The role of technetium-99m methoxyisobutylisonitrile scintigraphy in the differential diagnosis of cold thyroid nodules

Various diagnostic techniques have been successfully used in the clinical m anagement of cold nodules; however, the decision on whether to employ surge ry or a conservative treatment is not always easy. This study was designed to appraise the diagnostic value of technetium-99m methoxyisobutylisonitril e (MIBI) scintigraphy in the assessment of cold nodules detected using Tc-9 9m-pertechnetate. Fifty-two patients were included in the study. All had al ready been selected fur surgery, based on their clinical and laboratory fin dings, including fine-needle aspiration biopsy. The total number of cold no dules on 99mTc-pertechnetate scans was 59. The thyroid scan was performed 2 0-40 min after i.v. injection of 400 MBq of Tc-99m-MIBI. Uptake of MIBI in thyroid nodules was compared with that in the surrounding normal thyroid ti ssue, and a score of between 0 and 3 was assigned to each nodule as follows : 0, cold; I, decreased; 2, equal; 3, hot. Definitive histology revealed no dular goitre in 24 cases, adenoma in 19, thyroiditis in I, differentiated c ancer in 12, medullary cancer in 2, and anaplastic cancer in 1, None of the degenerative nodules were hot on MIBI scan, while the adenomas showed a va riety of MIBI imaging patterns, most frequently the score 3 pattern. In the diagnosis of differentiated thyroid cancer the sensitivities of score 3 an d score 2+3 MIBI uptake patterns were 83% (10/12) and 100%, respectively. T he score 3 MIBI uptake pattern had a specificity of 100% and a positive pre dictive value of 100% with respect to thyroid (benign and malignant) neopla stic diseases, whereas a specificity of 72% and a positive predictive value of 43% were observed in the detection of differentiated cancer. After a co ld nodule had been detected using Tc-99m-pertechnetate, a second scan with high MIBI uptake increased by 7.8 times the probability that this nodule wo uld be a differentiated cancer. In conclusion, Tc-99m-MIBI scintigraphy is a useful method in the differential diagnosis of cold thyroid nodules if th e primary aim is to differentiate degenerative from neoplastic diseases rat her than to differentiate benign from malignant nodules. High MIBI uptake c onsiderably increases the probability of a differentiated thyroid cancer an d facilitates immediate surgical removal, while decreased uptake actually e xcludes it. We suggest a combination of fine-needle aspiration biopsy and M IBI scan as a routine diagnostic approach to cold thyroid nodules.