Small vessel disease in chronic thromboembolic pulmonary hypertension: a comprehensive narrative review of multimodality imaging evaluation

Background and Objective Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare form of pulmonary hypertension (PH) resulting from unresolved, organized thromboemboli within the pulmonary arterial tree, most often following an acute pulmonary embolic event. A distinctive feature of CTEPH is the development of secondary microvascular or small vessel disease (SVD), which has been associated with adverse surgical outcomes and persistent PH after pulmonary endarterectomy (PEA). While macrovascular disease can be reliably assessed with current imaging techniques, preoperative evaluation of SVD remains a significant diagnostic challenge. This focused review aims to summarize current imaging approaches to SVD in CTEPH, discuss their limitations, and highlight emerging techniques and future directions for improved assessment. Methods Comprehensive literature review was conducted between January 2025 and January 2026, primarily using PubMed/MEDLINE and Scopus as databases, focusing on peer-reviewed English-language publications, from the past 10 years. Search terms and combined keywords including CTEPH, microvasculopathy or SVD, and imaging modalities were used. Key Content and Findings Imaging plays a crucial role in diagnosis and risk stratification of these patients. Preoperative imaging using various tools allows confident diagnosis of CTEPH and determines patients’ surgical suitability for PEA or balloon pulmonary angioplasty (BPA). Assessment of SVD still continues to be a challenge, although significant progress has been made. The presence of distal pulmonary artery (PA) obstructions and pulmonary vascular resistance (PVR) out of proportion to the degree of mechanical obstruction, are strongly suggestive of underlying microvascular disease. Preoperative recognition of SVD is crucial as these are associated with worse clinical outcomes and may result in recurrent/residual PH following surgery. Conclusions Several imaging findings on various imaging modalities can provide clue to the presence of microvascular disease, although requires careful assessment and multidisciplinary input.