Background: Thyroid swellings, especially thyroid nodules, are common and the primary clinical goal is to detect malignancy accurately and to avoid unnecessary surgery. Usually reported by the Bethesda System, FNAC or Fine needle aspiration cytology is the first line diagnostic test. Whereas, post-operative histopathology is the gold standard for definitive diagnosis. In the nondiagnosis and indeterminate categories, discordance between FNAC and histopathology is most common; which may lead to overtreatment and delayed diagnosis.
Aim: To evaluate pre-operative FNAC findings with post-operative histopathological result of thyroid swellings and to evaluate the factors and adjuncts (ultrasound risk systems, repeat sampling/core-needle biopsy, and molecular testing) impacting cytology-histology correlation.
Methods: We employed a PRISMA-style narrative review framework. Information from the major guideline and evidence-based sources on reporting thyroid cytology (Bethesda), ultrasound risk stratification (ACR TI-RADS/EU-TIRADS), and problem-solving strategies for nondiagnostic or indeterminate FNAC (repeat FNAC, core-needle biopsy and molecular classifiers such as Afirma and ThyroSeq) were synthesised. The study aimed to obtain cytology-histology concordance patterns by Bethesda category and malignancy risk trends and common causes of false-negative/false-positive FNAC.
Key findings: Overall high concordance between cytology and histology is seen at the extremes. Most resected lesions with an FNAC diagnosis of benign (Bethesda II) correlate with benign histology. Malignant FNAC (Bethesda VI) shows very strong correlation with carcinoma on histopathology. Most clinically meaningful discordance occurs in Bethesda category I, which are nondiagnostic cases, and in Bethesda categories III and IV, which are the AUS/FLUS and follicular-patterned lesions, respectively. These mismatches are caused by sampling limitations, interpretive variability and the fact that cytology cannot assess capsular or vascular invasion. Risk stratification by ultrasound increases pre-test probability and facilitates triaging of discordant cases; core-needle biopsy reduces nondiagnostic results and may give more definitive information about tissue architecture in selected nodules; molecular testing refines risk stratification and may obviate the need for diagnostic surgery in appropriately selected indeterminate nodules. The risk of malignancy estimates were centred around NIFTPs, therefore the impact of this reclassification must be evaluated for historical ROM values.
Conclusion: When interpreted with the Bethesda categories and integrated with ultrasound risk stratification, FNAC is effective in the preoperative triage of thyroid swellings. Nonetheless, the main contributors of discrepancies between cytology and histology occur owing these categories. Using the TI-RADS/EU-TIRADS score in conjunction with selective repeat sampling/CNB and molecular testing will improve histo-pathological agreement for post-operative diagnosis and allow for more tailor made conservative surgery decision making.
International Journal of Advanced Research in Medicine
