Quantitative CT analysis of small pulmonary vessels in lymphangioleiomyomatosis

BackgroundsLymphangioleiomyomatosis (LAM) is a destructive lung disease that share clinical, physiologic, and radiologic features with chronic obstructive pulmonary disease (COPD). This study aims to identify those features that are unique to LAM by using quantitative CT analysis.MethodsWe measured total cross-sectional areas of small pulmonary vessels (CSA) less than 5 mm2 and 5-10 mm2 and calculated percentages of those lung areas (%CSA), respectively, in 50 LAM and 42 COPD patients. The extent of cystic destruction (LAA%) and mean parenchymal CT value were also calculated and correlated with pulmonary function.ResultsThe diffusing capacity for carbon monoxide/alveolar volume (DLCO/VA %predicted) was similar for both groups (LAM, 44.4 ± 19.8% vs. COPD, 45.7 ± 16.0%, p = 0.763), but less tissue damage occurred in LAM than COPD (LAA% 21.7 ± 16.3% vs. 29.3 ± 17.0; p < 0.05). Pulmonary function correlated negatively with LAA% (p < 0.001) in both groups, yet the correlation with %CSA was significant only in COPD (p < 0.001). When the same analysis was conducted in two groups with equal levels of LAA% and DLCO/VA %predicted, %CSA and mean parenchymal CT value were still greater for LAM than COPD (p < 0.05).ConclusionsQuantitative CT analysis revealing a correlation between cystic destruction and CSA in COPD but not LAM indicates that this approach successfully reflects different mechanisms governing the two pathologic courses. Such determinations of small pulmonary vessel density may serve to differentiate LAM from COPD even in patients with severe lung destruction.