Measurement of fine‐needle aspiration thyroglobulin levels increases the detection of metastatic papillary thyroid carcinoma in cystic neck lesions

Abstract

Patients with previously resected papillary thyroid carcinoma (PTC) are monitored for disease recurrence/metastasis by ultrasound surveillance and fine-needle aspiration (FNA) cytology. However, accurate diagnosis in lesions with cystic degeneration may be difficult due to scant cellularity. In the current study, the authors evaluated thyroglobulin in FNA (Tg-FNA) for detecting metastatic and/or recurrent PTC in patients with cystic neck lesions after thyroidectomy. The pathology records were retrospectively searched for patients with previously resected PTC and subsequent Tg-FNA on a cystic neck mass. Tg-FNA was measured in needle rinses using a Tg assay. The ultrasound findings, Tg-FNA concentrations, and cytological and follow-up histological diagnoses were correlated. A total of 21 FNA specimens of cystic lesions from 19 patients were identified. Of 7 cases with cytologic and subsequent histologic diagnoses of metastatic PTC, the median Tg-FNA level was 100,982 ng/mL. Of 8 cytologically benign cases, 7 cases had Tg-FNA levels < 0.2 ng/mL, and 1 aberrant case demonstrated elevated Tg-FNA of > 1000 ng/mL. For 6 cytologically equivocal cases, including 3 classified as atypical/suspicious for carcinoma, 2 classified as insufficient/acellular debris, and 1 classified as spindle cell neoplasm, 4 patients demonstrated markedly elevated Tg-FNA levels (> 150 ng/mL) with subsequent surgical confirmation of metastatic PTC, whereas 2 patients had Tg-FNA levels of < 0.2 ng/mL with negative follow-up. Using a cutoff value of 0.2 ng/mL, Tg-FNA demonstrated a sensitivity of 100% and specificity of 87.5%. Tg-FNA is a useful ancillary test that improves the detection of cystic PTC metastases. Particularly in cytologically nondiagnostic cases, the measurement of Tg-FNA helps to distinguish benign from malignant cystic lesions.