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Tracheomalacia

Tracheomalacia is a common incidental finding on imaging of the chest of older patients and manifests as an increase in tracheal diameter as well as a tendency to collapse on expiration. 

Tracheomalacia can be broadly considered as being congenital or acquired. The remainder of this article relates to acquired tracheomalacia, while a separate article considers the specifics of congenital tracheomalacia.

There is overlap and inconsistency in the definition of tracheomalacia. Most authors state that the cardinal finding is that of expiratory tracheal collapse. However, some expand the definition such that there must also be inspiratory tracheal dilatation. For the purpose of this article, the former broader definition is used.

Epidemiology

The true incidence of tracheomalacia is uncertain, but has been identified in up to 23% of bronchoscopy and autopsy series and 10% of CT series 1.

There are numerous causes of tracheomalacia, the commonest of which are:

Clinical presentation

In many instances the diagnosis is made incidentally on imaging of the chest. Patients frequently complain of shortness of breath, chronic cough and recurrent respiratory tract infection, although a causal links are difficult to establish in many cases 1-2.

Pathology

The underlying aetiology is one of reduced or abnormal connective tissues in the trachea, particularly the cartilaginous rings.

Radiographic features

Plain film

Plain inspiratory radiographs are usually normal or may demonstrate a dilated trachea. If expiratory films are obtained in lateral projection then the diagnosis may be evident, however these are uncommonly performed.

CT

CT with inspiratory and expiratory phases is particularly useful in the assessment of tracheomalacia. Inspiratory only CT is unable to make the diagnosis, however a dilated trachea ( > 3 cm), especially with posterior bowing of the membranous portion (thus becoming circular) may indicate over compliance of the trachea and thus suggest the diagnosis. 

During expiration collapse of the trachea is seen, with bowing of the posterior membranous portion anteriorly, creating a crescent shape in the axial plane 1. Typically a decrease of the anterior-posterior diameter by 50% or greater is used as a cut-off 1-2,5.

Scanning during voluntary coughing has also been described, and is probably more sensitive than using end-expiratory scanning, as the degree of increased intrathoracic pressure is greater 2

It is also important to note that the degree of AP diameter reduction in a normal paediatric trachea is greater than that in adults, and thus care should be taken in correlating borderline findings with symptoms 3. In some instances a cut-off of 70% reduction of AP diameter may be a more specific finding 5.

In most cases the tracheal wall is normal or thin, although tracheomalacia with thickened tracheal wall has been reported in relapsing polychondritis 1.

Treatment and prognosis

In most cases no treatment is required nor offered. In severe cases where significant symptoms can be ascribed to tracheomalacia, splinting of the membranous portion of the trachea with a variety of materials may be employed 4.

Differential diagnosis

As long as true dynamic expiratory collapse is seen then the diagnosis is usually obvious, however many underlying causes should be considered (see causes of tracheomalacia). In many instances the diagnosis will be evident and thus features of each individual condition should be sought.

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