Fibrosis

Fibrotic processes in the lungs

Respiratory system fibrosis has various morphological manifestations depending on the nosology.

Cryptogenic organizing pneumonia This disease differs from other forms of idiopathic fibrosing alveolitis in that the lesion is localized predominantly at the level of terminal bronchioles and alveolar ducts. An important feature is the preservation of the general lung angioarchitecture with uniformity of lesions.

The process has distinct stages:

1. Early stage: characterized by pronounced exudation in the alveolar lumens, lymphohistiocytic infiltration, and intra-alveolar edema. Young granulation tissue forms around the peribronchiolar zone.
2. Late stage: pronounced peribronchial sclerosis develops. Foci of carnification are formed — alveoli are replaced by dense connective tissue. Bronchioles are deformed, their basal cells proliferate and acquire signs of atypia. A key pathogenetic factor of this stage is an increase in the expression of growth factors — TGFβ and FGFb — by the epithelium and interstitial cells.

Chronic obstructive pulmonary emphysema (COPD) In emphysema, fibrosis and sclerosis affect predominantly the vascular bed. Reduction of alveolar-capillary blood flow occurs, leading to its blockade and sclerosis. This triggers a severe hemodynamic cascade: microcirculation disorders in the pulmonary circulation lead to pulmonary hypertension, right ventricular hypertrophy, and the development of cor pulmonale (cor pulmonale).

Fibrosis in lesions of the male reproductive system

Proliferation of connective tissue is a predictable outcome of chronic inflammation of the epididymis.

• Chronic ascending bacterial epididymitis: accompanied by diffuse infiltration of the wall by macrophages, lymphocytes, and plasma cells. The outcome is pronounced fibrosis leading to complete obliteration (overgrowth) of the duct lumen.
• Tuberculous epididymitis: occurs with retrograde infection spread. Morphologically characterized by typical granulomatous inflammation (epithelioid cell granulomas with caseous necrosis) and severe interstitial sclerosis. Macroscopically, the epididymis becomes very dense and enlarged.

Elements of fibrosis are also found in benign neoplasms. For example, in adenomatoid tumor (accounting for about 60% of all epididymal neoplasms), the tumor tissue stroma is heavily sclerosed, containing areas of pronounced hyalinosis and smooth muscle fibers.

Fibrous encapsulation in parasitoses

Fibrosis can act as a defense reaction of the organism aimed at isolating a foreign agent. A striking example is echinococcosis.

When a hydatid echinococcus is localized in the liver, lungs, or kidneys, chronic productive inflammation develops at the border with the parasite. The body's tissues form a dense fibrous capsule around the cyst. This capsule is abundantly infiltrated by lymphocytes, eosinophils, macrophages, and foreign body giant cells.

Over time, the fibrous capsule undergoes dystrophic changes and calcifies (petrifies). Meanwhile, the surrounding organ parenchyma is compressed by the growing cyst and dense capsule, leading to its atrophy, deformation, and an increase in the organ's size.

Class and exam questions

What else to study on this topic

• Morphological differences between the early and late stages of cryptogenic organizing pneumonia
• Cascade of hemodynamic disorders in chronic obstructive pulmonary emphysema
• Differential diagnosis of bacterial and tuberculous epididymitis
• Structure and life cycle of the parasite in echinococcosis and cysticercosis
• Morphological characteristics of the adenomatoid tumor of the epididymis

Other topics in the "Lung Diseases" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.