Purpose: The detection by US (in contrast to CT) of lymph nodes of any size in the mediastinum is usually considered to be a pathological finding. The aim of this study was to find out whether it was possible to detect normal lymph nodes by high-resolution mediastinal US.
Material and methods: Six different mediastinal regions in 80 healthy asymptomatic volunteers and in 20 human cadavers were examined by means of US (with colour Doppler imaging) to assess US access to the respective regions and to demonstrate the number and size of detectable lymph nodes. All the cadaveric lymph nodes that were detected were examined histologically to exclude inflammatory or malignant infiltration.
Results: In almost all subjects, we obtained US access to the supra-aortic (100%), paratracheal (95%), prevascular (99%), and pericardial (98%) regions, and to the aorticopulmonary window (98%). US access to the subcarinal region was more difficult (75%). In the healthy subjects, lymph nodes were detected in the paratracheal region (in 35% of these subjects, mean lymph-node diameter 12 x 7 mm), in the aorticopulmonary window (45%, 14 x 8 mm), and in the subcarinal region (13%, 13 x 7 mm). In the cadavers, histologically normal lymph nodes were detected frequently in the paratracheal region (85%, mean size 11 x 6 mm) and in the aorticopulmonary window (90%, 11 x 5 mm).
Conclusion: These results indicate that normal lymph nodes (and not only pathological lymph nodes) can be demonstrated by high-resolution mediastinal US.