Needle Tract Implantation of Follicular Neoplasm After Fine-Needle Aspiration Biopsy: Report of a Case

We herein report a 28-year-old woman with a follicular neoplasm showing subcutaneous needle tract implantation. One month after fine-needle aspiration biopsy (FNAB) for a tumor measuring 2.5 cm, the patient became aware of a subcutaneous nodule measuring about 1 cm at the needle insertion site. FNAB smear of this nodule showed poorly cohesive clusters of follicular cells with nuclear crowding, overlapping and resetting with some microfollicular architecture. Total thyroidectomy and resection of the subcutaneous nodule were performed. Although there was no capsular or vascular invasion of the nodule, the lesion was diagnosed as follicular carcinoma because of the subcutaneous seeding. Ki-67 labeling indices of the thyroid nodule and implanted tumor were higher than 5%. Furthermore, although galectin-3 was completely negative in the thyroid nodule, it was heterogeneously positive in the implanted tumor. It is therefore suggested that high cell proliferating activity as a characteristic of the original nodule and the subsequently obtained invasive characteristic of the implanted tumor contributed to this event. To date, there has not been any recurrence of the implanted lesion. Because implanted follicular carcinoma can be surgically removed, this complication should not impair the usefulness of FNAB.