Nodal staging of differentiated thyroid carcinoma and SPECT-CT

Objectives The aim of our study was to assess the diagnostic value of 131I SPECT-CT on nodal staging of patients with Differentiated Thyroid Carcinoma (DTC).

Methods We studied 100 patients aged between 16 - 78 years, previously underwent total thyroidectomy for DTC . These patients underwent planar imaging and SPECT-CT after 3 weeks of L-thyroxine withdrawal and 4 days after oral administration of 3,7-5,55 GBq (100-150mCi) of 131I. Indication for treatment was remnant ablation or additional radioiodine therapy (in cases of metastatic disease) with rising thyroglobulin levels. SPECT -low dose CT of the neck was acquired with a Symbia T camera with high energy collimators. Planar scans and SPECT-CT images were evaluated for cervical tracer uptake independently of each other and of the clinical findings.

Results Planar imaging and SPECT-CT showed respectively 70 and 87 foci of uptake in 89 of 100 patients. SPECT-CT confirmed all foci seen on planar imaging and identified 17 occult additional foci . SPECT-CT allowed the identification of lymph node metastases classified as thyroid remnant or as indeterminate on planar imaging. Based on this revision, SPECT-CT yielded a gain in information on nodal stage in 20 of the 100 patients studied (20%).

Conclusions SPECT-CT determines lymph node involvement at radioablation performed for DTC more accurately than does planar imaging. By upstaging or downstaging disease, SPECT-CT may alter the management of roughly one quarter of patients with DTC.