Primary pulmonary tuberculosis is the most common form of primary tuberculosis. It occurs as a primary infection in the lungs following the initial invasion of Mycobacterium tuberculosis, and it is the predominant type of pulmonary tuberculosis in children, accounting for 85.3% of all cases of pediatric pulmonary tuberculosis. This condition includes primary complex and tuberculous bronchial lymphadenitis. The former consists of a pulmonary primary lesion, regional lymph node involvement, and connecting lymphangitis. The latter is characterized predominantly by enlargement of intrathoracic lymph nodes. Pulmonary lesions may be undetectable on X-rays due to their small size, obstruction by the mediastinal opacity, or resolution of primary lesions, leaving only enlarged local lymph nodes. Clinically, these cases are often diagnosed as tuberculous bronchial lymphadenitis. Both conditions are considered a single entity, referred to as primary pulmonary tuberculosis.
Pathology
Pulmonary primary lesions are often located on the right side, at the base of the upper lobe or the upper part of the lower lobe, near the pleura. The basic pathological changes include exudation, proliferation, and necrosis.
- Exudative Changes: Composed mainly of inflammatory cells, monocytes, and fibrin.
- Proliferative Changes: Dominated by tuberculous nodules and tuberculous granulomas.
- Necrosis: Typically caseous in nature, often observed within exudative lesions.
The hallmark of tuberculous inflammation involves epithelioid cell nodules and Langerhans cells.
The classic primary complex exhibits a "bipolar" pattern of lesions, comprising a primary lesion at one end and hypertrophic hilar or mediastinal lymph nodes at the other. In children with heightened sensitivity, extensive inflammation occurs surrounding the lesion, with the primary lesion enlarging to involve an entire lung segment or even a lobe. Younger children exhibit more pronounced large-scale lesions. Involved lymph nodes are often unilateral, although contralateral nodes may occasionally be affected.
Clinical Manifestations
The severity of symptoms varies. Mild cases may be asymptomatic and typically have an insidious onset. Symptoms such as low-grade fever, poor appetite, fatigue, night sweats, and general toxicity signs are more commonly observed in older children. Infants and those with severe symptoms may have an acute onset, with high fever reaching 39–40°C. Despite the high fever, the general condition is relatively preserved. After 2–3 weeks, the fever often transitions to low-grade levels, accompanied by signs of tuberculosis toxicity. Dry cough and mild dyspnea are the most common symptoms. Infants may present with failure to gain weight or developmental delays. Children with significant hypersensitivity may develop herpetic conjunctivitis, erythema nodosum, and/or transient polyarthritis.
Marked enlargement of intrathoracic lymph nodes may lead to a variety of compressive symptoms:
- Tracheal compression at the bifurcation may cause pertussis-like paroxysmal coughing.
- Partial bronchial obstruction may result in wheezing.
- Compression of the recurrent laryngeal nerve may cause hoarseness.
- Compression of veins may lead to visible venous distension on one or both sides of the chest.
Physical examination often reveals varying degrees of peripheral lymphadenopathy. Pulmonary signs may be inconspicuous and not proportional to the extent of parenchymal involvement. In over 50% of cases with moderate to severe pulmonary tuberculosis evident on chest X-ray, no physical signs are detectable. Large primary lesions may present with dullness on percussion, decreased breath sounds, or minimal dry and wet rales. Hepatomegaly may also be noted in infants.
Diagnosis and Differential Diagnosis
Diagnosis requires comprehensive analysis of the patient's medical history, clinical manifestations, laboratory tests, tuberculin skin test results, and pulmonary imaging.
Primary Complex
This is characterized by pulmonary parenchymal infiltration, accompanied by hypertrophic hilar and mediastinal lymph nodes. The hallmark of primary pulmonary tuberculosis is relatively prominent local lymph node enlargement compared to the smaller primary pulmonary lesion. In infants, lesions are often extensive, involving an entire lung segment or lobe, while older children exhibit milder perilesional inflammation with smaller, round, or patchy opacities on imaging. Pleural involvement may occur in some cases. The classic dumbbell-shaped bipolar opacity on pediatric chest X-rays is now rarely observed.
Tuberculous Bronchial Lymphadenitis
This is the most common X-ray finding of primary pulmonary tuberculosis in children and is classified into three types:
- Inflammatory Type: Enlargement of hilar lymph nodes with increased density extending outward from the hilar region, showing blurred margins.
- Nodular Type: Dense, round or oval opacities with clear margins protruding into the lung field in the hilar region.
- Micronodular Type: Features include disordered pulmonary markings, abnormal hilar morphology, and small nodular or patchy blurred opacities surrounding the hilar region.
Laboratory and Imaging Examinations
CT Scan
CT imaging demonstrates superior sensitivity in identifying small primary lesions, lymph node enlargement, pleural changes, and cavitations compared to standard X-rays. CT is particularly useful for diagnosing primary complexes when chest X-rays show no abnormalities. Features such as lymph node compression or lymph node–bronchial fistulas causing tracheal or bronchial stenosis, distortion, or atelectasis can also be observed. Contrast-enhanced CT reveals annular enhancement around lymph nodes, with the central area displaying low density due to caseous necrosis.
Fiberoptic Bronchoscopy
This procedure is helpful for identifying bronchial tuberculosis complicating tuberculosis infection. Common findings include:
- Narrowing of the bronchial lumen caused by pressure from enlarged lymph nodes or adhesion of lymph nodes to bronchial walls, leading to restricted movement.
- Mucosal hyperemia, edema, ulceration, or granuloma formation.
- Masslike projections into the bronchial lumen in the pre-perforation stage of lymph node collapse.
- Lymph node perforation forming a lymph node–bronchial fistula, with the perforation resembling a volcano surrounded by red, caseous discharge.
Differential diagnoses include upper respiratory infections, bronchitis, pertussis, rheumatic fever, typhoid, various pneumonias, bronchial foreign bodies, bronchiectasis, and benign or malignant mediastinal tumors.
Treatment
General treatment and treatment principles align with those for tuberculosis. Specific protocols depend on individual cases and disease dynamics.