[Computed tomography of the solitary pulmonary nodule]

The value of computed tomography (CT) using thin-slice technique in the differentiation between benign and malignant pulmonary nodules was evaluated both experimentally and clinically. Experiments using a standard reference phantom and simulation nodules showed that CT number varies according to the size of the nodule and the difference of CT unit. A standard CT number above which a nodule should be considered as calcified and benign was first calculated for various sizes of nodules and then was applied to clinical cases. Motion artifact which can give falsely high CT numbers was also created and its characteristic appearance was identified. Clinically 101 cases of solitary pulmonary nodules whose diagnoses were confirmed either histologically or on follow-up were studied. There were 40 benign nodules, 53 primary lung cancers, and 8 metastatic lung tumors. There was no case of malignancy in which calcification was diagnosed to be present on CT. On the other hand, 14 of 40 benign nodules (35.0%) was diagnosed to contain calcium and therefore benign on CT. As for the margin of the nodule described on CT, a moderate to marked irregularity was predominantly seen in primary lung cancers, while most benign nodules and metastatic lung tumors had smooth margins. If CT criteria for benignancy are limited to the nodule both with calcification and smooth margin, 13 of 40 cases (32.5%) would be correctly diagnosed. CT is considered to be useful in distinguishing between benign and malignant solitary pulmonary nodules as far as herein described technique is observed.