Multidimensional evaluation of tracheobronchial disease in adults
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The large airways can be affected by a wide spectrum of acquired benign and malignant diseases. These lesions may present as focal or diffuse processes and with narrowing or widening of the airway. Some of these may be asymptomatic for quite some time and may be incidentally detected on imaging, while others may be symptomatic, causing airway compromise. There may be a characteristic radiograph and computed tomography (CT) appearance, suggesting a narrow differential. When the imaging findings are not definitive, tissue may be obtained for pathological analysis. It behooves the radiologist to be familiar with the pathologic findings that correlate with the radiographic or CT appearance of the most frequently seen large airway lesions. In this way, we may improve our diagnostic accuracy. This paper will present the imaging findings of the most prevalent tracheobronchial lesions along with any associated pathology.
• The large airways can be affected by many acquired benign and malignant diseases.
• Large airway lesions may present as focal or diffuse processes, with narrowing or widening.
• There may or may not be characteristic imaging appearance of large airway disease.
• If imaging findings are not definitive, tissue may be obtained for pathological analysis.
KeywordsComputed tomography Pathology Trachea Bronchi Adult
There is a wide range of lesions found on imaging of the large airways. These lesions can fall into a number of categories, namely benign or malignant, focal or diffuse, and narrowing or widening of the airway. Observation of the morphology of the lesion on radiographs and computed tomography (CT) can often narrow the differential substantially; therefore, knowledge of the radiographic presentation of various large airway masses can be instrumental in determining the next step in management.
The trachea conveys air from the larynx to the bronchi. In addition, it assists with humidification and warming of the inspired air and with mucocilliary clearance . It extends from the level of the C6 vertebra to its bifurcation at the level of T5 and is approximately 11 cm in length . There are 15–20 C-shaped hyaline cartilage segments that maintain lumen patency.
The tracheal wall constitutes of the inner mucosa, sub-mucosa, cartilage, longitudinal and transverse muscle fibres, and an outer adventitial layer. The endoluminal diameter in the coronal plane ranges from 13 to 25 mm in men and 10 to 21 mm in women. The sagittal diameter ranges from 13 to 27 mm in men and 10 to 23 mm in women .
At the tracheal bifurcation, the right mainstem bronchus emerges as a shorter, more vertically oriented structure with a larger diameter than the left mainstem bronchus. The right and left mainstem bronchi form 20–30° and 45° angles with the trachea, and are approximately 2.5 and 5 cm long, respectively .
Lesions of the large airways
Benign – focal – narrowing
Squamous cell papilloma
Benign – focal – widening
Allergic bronchopulmonary aspergillosis
Benign – diffuse – narrowing – without wall thickening
Saber sheath trachea
Benign – diffuse – narrowing – with wall thickening – acute
Benign – diffuse – narrowing – with wall thickening – chronic
Granulomatosis with polyangiitis (Wegener granulomatosis)
Benign – diffuse – widening
Malignant – focal – narrowing – primary
The symptoms of a tracheal neoplasm are nonspecific and include cough, wheeze, hemoptysis, and stridor. Dysphagia and recurrent laryngeal nerve paralysis can indicate involvement of adjacent structures. Primary malignancies of the trachea are rare and account for only 0.1 to 0.4 % of all malignancies in adults. However, 80–90 % of tracheal tumours are malignant . Primary malignant tumours can be classified by tissue subtype such as surface epithelium, salivary gland, and mesenchymal tissues. The most common histological types are squamous cell carcinoma and adenoid cystic carcinoma.
Adenoid cystic carcinoma
Malignant – focal – narrowing – secondary – direct
Metastatic lesions to the trachea can occur from either direct or hematogeneous spread, with direct invasion being more common . The CT imaging is nonspecific as there may be a solitary lesion, multiple lesions, or eccentric wall thickening.
Malignant – focal – narrowing – secondary – hematogenous
We have reviewed a wide range of lesions found on imaging of the large airways, lesions that fall into a number of categories, specifically benign versus malignant, focal versus diffuse, and narrowing versus widening of the airway. In addition to this algorithm, evaluation of the circumferential or membranous location of the lesion may also be used to aid in diagnosis, and where appropriate this has been described in the text. Knowledge of the radiologic appearance of these lesions is crucial in developing a differential diagnosis and determining the next step in management. When a pathological specimen is obtained, critical radiologic-pathologic connections can be determined, and diagnostic accuracy may be improved.
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