Detection of Subcentimeter Metastatic Cervical Lymph Node by 18F-FDG PET/CT in Patients With Well-Differentiated Thyroid Carcinoma and High Serum Thyroglobulin But Negative 131I Whole-Body Scan

• Published in: Clinical nuclear medicine 2012-06, Vol.37 (6), p.561-567
• Main Authors: Kunawudhi, Anchisa, Pak-art, Rattaplee, Keelawat, Somboon, Tepmongkol, Supatporn
• Format: Article
• Language: English
• Subjects: Adult; Aged; Female; Fluorodeoxyglucose F18; Humans; Iodine Radioisotopes; Lymphatic Metastasis; Male; Middle Aged; Multimodal Imaging; Neck; Positron-Emission Tomography; Thyroglobulin - blood; Thyroid Neoplasms - blood; Thyroid Neoplasms - diagnostic imaging; Thyroid Neoplasms - pathology; Thyroid Neoplasms - surgery; Time Factors; Tomography, X-Ray Computed; Treatment Outcome; Tumor Burden; Whole Body Imaging
• ISSN: 0363-9762; 1536-0229
• DOI: 10.1097/RLU.0b013e318252d30e

PURPOSEThis study aimed to evaluate the diagnostic value of F-FDG PET/CT and identify the best parameter to detect subcentimeter cervical nodal metastasis in patients with a well-differentiated thyroid carcinoma (WDTC), elevated serum thyroglobulin (Tg) levels, but negative findings in the I whole-body scan (WBS). MATERIALS AND METHODSWe prospectively studied 30 consecutive patients with WDTC after standard surgery and radioiodine treatment. All patients had serum Tg greater than 10 ng/mL during thyroid hormone withdrawal but negative findings in the therapeutic I WBS. One whole-body CT scan and serial whole-body and neck PET scans were performed between 10 and 170 minutes after F-FDG injection. Parameters studied were SUVmax, percent change in SUVmax, SUV ratios of lesions to reference organs, and their percent change. Result in the PET/CT scan was correlated with histopathology and follow-up information. Patient-based and lesion-based (subcentimeter cervical lymph nodes) analyses were performed. Outcome of Tg level after lymph node resection was also analyzed. RESULTSThe overall sensitivity, specificity, accuracy, and positive and negative predictive values were 100%, 78%, 93%, 91%, and 100%, respectively. In lesion-based analysis, the differential SUVmax between 2 time points did not provide higher sensitivity than the individual SUVmax at the 60th or 90th minute. A combined SUVmax at the 90th minute greater than 2.75 and a percent change of SUVmax between the 60th and 90th minute greater than −1.1% provides the best diagnostic value with sensitivity, specificity, accuracy, and positive and negative predictive values of 81%, 90%, 83%, 97%, and 56%, respectively. After surgery, patients with completely resected PET-positive nodes without distant metastasis showed reduction of suppressed Tg to less than 2 ng/mL. CONCLUSIONSCombined SUVmax at the 90th minute and the percent change of SUVmax between the 60th and 90th minute provides the best diagnostic value to differentiate benign from malignant conditions in subcentimeter lymph nodes.