Pulmonary tuberculosis is a chronic infectious disease of the lungs caused by Mycobacterium tuberculosis or Mycobacterium bovis. In recent years, its incidence has been on the rise.
Clinical presentation and pathology
The basic pathological changes of pulmonary tuberculosis are exudation, hyperplasia, and degeneration. Exudative lesion occurs in the early stage or when there is low immunity, high bacterial load, strong virulence, or strong allergic reaction; the main manifestations are serous or fibrinous alveolitis; the exudate can be completely resorbed or results in proliferative lesion. When there is low bacterial load, weak virulence, or strong immunity, proliferative lesion is dominant, forming typical tuberculous granuloma;
When there is high bacterial load, strong virulence, low human body resistance, or significant allergic reaction is, or this disease is not properly treated, exudative and proliferative lesion can often develop into necrotic lesion, presenting caseous changes. The three types of lesions can exist simultaneously, but one type is often dominant. When the human body resistance is enhanced or the disease is treated with regular antituberculosis drugs, the bacteria can be gradually inhibited and eliminated, and the lesion can subside, or can be fibrotic or calcified. When the lesion develops, the lesion can expand, dissolve, liquefy, and form a cavity, and spreads through the bronchi to the lungs, or can be disseminated to other organs through bloodstream.
Clinically, pulmonary tuberculosis often has a slow onset and a long course, and may have no clinical symptoms; or there may be low-grade fever in the afternoon, diaphoresis, emaciation, anorexia, cough, thoracodynia, and hemoptysis. Acute hematogenous dissemination may present with high fever, rigors, cough, and drowsiness.
Pulmonary tuberculosis requires a comprehensive diagnosis based on clinical symptoms, imaging manifestations, and sputum bacterial examination. Tuberculosis can be divided into five types.
Primary pulmonary (Type I) includes primary complex and tuberculosis of intrathoracic lymph nodes.
Hematogenous disseminated pulmonary tuberculosis (Type II) includes acute hematogenous disseminated pulmonary tuberculosis, also known as acute miliary pulmonary tuberculosis, and subacute and chronic hematogenous disseminated pulmonary tuberculosis.
Secondary pulmonary tuberculosis (Type III) includes infiltrative pulmonary tuberculosis and fibrocavitary pulmonary tuberculosis.
Tuberculous pleuritis (Type IV) includes tuberculous dry pleurisy, tuberculous exudative pleurisy, and tuberculous empyema.
Other extrapulmonary tuberculosis (Type V) is named according to the location and organ.
In addition, based on the practicality of tuberculosis control and treatment, bacteria-negative pulmonary tuberculosis is introduced, which refers to pulmonary tuberculosis with three negative sputum smears and one negative culture, but with typical clinical and imaging manifestations of pulmonary tuberculosis and effective antituberculosis treatment.
Imaging manifestations
Primary pulmonary tuberculosis
Primary pulmonary tuberculosis includes primary complex and intrathoracic lymph node tuberculosis, mostly in children and adolescents, but also in adults.
X-ray
Primary complex typically shows doughnut sign. Primary infiltrative lesion is primary lesion adjacent to the pleura, mostly in the middle and upper lung field, and shows rounded, subrounded, or localized patchy opacity. Lymphangitis shows irregular linear opacities running from the primary lesion to the hilum. Enlargement of hilar and mediastinal lymph nodes is manifested by enlarged hilar opacity or enlarged mediastinal lymph nodes, protruding into the lung field. If the primary lesion and aerated bronchus subside, and only the hilar and/or mediastinal lymph nodes are enlarged, which is intrathoracic lymph node tuberculosis. Caseous necrotic lesion in lymph nodes can rupture into blood vessels and bronchi, causing hematogenous or bronchial dissemination.
Figure 1 Primary complex
Chest x-ray film shows typical doughnut sign composed of patchy primary infiltrative lesion in the outer zone of the middle field of the right lung (black ↗), irregular linear lymphangitis (white ↗), and enlarged right hilar opacity (enlarged lymph nodes) protruding into the lung field.
CT
In primary pulmonary tuberculosis, CT is easier to find enlarged hilar and mediastinal lymph nodes than x-ray, and clearly shows their morphology, size, number, edge, and density. Because the center of enlarged lymph nodes is often caseous necrotic, on contrast-enhanced CT, the center is not enhanced, the periphery is enhanced, and annular enhancement can be seen.
Figure 2 Intrathoracic lymph node tuberculosis
Coronal contrast-enhanced CT shows multiple enlarged and fused lymph nodes in the mediastinum, no enhancement in the central necrosis, and thin annular enhancement in the periphery.
Hematogenous disseminated pulmonary tuberculosis
It is caused by the hematogenous dissemination of Mycobacterium tuberculosis, and can be divided into acute, and subacute and chronic hematogenous disseminated pulmonary tuberculosis.
Acute hematogenous disseminated pulmonary tuberculosis is also known as acute miliary pulmonary tuberculosis.
X-ray
Diffuse, 1 - 3 mm, sharply marginated, homogeneous, miliary opacities in both lungs can be seen. The typical manifestations are homogeneous distribution, homogeneous size, and homogeneous density.
Figure 3 Acute miliary pulmonary tuberculosis
Chest x-ray film shows the decreased lucency of lung fields and diffuse miliary opacities (diameter < 3mm), with homogeneous size, homogeneous distribution, and homogeneous density.
CT
CT can show miliary lesions more clearly, particularly in early acute miliary pulmonary tuberculosis, and is helpful for early diagnosis. It has the same typical manifestations as x-ray.
Figure 4 Acute miliary pulmonary tuberculosis
CT lung window shows the collapsed right thorax, and diffuse, sharply marginated, miliary nodular opacities, with homogeneous size, homogeneous distribution, and homogeneous density.
Subacute and chronic hematogenous disseminated pulmonary tuberculosis is caused by multiple hematogenous disseminations of small amounts of Mycobacterium tuberculosis.
X-ray
Military or small nodular opacities in the upper and middle field of both lungs, with inhomogeneous size, inhomogeneous density, and inhomogeneous distribution, can be seen. The lesions at the apex of the lung and below the clavicle may present with induration, calcification, and fibrosis, while other lesions present with proliferation or exudation. When this type of pulmonary tuberculosis improves, the lesions can subside, and induration or calcification can occur; when the lesions progress, they can expand to form cavities and develop into fibrocavitary pulmonary tuberculosis.
CT
CT resembles chest x-ray in the manifestations, but can show clearly the details of the lesions and the overlapping parts.
Secondary pulmonary tuberculosis
It is the most common type of pulmonary tuberculosis in adults, including infiltrative pulmonary tuberculosis, tuberculoma, caseous pneumonia, and fibrocavitary pulmonary tuberculosis.
Infiltrative pulmonary tuberculosis is caused by reinfection with Mycobacterium tuberculosis or reactivation of dormant primary lesions. In this case, since the body has developed specific immunity to Mycobacterium tuberculosis, the lesions are often localized, mostly in the apical segment and posterior segment of the upper lobe and dorsal segment of the lower lobe of the lung.
X-ray and CT
The manifestations are varied, with one or multiple signs. CT is easier to detect subtle changes and spatial structural relationships of tuberculosis than x-ray, and is helpful for activity determination and differential diagnosis.
Localized patchy opacity can be seen in the apical segment and posterior segment of the upper lobe and dorsal segment of the lower lobe of both lungs.
Lobar caseous pneumonia shows massive dense consolidation in a lung segment or lobe, with irregular mottled cavities and hazy edges.
Figure 5 Lobar caseous pneumonia
Thin-slice high-resolution CT shows lobar lung consolidation in the right upper lung, with multiple mottled cavities.
Proliferative lesions show punctate opacities with clear edges and tree-in-bud sign, which are typical manifestations of tuberculosis.
Tuberculoma shows round or oval opacity, ranging in size from 0.5 to 4 cm, mostly 2 - 3 cm, with clear edges, smooth contours, occasional lobulation, high density, and visible punctate, laminated, or annular calcification; peripheral, scattered, fibroproliferative lesions are termed satellite lesions; on contrast-enhanced CT, tuberculoma often has no or annular enhancement.
Figure 6 Tuberculoma
Contrast-enhanced CT shows a tuberculoma in the right upper lung with peripheral annular enhancement (↗), with posterolateral satellite lesions.
Tuberculous cavity is with thin cavity wall, relatively smooth inner and outer edges, and satellite lesions.
Figure 7 Tuberculous cavity
CT lung window shows a subrounded thin-walled cavity in the posterior segment of the right upper lung, with smooth inner wall and rough outer edges.
In bronchial dissemination lesion, the caseous content in the tuberculous cavity is discharged through the aerated bronchus, causing bronchial dissemination in the ipsilateral or contralateral lung field, and the manifestations are patchy opacity or tree-in-bud sign along the bronchus.
Interstitial changes are manifested by intralobular fine reticular opacities, micronodules, tree-in-bud sign, ground-glass opacity, and thickening of interlobular septa and airway walls.
Figure 8 Interstitial changes
CT lung window shows diffuse ground-glass opacities, reticular opacities, micronodules, and thickening of interlobular septa in both lungs; and a small cavity in the lesions in the left lower lung.
Calcification, induration, or irregular linear opacities suggest healing of lesions.
Fibrocavitary pulmonary tuberculosis is in the late stage of secondary pulmonary tuberculosis. The persistent and unhealed tuberculosis lesions in the lungs seriously damage the lung tissue, forming fibrous cavity.
X-ray and CT
Fibrous cavity is common in the upper and middle lung field, with thick wall and smooth inner wall.
Pericavitary changes include massive exudative and caseous lesion, and calcified or fibrous lesion.
Lobar deformation is caused by shrinkage of the affected lobe, the hilum of the affected side is often lifted, and the lung markings are vertically downward.
Compensatory emphysema is often in the healthy lung.
Pleural hypertrophy and adhesion and mediastinum shifted to the affected side can be seen
Figure 9 Chronic fibrocavitary pulmonary tuberculosis
Chest x-ray film shows numerous irregular linear opacities and multiple irregular cavitary opacities in both upper lungs, with adjacent pleural adhesion and thickening; lifted hila, and vertically downward lung markings in both lower lungs.
Tuberculous pleurisy
Tuberculous pleurisy is divided into dry pleurisy and exudative pleurisy. The latter is more common, often with unilateral pleural effusion, generally serous, and occasionally bloody. Tuberculous pleurisy occurs when Mycobacterium tuberculosis directly invade the pleura through the lungs or chest wall, Mycobacterium tuberculosis in lymph node tuberculosis flows to the pleura through the lymphatic vessels, or there is hematogenous dissemination. Tuberculous pleurisy can occur alone or in combination with pulmonary tuberculosis lesions. Clinical symptoms are often thoracodynia and/or dyspnea.
X-ray and CT
The manifestation is pleural effusion. In chronic patients, extensive or localized thickening of the pleura, sometimes accompanied by pleural calcification, can be seen. CT can clearly show interlobar, basal, and encapsulated effusion.
Diagnosis and differential diagnosis
The imaging manifestations of pulmonary tuberculosis are diverse. It is generally not difficult to make a diagnosis based on the medical history, imaging manifestations, and laboratory test results.
Tuberculoma should be differentiated from peripheral lung cancer, the latter is mostly a lobulated mass with peripheral spicules, and there may be pleural indentation sign, but calcification and satellite lesions are less common.
Tuberculous cavity should be differentiated from cancerous cavity, the latter is mostly thick-walled, often eccentric, with rough inner edges, and may have wall nodules; the outer edges are mostly lobulated; there may be spiculation sign, but not satellite lesions.