Pulmonary Vessel Cross-Sectional Area Before And After Liver Transplantation: Quantification With Computed Tomography

Rationale: Pulmonary vascular complications of liver disease are poorly understood but contribute significantly to morbidity and mortality. While Model for End-stage Liver Disease (MELD) exception points are sometimes given for these entities to expedite liver transplantation, the effect of liver transplantation on pulmonary vascular disease is variable. This study was undertaken to further characterize the effect of liver transplantation on the cross-sectional area (CSA) of small pulmonary vessels. Methods: We performed a retrospective review of all patients who had undergone a liver transplantation at our institution from 2002 to 2012. Medical records were reviewed to identify subjects with clinical evidence of portal hypertension that had a computed tomography (CT) scan of the chest during both the year prior and the year after liver transplantation. Using Image J software, we measured the CSA of small pulmonary vessels (0-5mm) and the total lung CSA at three anatomical levels of each CT scan: the aortic arch, carina, and the right inferior pulmonary vein. We then calculated the percentage of small vessel cross-sectional area (%CSA<5) compared to the total CSA, and compared pre and post transplantation values using a two-tailed paired t-test. Results: We identified 109 subjects who had CT scans of the chest before and after liver transplantation. 34 subjects were excluded due to lack of similar chest imaging for comparison (ie. contrast vs non-contrast studies) and 13 subjects were excluded due to the presence of parenchymal abnormalities or large effusions that precluded reliable CSA calculations. At this time, CT scans have been analyzed for 37 subjects. Characteristics of the study population are detailed in Table 1. Overall, there was a decrease in mean %CSA<5 after liver transplantation (0.23+0.14% pre-transplant vs 0.20+0.07% post-transplant, p=0.139) at all three anatomical levels which was significantly different at the level of the right inferior pulmonary vein (0.22+0.14% pre-transplant vs 0.17+0.07% post-transplant, p=0.012). Conclusions: The CT method presented in this study helps to characterize regional changes in pulmonary vasculature that occur after liver transplantation. We found that the percentage of small pulmonary vessel cross-sectional area decreases after liver transplantation, and that the lower lung vessels significantly contribute to this decrease. Ongoing data analysis in the patients not yet included will allow us to further analyze the relationship between pulmonary vessel cross-sectional area and other characteristics such as the MELD score and the etiology of liver disease.