Infiltrative pulmonary tuberculosis

Infiltrative pulmonary tuberculosis is a clinical form of tuberculosis that occurs against the background of specific hypersensitization of lung tissue and a significant increase in the exudative tissue reaction in the area of inflammation.

The clinical and morphological feature of infiltrative tuberculosis is considered to be widespread lung damage with a tendency to rapid progression of the tuberculosis process.

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Infiltrative pulmonary tuberculosis: epidemiology

Infiltrative tuberculosis mainly affects adults, more often young people. The probability of developing infiltrative tuberculosis increases with poorly organized detection of earlier forms of the disease. Infiltrative tuberculosis is diagnosed in 65-75% of newly diagnosed patients with pulmonary tuberculosis. Patients with this form make up 45-50% of patients with active tuberculosis observed in tuberculosis dispensaries.

In the structure of mortality from tuberculosis, infiltrative tuberculosis accounts for about 1%. A fatal outcome of the disease is observed mainly with the development of complications: caseous pneumonia, pulmonary hemorrhage.

What causes infiltrative pulmonary tuberculosis?

The development of infiltrative tuberculosis is associated with the progression of focal tuberculosis, the appearance and rapid increase in the infiltration zone around fresh or old tuberculous foci. The spread of perifocal inflammation leads to a significant increase in the volume of lung tissue damage. Tuberculous infiltrate is a complex of a fresh or old focus with an extensive zone of perifocal inflammation. Infiltrates are most often localized in the 1st, 2nd and 6th segments of the lung, i.e. in those areas where tuberculous foci are usually located.

Depending on the localization and volume of lung tissue damage, there are broncholobular, usually affecting 2-3 pulmonary lobules, segmental (within one segment), and polysegmental, or lobar, infiltrates. An infiltrate developing along the main or additional interlobar fissure is called periscissuritis.

The inflammatory reaction around the foci is enhanced by massive tuberculosis superinfection and concomitant diseases (diabetes, alcoholism, drug addiction, HIV infection). These factors create the prerequisites for rapid growth of the microbial population. An inflammatory reaction with a pronounced exudative component develops around the tuberculosis focus. Specific inflammation spreads beyond the pulmonary lobule, the total volume of damage increases. This is how a broncholobular infiltrate is formed.

With relatively moderate disturbances of immunological reactivity, the intensity of exudation is relatively low, cellular infiltration is moderately expressed. The alveoli are filled with macrophages, epithelioid and plasma cells and a relatively small amount of exudate. Inflammatory changes have a mixed exudative-proliferative character and spread relatively slowly. The zone of tuberculous inflammation is usually limited to the segment, in which an infiltrate is formed, which is usually called rounded.

A significant weakening of local and general immunity contributes to higher growth rates of the microbial population. The hyperergic reaction of the lung tissue to a large population of virulent and rapidly multiplying mycobacteria causes pronounced exudation. Perifocal inflammation is characterized by a poor cellular composition and weak signs of specific inflammation. The alveoli are filled with tissue fluid containing mainly neutrophils and a small number of macrophages. There is a tendency for tuberculosis to progress with rapid damage to many segments of the lung (cloud-like infiltrate). Further progression of immunological disorders is characterized by increased activity of T-suppressors and inhibition of DTH. Macrophage cells die, forming a zone of caseous necrosis. Caseous masses gradually melt and are released into the draining bronchus. Thus, in the zone of progressive tuberculous inflammation, a destruction area appears, limited by inflamed-altered lung tissue. Gradually, a decay cavity is formed, which serves as a source of further bronchogenic and lymphogenic spread of mycobacteria. Involvement in the pathological process of almost the entire lobe of the lung and the formation of multiple decay cavities in the affected lobe indicate the formation of lobitis.

Over time, the differences between different infiltrates are largely lost. With a progressive course, infiltrative pulmonary tuberculosis is transformed into caseous pneumonia or cavernous tuberculosis.

The rate of regression of infiltrative tuberculosis depends on the nature of the exudate, the prevalence of the lesion, the extent of caseous necrosis, and the reactivity of the patient's body. Small infiltrates with serous exudate can resolve relatively quickly with adequate treatment. With serous-fibrinous or hemorrhagic exudate, resorption occurs more slowly and is combined with the development of fibrosis. Caseous masses become denser and encapsulated as the infiltrative changes resolve. A fibrous lesion with caseous inclusions forms at the site of the decay cavity. A linear or stellate scar may subsequently form at the site of the lesion.

Symptoms of infiltrative pulmonary tuberculosis

In patients with broncholobular or rounded infiltrate, the symptoms of infiltrative pulmonary tuberculosis are mild (increased fatigue, decreased appetite, episodic increases in body temperature), and the disease is often detected during a routine medical examination.

Cloud-shaped infiltrate with damage to one or more pulmonary segments and periscissuritis are usually characterized by an acute onset with pronounced symptoms of intoxication, a slight cough with sputum, and sometimes hemoptysis. Involvement of the pleura in the pathological process leads to the appearance of pain in the chest on the affected side, which is associated with respiratory movements. Further progression of tuberculous inflammation with the development of lobitis is characterized by a sharp deterioration in the patient's condition, increased intoxication and respiratory symptoms.

Stetoacoustic changes in patients with broncholobular and rounded infiltrate are usually absent. In cloudy infiltrate, periscissuritis, lobitis, shortening of percussion sound, increased vocal fremitus, and bronchial breathing can be detected above the affected area. Sometimes a few moist fine-bubble rales are heard, and above the cavity of decay - inconstant medium-bubble rales, which often appear only on inhalation after the patient coughs.

Diagnosis of infiltrative pulmonary tuberculosis

X-ray diagnostics of infiltrative pulmonary tuberculosis allows us to establish the clinical and radiological type of infiltrate and a number of details of the lesion.

In case of broncholobular infiltrate in the cortical zone of the pulmonary field, more often in the 1st, 2nd or 6th segments, a limited darkening is detected, often of low intensity, with blurred contours, up to 3 cm in size. The infiltrate has a polygonal shape, elongated towards the root of the lung. CT examination allows to identify the lumen and division of the small bronchus around which the infiltrate has formed. The lumen of the bronchus is sometimes filled with dense caseous masses. On a tomogram, a broncholobular infiltrate often looks like a conglomerate of several more or less dense small foci, united by a zone of perifocal inflammation.

The rounded infiltrate is represented by a limited darkening of a rounded shape, mainly of medium intensity with clear but not sharp outlines. The classic type of Assmann-Redeker infiltrate is localized in the subclavian region.

An inflammatory path extends from the medial sections of the darkening to the root of the lung, in which the projection of the draining bronchus is sometimes revealed (the "tennis racket" symptom). When the infiltrate disintegrates, cavities are usually revealed in its central sections. In the lower sections of the lung, foci of bronchogenic seeding are often noticeable.

A cloud-like infiltrate on a radiograph looks like an uneven darkening, limited by one or more segments and not having clear boundaries. When the infiltrate is localized near the interlobar fissure (periscissuritis), it approaches a triangular shape with a vague upper border and a fairly clear lower one, which runs along the interlobar fissure. CT allows us to examine the structure of the infiltrate formed by the fusion of many foci. A cloud-like infiltrate is characterized by the presence of several small cavities of decay in the affected area, limited by inflammatory-compacted lung tissue; the formation of large cavities is possible.

In lobar infiltrate (lobitis), the location and shape of the darkening depend on which lobe of the lung is affected. On CT, lobititis is sometimes visualized as a continuous, almost homogeneous compaction of the lung lobe. In the affected lobe, deformed and partially obstructed by caseous masses bronchi are found, as well as multiple cavities of small and medium diameter ("honeycomb" or "bread crumb"). As lobititis progresses, focal dissemination is often detected in the opposite lung, mainly in the 4th and 5th segments.

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