Histopathological Evaluation of Pulmonary Thromboendarterectomy Specimens of Chronic Thromboembolic Pulmonary Hypertension

Aims: Chronic thromboembolic pulmonary hypertension (CTEPH) is a condition with a poor prognosis in which the pulmonary arteries are occluded by organized thrombi. Pulmonary thromboendarterectomy (PEA) is an effective treatment for CTEPH; however, the literature on its histopathological examination is lacking. This study aimed to investigate the histopathological findings and protein and gene expression in PEA specimens, establish an optimal histopathological evaluation method, and clarify the mechanisms of thrombus organization and disease progression in CTEPH. Methods: In total, 50 patients with CTEPH who underwent PEA were analyzed. The patients were categorized according to their clinical data into two groups: good and poor postoperative courses. The relationship between their histopathological findings and the clinical course was examined. Immunohistochemical studies confirmed the expression of oxidants, antioxidants, and smooth muscle cell (SMC) differentiation markers and their changes during the progression of thrombus organization. The mRNA expression analysis of 102 samples from 27 cases included oxidants, antioxidants, and vasoconstrictor endothelin-1. Results: In the PEA specimens, colander-like lesions (aggregations of recanalized blood vessels with well-differentiated SMCs) were significantly more common in the good postoperative course group than in the poor postoperative course group; analysis of proteins and genes proposed that oxidative and antioxidant mechanisms were involved. In the colander-like lesions, there was an increase in endothelin-1 mRNA and protein expression of endothelin receptor A. Conclusions: Colander-like lesions in PEA specimens must be identified. Additionally, SMC differentiation in recanalized vessels and the expression of vasoconstrictors and their receptors may contribute to the progression of CTEPH.