Accuracy of FNAC in Diagnosing Thyroid Swelling - A Retrospective Study

Introduction

Fine needle aspiration cytology is a simple and cost effective method to sample superficial masses found in the region of head and neck [1]. The technique is performed in the outpatient department and causes minimal trauma to the patient and carries virtually no risk of complications.Swellings located in the head and neck region including thyroid can be readily diagnosed using this technique [2, 3]. FNAC is particularly important in planing the further treatment of the neck swelling as it helps in differentiating between benign and malignant disease.There is no evidence that tumour spreads through the skin tract created by fine hypodermic needle used in this technique [4]. FNAC does not give same architectural detail as histology but it can provide cells from the entire lesion, as many passes through the lesion can be made while aspirating [5]. Materials and Methods-A retrospective study of 96 patients who presented with thyroid swelling to the ENT outpatient department over a period of 1 yr in our institute was done . After taking a detailed case history and completing the clinical examination, all the above patients were subjected to FNAC.FNAC was done using 22-23gauge, 3-5cms long needle with 10ml syringe. 54 out of 96 patients who underwent surgical excision for the thyroid swelling were included in our study. The histopathological report of the excised specimen post -operatively was obtained in these 54 patients. The pre-operative FNAC report was compared with the histopathology report to determine the accuracy of FNAC in establishing a correct diagnosis.

Results

The present study included 54 patients in the age group of 11 to 70yrs, with maximum incidence amongst those in their 3rd decade of life . Majority were females-45 patients and males-9 patients. On Clinical examination, out of the 54 patients only 4 patients had tenderness over the swelling (Table 1) and consistency varied amongst different swellings (Table 2).

Classification of Cytological reports (Table 3) In cases where the FNAC features of swelling were similar to HPE report –These were considered as positive. In cases where cytological features were suspicious of a lesion which was confirmed by histopathology-these were considered as doubtful or inconclusive.In our study out of 54 patients with thyroid swelling who underwent surgery, 4 of them had a doubtful FNAC, 2 of these were reported as suspicious of malignancy and the other 2 as suspicious of hashimoto’s thyroiditis on FNAC.Since clinically diagnosis seemed more in favour of multinodular goitre, all these 4 cases underwent total thyroidectomy. In cases where the cytological features did not correlate with histopathological features –these were considered as negative.

Discussion

The use of needle aspiration in the diagnosis of neck swellings was reported by Greig and Gray in 1904, when they aspirated lymph nodes for the identification of trypanosomes. But it was popularised in 1930’s by Martin et al. Since then several reports on cytodiagnosis of neck swellings have been published from different parts of the world. The advantages of aspiration biopsy are that it is simple, rapid and economical procedure.It may clear up a questionable diagnosis or provide histological material in an obvious case without need for hospitalisation.It can easily distinguish inflammatory lesion from neoplastic lesion.It frequently eliminates a more formidable open biopsy procedure with its attendant hazards of non healing and other operative complications. The usefulness of FNAC has been questioned through many studies in cases of small, non palpable masses (<1.5cm) [6, 7, 8, 9]. In our study, the accuracy of FNAC in diagnosing thyroid swelling is encouraging, the overall accuracy rate in our study is 77.78%, which is comparable to the findings in earlier studies, Jens Thomsen had 75% accuracy in their 17 aspirates from thyroid gland, Hamming JF reported 75% accuracy in 169 cases and Mondal A reported 92.7% of accuracy in 192 thyroid tumours.

Conclusion

Fine needle aspiration cytology is a simple, quick, economical and least traumatic procedure that can be easily carried out in outpatient department or at bedside with high degree of accuracy in diagnosing thyroid swellings. However the small percentage of false negative results can also be overcome if the pathologist work more closely with the clinician and correlate the clinical findings while reporting the cytological slides as well as to determine the best possible sites of aspirates from swelling .

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