Intratumoral necrosis of lung carcinoma: A potential diagnostic pitfall in incremental dynamic computed tomography analysis of solitary pulmonary nodules?

The authors determined the pattern and enhancement range of necrotic lung carcinoma using incremental dynamic computed tomography (CT). Thirty-seven pathologically proven lung cancers (range, 8-57 mm in diameter) were evaluated using incremental dynamic CT. Scans were obtained before and 30 seconds, 2 minutes, and 5 minutes after the onset of contrast material injection. Computed tomography numbers in circular regions of interest (60% of tumor diameter) were calculated, and the difference in CT number between nonenhanced and the scan showing maximum attenuation was determined. In cavitary necrotic carcinomas, regions of interest were established excluding areas of cavitation. Nine (24%) of 37 lung carcinomas had intratumoral necrosis; four (11%) had noncavitary necrosis, and five (14%) had cavitary necrosis. Maximum attenuation of four noncavitary necrotic carcinomas (mean 31 +/- standard deviation 25 HU; range, -3-56 HU) was lower than cavitary necrotic carcinomas (42 +/- 8 HU; range, 35-51 HU; p = 0.36) and non-necrotic carcinomas (48 +/- 17 HU; range, 25-91 HU; p = 0.07). All carcinomas showed maximum attenuation greater than or equal to 25 HU except for one noncavitary necrotic carcinoma (maximum attenuation = -3 HU; 36 mm in diameter). Noncavitary necrosis was recognized as low attenuation on noncontrast scan in two of four cases and as an unenhanced area on enhanced scan in four of four cases. Although noncavitary necrotic lung carcinoma may rarely show maximum attenuation less than or equal to 15 HU, necrotic material is recognized as unenhanced area on enhanced scan.