Potential pitfalls of needle tract effects on repeat thyroid fine-needle aspiration.

Background: Fine-needle aspiration (FNA) is a screening and diagnostic tool used in the evaluation of thyroid nodules. Its use has resulted in an increase in the ratio of malignant versus benign thyroid nodules undergoing surgical excision. However, the FNA procedure produces some histological and cytologic alterations, which may lead to misinterpretation on repeat FNA. The goal of the current study was to characterize FNA-induced morphological alterations and their potential influence on interpretations in repeat FNA specimens.

Method: Thyroidectomy specimens that had benign histological diagnoses and for which previous FNA specimens were available were retrieved. The FNA-induced histological alterations were evaluated and grouped based on the interval between the FNA procedure and surgical excision. Repeat thyroid FNA specimens with a cytologic diagnosis of "atypical cells/follicular lesion" were reviewed. Worrisome cytologic features that might occur after the previous FNA procedure were discussed.

Results: Needle tracts were identified in 68 of the 96 thyroidectomy specimens studied. FNA-induced histological alterations included hemorrhage, granulation, exuberant fibroblastic reaction, reactive follicular cells, infarction, and scarring. The presence of plump endothelial cells, myofibroblasts, and, particularly, reactive follicular cells with nuclear grooving and nuclear clearing are potential pitfalls in repeat FNA and these changes are reported to peak within 20 to 40 days after the FNA procedure. Sixteen of 152 repeat FNA cases were diagnosed as atypical cells/follicular lesion, and FNA-induced changes might have contributed to the diagnosis in 2 of these 16 cases.

Conclusions: Cytologists should be aware of atypical cellular changes caused by previous FNA procedures. Although uncommon, these changes may become potential pitfalls in the cytologic diagnosis of repeat thyroid FNA specimens.