Densitometric CT evaluation of acute and chronic thromboembolic filling defects of the pulmonary arteries before and after contrast injection

The aim of this study was to assess the baseline computed tomography (CT) attenuation of acute and chronic pulmonary thromboemboli, their contrast enhancement (CE), correlation with haematocrit (Ht) levels and the presence of hypertrophic bronchial arteries. From January 2006 to October 2009, we measured the baseline and postcontrast attenuation values of acute pulmonary thrombi emboli on CT angiograms of 86 patients with acute pulmonary embolism (PE) and those of chronic thrombi in 29 patients with pulmonary hypertension of various origins. The attenuation of acute thrombi was correlated with Ht and CE of chronic thrombi with the presence of hypertrophic bronchial arteries. Acute emboli had a mean baseline attenuation of 54.9 Hounsfield units (HU) and showed no CE. The attenuation of acute thrombi was not dependent on Ht. Chronic thrombi had a mean baseline attenuation of 33.8 HU, and 54% of thrombi showed significant CE. In 57% of cases, a collateral circulation had developed. In 76.5% of cases, CE and hypertrophic bronchial arteries coexisted (p=0.026). Neither thrombotic CE nor bronchial artery hypertrophy predominated in any one of the diseases associated with chronic thrombosis. Before contrast administration, acute emboli coare prevalently hyperattenuating and therefore more conspicuous. Only chronic thrombi exhibit CE, and CE is significantly associated with the development of collateral circulation, which may be involved in the process of thrombotic recanalisation.