Radiology, Vol 192, 165-169, Copyright © 1994 by Radiological Society of North America
Anterior clear space: how clear? How often? How come?
MJ Landay
Department of Radiology, University of Texas Southwestern Medical School, Dallas 75235.
PURPOSE: To compare the opacity of the retrosternal clear space with that
of the retrocardiac region on normal lateral chest radiographs, to measure
the clear space, and to evaluate the reasons for these findings. MATERIALS
AND METHODS: Left lateral chest radiographs and computed tomographic scans
of 38 patients with normal studies were evaluated and the results were
correlated. RESULTS: In 19 (50%) patients, retrosternal and retrocardiac
opacity were equal. In 16 (42%), the retrosternal region was more opaque
than the retrocardiac region (10 of 12 women, six of 26 men). The
difference between the sexes was statistically significant (P = .002). In
only nine (24%) patients was the anterior margin of the ascending aorta
defined on the lateral study. Mean sternum-to-aorta distance in these
patients was 29 mm. CONCLUSIONS: Retrosternal opacity greater than
retrocardiac opacity on lateral chest radiographs is a frequent normal
finding, especially in women. Sternum-to-aorta distance may be difficult to
measure, and distance greater than 2.5 cm may be normal in some persons.
