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The Neonatal Diaphragmatic Crura Are Hypertrophied

A Necessary Preparation for the First Breath?

Department of Radiology, University of California, San Francisco, San Francisco, California USA.

Address correspondence and reprint requests to Maria J. Moes, MD, Department of Radiology, University of California, San Francisco, 505 Parnassus Ave, L374, San Francisco, CA 94143-0628 USA; e-mail: maria.moes{at}radiology.ucsf.edu.

Objective. To sonographically show that the neonatal crura are markedly hypertrophied. Methods. Fifty patients in each of 2 groups, ages 0 to 2 months and 18 to 40 years, were randomly chosen from patients who recently underwent abdominal sonography. A single longitudinal plane of a section was used to measure both the anteroposterior diameter of the aorta and the diaphragmatic crus. The ratios of these were compared in the 2 groups. Results. A significant difference was shown between the sizes of the diaphragmatic crura of the neonate and the adult when the aorta was used as an internal standard of size variability. The mean ratio of the aorta to the right crus in neonates was 2.95, and in young adults it was 1.04 (P < .0001). Conclusions. The neonatal crura are hypertrophied at birth, likely to allow the markedly atelectatic and fluid-filled lungs to fully expand in relatively few breaths.

Key Words: diaphragm • hypertrophy • neonatal • sonography