Quantitative CT assessment of emphysema in patients evaluated for lung volume reduction surgery

Purpose: Many candidates are excluded from lung volume reduction surgery (LVRS) after visual assessment of imaging studies, due to an unsuitable severity and distribution of emphysema. This study was performed to determine if global and regional lung density in patients excluded from LVRS differ quantitatively from patients selected for LVRS. Methods: Thirty-five patients excluded from LVRS because of a morphologic pattern of emphysema on CT and perfusion scintigraphy that was considered unsuitable for LVRS were identified by retrospective chart review. Global and regional quantitative indexes of emphysema morphology based on lung density from CT scans and physiologic indexes of lung function in these patients were compared with those obtained from 43 patients selected for surgery, using unpaired, two-tailed t tests and scatter plots. Results: The excluded patients had less emphysematous and less severely emphysematous lung tissue, defined as the percent having density lower than thresholds of-900 Hounsfield units (HU) (58 ± 10% vs. 62±8%, p<.05) and -960 HU (14±7% vs. 28±10%, p<.0001), respectively. Emphysema in the upper half of the lungs was less severe in the excluded patients (61±11% <-900 HU vs. 72±12% <-900 HU, p<.0001), but was similar in the lower lungs (53±10% <-900 HU vs. 52±13% <-900 HU, p=.47). There was substantial overlap between the two groups in all CT emphysema indexes. The lung volume having normal density was the same in both groups (1.1 L). There were no significant differences in FEV1, PaO2, or PaCO2, but the excluded patients were slightly less hyperinflated (TLC 134±15 % vs. 145±18 % of predicted, p<.01) and were older (66±7 yrs vs. 58±9 vrs, p<.0001). Conclusions: Excluded patients overall had less severe emphysema more evenly distributed between the upper and lower lungs. Overlap between the two groups suggests that some excluded patients may be favorable candidates based on measurements of lung density. Clinical Implications: Subjective assessment of radiologic studies results in the desired selection of patients with more severe, upper lobe-predominant emphysema. It may be possible to identify additional favorable candidates from quantitative CT indexes of emphysema.