Evaluation of mosaic pattern areas in HRCT with Min-IP reconstructions in patients with pulmonary hypertension: could this evaluation replace lung perfusion scintigraphy?

PURPOSE: The aim of this study is to evaluate a possible correlation between areas of lung attenuation, found in minimum intensity projection (Min-IP) reconstruction images performed with high resolution computed tomography without contrast medium (HRCT), and areas of lung perfusion alteration, found in lung perfusion scintigraphy (LPS).
MATERIALS AND METHODS: Two independent radiologists, unaware of LPS results, evaluated retrospectively a group of 113 patients affected by pulmonary hypertension (HP) of different aetiology. These have been examined in a period of two years in our centre both by spiral computed tomography (CT) with and without contrast-medium and by LPS. The final diagnosis was determined on clinical data, right heart catheterisation and contrast enhanced CT in angiographic phase (CTPA). We reconstructed the Min-IP images of lung parenchyma in all the cases both in HRCT without contrast-medium, and in contrast enhanced CT in angiographic phase (CTPA) in axial, sagittal and coronal planes. The obtained images were qualitatively graded into three categories of pulmonary attenuation: homogeneous, inhomogeneous with non-segmental patchy defects, inhomogeneous with segmental defects. The same criteria of classification were used also for LPS images. In the group of patients with chronic thromboembolic pulmonary hypertension (CTEPH) we also compared the number of areas of lung attenuation found in Min-IP images in HRCT without contrast-medium, and their exact localization, with not perfused areas in LPS. Gold standard for the diagnosis of pulmonary embolism was spiral contrast enhanced CT in angiographic phase (CTPA).
RESULTS: In all cases we found exact correspondence between the Min-IP images in HRCT with and without contras agent. The attenuation pattern seen on Min-IP images was concordant with those of LPS in 96 out of 113 patients (85%). In the remaining 17 cases (15%) it was discordant: in 12 cases inhomogeneous in Min-IP images (7 with non-segmental patchy defects, 5 with segmental defects) and homogeneous in LPS, in 5 cases inhomogeneous (1 with non-segmental patchy defects, 4 with segmental defects) in LPS images and homogeneous in Min-IP. In a general view, Min-IP reconstruction without contrast-medium showed a sensitivity of 100% and specificity of 96.1%, positive predictive value (PPV) of 92.3% and negative predictive value (NPV) of 100%, to recognize a pattern of lung attenuation inhomogeneous with segmental defects correspondent to a chronic thromboembolic condition, no false negative cases and three false positive cases; on the other hand LPS, on its own, showed a sensitivity of 91.67% and specificity of 93.51%, positive predictive value (PPV) of 86.84% and negative predictive value (NPV) of 96%, 3 false negative cases and 5 false positive cases.
CONCLUSION: Min-IP obtained in HRCT without contrast-medium and in CTPA were equivalent. Min-IP images generally showed a higher sensitivity and specificity than LPS in the evaluation of lung perfusion regarding patients with pulmonary hypertension caused by different etiology, particularly in CTEPH patients. These results can be completed with the evaluation of HRCT and CTPA basal scans, providing more informations than ventilation/perfusion lung scintigraphy. HRCT images integrated by Min-IP reconstruction can represent the first step in the diagnostic algorithm of patients affected by dyspnoea and pulmonary hypertension of unknown causes, reserving the use of contrast-medium only in selected patients and reducing the patients' X-ray-exposition.