Assessment of Accuracy of Fine Needle Aspiration Cytology and Ultrasonography in Relation to Histopathology in Cases of Solitary Thyroid Nodule

Abstract

The thyroid gland is an endocrine gland situated in the lower part of front and the sides of the neck. Thyroid nodules are very common with estimated prevalence that ranges from 4% by palpation to 67% by Ultrasonography. The main purpose of our study was to detect cases of thyroid carcinoma preoperatively in patients with solitary thyroid nodules and subsequently advise surgery in these selected patients only, without missing any malignancy. The goal of the investigating modalities used was that they should detect maximum (ideally all) cases of carcinoma and minimize the number of patients who might end up with unnecessary surgery. The present study was to be undertaken for assessment of accuracy of FNAC & USG in relation to Histopathology in cases of solitary thyroid nodule (accuracy in terms of sensitivity, specificity, positive predictive value, negative predictive value). In our series of total 102 pateints, 90 patients were females (88.2%) and 12 cases were males (11.8%). The overall incidence of malignancy in solitary thyroid nodules is 15.68%. In our series the sensitivity and specificity of Fine needle aspiration cytology and Ultrasonography was 81.25% & 98.84% and 75% and 77.91% respectively. The closest method to ideal was fine needle aspiration cytology. However, a combination of techniques, rather than a single technique, give optimum results & avoid unnecessary surgery in a greater number of patients without missing any malignancy.

Introduction

The thyroid gland is an endocrine gland situated in the lower part of front and the sides of the neck. Its main function is regulation of the basal metabolic rate, stimulates somatic and psychic growth and plays important role in calcium metabolism. The term thyroid is derived from Greek, which means shield (Thyros – shield, eidos – form).

Any enlargement of the thyroid gland is called goiter. A solitary nodule is a goiter which, on clinical examination appears to be a single nodule in one lobe of the thyroid with no palpable abnormality elsewhere in the gland [1].

Thyroid nodules are very common with estimated prevalence that ranges from 4% by palpation to 67% by Ultrasonography [2, 3]. Autopsy studies reveal that 50% of adults had nodules, the majority of which are impalpable [4]. Thyroid nodules are 4 times more common in females than in men [5].

Because thyroid nodularity is so common, it would be impossible to operate on every patient with a thyroid mass, as the incidence of malignancy is quite low compared with the overall incidence of thyroid nodularity. So, the goal of diagnostic workup now is to select those patients for surgery who have a high likelihood of harboring malignancy in the nodule.

Many investigations are used to differentiate between benign and malignant nodules so as to avoid surgery in those who don't need it. Among these, FNAC and USG are commonly used in association with clinical features but there are drawbacks of each technique. The present study is to be undertaken for assessment of accuracy of FNAC & USG in relation to Histopathology in cases of Solitary Thyroid Nodule. Thyroid imaging recording and data system (TIRADS) is a risk stratification system for classifying thyroid nodules. It was first proposed by Horvath et al. [6] Recently, thyroid nodules have been classified into 5 TIRADS categories based on 5 descriptors (composition,echogenicity, shape, margin, echogenic foci/calcification). Each descriptor gives a point, adding all points of all descriptors a numerical value is calculated which gives the TIRADS score. Sonographic findings suggestive of malignancy are solid nodules, hypoechogenicity, irregular margins, microcalcifications, and a shape taller than wide on a transverse view.

According to current standards of thyroid cytopathology, Bethesda classification is used for determining which patients should undergo surgery.

The aspiration cytology helps clinician to decide:

• Which additional investigation may be needed.

• Which cases should have surgery performed foe a histological diagnosis.

• The type of surgery required for a cytologically diagnosed neoplasm.

• Which patient with unequivocal criteria of malignancy may benefit more from non surgical than surgical treatment.

Although needle aspiration cytology offer preoperative pathologic or cytologic information about a nodule but has certain limitations.

• A high incidence of false negative for malignancy in degenerated nodule.

• Confusion between follicular adenoma & carcinoma.

• Size constraints.

• Lack of sampling capsules or vessels by a limited core of tissue.

Uses of USG in Thyroid Nodules

Diagnostic

1. The detection of multinodular gland when only one nodule is suspected clinically and by radionuclide study. The importance of the detection of multinodularity lies in the fact that a solitary cold nodule carries a probability of malignancy between 15–25%. However the probability in multinodular gland is reported to be less than 1% in various studies.

2. Determination of the size and volume of gland and nodule as well.

3. For screening purposes in patients with head & neck irradiation.

4. Distinguishes benign from malignant nodules.

5. In selected cases direction of thin needle aspiration biopsy might be best accomplished with Ultrasonography. Areas of hemorrhage or necrosis have a poor cytologic yield and should be avoided to minimize sampling error.

Therapeutic

1. Volumetric assay for radioiodine dosage.

2. Assess response of nodules to suppressive therapy.

Aims and Objectives

• To find out the accuracy of FNAC & USG for differentiating nature of tumor (malignant or benign) against histopathology among solitary thyroid nodule cases. (Accuracy in terms of sensitivity, specificity, Positive PredictiveValue, Negative Predictive Value)

Material and Methods

• Study design Observational descriptive analysis.

• Study location Department of ENT, SMS Medical College & attached group of hospitals, Jaipur.

• Sample size The sample size required is 49 cases at 95% confidence, 80% power and 10% absolute errors to verify the expected 86% accuracy of USG against histopathology in differentiating between benign & malignant solitary thyroid nodule. This sample size is also adequate to verify the 92% accuracy of FNAC against histopathology. In present study we included 102 cases, which is more than required sample size.

• Study duration May 2014–Nov 2015.

• Study population Patients presenting with Solitary thyroid Nodule.

Statistical Analysis

Validity of FNAC & USG was analyzed against gold standard histopathology by 2 × 2 table. Sensitivity, specificity, Positive predictive value, Negative predictive value, Kappa Statics was found.

Inclusion criteria

• All Euthyroid cases of solitary thyroid nodule attending the ENT OPD of SMS Medical College & attached group of Hospitals, Jaipur and who had given the consent & fit for surgery.

Exclusion criteria

• Patients with diffuse thyroid swelling.

• All toxic and multinodular goiters confirmed by clinical evaluation.

• Patients with history of any type of thyroid surgery.

• Patients who were not fit for surgery.

• Patients who were not giving consent for surgery.

After taking informed consent, only euthyroid patients with solitary thyroid nodule were subjected to a detailed history & clinical examination and further investigations. They were first subjected to Ultrasonography. Sonographically the nodules were evaluated for size, location, echotexture, margins, presence of halo, calcification, accessory nodules and associated cervical lymphadenopathy. Then FNAC was done. The cytopathological diagnosis were done by the cytopathologist and after that they were subjected to surgery in the department of ENT, SMS hospital Jaipur. Operative findings were carefully recorded in all cases. Specimen were sent for histopathological examination in order to differentiate between benign and malignant nodules. The histopathological findings were determined by an independent pathologist, who was blind to the findings of FNAC reports.

Accuracy of FNAC & Ultrasonography was analyzed against gold standard histopathology by 2 × 2 tables. Sensitivity, specificity, positive predictive value, negative predictive value, kappa statistics was found for both FNAC & USG against histopathology.

Method of performing FNAC

The thyroid and surrounding areas were first carefully palpated in order to locate the target lesion. The patient is put in supine position and neck is rested so that neck muscles are relaxed and gland is fixed between investigator’s fingers. A disposable needle of 23G (external diameter of 0.6 mm) & 2.5 cm in length is inserted into the target lesion without creating negative pressure into the syringe. The plunger is then drawn back to create vacuum in to the syringe and then needle is moved back & forth to obtain adequate cell sample. Suction should be terminated if blood appear in the syringe. Syringe is detached from the needle & then needle is withdrawn. Withdrawn needle is then attached to syringe again, filled with air and contents of needle are put on the slide. Slides are air dried or fixed with absolute alcohol for 30 min. The dried smear are stained with MGG ( Maygrunwald Giemsa stain) & alcohol fixed smears stained with hematoxylene & eosin stain.

Method of Performing Ultrasonography of Thyroid

All thyroids were examined using high resolution real time Ultrasonography using a 10 MHz transducer focused at approximately 1.5 cm from the skin surface. The transducer is housed in a water bath & is mechanically driven in a linear fashion, producing a rectangular image with a 3 × 4 cm. field of view. The instrument’s dynamic range is 40 dB & the axial and lateral resolution capabilities are 0.5 mm & 1–2 mm respectively. A minimum line density of 120 lines per frame was utilized at the currently employed 30 frames per second display. If recording of dynamic events is desired the oscilloscope display is placed on videotape. The real time capability allows a rapid survey of the neck; a complete thyroid evaluation can be accomplished within 10–15 min.

Observations and Results

In our series, 90 patients were females constituting 88.2% of total cases and 12 cases were males constituting 11.8% of the total cases. The higher incidence of solitary thyroid nodules in females is more or less constant for all age groups. Solitary thyroid nodules were more frequent in the age group of 21–50 years, while they were less common at the extreme ages (Table 1).

Table 1.

Age and sex distribution

Sex	Age Group							Total	%
	0–20	21–30	31–40	41–50	51–60	61–70	> 70
Male	0	2	3	1	3	2	1	12	11.8
Female	5	24	27	23	7	2	2	90	88.2
Total	5	26	30	24	10	4	3	102	100%

Most of the malignant tumors were encountered in 31–50 years age group. In 61–70 years age group all 4 patients had encountered malignancy. In patients below 20 of age, 2 patients out of 5 had encountered malignancy (Table 2).

Table 2.

Distribution of malignancy in solitary thyroid nodules in different age groups

Age group (yrs)	Solitary thyroid nodules			Malignancy
	M	F	Total	M	F	Total
0–20	0	5	5	0	2	2
21–30	2	24	26	0	0	0
31–40	3	27	30	0	3	3
41–50	1	23	24	1	2	3
51–60	3	7	10	1	2	3
61–70	2	2	4	2	2	4
> 70	1	2	3	1	0	1
Total	12	90	102	5	11	16

Test applied: Fisher exact test p value = 0.001 (S)

Cytology of 102 aspirates gave a diagnosis of benign for 88 aspirates (86.2%) & malignant for 7 aspirates (6.9%). A cytologic diagnosis of suspect was rendered in 7 (6.9%) aspirates (Table 3).

Table 3.

Distribution of patients according to FNAC

	Frequency	Percentage
Benign	88	86.2
Suspicious	7	6.9
Malignant	7	6.9
Total	102	100.0

Histopathology revealed adenomatous goitre to be the commonest (46 cases—45.1%) pathology followed by colloid goiter—28cases (27.5%). Thyroiditis was reported in 4 cases (3.92%) & follicular adenoma in 4 cases (3.92%). The overall incidence of carcinoma was 15.68% (Table 4).

Table 4.

Histopathology diagnosis

Benign thyroid nodules	Diagnosis	No. of patients		Total	%
		Male	Female
	Adenomatous goitre	3	43	46	45.10
	Colloid goitre	4	24	28	27.45
	Follicular adenoma	0	4	4	3.92
	Adenomatous goitre	3	43	46	45.10
	Follicular adenoma and Nodular goitre	0	2	2	1.96
	Hashimoto`s thyroiditis	0	4	4	3.92
	Goitre with cystic degeneration	0	2	2	1.96
Malignant thyroid nodules	Papillary carcinoma	3	10	13	12.75
	Follicular carcinoma	2	1	3	2.94
	Total	12	90	102	100

Test applied: Fisher Exact test p value = 0.001 (S)

The cytology diagnosis of benign was confirmed in 85 (96.6%) of the 88 biopsied patients and disputed in 3 (3.4%) patient which was shown to be malignant.

In 7 cytologic suspects histopathology revealed benign lesion in 1 cases & malignant lesion in 6 cases. Of these 6 malignancies 3 patients had papillary carcinoma and 3 had follicular carcinoma.

All malignant interpretations on cytology were confirmed by histopathology accurately (Table 5).

Table 5.

Correlation of FNAC with histopathology

Histopathologic diagnosis	FNAC			Total
	Benign	Suspicious	Malignant
Benign	85	1	–	86
Malignant	3	6	7	16
Total	88	7	7	102

Test applied: Fisher Exact test p value = 0.001 (S)

The overall incidence of malignancy in solitary thyroid nodules was 15.68%. The incidence of malignancy in solitary thyroid nodules in males was very high – 5 out of 12 males (41.66%) as compared to 11 out of 90 females (12.22) had malignancy in the nodules.

The ultrasonographic echotexture of solitary thyroid nodules showed 13(12.75%) of the solitary thyroid nodules were cystic, 71 (69.6%) were solid & 18 (17.65%) were mixed. 10 out of 71 (14.08%) patients with a solid lesion and 6 out of 18 (33.3%) patients with a mixed solid-cystic lesion were subsequently found to have a malignant thyroid nodule. None of the cystic nodule showed malignancy (Table 6).

Table 6.

Correlation of ultrasonography echotexture with malignancy

Echotexture	No. of cases	Histopathology		% Malignancy
		Benign	Malignant
Cystic	13	13	0	0
Solid	71	61	10	14.08%
Mixed	18	12	6	33.33%
Total	102	86	16	15.68%

Test applied: Fisher Exact test p value = 0.001 (S)

All cases in this series had solitary thyroid nodules on clinical examination. Ultrasonography revealed multiple nodules in these 22(21.6%) so called solitary nodular glands. Per-operatively 28 glands (27.5%) were found to have more than one nodule. Thus ultrasonography is very sensitive in identifying multiple nodules in the so called solitary nodular glands. (Table 7).

Table 7.

Assessment of nodularity by various techniques

Modality	Nodularity		Total
	Solitary	Multiple
Clinically	102	0	102
Ultrasonographically	80	22	102
Per operative	74	28	102

Test applied: chi-square test p value = 0.12

Out of 88 cytological benign nodules 67 (76.1%) were solitary and 21(23.9%) were multinodular. All cytological malignant nodules were solitary on ultrasound. One out of 7 cytological suspicious was found multinodular.

We observed that fine needle aspiration cytology was 81.25% sensitive & 98.84% specific in detection of malignancy in solitary thyroid nodules while the ultrasound had a sensitivity of 75% & specificity of 77.91% in the same regard.

Accuracy of fine needle aspiration cytology & ultrasound was 96.07% and 77.45% respectively (Table 8).

Table 8.

Comparison of Statistical analysis

	FNAC	USG
Sensitivity	81.25%	75%
Specificity	98.84%	77.91%
PPV	92.86%	38.7%
NPV	96.59%	94.36%
Accuracy	96.07%	77.45%
Kappa index value	0.84	0.38

Disscussion

The purpose of this study was to assess accuracy of FNAC & USG ( in terms of sensitivity, specificity, Positive Predictive Value, Negative Predictive Value) in relation to Histopathology in cases of Solitary Thyroid Nodule. In addition some related demographic features were also studied.

The main purpose of all this exercise was to detect cases of thyroid carcinoma preoperatively in patients with solitary thyroid nodules and subsequently advise surgery in these selected patients only, without missing any malignancy. The goal of the investigating modalities used is that they should detect maximum (ideally all) cases of carcinoma and minimize the number of patients who might end up with unnecessary surgery.

Age & Sex Distribution

Age distribution showed that maximum number of patients were in 3rd 4th and 5th decade of age. The mean age of the patients was 38.8 years with the males having a higher mean age of 47.4 years than females (37.6 years). Patients with the thyroid cancer had a mean age more than the average of the group (49.1 years versus 38.8 years in overall group).This is in consistency with the observation of Arun Kumar et al. [7] where the maximum number of patients were in the age group of 20–40 years (66.2%) but in the series males had a lower mean age of 39.4 years in contrast to our study.

The usual victims of thyroid enlargement were females as indicated in this study where 90 patients were females constituting 88.24% of total cases and 12 patients were male constituting 11.76% of total cases. Female to Male ratio being 7.5:1. Belfiore and Rosa et al. [8] reported 84.8% females and 14.2% males with female to male ratio of 8.3:1 in their Series. Arun Kumar [7] reported female preponderance with a male to female ratio of 1:6.5.

Solitary Thyroid Nodules and Malignancy

The overall incidence of malignancy in solitary thyroid nodules varies from 9 to 30% according to various reports. In this series the overall incidence of malignancy in solitary thyroid nodules was very high in males -5 out of 12 males (41.66%) as compared to females—11 out of 90 (12.22%) and the overall incidence was 15.68%.

This is in consistency with the Mazzaferri [9] who stated that males had a two fold greater likelihood of having cancer than females in solitary thyroid nodules. Messaries & Kyriakou et al. [10] in their series found 14% overall incidence of malignancy in clinically STN.

Age less than 20 years and more than 60 years has been used as strong indication of malignancy & surgery should be recommended for all patients in these age groups if the decision is based upon clinical criteria [11]. In this study, 2 out of the 5 patients (40%) of less than 20 years of age had carcinoma. In patients of more than 50 years of age 8 out of 17 (47.1%) patients had carcinoma. Extremes of age had very high figure when compared with the group average.

It has been consistently observed in the literature that patients with solitary thyroid nodules above 40 years of age are at higher risk of developing malignancy than the overall incidence. This is consistent with our study where 11 out of 41 patients (26.8%) above 40 years of age had malignancy. While on the other hand Arun Kumar et al [6] reported 36% incidence of malignancy in solitary thyroid nodules in patients above 40 years of age. This variation may be attributed to the subclinical iodine deficiency which leads to an earlier onset of goitre & so malignancy later on.

Fine Needle Aspiration Cytology (FNAC)

Fine needle aspiration cytology appears to be a safe, reliable & cost effective method which provides valuable information to assist in selection of patients, with solitary thyroid nodules, for surgery. As it distinguishes the benign from malignant lesions quite effectively preoperatively, it has been proposed as- a preoperative screening method of choice. Colloid containing aspirates almost always indicate the presence of benign nodule.

Out of the 102 aspirates obtained, cytology gave a diagnosis of benign for 88 aspirates (86.2%) & malignant for 7 aspirates (6.9%) while on final histopathologic examination 84.32% of the thyroid enlargement were found to be benign & 15.68% malignant. Out of the 82% benign enlargements, adenomatous goitre (45.1%) & colloid goitre (27.45%) form the main bulk.

The FNAC diagnosis was then compared with final histopathology diagnosis. We found that out of 86 cases found to be non malignant on histological examination 85 were correctly identified negative for malignancy on FNAC. The overall accuracy was 96.07% in our series, whereas in various other series it has varied from 79 to 98%. Accuracy rate of FNAC depends greatly on who reads the cytology smears & how the report is interpreted.

Ultrasonography(USG)

One of the main role of USG in the assessment of goitre is to distinguish non-operatively between cystic & solid nodules. This is of great importance to the patient on the basis of the observation that thyroid cysts are overwhelmingly benign & can be treated by needle aspiration,, submission of fluid for cytology, clinical follow up & thyroid feeding Some authors [12] have persued repeated aspirations and even the injections of sclerosants. However, it has been strongly emphasized by Rosen and Walfish [13] that thyroid cysts are not invariably benign and they encountered a 13% malignancy rate in the cyst population & 25% cancer rate in the mixed group. In our series there were 4 cystic nodules (8%), 38 solid nodules (76%) & 8 mixed nodules (16%). When the results of ultrasonography were compared with final histopathology we found that none of the cystic nodule contained malignancy. Out of the 71 solid nodules 10 (14.08%) were found to be malignant & out of 18 mixed nodules 6 (33.3%) were found to contain malignancy. Thus both solid & mixed nodules have a high chance of being malignant.

In this series we found the overall sensitivity of ultrasonography 75% and specificity of 77.91% in differentiating the benign from malignant nodules. In consistancy to our report Watters et al. [14] found that the sensitivity, specificity & positive predictive value of ultrasonography in suggesting a malignant disease were 74%, 83% & 51% respectively and they interpreted an ultrasound report as suggestive of malignancy if the nodule was solid or of a mixed solid-cystic variety & a hypoechoic and nonhaloed lesion. They emphasized that the ultrasonography has added advantage of allowing the whole gland to be examined rather than just the dominant nodule but limited by the fact that no features are pathognomic for malignancy and so it should be regarded as complementary rather than alternative to fine needle aspiration cytology for thyroid nodules.

Nodularity and Malignancy

It has been a consistent observation, according to the published literature, that the risk of thyroid cancer is less with multiple nodules than with the solitary nodules. Although clinical palpation is important; it is not regarded as a reliable assessment of nodule size or number & it is becoming increasingly clear that high resolution real—time ultrasonography is far better than clinical examination in detecting thyroid nodules [14].

In our series out of the 102 cases of clinically solitary thyroid nodules 22 (21.56%) cases were multinodular on ultrasonography. Per operatively 28 (27.45%) cases had multiple nodules in the gland. Thus ultrasonography is highly sensitive (78.44%) in detecting other nodules in the gland. We observed that none of the patient (out of 28) with multiple nodules in the gland harboured malignancy. The result of our study are consistent with findings of previous study. Brown et al. [15] reported in his series that ultrasonography revealed multiple nodules in 28% glands & none of the gland with multiple nodules was discovered as being malignant.

Sensitivity and Specificity

In our series the sensitivity and specificity of Fine needle aspiration cytology and Ultrasonography was 81.25% & 98.84% and 75 & 77.91% respectively. An ideal test would have a sensitivity of 100% as well as specificity of 100%. The closest method to ideal is fine needle aspiration cytology which gives a sensitivity of 81.25% & specificity of 98.84%. Thus as a single test FNAC turns out to be the best technique. However, a combination of techniques, rather than a single technique, give optimum results & avoid unnecessary surgery in a greater number of patients without missing any malignancy.

Jones et al. [16] reported the sensitivity & specificity of various tests in his series. They found the sensitivity and specificity of FNAC—92% & 85% and USG—75% & 61%.

In a study conducted by Manoj et al. [17], ultrasound has sensitivity of 80%, specificity of 75%, positive predictive value of 44%, negative predictive value of 93%, and accuracy of 76%.

Summary and Conclusion

The present study, a series of 102 patients, was undertaken with a view to evaluate the usefulness of FNAC & USG in the management of solitary thyroid nodules with a goal of selection of only those patients for surgery who have a higher likelihood of harbouring malignancy in the nodule.

Solitary thyroid nodules occur predominately in females in all age groups. Solitary thyroid nodules occur more frequently in the age group of 21–50 years. Patients in extremes of age had higher likelihood of harbouring malignancy in solitary thyroid nodules.

The overall incidence of malignancy in solitary thyroid nodules is 15.68%. The incidence is higher in males (41.66%) as compared to females (12.22%).

FNAC is a safe, reliable & cost effective preoperative investigating modality for selection of cases for surgery with a high sensitivity of 81.25% & specificity of 98.84% & turns out to be single best technique of preoperative investigations. FNAC fails to differenciate follicular adenoma from follicular carcinoma.

High resolution real time ultrasonography is a safe, non-invasive, non-tissue damaging procedure which elucidates the physical characteristics of the thyroid nodule. Ultrasonography has sensitivity of 75% and specificity of 77.91% in terms of identifying malignancy in solitary thyroid nodules. Ultrasound does not differentiate thyroiditis from the thyroid carcinoma.

Ultrasound is the best method to evaluate the nodularity of thyroid gland.. This finding is of paramount importance as multinodular glands do not harbour malignancy. Malignancy occur exclusively in solitary thyroid nodules.

As a single mode of investigation fine needle aspiration cytology stands out in present study with better sensitivity (81.25%), specificity (98.84%), positive predictive value (92.86%), negative predictive value (96.59%), accuracy (96.07%) & kappa index value (0.84) in comparison to Ultrasonography which has, sensitivity (75%), specificity (77.91%), positive predictive value (38.7%), negative predictive value (94.36%), accuracy (77.45%) & kappa index value (0.38).

A tremendous effort has been applied to the determination of optimum management strategies in patients with solitary thyroid nodules. Therefore, a combination of techniques, rather than a single technique, give optimum results & avoid unnecessary surgery in a greater number of patients without missing any malignancy.

Funding

None.

Compliance with Ethical Standards

Conflict of interest

None.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and /or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed Consent

Informed consent was obtained from all individual participants included in the study.