Ultrasound-guided fine-needle aspiration biopsy of the thyroid bed

Background: Ultrasound (US) has been shown to be a sensitive technique for monitoring patients for recurrent thyroid carcinoma in the thyroid bed after total thyroidectomy. However, the role of US-guided fine-needle aspiration biopsy (FNAB) in the confirmation of sonographically indeterminate or suspicious masses has not been adequately addressed. The purposes of this study were to determine the sensitivity and specificity of US-guided FNAB of the thyroid bed for diagnosing recurrent carcinoma after total thyroidectomy and to highlight potential diagnostic pitfalls.

Methods: Twenty-one patients with a history of total thyroidectomy and histologically confirmed thyroid carcinoma who had undergone US-guided FNAB of hypoechoic lesions in the thyroid bed were included in this retrospective study. Fifteen of the 21 had papillary carcinoma (PC), 5 had medullary carcinoma (MC), and 1 had Hürthle cell carcinoma (HTC). The cytologic features of the aspirates were compared with histopathologic findings of pre- and post-FNA surgery. Immunohistochemical staining for thyroglobulin, calcitonin, and parathyroid hormone was performed in four cases.

Results: The cytologic diagnosis from the US-guided FNABs was conclusive in 20 of 21 cases. Fifteen cases were diagnosed as recurrent tumor (12 PC, 2 MC, and 1 HTC), and 13 of the 15 were confirmed subsequently by histology. Five cases were diagnosed as benign (two residual benign thyroid tissue, one parathyroid gland [PG] tissue, and two reparative changes) and hence were not resected. There was one false-positive diagnosis in which PG was misdiagnosed as PC. Immunohistochemical studies helped to confirm the diagnosis of PG tissue in two cases and of MC in two cases. The sensitivity of US-guided FNA for diagnosing recurrent carcinoma in the thyroid bed after total thyroidectomy was 100% and the specificity was 85.7%.

Conclusions: US-guided FNAB was found to be a sensitive and specific test for diagnosing sonographically indeterminate lesions in the thyroid bed. One potential diagnostic pitfall was the misdiagnosis of normal residual thyroid or PG tissue as recurrent tumor. Careful attention to cytologic details and the use of selected immunohistochemical staining may help to prevent these misdiagnoses.