Needle tract implantation of papillary thyroid carcinoma after fine-needle aspiration biopsy.

Although fine-needle aspiration biopsy (FNAB) is a useful tool for diagnosing thyroid carcinoma, there are some risks of complications. In this study, we investigated tumor implantation by FNAB of papillary carcinoma. We compared the characteristics of the main tumors and implanted tumors of patients showing FNAB implantations. Between 1990 and 2002, 4912 patients underwent FNAB and were diagnosed as having papillary carcinoma. We encountered 7 cases of needle tract implantation, which account only for 0.14%. We reviewed these 7 cases as well as 3 other patients who underwent FNAB in other hospitals. The intervals between FNAB and detection of the implanted tumor ranged from 2 to 131 months. For these 10 patients, the main tumors in 6 were diagnosed as poorly differentiated carcinoma, and 7 showed extrathyroid extension. Five showed the development of implanted tumor after comparatively shorter intervals (2-68 months), and we classified these as the short interval group. The remaining 5 were classified as the long interval group, because tumor development occurred after 87-131 months. All 5 cases in the short interval group involved preoperatively detectable lymph node metastasis; those in the long interval group did not. The MIB-1 labeling index of the implanted tumor was high in 4 cases in the short interval group, but it was low in all cases in the long interval group. The implanted tumors could be surgically removed without recurrence at the focal sites. These findings indicate that, although high growth activity in the metastatic lesions may be a risk factor of FNAB, inducing the growth of implanted tumors along the needle tract within a short interval after the procedure, FNAB remains the most useful technique for diagnosing thyroid carcinoma. The incidence of implantation was low, and when it did occur, the tumors could be surgically removed without recurrence.