Fine needle aspiration of thyroid

Fine needle aspiration of thyroid:

A cyto-histopathological  correlation in 470 cases of  Ramathibodi hospital
Himakoun W., MD, Chansom R., Bsc.,  Pongtippan A., MD
Department of Pathology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand

Introduction: Thyroid nodules are common clinical findings and about 5 to 10% are malignant1. Appropriate management can decrease morbid and mortality. Fine needle aspiration cytology (FNAC) has been used to evaluate the patients, whether further surgical intervention is required. FNAC is the most accurate, cost-effective and simplest screening test for diagnosing of thyroid nodules. In our study, we review the accuracy of FNAC of all 470 thyroid nodules; correlated with surgical pathology results in Ramathibodi patients.

Method: A retrospective review is performed on 470 cases of thyroid surgical pathology specimens with previous FNAC reports; during January 2005 to January 2007. All histopathology reports are compared to the latest previous cytopathology results which are categorized as unsatisfactory, benign, inconclusive (including follicular and Hurthle cell lesion) / borderline, and malignancy. The aspirates classified as "benign" include adenomatoid nodules, Hashimoto thyroiditis, and subacute thyroiditis. The aspirates classified as "inconclusive" include follicular and Hurthle cell neoplasms / lesions. The aspirates classified as "borderline" include lesions with atypical features, but not diagnostic for malignancy. The aspirates classified as "malignant" include both primary and metastatic tumors. Aspirated specimens with insufficient cellularity or suboptimal in quality of smears are classified as “unsatisfactory”.

Statistic analysis: Thyroid FNAC results are compared to the results of histopathological diagnosis of the excised specimens. They are calculated for sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy. Unsatisfactory, borderline, and inconclusive groups are excluded
Results:
From total 470 cases (71 males and 399 females), the cytopathology results show 74 cases (15.7%) of unsatisfactory specimens, 244 cases (51.9%) of benign lesions (fig. 1a), 34 cases (7.2%) of inconclusive (follicular and Hurthle cell) lesions (fig. 2a), 14 cases (2.9%) of borderline lesions, and 104 cases (22%) of malignant lesions (fig.3a). The histopathology results for benign lesions reveal adenomatoid nodules of 236 cases, follicular adenoma of 31 cases, Hurthle cell adenoma of 3 cases Hashimoto thyroiditis of 3 cases and other diagnoses of 17 cases. The histopathology results for malignant lesions are papillary carcinoma of 148 cases (fig 1b and 3b), follicular carcinoma of 24 cases (fig 2b), and other malignancies (medullary carcinoma, anaplastic carcinoma, malignant lymphoma and metastatic carcinoma) of 8 cases. Among 244 cases of benign lesions from FNAC; 24 cases turn out to be malignant (fig 1a an 1b) while 104 cases of malignant lesions from FNAC show no false positive. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of FNAC are 81.25%, 100%, 100%, 90.16% and 93.10%, respectively.

Discussion:
FNAC is a simple, reliable and cost effective test to determine malignancy of thyroid nodules. Diagnostic accuracy varies between different series (table 12-7), depending on method and data analysis. Experienced cytopathologist and optimal specimens are important for high diagnostic accuracy. Eventhough there is no false positive case in our series, papillary carcinoma is most common among the false negative lesions (16 out of total 24 cases); including some in a group of cystic papillary carcinoma which are previously diagnosed as “benign” cystic lesions / nodules and a group of papillary microcarcinoma (or occult papillary carcinoma) that is also incidentally found in the excised specimens. The clinician should aware and follow up for any clinically suspicious cystic lesions and "inappropriate medical response” nodules.