Lung microvasculopathy in chronic thromboembolic pulmonary hypertension: high-resolution findings with photon-counting detector CT in 29 patients.

Purpose: To evaluate CT findings suggestive of lung microvasculopathy in patients with chronic thromboembolic pulmonary hypertension (CTEPH).

Materials and methods: Twenty-nine patients were scanned with high-spatial resolution on a photon-counting detector (PCD)-CT unit. A maximum of three pairs per patient, each composed of hyper- and hypo-attenuating areas of mosaic perfusion, were selected.

Results: Comparative analysis of the 86 selected pairs showed: (a) a higher frequency of ill-defined micronodules (p = 0.008), lobular ground-glass opacities (p = 0.01) and haziness (p = 0.003) in hypoattenuated areas; (b) there was no significant difference in the frequency of neovascularity (p = 0.43). Similar trends were observed in hypoattenuating areas of the 66 pairs studied in the 22 patients with central and peripheral CTEPH; an absence of ill-defined micronodules, lobular ground-glass opacities, and haziness in hyperattenuating areas was noticed in the 20 pairs studied in the 7 patients with peripheral CTEPH. Patients with a mean pulmonary artery pressure ≤ 42 mmHg (i.e., the median value of mean pulmonary artery pressure) had 45 pairs compared, showing a higher frequency of ill-defined micronodules (p = 0.003) and haziness (p < 0.001) in hypoattenuated areas, together with a higher frequency of subpleural systemic-to-pulmonary anastomoses (p = 0.02). There were no statistical differences in the frequency of CT findings between hypo- and hyper-attenuating areas in the 41 pairs of patients with a mean pulmonary artery pressure > 42 mm Hg.

Conclusion: CT features suggestive of microvasculopathy were more frequent in areas of hypoperfusion, with a trend toward homogenization of CT findings in patients with severe PH.

Key points: Question Lung microvascular lesions play a crucial role in the origin of residual pulmonary hypertension after successful thromboendarterectomy, currently beyond the scope of imaging. Findings The expected morphological abnormalities at the level of distal pulmonary circulation in CTEPH were found to be depictable in each zone of mosaic perfusion. Clinical relevance This study suggests that the high-spatial resolution of PCD-CT has the capability of approaching the complex pathophysiology of small-vessel disease in CTEPH, providing important information prior to therapeutic decisions.