Purpose or Case Report: Dynamic Airway CT (DACT) has risen in popularity in recent years, however, studies of Tracheobronchomalacia (TBM) are hindered by inconsistent definitions which variously rely on airway area, airway diameter, and qualitative measures. We explore the interrater reliability of these measures.
Methods & Materials: Retrospective review of our PACS was undertaken for cases of DACT cases demonstrating TBM. Our dynamic airway CT protocol included 6 sequential CT series imaging over 1-2 breath cycles. Studies were independently reviewed by 3 pediatric radiologists. Specific malacic segments for analysis were agreed upon in advance. The following features were assessed in end-inspiration and end-expiration:(1) max AP diameter, (2) max cross-sectional area and (3) length of malacic segment. Subjective categorical assessment of TBM was recorded. A subset of 2 raters used Aquarius iNtuition to measure the volume of collapse at end inspiration and expiration from the junction of the malacic segment with the normal airway. Intraclass correlation coefficient (ICC) was used for numeric variables and Fleiss’s kappa (κ) was used for categorical variables.
Results: 8 patients with DACT demonstrated TBM. Mean age at presentation was 23 months (range 0 - 157). 4 lesions (50 %) were associated with extrinsic compression.

Substantial agreement was seen with subjective scoring of TBM severity (κ=0.69, p<0.001). Agreement across all 3 raters was seen with 6/8 patients (75%). Poor reliability was seen with length of TBM segment (ICC=0.40, p=0.04).

Moderate reliability of max AP diameter in inspiration and expiration was seen (ICC=0.634, ICC=0.541). Good reliability was seen with max cross-sectional area measurement in inspiration and expiration (ICC = 0.822, p=<0.001, ICC = 0.86, p<0.001). However, there was poor agreement for the percentage airway area collapse with ICC 0.13, p=0.274. Airway volume demonstrated good reliability on max inspiration (ICC = 0.862, p<0.001) and poor reliability on max expiration (ICC = -0.16, p<0.001). Poor reliability was seen when considering the percentage of volume collapse (ICC = 0.31, p=0.124).
Conclusions: Our data suggests that pediatric DACT may suffer from a lack of reproducible quantitative measures of TBM. In fact, percentage of diameter and cross-sectional area collapse demonstrated poor-moderate agreement. A 3D approach did not improve this. Interestingly, the only domain of robust agreement regarding TBM was the subjective rating, where 75% of cases generated complete agreement.