The utility of lymph node mapping sonogram and thyroglobulin surveillance in post thyroidectomy papillary thyroid cancer patients.

Background: The American Thyroid Association recommends lymph node mapping (LNM) ultrasonography 6-12 months after thyroidectomy for patients with papillary thyroid cancer (PTC). The yield of LNM over thyroglobulin (TG) screening is not well defined. We sought to investigate this relationship.

Methods: Post thyroidectomy LNM was performed on 163 patients with PTC. LNM was considered positive based on these criteria: Loss of fatty hilum (LOFH), microcalcifications, hypervascularity, architectural distortion, or short axis (>8 mm). Serum TG levels were compared to LNM and fine needle aspiration (FNA).

Results: Sixty-nine patients had suspicious LNM (42%) and 17 had PTC on FNA (25%). There were 135 suspicious lymph nodes described with malignant nodes found in 6 of 65 patients (9%) with LOFH, 13 of 18 patients (76%) with microcalcifications, 11 of 12 patients (92%) with hypervascularity, 16 of 28 patients (52%) with architectural distortion, and 4 of 7 patients (52%) with enlarged size on FNA. The positive predictive value of LNM was 0.34, increasing to 0.66 when LOFH was excluded. Among 152 patients with documented TG data, LNM identified cervical nodal metastasis in 4 patients with TG < 0.5 pg/mL (anti-TG antibody negative, thyroid-stimulating hormone suppressed). Of the 15 patients with positive anti-TG antibody, 3 with recurrence were found on LNM.

Conclusion: LNM can detect recurrent PTC when TG level is undetectable, and LOFH is a low-yield sonographic characteristic.