Histologic and immunohistochemical changes of the lung vascular and perivascular structures in 37 clinical and paraclinical COBP diagnosed were studied. We noted the deterioration of an important part of the pulmonary capillary network because of the destruction of interalveolar septae, with an intense vascular congestion within restant capillaries. The venules and arterioles have had a fibrosis wall by the replacing of the elastic and muscular fibers with inextensible fibers of collagen. The perivascular stroma was infiltrated by fibroblasts, macrophages, lymphocytes and plasma cells.