Tracheobronchomalacia: Pathology and CT Findings
Normally, the trachea possesses physiological compliance, allowing its lumen to narrow by up to 50% during expiration. However, if pronounced airway collapse (collapse exceeding 70–80%) occurs during the expiratory phase, tracheomalacia is diagnosed (or tracheobronchomalacia if the main bronchi, such as the left main or right intermediate bronchus, are involved).
To assess this condition, dynamic expiratory MSCT is used, scanning the patient at full expiration.
- Shape of narrowing: The lumen typically assumes a characteristic crescentic (crescentic) or oval shape.
- Mechanism of deformation: The crescentic configuration arises as a result of pathological inward bowing and anterior protrusion of the posterior membranous wall of the trachea (posterior membranous trachea).
- Distribution: Involvement of the central tracheobronchial tree can be either diffuse or strictly localized (focal).
Tracheobronchomegaly and Reconstruction Techniques
Tracheobronchomegaly is the opposing condition characterized by marked widening of the tracheal lumen. Pathological dilatation is often not restricted to the trachea and extends into the lumen of the main bronchi.
Assessment of anatomical changes in megaly is performed not only on standard axial CT slices. Coronal oblique multiplanar reconstructions serve as a crucial imaging tool. Minimum intensity projection (MinIP) is used to maximize the contrast of the air column against soft tissues.
Associated Tracheal Deformities: Key Points to Watch For
When evaluating the central airways with imaging, it is important to differentiate classical malacia from other specific syndromes:
- Saber-Sheath Trachea (Saber-Sheath Trachea). This pathology is closely associated with chronic obstructive pulmonary disease (COPD). Axial slices reveal a significant reduction in the coronal (frontal) diameter. Key diagnostic marker: the portion of the trachea located above the thoracic inlet (thoracic inlet) remains normal in appearance and is not narrowed. The changes are frequently accompanied by upper-lobe emphysema.
- Tracheopathia osteochondroplastica (Tracheopathy Osteochondroplastica). Axial CT demonstrates calcified nodules (nodules) in the upper intrathoracic trachea. They grow from the inner surface of the wall and protrude into the lumen.
- Neoplastic and inflammatory processes. Diseases extending from the trachea to the bronchi require thin CT slices to assess intraluminal and extraluminal spread, wall thickening, and potential calcifications.
Tracheobronchial Fistulas and Suture Dehiscence
Thin-collimation MSCT with MinIP reconstruction is the method of choice for detecting fistulas and bronchial wall defects.
- Peripheral bronchopleural fistulas: Often form as a secondary complication of necrotizing pneumonia or trauma. CT visualizes a fistulous tract connecting the area of pulmonary consolidation to a large collection of gas in the pleural cavity.
- Nodobronchial fistulas: Induced by Mycobacterium tuberculosis infection. Imaging sign: the presence of gas within cavitated mediastinal or hilar lymph nodes adjacent to the bronchi.
- Tracheoesophageal fistulas: In adult patients, the most frequent cause is malignant tumors (esophageal cancer). Non-malignant factors include trauma, infections, and manifestation of congenital anomalies.
- Bronchial dehiscence (Bronchial dehiscence): A complication following lung transplantation. MSCT demonstrates a bronchial wall defect combined with an accumulation of extraluminal air.
Briefly: answers to topical questions
What are the main causes and risk factors for tracheoesophageal fistulas in adults?
The primary cause of tracheoesophageal fistula formation in adults is malignant neoplasms.
- Malignant tumors are the most common cause of the pathology, particularly esophageal cancer.
- Congenital anomalies — congenital fistulas may first manifest in adulthood.
- Infections and trauma are the most frequent non-malignant causes of fistula formation.
What are the main causes of peripheral bronchopleural fistula formation?
The main causes of peripheral bronchopleural fistula formation are:
- Necrotizing pneumonia (necrotising pneumonia) — the fistula can be its secondary complication.
- Traumatic injuries (traumatic lesions) — can lead to fistula formation as a result of secondary changes.
What pathogenetic mechanisms lead to the formation of nodobronchial fistulas in tuberculosis?
Nodobronchial fistulas in tuberculosis are associated with Mycobacterium tuberculosis infection and involvement of the hilar or mediastinal lymph nodes adjacent to the airways. They are diagnosed by the presence of gas in cavitated lymph nodes.
The "50 to 70" rule: normally, the trachea narrows by up to 50% on expiration, and if collapse exceeds 70–80%, it is tracheomalacia.
Class and exam questions
What is the main difference between physiological tracheal narrowing and tracheomalacia?
Normally, tracheal elasticity allows its lumen to narrow by up to 50% on expiration. A diagnosis of "tracheomalacia" is made when the cross-sectional area on expiration decreases by more than 70–80%.
Why does the lumen acquire a crescentic shape in tracheobronchomalacia?
The crescentic configuration results from pathological inward bowing and anterior protrusion of the posterior membranous wall of the trachea during the expiratory maneuver.
What key sign distinguishes saber-sheath trachea in COPD?
In saber-sheath trachea, the coronal diameter of the intrathoracic trachea is narrowed, whereas the segment located above the thoracic inlet always remains unchanged.
How to confirm the presence of a nodobronchial fistula in tuberculosis on CT?
The primary imaging sign is the visualization of gas bubbles in cavitated lymph nodes of the pulmonary hilum or mediastinum adjacent to the airways.
What else to study on this topic
- Mechanisms of bronchiectasis development (obstruction, traction, wall injury)
- Congenital syndromes leading to bronchial pathology (Williams-Campbell syndrome)
- The role of MinIP algorithms in visualizing the pulmonary parenchyma and airways
- Differential CT diagnosis of centrilobular and paraseptal emphysema in COPD
- Assessment of extraluminal spread of malignant tracheal tumors
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