Comparison on fine needle aspiration cytology (FNAC) and thyroid ultrasonography in management of thyroid nodules

Abstract

A nodular thyroid gland is a common occurrence, especially among females; although chances of these lesions being malignant are rare [1]. In Sri Lanka, thyroid cancer is one of the five leading sites of cancer in females, and has a life time risk of 0.357% for both males and females [2]. The gold standard for diagnosis of thyroid pathologies is histopathology. However it is important to correctly diagnose during initial investigations for management plans. The available investigations for diagnosis range from biochemical, cytological and imaging to histopathology. Of these, FNAC is one of the most accurate and cost-effective methods of evaluating thyroid nodules, which is further improved by incorporation of genetic and immunohistochemical tests [3,4]. In recent studies sensitivity, specificity and accuracy of FNAC have been reported as high as 65-98%, 72-100, 95% respectively [3]. However The Royal College of Pathologists recommend a wide range of values for sensitivity, specificity and accuracy of FNAC with regard to detection of thyroid neoplasms [5]. Thy roid FNAC has some limitations in cases of suspi cious, inadequate, and indeterminate cytology and it is reported that, even in adequate cellular specimens, an “undetermined” result can occur in 4–15% of all cases [6]. Therefore, a definitive distinction between neoplasms and nonneoplasms is difficult. In addition, there are false-positives and false-negatives. Therefore, another investigation is used in combination to compensate for these lim itations. Ultrasonography (USS) of the thyroid gland is considered as the most sensitive method for diagnosis of intrathyroidlesions in some research [7]. The reported features of malignancy in USS include marked hypoechogenecity, presence of microcalcifications, irregular margins, nodule with shape taller than wide and intra-nodular hypervascularity in color Doppler [8]. The presence of more than one of the above features, and combination of some features, increase the probability that a thyroid nodule represents a malignancy [8]. In addition, it is non invasive, relatively inexpensive and widely available in Sri Lanka. Therefore it is necessary to assess the ability of FNAC and USS in diagnosis of thyroid pathologies in the local setting.