Postablative 131I SPECT/CT Is Much More Sensitive Than Cervical Ultrasonography for the Detection of Thyroid Remnants in Patients After Total Thyroidectomy for Differentiated Thyroid Cancer.

PURPOSE: Evaluation of utility of cervical ultrasound (US) for detection of thyroid remnants (ThR) in patients after thyroidectomy for differentiated thyroid cancer.

METHODS: Included were 154 consecutive patients (17-89 years, 123 female and 31 male patients), without known cancer residues or cervical lymph nodes metastases, admitted for ThR ablation with I, 14 to 20 weeks after surgery. Neck uptake of I (Tup) and thyroglobulin were determined, and location and volume of ThR detected by cervical US were recorded. On days 3 to 4 after ablation (1.7-4.6GBq, 46-124.3 mCi I), neck SPECT/CT was performed, and I uptake foci were assigned to one of the regions as described below. The anterior neck was divided into 2 compartments: superior and inferior to lower margin of thyroid cartilage, and each compartment was subdivided into middle and lateral regions (in SPECT/CT, posterolateral and anterolateral regions were also marked out). I uptake sites and ThR detected by US, if congruent with SPECT/CT, were counted and analyzed.

RESULTS: In total, 341 I uptake foci were found in 150 patients (97.4%) by SPECT/CT and 213 corresponding ThR in 118 patients (76.6%) by US. Ultrasound detected 30% to 46% of I uptake foci in superior lateral regions, 49% in pyramidal lobe/thyroglossal duct area (both P < 0.05), 74% to 77% in inferior lateral regions, and 22% in isthmus (both P > 0.05). Correlation between ThR volume and Tup was strong (r = 0.79), and that between ThR volume and thyroglobulin was weak (r = 0.24).

CONCLUSIONS: Ultrasound is less sensitive than I posttherapy scans for ThR detection in patients after thyroidectomy, especially for remnants located above the lower margin of thyroid cartilage.