In the British Journal of Radiology article, researchers from the Shinshu University School of Medicine in Asahi, Japan, set out to characterize the natural history of rapidly growing lesions that are found, tracked with CT, surgically removed, and then confirmed by histopathology.
"The essential issue for successful surgical excision is detection of early-stage lung cancers," they said. "Thus, accurate characterization of the CT features of rapidly growing small cancers is crucial for early diagnosis and treatment," (British Journal of Radiology, September 2000, Vol. 73:873, pp.930-937).
Through an annual screening program in Nagano, the investigators fashioned a study population of 12 patients, the majority of whom were heavy-to-moderate smokers. A rapidly growing peripheral tumor was defined as smaller than 2 cm in diameter and a solitary parenchymal nodule with a volume-doubling time (VDT) of less than 150 days.
Initial screening exams were performed with a low-dose spiral CT scanner (CT-W950SR, Hitachi Medical, Tokyo). For the diagnostic exam, a HiSpeed Advantage scanner by GE Medical Systems (Waukesha, WI) was used. CT images were obtained from the lung apices to the lung bases with 10-mm collimation.
"One additional targeted spiral CT sequence was performed through the nodule with 1-mm collimation in each patient and CT images were reconstructed with a bone algorithm, 20-cm field of view and 0.5-mm reconstruction interval. All CT images were obtained during breath-holding at mid-inspiration," they explained.
Two observers who were blinded to the pathological findings reviewed the CT image and recorded distinctive tumor features such as density, margin, and internal texture. The margin and internal texture of each tumor was assessed with thin-section CT and then correlated with pathological findings.
In eight cases, adenocarcinomas were present, with half of them registering as well-differentiated. They investigators determined that most of the rapidly growing peripheral lung cancers were adenocarcinomas, with such CT features as soft-tissue density and a lack of an air bronchogram pattern.
The remaining four cases included one poorly differentiated squamous cell carcinoma (SCC), and three small cell lung cancers (SCLCs) in the lung periphery.
"The CT features of small nodules of SCLCs has not been adequately described. In this study…they appeared as well-defined, homogenous, soft-tissue density nodules with smooth margins and a lobulated configuration on CT images," they said. The VDT for these tumors ranged from 54 to 132 days.
Overall, tumors with homogenous attenuation and well-defined, smooth margins were more common than tumors with heterogeneous attenuation and ill-defined, irregular margins.
