PET imaging in differentiated thyroid cancer: where does it fit and how do we use it?

Positron emission tomography (PET) is a rapidly evolving imaging modality that has gained widespread acceptance in oncology, with several radionuclides applicable to thyroid cancer. Thyroid cancer patients have been studied most commonly using 18F-Fluorodeoxyglucose (FDG)-PET, with perhaps the greatest utility being the potential localization of tumor in differentiated thyroid cancer (DTC) patients who are radioiodine whole body scan (WBS) negative and thyroglobulin (Tg) positive. Also of value is the identification of patients unlikely to benefit from additional 131I therapy and identification of patients at highest risk of disease-specific mortality, which may prompt more aggressive therapy or enrollment in clinical trials. Emerging data suggest that PET/CT fusion studies provide increased accuracy and modify the treatment plan in a significant number of DTC cases when compared to PET images alone. However, studies documenting improvements in survival and tumor recurrence attributable to FDG-PET imaging in thyroid cancer patients are lacking. Specific case examples of thyroid cancer patients who appear to have benefited from FDG-PET imaging do exist, while less data are available in the setting of anaplastic or medullary thyroid carcinoma. This article reviews the utility and limitations of FDG-PET in DTC management, and offers practical recommendations.

[Diagnostic value of positron emission tomography/computed tomography with fluorine-18 fluordeoxyglucose in patients with differentiated thyroid gland carcinoma, high thyroglobulin serum levels and negative iodine whole body scan]. / Valor diagnóstico da tomografia por emissão de pósitrons/tomografia computadorizada (PET-CT) com flúor-18 fluordeoxiglicose (FDG-18F) em pacientes com carcinoma diferenciado da tireóide, níveis séricos de tireoglobulina elevados e pesquisa de corpo inteiro com iodo negativa.

PURPOSE: To evaluate the role of PET-CT with FDG-18F in the detection of recurrence and/or metastasis of differentiated thyroid carcinoma (DTC) in patients with elevated levels of thyroglobulin (TG) and negative whole body scan (WBS). PATIENTS AND METHOD: PET-CT findings of 25 patients were compared to histopathology evaluation and conventional imaging (CI). RESULTS: PET-CT scan was positive in 16 patients finding 14 true-positive and 2 false-positive cases (positive predictive value 87.5%). Nine patients had negative PET-CT; two had decrease of TG to undetectable levels. One patient had residual disease detected by post-therapeutic WBS. Six patients had no evidence of tumor during follow-up (mean time 16 months). PET-CT was concordant with CI in 52%, partially concordant in 12% and discordant in 36% (6 false-negatives and 3 false-positive of CI). We observed a tendency of increasing proportion of positive PET-CT with increasing TG. CONCLUSION: PET-CT scan with FDG-18F is useful in the detection of recurrence and/or metastases of DTC with high TG levels but negative WBS. It presents elevated positive predictive value and is superior to CI being more effective as higher the serum TG levels.

Carcinoma medular de tiroides: hallazgos ecográficos en 5 casos de un mismo grupo familiar / Hereditary medullary thyroid carcinoma: US findings in 5 cases of a single familiar group

El carcinoma medular de tiroides (CMT) es un tumor de baja incidencia y elevada mortalidad que representa entre el 3 y 10 por ciento de los tumores malignos de la tiroides. Un 25 por ciento de éstos corresponde a la forma familiar de la enfermedad. Con el objeto de demostrar el rol de la ecografía en la detección y seguimiento del carcinoma medular de tiroides familiar (CMTf) se evaluaron retrospectivamente los exámenes de 8 pacientes de una misma familia, 5 de ellos con diagnóstico de CA medular confirmado por anatomía patológica. Se efectuaron marcadores genéticos, correlacionando los resultados con el análisis bioquímico. Se encontraron idénticos hallazgos tanto en la Ecografía en modo B como en el Doppler Color con una sensibilidad superior al tradicional screening bioquímico, por lo que proponemos este método como una buena alternativa para el diagnóstico y seguimiento de los pacientes de alto riesgo (AU)

Combined ultrasonographic and cytological studies in the diagnosis of thyroid nodules.

Many aspects of thyroid nodule evaluation and management remain controversial. Widespread application of ultrasonography has resulted in frequent discovery of incidental nodules in the general population which has created a management dilemma for physicians. In this paper we have introduced a novel approach for evaluation of solid nodules, using an index derived from ultrasonographic and cytologic studies. Briefly thyroid nodules were classified ultrasonographically into four grades, with increasing score numbers (1-4) as progression to malignantly suspicious lesions was present. Similarly, four grades of a cytologic classification of fine needle biopsy aspirates were introduced with scores of 1-6 (benign to malignant diagnosis). The sum of the ultrasonographic and cytologic scores were the basis of a diagnostic index: benign (2-4), doubtful (5), suspicious (6) and malignant (7-10). Sixty patients with an index equal or higher than 6 were submitted to thyroidectomy and the prevalence of thyroid cancer (n = 46) in the excised nodules was 76.6%. Most series report a 10% to 30% incidence of malignancy in excised nodules with suspicious diagnosis. We concluded that using an index derived from combined ultrasonographic and cytologic studies will result in a better patient selection for surgery.