The association between cytology and histopathology in thyroid nodules over a 6-year period in an urban hospital in South Africa.

Background: Thyroid cancer is prevalent both internationally and locally, and is the most common cause of endocrine malignancies in Africa. The prognosis of thyroid cancer in general is quite good, but to achieve good outcomes, appropriate methods for diagnosis are important. A cytology result obtained from a fine needle aspiration and biopsy (FNAB) is one such method, and is less invasive and has less risk compared with obtaining a histological result via open surgery. However, there are accuracy differences that have been reported in different literature findings.

Objectives: To determine the diagnostic accuracy rate of thyroid FNAB compared with histopathological samples at an urban hospital in South Africa (SA), and compare this with international standards.

Methods: A retrospective observational study was conducted of patients who had undergone both FNAB and thyroidectomies at Helen Joseph Hospital, Gauteng Province, SA, a public tertiary hospital, between 1  January 2016 and 31  December 2021. Various analytical methods were used, including Poisson generalised linear model, binomial generalised linear model, a two-proportion z-test, McNemar's test and the F1 score.

Results: There were 164 participants in this study who were between the ages of 21 and 82 years old. Thirty-six records were excluded for use as a comparison between cytology and histology, as they were in Bethesda categories 1, 3 and 4. Out of the 128 records that were compared, there was statistically significant agreement v. non-agreement between cytology and histology findings for thyroid nodules (109  v. 19, p<0.001, respectively). A comparison between our sample population and internationally published standards in terms of rate of malignancy noted that our rate of malignancy was slightly higher in Bethesda 2 patients (5.88%) v. internationally published standards (0 - 3%), and slightly lower in Bethesda 4 (23.52%) and 6 (77.77%) v. internationally published standards (25 - 40% and 97 - 99%, respectively.

Conclusion: There was good correlation between cytology and histology for thyroid nodules. Differences were noted between the percentage of malignant cases in the different Bethesda categories compared with international standards as noted above. We recommend that further studies are conducted locally to improve knowledge on this topic.