Variants and Pitfalls on Radioiodine Whole Body Scanning in Pediatric Patients with Differentiated Thyroid Carcinoma

Objectives Radioiodine whole body scanning is used to reveal functioning thyroid tissue (FTT) and/or functioning thyroid carcinomatous tissue (FTCT) in patients with differentiated thyroid carcinoma (DTC). However, FTT /FTCT on radioiodine whole body scans (RIWBSs), may be mimicked by some variants and pitfalls. We studied these variants and pitfalls and how they affect the diagnostic incrimination on RIWBSs of pediatric patients with DTC.

Methods A total of 223 RIWBSs, of 53 pediatric patients (37 female; mean age of 13.3) with DTC, were reviewed by two nuclear medicine physicians. The focal or regional activities, likely not representing FTT/ FTCT, were categorized as variants and pitfalls. The final diagnosis was confirmed by reviewing the concurrent and follow up clinical data, correlative ultrasonography, CT scanning, serum thyroglobulin and antithyroglobulin antibody levels. The frequency of these variants and pitfalls were calculated, on diagnostic and post-therapy RIWBSs.

Results Thymic activity was the most commonly revealed variant on overall RIWBSs (24/223, 10.8%). Among them, 7 were seen on diagnostic RIWBSs of 4 patients, and 17 on post-therapy RIWBSs of 11 patients. This thymic activity may be potentially misinterpreted as metastatic mediastinal lymph nodes. This was followed by the cardiac activity (overall 8/223 RIWBSs; 3.6%), and pulmonary activity (overall 5/223 RIWBSs; 2.2%). Among the pitfalls, star artifact, caused by prominent thyroid remnant, may obscure the diagnosis of metastatic mediastinal lymph nodes.

Conclusions Variants and pitfalls that mimic FTT /FTCT on RIWBS in pediatric patients with DTC are not infrequent and may lead to misinterpretation particularly on initial RIWBS. This can be minimized by proper knowledge of such variants and pitfalls and correlation with clinicolaboratory and imaging data.