Bronchocoele, also termed mucoid impaction, refers to mucous-filled dilated bronchi surrounded by aerated lung.
They may result from either obstructing or non-obstructing causes:
- asthma: due to increased mucus production
- cystic fibrosis: due to impaired ciliary movement and thick secretions
- allergic bronchopulmonary aspergillosis (ABPA)
- neoplasia: bronchogenic carcinoma, hamartoma, lipoma or bronchial carcinoid
- congenital bronchial atresia: most commonly affects the apicoposterior segment of the left upper lobe
- tuberculous stricture
- intralobar sequestration
- intrapulmonary bronchogenic cyst
- foreign body aspiration
The cause of bronchocoele formation will be different for peripheral and central locations. Peripheral bronchocoeles are most often seen in cystic fibrosis and post-tuberculous bronchiectasis. Central perihilar bronchocoeles result from:
- non-obstructive bronchiectasis: secondary to cystic fibrosis or ABPA
- obstructive bronchiectasis: secondary to an endobronchial tumour or bronchial atresia
They can be sometimes difficult to diagnose on plain radiography and may appear as a branching tubular opacity that is distinct from the normal vascular shadows.
CT would better define a tubular to branching intrapulmonary opacity that is again distinct from vascular shadows.
Their appearance is similar to a "finger in glove" or the shape of the letters V or Y depending on their location, length and orientation as well as the number of bronchi involved.
The CT attenuation of the mucus is generally that of soft tissue but may be modified by its composition (e.g. high-attenuation material in allergic bronchopulmonary aspergillosis).
In the case of bronchial atresia, the surrounding lung may be of decreased attenuation because of reduced ventilation and, thus, perfusion. The typical appearance for a bronchocoele resulting from bronchial atresia occurs immediately distal to the expected location of the apical segmental bronchus, where there will be a hyperlucent segment or lobe distal to the bronchocele owing to collateral air drift.
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