Uptake of Tc-99m MIBI for assessment of cold thyroid nodule

ABSTRACT

Presence of nodule in the thyroid is a common problem throughout the world, incidence of which varies from region to region. This study was designed to appraise the diagnostic strategy to differentiate between malignant and benign lesions in solitary cold thyroid nodules using technetium-99m MIBI scintigraphy. Forty-nine patients were included in the study. All had cold nodule based on Tc-99m pertechnetate scan.Tc-99m MIBI thyroid scan and FNAC were performed in all the patients. Tc-99m MIBI thyroid scan was performed 20-40 min after intravenous injection of 185-370 MBq of Tc-99m MIBI. Uptake of MIBI in thyroid nodules was compared with that in the surrounding normal thyroid tissue and designation of YY, YN and NN were assigned to each nodule .YY means Intense uptake or uptake more than surrounding normal Thyroid tissue, YN means Uptake is equal or nearly equal to surrounding normal Thyroid tissue and NN means no uptake. FNAC revealed nodular goitre in 29 cases, follicular lesion in 8, cysts and hemorrhage in 10, pleomorph in 2. None of the cystic nodules were YY on MIBI scan, while the follicular lesions showed a variety of MIBI imaging patterns most frequently the YY pattern. None of the follicular lesion showed NN uptake on MIBI scan. In the diagnosis of follicular lesion the sensitivities of YY and YY+YN MIBI uptake patterns were 80% and 100% respectively. The YY+YN MIBI uptake patterns had a negative predictive value of 100% and positive predictive value of 36%, whereas a specificity of 54% was observed. After a cold nodule had been detected using Tc-99m pertechnetate, a second scan with YY or YN MIBI uptake increases the probability that this nodule would be suspicious for malignancy. Having no uptake of Tc-99m MIBI in such nodules very safely excludes the possibility of malignancy. Tc-99m MIBI scintigraphy is a useful method in the differential diagnosis of cold thyroid nodules. High MIBI uptake considerably increases the probability of malignancy and facilitates immediate surgical removal while NN or no uptake actually excludes it. We suggest MIBI scan as a routine diagnostic approach to cold thyroid nodules before fine-needle aspiration cytology