity (%)	Accuracy (%)
El Hag et al.[30]	2003	86.7	97.6	-
Sangalli et al.[31]	2006	93.4	74.9	95.4
Aravinthan et al.[32]	2007	80.2	87.2	98.0
Guhamallick et al.[33]	2008	92.7	98.2	-
Handa et al.[34]	2008	97	100	-
Mandal et al.[35]	2011	90	84.6	-
Bamanikar et al.[36]	2014	50	100	94.2
Nandedkar et al.[37]	2018	85.7	98.6	97.1
Singh et al.[38]	2020	83.3%	100%	95.71%
Present study		90.91	94.12	92.31

According to this study, 18 out 39 cases were nonneoplastic on FNAC. Colloid goiter was the most common nonneoplastic lesion, which is similar to the studies conducted by Abdulkader et al., Jeelani et al., and Ramteke et al.[27,28,29]

Efficacy of FNAC of thyroid may be reduced because of inadequate sampling, inexperienced cytopathologist, and difficulty in differentiating between benign and malignant follicular lesions. Inadequate sampling may result from sclerotic nodule, calcified nodule, and nodule with cystic degeneration in large area.

From the results of our present study and previous studies conducted by various authors, we can make out that FNAC has high sensitivity and specificity in diagnosing thyroid lesions. Hence, FNAC helps to rule out malignancies in clinically suspected cases and manage the patients with better medical management, thus improving the quality of life by avoiding unnecessary thyroid surgery. Also if the thyroid lesions are diagnosed as neoplastic which requires surgeries, early diagnosis using FNAC may help to decide adequate surgeries and reduce the tumor burden as early as possible, resulting in a better prognosis and improving the quality of life of the patient.

Conclusion

FNAC being cost-effective, patient-friendly, quick result along with high sensitivity, specificity, and accuracy makes it an initial diagnostic tool for preoperative evaluation of patients with thyroid swelling. Cases with false-negative results can be improved by getting an adequate sample. Sampling can be improved by obtaining aspirates from multiple sites of the nodule rather than repeated aspiration from a single spot. While framing a diagnosis, cytopathologists should keep in mind that the absence of malignant cells in an otherwise acellular smear does not exclude malignancy. Confusions in the diagnosis of thyroid neoplasms can be confirmed by immunohistochemistry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.