What is primary tuberculosis? Tuberculosis caused by the first infection with the tubercle bacillus is called primary tuberculosis, usually called type I tuberculosis, and it occurs mostly in children, so it is also called childhood tuberculosis. However, it is also occasionally seen in adolescents or adults who have not been infected with the bacillus. The first lesion in the lung caused by the inhalation of the tuberculosis bacillus is called the primary focus. The primary focus is usually one, but occasionally two or more, and often involves the surrounding lymphatic vessels, resulting in lymphangitis. Further involvement of the hilar lymph nodes along the lymphatic vessels results in hilar lymph node tuberculosis. The three form a dumbbell pattern on the image, hence the name primary syndrome. Primary TB symptoms are mild and transient, often without obvious signs, and many children pass unnoticed, showing only a positive PPD test. A small number of patients can develop allergy-increasing syndromes such as erythema nodosum, polyarthritis, etc.; and may be accompanied by mild to moderate peripheral toxic symptoms such as lethargy, loss of appetite, fever, night sweats, etc. for 2 to 3 weeks or longer. There are often no obvious signs. If there is pulmonary atelectasis and pulmonary consolidation, turbid sounds can be heard on percussion and breath sounds can be reduced or bronchial breath sounds can be heard. Croup may be heard in cases of partial bronchial obstruction. In extensive bronchopneumonia or cavity formation, wet rales may be heard. The vast majority (98%) of patients with primary tuberculosis heal spontaneously as the body’s immune system gradually strengthens. Smaller lesions may be completely resorbed or fibrotic, while larger foci of caseous necrosis undergo fibrous encapsulation and calcification. Sometimes, although the primary lesions in the lungs have healed, the lesions in the hilar lymph nodes continue to develop, and the tuberculosis bacilli spread through the lymphatic tracts to nearby lymph nodes, so that more lymph nodes near the hilar lymph nodes are involved, and even spread to the mediastinal lymph nodes to form parabronchial lymph nodes. After appropriate treatment, these lesions can still be wrapped, calcified and healed. In a small number of children, malnutrition or other infectious diseases (such as influenza, measles, pertussis, diphtheria, etc.) during this period cause the body’s resistance to deteriorate, and the lesions in the lungs and hilar lymph nodes continue to expand and spread to other organs through the lymphatics, blood, and bronchi. How does primary tuberculosis occur? In China, about 80-90% of tuberculosis infection is through the respiratory tract to the lungs, so primary tuberculosis generally means primary pulmonary tuberculosis, mostly seen in the better ventilated parts of the lungs, such as the base of the upper lobe, the middle lobe or the upper part of the lower lobe, and often near the pleura, with the right lung being the most common, with a single onset. It quickly develops cheese-like changes, followed by fibrous encapsulation. The case-like material loses water, calcifies, and even heals by ossification. During the formation of the primary lesion, bacteria travel along the lymphatic vessels to the hilar lymph nodes, causing lymphangitis and lymph node tuberculosis, which also undergoes caseous changes. Most primary tuberculosis heals spontaneously, and whether the infection causes disease or not is related to the body’s immunity. The younger the person is, the more likely he or she is to develop the disease. Primary tuberculosis can also occur in adults who are first infected with the tubercle bacillus and are in a non-immune state. Progression of the primary lesion may result in cavitation and focal spread. Progression of hilar and mediastinal lymph nodes is more common, and caseous changes in the lymph nodes continue to develop, causing peri-lymph node inflammation; the lesions can then spread to nearby mediastinal lymph nodes either directly or through the lymphatics. The caseous lymph nodes may compress or collapse into the bronchi, forming bronchial lymphatic fistulas, causing bronchial tuberculosis and corresponding lung segmental changes such as atelectasis and obstructive pneumonia. The tuberculosis of the lymph nodes breaks down into the blood vessels and bacteria enter the circulation, causing varying degrees of hematogenous dissemination.