Differential diagnosis of thyroid nodules via real-time PET/ultrasound (US) fusion in a case of co-existing medullary thyroid cancer and adenoma.
Published on Sep 3, 2013in The Journal of Clinical Endocrinology and Metabolism5.399
· DOI :10.1210/JC.2013-2566
A 52-year-old woman presented with apparent carcinoid syndrome. Gallium 68 (Ga)-DOTATOC positron emission tomography (PET)/computed tomography (CT) found a 2.5-cm somatostatin receptor (SR)positive nodule in the left thyroid lobe. Basal serum calcitonin was 5184 ng/L, TSH was 0.63 mU/L, and free T4 was 16.98 pmol/L, so medullary thyroid cancer was suspected. Ultrasonography (Figure 1, A and B), F-fluorodeoxyglucose (FDG) PET/CT, and iodine 124 (I) PET/ CT, performed to allocate thyroid nodules to GaDOTATOC PET findings and exclude metastases, revealed an adjacent nodule 1 cm (Figures 1 and 2), believed to be adenoma. The patient provided informed consent for all procedures. To unambiguously characterize the nodules, we used a magnetic navigation system (VNav; GE Healthcare) to perform live fusion of metabolic/functional images acquired through PET and morphological images obtained with ultrasound (PET/ultrasonography) (1). Live fusion recently was reported to be a problem-solving tool in cases of unclear PET findings (2); although CT shows anatomical landmarks facilitating PET image interpretation, ultrasonography offers superior soft-tissue resolution to that of CT. Moreover, real-time coregistration allows immediate, interactive investigation. PET/CT data are acquired according to standard protocol, then loaded onto an ultrasonography system located in a separate room; images are aligned using anatomical landmarks, and three-dimensional PET/CT views are then automatically reoriented and fused to live ultrasonographic images according to ultrasound probe positioning (3) (Figure 2, A–C, and Movie 1). After thyroidectomy, histology confirmed our hypothesis regarding the lesions. Real-time fusion of PET/ultrasonography images thus differentiated an F-FDG-positive, I-negative, and SR-positive thyroid nodule, which proved to be medullary thyroid cancer, from an adjacent F-FDG-negative, I-positive, and SR-negative nodule, which turned out to be a compensated autonomous adenoma (Figure 2).