Role of Tc-99m MIBI in the evaluation of single pulmonary nodules: a preliminary report

Background-Survival in bronchial carcinoma is closely related to the stage of the disease at the time of diagnosis and a single pulmonary nodule repre sents a potentially curable stage. This study was conducted to assess the f easibility of using Tc-99m labelled 2-methoxy isobutyl isonitrile (MIBI) to differentiate benign from malignant single pulmonary nodules. Methods-A prospective study was conducted in the outpatient pulmonary clini c at the Cleveland Clinic Foundation. Twenty live patients with Single pulm onary nodules considered indeterminate by their physicians and undergoing a procedure for tissue diagnosis were evaluated by Tc-99m MIBI;I SPECT scann ing prior to definitive testing. Assessment of MIBI uptake was done qualita tively (subjectively) and quantitatively and correlated with the histopatho logy and nodule size. Results-Of the 21 patients with malignant lesions, 18 had increased uptake of MIBI corresponding to the location of the nodule and were considered pos itive. The predominant tumour types were large cell (n = 5) and adenocarcin oma (n = 10). All four patients with benign lesions had negative MIBI scans . For malignancy the overall specificity was 100%, sensitivity was 85.7%, p ositive predictive value was 100%, and negative predictive value was 57%. Q uantitative uptake of MIBI correlated with the diameter of the nodule with a correlation coefficient of 0.61. by Spearman's rank sum rest. This relati onship was statistically significant (p = 0.02). Conclusion-This preliminary study suggests that Tc-99m MIBI has a very high specificity and positive predictive value for malignant single pulmonary n odules and might be a useful non-invasive diagnostic modality in their mana gement.