Objective: The exact prevalence and clinical significance of ectopic thyroid or thyroglossal duct remnant (TGDR) in the general population have not yet been fully determined despite numerous case reports. This study was prepared to assess the prevalence of TGDR in asymptomatic subjects during hypothyroidism after a total thyroidectomy for differentiated thyroid cancer (DTC) and to clarify the clinical implication.
Design: Tc-99m pertechnetate scintigraphy (Tc-scan) of the head and neck before radioiodine ablation therapy and whole-body and pinhole I-131 scintigraphy (I-scan) after ablation therapy were reviewed for 131 consecutive DTC patients with hypothyroidism after a total thyroidectomy.
Main outcome: Forty-four among the 131 patients (33.6%) revealed an unexpected linear or focal radioactivity at the anterior midline of the neck, suggesting the presence of TGDR. The Tc-scan and pinhole I-scan were concordant in all cases of abnormal midline neck uptake, although the planar I-scan failed to delineate TGDR due to prominent photon scattering in most cases. Preoperative enhanced neck computed tomography scan was performed in 49 patients and showed no evidence of thyroid glandular tissue separated from thyroid gland in midline of the anterior neck except 1 case. The success rate after radioiodine ablation did not differ significantly between the positive and negative TGDR patients.
Conclusions: TGDR can be frequently observed in scintigraphy of hypothyroid subjects after a thyroidectomy, even when clinically unexpected. Therefore, care should be taken not to confuse the tracer uptake by TGDR with metastatic foci in I- and Tc-scans of patients with hypothyroidism after a thyroidectomy for DTC.