Flexible bronchoscopy is considered the gold standard for the evaluation
of the presence and severity of TBM. Rigid bronchoscopy tends to
underestimate the degree of the tracheal collapse because it “stents”
the airway51,86–88.
There was moderate agreement regarding the use of standard chest CT
because it may not capture the dynamic changes of the tracheobronchial
lumen that occur during the respiratory cycle (especially with cough).
Inspiratory and expiratory dynamic multi-detector chest CT scans were
considered superior because they are fast, relatively inexpensive, and
provide additional and detailed information about the airways, the lung
parenchyma, and the thoracic vasculature51,87,89,90.
However, at the moment they may not be available in every hospital.
Maximal expiratory flow-volume curves (MEFVCs) can be often diagnostic
of tracheomalacia91, showing a characteristic
flattening of the initial portion of the MEFVC (Figure 3A). Its
disadvantage is that it can only be performed in children over 4-5 years
of age, and it becomes less sensitive in older children and
adolescents44,92. Infants can be evaluated with the
raised-volume rapid thoracoabdominal compression (RVRTC) technique,
which allows the performance of MEFVCs without the patient’s cooperation
but is labor intensive and usually requires
sedation93. An alternative easy, non-invasive
technique to evaluate flow-limitation is with tidal flow volume
loops94 (Figure 3B). However, it is not well
standardized, and it may miss mild/moderate TBM.