Comparison of fine needle aspiration cytology with histopathology findings of thyroid lesions at Muhimbili national hospital

Abstract

Background: Thyroid lesions due to iodine deficiency and other causes is an endemic disease in our set up. Over 70% of patients are found to be referred due to nodular lesions, in which some nodular lesions are malignant in nature. The risk of malignancy in solitary and multinodular goiter occurring in endemic go it re areas is reported to be higher than in control areas.1 Several investigations have been recommended to assess thyroid lesions and these include thyroid function test, ultrasonography, radionuclide scans and fine needle aspiration cytology. Cytology is considered to be a precise diagnostic screening test for malignancy. However for a satisfactory result, a representative specimen and an experienced cytologist are mandatory. In a developing country where sophisticated technology and an experienced cytologists may not be readily available, the challenges of identifying patients with malignancy in thyroid lesion is even greater. Objective: The aim of the study was to determine sensitivity, specificity, positive predictive value, negative predictive value and accuracy of FNAC in comparison with gold standard histopathology findings. Methodology: This hospital based descriptive crossectional study was intended to compare FNAC to histopathological tissue findings of thyroid lesion sat Muhimbili National Hospital of hundred and twenty four patients. It included in patients in general surgery wards and surgical outpatient clinics. Results: A total of 124 patients with thyroid lesions were enrolled in the study. The mean age (± standard deviation) of the study participants was 40.5years (±11.66) years. Large percentages (33.1%) of the thyroid patients were in the 31-40 years age group. Fifteen (12.1%) of the 124 patients were male and 109 (87.9%) were female (M: F, 1:7.3). In FNACatotal of 124 patients with thyroid lesion, 80.6% showed benign lesion, 11.3% malignant lesion and 8.1% suspicious lesion.

In Tissue histopathologyatotal of 124 patients with thyroid lesion, 82.3% showed benign lesion, 17.7% malignant lesion. Most common benign thyroid lesions were colloid goiter 48 out of 102(47.1%). Out of 124 patients, 114 patients were analysed, as 10 patients were indeterminateon FNAC. Of the 100 samples which were negative for malignancy on FNAC, 9 aspirates showed non neoplastic lesion while confirmed by histopathology as papillary carcinoma in 4(44.4%) and follicular carcino main 5(55.6%). Out of 14 malignancieson FNAC, 13(92.9%) were malignant.one patient showed papillary carcinoma on FNAC while histological diagnosis confirmed the diagnosis as follicular adenoma. Sensitivity of FNACwas59.1%, specificity 98.9%, positive predictive value 92.9, negative predictive value 91% and accuracy was 91.2%. In FNAC out of 124 patients 70(56.5%) received their FNAC results by one week. The mean duration (± standard deviation) of reporting FNAC results was 8.2 days (±5.59) days. In Histology out of 124 patients 40(32.3%) received their histological results by third week. The mean duration (± standard deviation) of reporting histopathology results was 23.53 days (±17.17)days Conclusion: The results of this study are comparable with the current published data and demonstrate that FNA cytology is a specific, and accurate initial diagnostic test for evaluation of patients with thyroid swellings. However, FNAC has low sensitivity. Cytodiagnostic errors of some cases with overlapping cytological features can be avoided by paying attention to the possible pitfalls. The suspicious results can be resolved by diagnostic surgical resection. A benign FNAC diagnosis should be viewed with caution as false negative results do occur and these patients should be followed up clinic-radio logically for any progression that will require repeated FNAC and/or surgery. Recommendation: FNAC is a reliable preoperative tool for investigation. The sensitivity of the test could be improved by decreasing false negative rate through improving sample collection, appropriate sample preparation and accurate interpretation by cytopathologists.