Neck Lymph Node Metastasis Detection in Patients with Differentiated Thyroid Carcinoma (DTC) in Long-Term Follow-up: a ¹³¹I-SPECT/CT Study

Abstract

Background: The prognostic importance of neck lymph node (LN) metastases in differentiated thyroid carcinoma (DTC) is controversial even if their presence at surgery often correlates with tumor recurrences that it is mandatory to identify. To this purpose, in the present study, we used 131 I-SPECT/CT as diagnostic imaging procedure.Methods: We retrospectively evaluated 224 consecutive DTC patients already submitted to total thyroidectomy and radioiodine therapy, all of them with ascertained neck radioiodine-avid foci at ¹³¹I-SPECT/CT during long-term follow-up; at surgery, 62 patients were classified at high risk (H), 64 at low risk (L), 98 at very low risk. All patients underwent ¹³¹I-Whole body scan (WBS) followed by SPECT/CT. Result: In the 224 patients, 449 neck iodine avid foci were ascertained at SPECT/CT, while 322 were evidenced at WBS in 165/224 patients. WBS classified as residues 263/322 foci and as unclear 59/322 foci; among the former foci SPECT/CT correctly characterized 8 LN metastases and 3 physiologic uptakes and among the latter it pinpointed 26 LN metastases, 18 residues and 15 physiologic uptakes. SPECT/CT also classified 127 foci occult at WBS as 59 LN metastases and 68 residues. Globally, SPECT/CT identified 93 LN metastases in 59 patients (26 H, 20 L, 13 VL), while WBS evidenced 34 in 25 cases. All 13 VL patients,T1aN0M0, 5 of whom with LN near sub-mandibular glands, had thyroglobulin undetectable or <2.5 ng/ml. Globally, SPECT/CT obtained an incremental value than WBS in 45.5 % of patients, a more correct patient classification changing therapeutic approach in 30.3 % of cases and identified WBS false positive findings in 8% of cases. Conclusion: ¹³¹I-SPECT/CT proved to correctly detect and characterize neck LN metastases in DTC patients in long-term follow-up, improving WBS performance. SPECT/CT routine use is suggested, its role being particularly significant in patients with WBS inconclusive, VL, T1aN0M0 and with undetectable or very low thyroglobulin levels.