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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 13  |  Issue : 3  |  Page : 140-143

Accuracy of fine needle aspiration cytology of thyroid lesion with corresponding histopathology: A single institutional experience


1 Department of Allied Health Sciences, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman
2 Department of Pathology, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman
3 Department of Pathology, Sultan Qaboos University Hospital, Muscat, Sultanate of Oman

Date of Web Publication27-Oct-2016

Correspondence Address:
Nasar Alwahaibi
Department of Allied Health Sciences, College of Medicine and Health Sciences, Sultan Qaboos University, P.O. Box 35, Postal Code 123, Muscat
Sultanate of Oman
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-0354.193136

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  Abstract 

Aim: The aim of this study was to evaluate and compare the accuracy of fine needle aspiration cytology (FNAC) in the diagnosis of thyroid lesions with the final histopathologic diagnosis in the surgical specimens. Materials and Methods: A retrospective study was performed over an 11-year-period at Sultan Qaboos University Hospital, Sultanate of Oman. The records of all patients who had undergone FNAC and subsequent surgery for thyroid cancer were included. Cytological diagnosis was classified into five categories: Unsatisfactory, benign, papillary carcinoma, undifferentiated thyroid carcinoma, and suspicious for malignancy. Histopathological diagnosis was classified into two categories: Papillary carcinoma and other thyroid carcinomas. Results: A total of 1460 cases of FNAC thyroid were retrieved. Female to male ratio was 6.3:1, and the mean age was 43.4 years. There were 20 papillary carcinomas, two undifferentiated thyroid carcinomas, and 118 suspicious for malignancy representing 9.6% of all cases. Of these 140 FNAC cases, subsequent histopathologic diagnosis found in only 95 cases. Papillary carcinoma was seen in 83.16% followed by follicular and medullary types with a rate of 12.6% and 2.1%, respectively. Conclusion: The findings of this study showed that FNAC is a sensitive method for the diagnosis of thyroid lesion if cytological yield is adequate and papillary carcinoma is the most common type of thyroid cancer in our institution.

Keywords: Fine needle aspiration cytology, papillary carcinoma, thyroid cancer


How to cite this article:
Alwahaibi N, Alsalami J, Bai UR, Lakhtakia R. Accuracy of fine needle aspiration cytology of thyroid lesion with corresponding histopathology: A single institutional experience. Thyroid Res Pract 2016;13:140-3

How to cite this URL:
Alwahaibi N, Alsalami J, Bai UR, Lakhtakia R. Accuracy of fine needle aspiration cytology of thyroid lesion with corresponding histopathology: A single institutional experience. Thyroid Res Pract [serial online] 2016 [cited 2020 Feb 18];13:140-3. Available from: http://www.thetrp.net/text.asp?2016/13/3/140/193136


  Introduction Top


Despite the improvement in the diagnosis of thyroid lesions using ultrasonography and radionucleotide scanning, fine needle aspiration cytology (FNAC) of thyroid is still the method of choice to conclusively prove the diagnosis of cancer. [1] FNAC, as reported in the literature, is the most accurate, relatively expensive and provides rapid diagnosis for thyroid lesions. [2] In fact, the American Thyroid Association and the National Comprehensive Cancer Network recommend that FNAC should be used as the initial diagnostic test before ultrasonography. [3] However, other than papillary carcinoma, the diagnosis of other thyroid cancers is a challenge. Even papillary carcinoma is sometimes difficult to diagnose because of inadequate cells on FNAC specimens. The conclusion diagnosis may only be made on frozen section or the final resected specimens. Papillary carcinoma is the most common type of thyroid cancer; [4] others include follicular, medullary, and anaplastic thyroid carcinoma.

Worldwide, the incidence of thyroid cancer is on the rise as a report showed that thyroid cancer increased from 3.6/100,000 in 1972 to 8.7/100,000 in 2002. [5] The cause of thyroid cancer is not known, but several reports indicate that exposure to radiation and low dietary iodine may contribute to the development of thyroid cancer. [6]

The Oman National Cancer Registry reported that thyroid cancer is the second most common cancer in females with 8.2% incidence after breast cancer and followed by cervical cancer. [7] The aim of this study was to identify different types of thyroid cancers as well as to correlate the FNAC of thyroid lesions with corresponding histopathology from the experience of a Tertiary Care University Hospital in Oman.


  Materials and methods Top


A retrospective review of FNAC of the thyroid over 11 years from January 2000 to December 2010 was performed in the Department of Pathology, Sultan Qaboos University Hospital, Sultanate of Oman. The reports of all patients who had subsequently undergone thyroid surgery were retrieved. FNAC was performed through a 21- or 23-gauge needle attached to a 10 ml syringe, which was mounted on an aspiration gun. Minimum passes were made into the lesion with the needle. Usually, two aspirations for each nodule were performed without local anesthesia. The specimen was expelled onto one or more glass slides depending on the amount of the material and smeared using a gentle pressure with a second slide placed flat on the first. The minimum number of slides obtained from each nodule was two, but usually, four slides were obtained. Slides were stained with Papanicolaou, hematoxylin and eosin (H and E), and Diff-Quik stains and were examined under the light microscope. For histopathologic diagnosis, the thyroid specimen was fixed in 10% neutral buffered formalin for 24 h, histoprocessed, cut into 3 µm thickness in diameter, and stained with H and E method. Cytological diagnosis was classified into five categories: Unsatisfactory, benign, papillary carcinoma, undifferentiated thyroid carcinoma, and suspicious for malignancy. Histopathological diagnosis was classified into two categories: Papillary carcinoma and other thyroid carcinomas. This study was conducted after approval from the Medical Research Committee and Ethics Committee (MREC No. 511) from the College of Medicine and Health Sciences, Sultan Qaboos University, Sultanate of Oman.


  Results Top


During the study period, 1460 thyroid FNAC cases were found. A total of 1260 cases (86.3%) were female and 200 cases (13.7%) were male, with female to male ratio of 6.3:1. The mean age was 43.4 years (range 7-87). The mean age of female patients was 43.6 years whereas for male patients was 47.5 years.

[Table 1] shows papillary carcinoma, undifferentiated thyroid carcinoma, and suspicious for malignancy representing 9.6% of all cases. The majority of diagnosis on FNAC was benign (53.1%), and the remaining 37.3% were for unsatisfactory cases. Among the 140 cases reported as malignant, the female to male ratio was 2.3:1 with 98-42 cases, respectively. Of 140 positive FNAC cases, 118 cases were suspicious for malignancy (84.3%).
Table 1: Fine needle aspiration cytology diagnosis of thyroid lesions


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Of 140 positive FNAC cases, only 95 cases had subsequent hemi- or near-total thyroidectomy. A total of 45 cases did not do surgery in this hospital, which included 38 cases for suspicious for malignancy, 6 for papillary carcinoma, and one case for undifferentiated thyroid carcinoma. The correlation between FNAC and final histopathology diagnosis for thyroid lesions is shown in [Table 2]. A total of 80 of the 95 FNAC cases were read as suspicious for malignancy; of these, 65 were papillary carcinoma, 12 cases were follicular thyroid carcinoma, two cases were medullary thyroid carcinoma, and one was undifferentiated carcinoma based on histopathological report.
Table 2: Correlation between fine needle aspiration cytology and histopathology diagnosis for thyroid cancer


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  Discussion Top


The findings of this study showed that papillary carcinoma was the most common type of thyroid cancer constituting 83.16% of all our cases followed by follicular and medullary types with a rate of 12.6% and 2.1%, respectively. This finding is consistent with previous studies. [8],[9] In fact, papillary carcinoma is on the rise worldwide as reported in the literature. [5],[10],[11],[12],[13],[14]

In our study, there was a female predominance over males with a ratio of 6.3:1. This finding is consistent with American and Egyptian studies which reported a female to male ratios with 5.7:1 and 5.2:1, respectively. [8],[15] Other study reported a lower ratio. [16] Despite being a universal phenomenon, an additional reason in our population could be higher detection rates since women are usually more frequent visitors to healthcare centers, especially during pregnancy. [17] Other risk factors such as hormones and cigarette smoking have also been proposed. [16],[18]

It was observed that papillary carcinoma had a peak at the age of 20-40 years followed by 41-60 years. Further, patients >20 years of age and above 60 years had low incidence of papillary carcinoma. These findings are consistent with the data of Oman National Cancer Registry, which reported that thyroid cancer peaked at the age of 40-49 years. [7] A similar finding was also reported. [14] In contrast, other studies reported that thyroid cancer is higher in older patients. [19],[20]

FNAC is reported to be safe, painless, simple, rapid, and inexpensive. It can be performed in outpatient clinic without anesthesia. [21] However, interpretation of FNAC of thyroid lesion is difficult and requires vast experience. [22] The results of this study showed that the ability of FNA to detect different types of thyroid cancer is low as 84.3% showed suspicious for malignancy. However, 14 cases out of 140 were definite papillary carcinoma. FNAC shows that all cases of papillary, suspicious, or other thyroid carcinomas were proven to be in the same category as reported by histopathology. Papillary carcinoma is easy to identify if papillary formations are present. However, papillary carcinoma is a mixture of thyroid follicles and neoplastic papillae. [14] One of the major advantages of using thyroid surgery is the ability to identify different types of thyroid cancer and has a minimum false-positive and false-negative rates. In addition, immunohistochemistry can be easily performed. However, thyroid surgery is costly and painfull and needs anesthesia, and the diagnosis is lengthy. [23]

The incidence of unsatisfactory cases in this study was 37.3% which is higher than the reported range (2-20%). [24],[25] This higher number of unsatisfactory cases could be due to inadequate yield of follicular cells, thick smears, obscuring blood or inflammatory cells, and air-dry crush or artifacts. These common limiting factors have been also reported in the literature. [14] In our department, at least 6-8 follicular groups and 8-10 cells in each group are needed for a satisfactory diagnosis. In addition, the adequacy of the samples depends on the right way of identifying the lesion with the help of ultrasound and the method of aspiration. It needs vast experience in performing a proper aspiration to get adequate material. It is recommended to overcome this problem by on-site adequacy testing by a cytotechnologist.

In this study, the accuracy which includes sensitivity and specificity of thyroid FNA was difficult to measure as many patients with unsatisfactory or benign results did not opt for thyroid surgery. In the literature, thyroid FNA has a sensitivity and specificity of 55-94% and 74-100%, respectively. [26],[27],[28] Very few studies reported the accuracy of thyroid FNA cytology as estimated rate of 1-3% for both false-positive and false-negative results has been reported. [29],[30] Sampling and interpretation errors almost equally contribute to these findings. [31] As a limitation of this study, we should mention that this study was based on data acquired from a single hospital, even though it serves as a tertiary referral hospital in Oman, as well as the absence of follow-up histopathology report for benign cases.

The American Thyroid Association, National Comprehensive Cancer Network, and European Consensus Group provide guidelines for the management of patients with thyroid cancer. [32],[33],[34] Surgery is usually performed in patients with papillary carcinoma. Surgery can be classified into total thyroidectomy, near total thyroidectomy, unilateral lobectomy, and isthmusectomy. [35] The choice of different type of surgery depends on the age of the patient, the extent of disease, and other complications. Each method has its own advantages and disadvantages.


  Conclusion Top


The findings of this study showed that FNAC is a sensitive method for the diagnosis of thyroid lesion if cytological yield is adequate and papillary carcinoma is the most common type of thyroid cancer in Oman.

Acknowledgments

We would like to thank all staff in Pathology Department at Sultan Qaboos University Hospital, Muscat, Sultanate of Oman, for their cooperation and help in providing the data.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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