Background: Pulmonary capillary hemangiomatosis (PCH) is an idiopathic disease with the anomalous proliferation of a small capillary-like vessel in the pulmonary tissue, which can lead to a severe form of PH. There are only several cases of PCH described in veterinary literature: 27 cases in dogs and 2 cases in cats. In veterinary medicine, PH is mostly recognized as a consequence of left heart failure as a progression of the postcapillary PH to the precapillary form. PCH is mostly described as a primary disease, but resistant postcapillary PH with the high possibility of pulmonary edema raises a speculation that PCH could be a secondary malformation to the left heart disease. Aim: Discover the features associated with the shift between left- and right-sided heart disease in the context of PH development Methods: Retrospective analysis of materials from cats and dogs with histological markers of PCH (sPCH) versus those with right heart failure (RHF). Results: Animals with histological and immunohistochemistry markers of PCH had previous history of disease with the left heart volume overload. There were no differences between the groups in radiography and gross pathology. Histologically, pulmonary fibrosis and arteriopathy could be found in RHF; in sPCH – a duplication of capillaries in alveolar septa and bizarre proliferation in surroundings structures. Conclusion: PCH could be a secondary pattern of vascular remodeling due to volume overload
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