ABSTRACT
Contrast enhanced CT manifestations of 141 pulmonary nodules having internal density less than 40 HU were evaluated to study the prevalence of causative disease and their differential points. Tuberculosis (n = 79) was most common, active in 96%. There were 22 cancers, 10 abscesses, 9 paragonimiases, 8 cysts, 7 metastases, 4 aspergillomas without air meniscus sign, and so on. 35% of the benign lesions were greater than 3 cm in diameter and 67% of benign lesions did not show a smooth outer margin. Lung cysts and aspergillomas showed relatively thin peripheral enhanced rim (PER), sharp transitional zone (TZ), a smooth inner border (IB), and homogeneous low densities (LD). Tuberculous nodules tended to be smaller in size with thin PER and most had smooth IB and homogeneous LD. Paragonimiasis, abscess, and cancer tended to present with thick PER and lobulated IB. Lung abscess and paragonimiasis both showed homogeneous LD and narrow TZ. However, in paragonimiasis, multiple locules were seen. Lung cancer showed wider TZ and heterogeneous LD. The size and outer margin of pulmonary nodules as a diagnostic criteria is less useful in LD pulmonary nodule. Therefore, CT can be more useful in differentiating the benign from the malignant lesions by observing a more specific and characteristic pattern of peripheral enhanced rim, transitional zone, inner border, and homogeneity of low density area.