Chest X-ray for Tuberculosis: Deciphering the Signs on the Film

Chest X-rays are a crucial imaging tool in the detection and monitoring of pulmonary tuberculosis (TB). This article aims to provide a comprehensive understanding of the typical signs of TB on X-rays, how to analyze them, and essential considerations when reading these images.

1. Fundamental Signs:

• Hilar Opacity:
  • The hilar region (where major airways and blood vessels enter the lungs) shows a hazy shadow, but underlying blood vessels can still be seen.
  • Common causes:
    • Tuberculous lymphadenitis: Inflamed and enlarged lymph nodes causing opacity.
    • Mediastinal tumor: A tumor growing in the mediastinum (space between the lungs) causing opacity.
• Hilar Convergence:
  • Blood vessels behind the hilum converge towards the opaque region.
  • Usually observed in vascular diseases like vascular dilation or blockage.

2. Considerations Regarding Imaging Position:

Differences Between Upright and Supine Films:

• Supine: The X-ray beam travels from front to back, ideal for evaluating lower lung lesions.
• Upright: The X-ray beam travels from back to front, offering a more accurate assessment of lung structures, especially the mediastinum.
• Note: Supine films cannot evaluate mediastinal widening, air trapping, or cardiomegaly (enlarged heart).

Comparison of Right and Left Lateral Films:

• Lesions on one side will be clearer on the corresponding lateral film.
• Right lateral: Both hemidiaphragms (muscles separating chest and abdomen) are parallel.
• Left lateral: Both hemidiaphragms intersect.

3. Digital Film Technical Standards:

• Contrast: Neither too hard nor too soft, ensuring clear visualization of structural details.
• Sharpness: The image is sharp and easy to identify structures.
• Visibility of Pulmonary Vessels: Blood vessels behind the diaphragm and heart should be clearly visible.

4. Order of Film Reading:

1. Heart: Size, shape, position, and function.
2. Pulmonary Vessels: Thickness, shape, direction, and any abnormalities.
3. Mediastinum: Width, shape, presence of fluid or tumors.
4. Bilateral Hilum: Opacities or convergence.
5. Both Lungs: Analysis of lesions in each lobe.
6. Recesses: Areas behind the heart, hilum, diaphragm, and lung apices.
7. Lines in the Lungs: Bronchial markings, interlobar fissures.
8. Pleural Space: Presence of fluid or air in the pleural space.
9. Bones and Chest Wall: Examination of ribs, clavicle, scapula.

5. Recesses:

• Posterior to the Heart: Masked by the cardiac shadow, difficult to observe.
• Posterior to the Hilum: Requires careful attention for any abnormalities.
• Posterior to the Diaphragm: Opacity due to the liver and spleen.
• Lung Apices: Easily overlooked, needs careful scrutiny.

6. Common TB Lesions:

Active Phase:

• Tubercle: Round or oval, homogeneous opacity, well-defined borders, size 2mm – several cm. Location: upper lung zones.
• Infiltration: Dense opacity, heterogeneous, ill-defined borders, area >1cm.
• Tuberculous Cavity: Round or oval lucency, closed borders, present within a dense opacity. Location: upper lung zones.

Late Stage:

• Fibrosis: Linear appearance, pulling trachea, hilar structures, heart, and mediastinum.
• Calcification: Found within cavities and tubercles.

Note: Cavitary lesions are highly dangerous, harboring a significant number of TB bacteria.

7. Sequelae After TB Treatment:

• Post-TB Bronchiectasis: Hemoptysis (coughing up blood).
• Fungal Ball: Recurring cough.
• Lung Cancer: Developing on pre-existing TB lesions.
• COPD: Chronic bronchitis, chronic obstructive pulmonary disease.

8. Lesions on Chest X-ray:

Nodules:

• Solitary Nodule: Cancer, TB, benign lung tumors, lung fluke.
• Reticulonodular Pattern: Miliary TB, congestive heart failure, interstitial pneumonia, fungal pneumonia.

Infiltration:

Oval, cloud-like, triangular shapes.

Cavitary Lesions:

• New Cavity: Thick walls, irregular borders, surrounding infiltration.
• Old Cavity: Thin walls, surrounding fibrosis, shrinkage.
• Classic Appearance: “Honeycomb,” “bread crumbs.”

Note: Differentiate TB cavities from air cysts, pneumothorax, and COPD.

9. Fibrosis and Calcification:

• Fibrosis: Linear appearance, pulling structures.
• Calcification: Found within cavities and tubercles.

10. Pleural Effusion:

• Pleural Effusion: Homogeneous opacity in the lung bases, loss of costophrenic angle (where the rib cage and diaphragm meet), displacing the heart and mediastinum.
• Loculated Pleural Effusion: Similar to pleural effusion but confined to a specific region.

11. Damaseau Line:

• Principle: Due to negative pressure in the pleural space and surface tension of the fluid.
• Appearance: Hyperpol (a bright line), present in moderate effusions.
• Significance: Indicates free fluid in the pleural space, exudate, and moderate volume.

12. Pneumothorax:

• Appearance: Hyperlucency (increased brightness) of the pleural space, absence of lung markings, lung tissue collapsing towards the center, visibility of visceral pleural line.
• Mediastinum: Shifted towards the opposite side.
• Diaphragm: Lowered.
• Hilar Structures: Widened.

13. Pneumothorax Severity:

• Mild: No intervention required, resolves spontaneously.
• Severe: Requires chest tube drainage.

14. Three Key Features of TB Lesions on X-ray:

• Upper Lung Zones: Lesions are commonly found in the apices of the lungs.
• Multifaceted Appearance: Lesions can be nodules, infiltrates, cavities, fibrosis, or calcifications.
• Slow Progression: Lesions may take time to disappear, even with treatment.

15. Lesion Severity Grading:

• Grade 1: No cavities, lesion width not exceeding the transverse diameter of the 2nd rib-sternal joint.
• Grade 2: Scattered, area not exceeding one lung, total cavity diameter < 4cm.
• Grade 3: Exceeds Grade 2.

Note:

• Chest X-rays are only one component of the TB diagnostic process.
• Other tests are needed, including sputum smear and culture, and blood tests.
• TB treatment must be managed under the guidance of a specialized physician.

In conclusion, chest X-rays are a valuable tool in the diagnosis and monitoring of pulmonary tuberculosis. Understanding the basic signs, imaging position considerations, and analysis techniques provide a more comprehensive view of the patient’s condition. Combining these findings with other tests and appropriate treatment is essential to control and eradicate TB.