Variability in Mediastinal Lymph Node Measurements in Chest Contrast-enhanced CT: Time to Change the Paradigm?

Measurement of mediastinal lymph nodes (LNs) is an integral part of patient assessment, and is performed by manually measuring the short axis length (SAL) of the LNs on axial slices. LNs with SAL ≥10 mm are considered pathologically enlarged. We aimed to quantify the interobserver agreement and variability of SAL measurements, compare them to automatically computed SALs from manual LN delineations, and establish the mean SAL measurement error.

Two radiologists independently measured the SALs of 451 LNs in 40 contrast-enhanced chest CT (CECT) scans. One of them also manually delineated the LN contours in each CECT slice, and this served to automatically classify LN as normal/enlarged based on their SALs. Differences between SAL measurements and Bland-Altman statistics were computed.

The normal/enlarged LN overall agreement (371 normal, 52 enlarged) between both radiologists was 93.8% (423/451). For agreement/disagreement, the SAL differences were 1.1 (1.0) mm (17%) and 3.5 (3.2) mm (40%). The disagreement differences were nearly twice as large as the agreement differences. The agreement between the manual and the computed SALs for both radiologists was 92.7% (418/451), similar to the interobserver variability.

Classification of mediastinal lymph nodes based on SAL measurements demonstrates high agreement. It indicates that SAL measurements automatically computed from manual LN delineations could be a reliable and time-saving tool. In cases of disagreement, the ±2 mm error supports the use of 3 size categories: normal (<8 mm), possibly enlarged (8 to 12 mm), and definitely enlarged (>12 mm).