Purpose or Case Report: The indications for high resolution CT (HRCT) and bronchoscopy often coincide in patients
with recurrent respiratory tract infections, chronic cough and wheezing, symptoms often related to tracheomalacia (TM). However, the efficacy for detecting TM in young children by HRCT has not been investigated. The aim of this investigation is to evaluate the ability to detect TM on clinical HRCT relative to bronchoscopy as a reference standard and compare several quantitative methods of determining the presence of TM on CT.
Methods & Materials: Patients were identified that had both HRCT and bronchoscopy. HRCT technique depended on sedation and airway status, but all were included. Reports were abstracted for presence and severity of reported TM.
Three measurements were obtained at the narrowest segment of the trachea on CT: short axis, long axis, and crosssection area(CSA). These values were then “self-normalized” by using the CSA of the most normal section of the trachea or as a ratio of short/long axis.
Results: 280 patients were identified (5.4 years(5.08)), 103 had TM on bronchoscopy. When TM was absent by bronchoscopy, the inspiratory and expiratory ratio of the diameters was statistically larger than mild, moderate and severe grades of TM (p<0.001) and mild TM was larger than severe (p<0.0001). These relationships were confirmed by pairwise comparison using Tukey’s method. The change in cross-sectional area of the trachea from inspiration to expiration was statistically smaller only between the normal patients versus moderate or severe TM subjects (p<0.0001). Using a short/long axis cut-off ratio of 0.7 results in a sensitivity of 91% and specificity of 90% for inspiratory CT, compared to bronchoscopy, and improves to 96% sensitivity and 95% specificity for expiratory CT. No similar cut-off was as efficacious for cross-sectional area change.
Conclusions: The current clinical paradigm for identifying TM by HRCT only identifies a small fraction of TM compared
to bronchoscopy. Applying a simple ratio of two measures, short axis to long axis, can allow more accurate
identification of TM. A ratio of less than 0.7 is adequately accurate on either inspiratory or expiratory images.
Additionally, this CT measured ratio follows a general trend related to bronchoscopic severity grade. However, the accuracy of this trend is limited, probably due to poorly controlled inspiration and expiration parameters during imaging, as well as, lack of standardization for bronchoscopy.