<p><b>BACKGROUND</b>To improve the differential diagnosis accuracy for solitary pulmonary nodules (SPNs), and to study the basis and mechanisms of enhancement by comparing with the microvessel constructions (microvessel density and basement membrane of microvessels) in SPNs.</p><p><b>METHODS</b>Dynamic contrast enhancement CT scanning were performed in 38 peripheral lung cancer, 5 hamartoma and 10 inflammatory lesions which were less than 3 cm in diameter with Siemens Plus S or Marconi MX 8000 spiral CT scanner. The CT time-attenuation curves were interpreted. The microvessel density (MVD) and the basement membrane of microvessels of the resected specimens were observed with the ABC immuno-histochemical method in all patients.</p><p><b>RESULTS</b>The CT contrasted value of lung cancer [(49.05±16.08) HU] and inflammatory lesions [(49.59±21.30) HU] were significantly higher than that of hamartoma [(8.98±4.56) HU] (t=7.48, P < 0.05; t=8.35, P < 0.05), but the enhancement of lung cancer was similar to that of inflammatory lesions (t=0.76, P > 0.05). The time-attenuation curve of inflammatory lesions tended to increase faster and reach a higher peak value than that of lung cancer, and both of them maintained a high plateau after crossing. The hamartoma showed a slight increase and demonstrated a low plateau curve. The MVD of SPNs was positively related to CT enhancement (r=0.805 1). The microvessel counts of peripheral lung cancer (48.45±10.09) and inflammatory lesions (49.60±19.94) were significantly higher than that of hamartoma (8.70±7.30) (t=11.64, P < 0.001; t=6.09, P < 0.001), but no significant difference was found between lung cancer and inflammatory lesions (t=-0.26, P=0.799). There was no any difference in continuity of basement membrane between nodules with enhanced CT less than 30 HU and higher than 30 U (Chi-square=3.13, P > 0.05).</p><p><b>CONCLUSIONS</b>The microvessel counts mainly contribute to the enhancement of SPNs. The basement membrane is not related to nodule enhancement, but it might influence the pattern of time-attenuation curve.</p>