Growth and asymmetry of the human liver during the embryonic period

Previous studies had suggested that the development of asymmetry in the human liver could occur as a consequence of the earlier developing asymmetry of the heart and that the preferential right-sidedness of hepatic volume was secondary to favored venous return on the right. To examine this question we reconstructed the liver from serial histologic sections of human embryos in the Carnegie Embryological Collection of stages 11 through 23. Photomicrographs of embryo sections were projected, traced into the digitizing pad on an image analyzer microcomputer, and the liver volume and relative volumes to right and left of the median plane of the body calculated. The 38 embryos studied represent each Carnegie stage, sectioned in transverse, frontal, or sagittal (except stage 11) planes. The liver appears in stage 11 and grows to over 90 mm3 at stage 23, as the embryo enlarges from 3 to 30 mm crown-rump length (CRL). A significantly greater proportion of the liver was found on the right of the median plane in all embryos from stage 11 onward (p less than 0.001). Volume in mm3 is given by the semilogarithmic regression formulas volume = 1.49 x 10(-6)e0.826 stage, or volume = 0.0177 e0.333 CRL. Insignificant variation from the average proportion of 57.8% (SE +/- 0.8%, range 51-70%) on the right of the median plane was present throughout the embryonic period. The observation that the liver is right-sided from its first appearance is not well explained by properties of the vascular pattern. The explanation for this intrinsic hepatic asymmetry remains obscure.