There have been some metrical studies on the aorta of human adults. However, little work has been done on Japanese fetuses. This study was carried out to investigate such arterial changes during the fetal age period of 6-8 months as (1) lengths of the aortic arch, thoracic aorta and abdominal aorta, (2) relative positions on the aorta where main aortic branches arise, and (3) diameters of the main aortic branches.
The results were as follows:
1) The total length of the aorta increased with fetal age. Growth rates of the aortic subdivisions were different from one another. During the 6-7 month period, proportions of the aortic arch and the abdominal aorta to the whole aorta increased. On the other hand, the proportion of the thoracic aorta decreased during this period. During the 7-8 month period, the proportions of each subdivision were unchanged.
2) Diameters of the main aortic branches and distances between these branches and the brachiocephalic artery were measured. During the 6-7 month period, the relative positions of arteries arising from the aortic arch moved toward the heart along the aorta, while the celiac artery, superior mesenteric artery and renal artery moved downward. The relative positions of the ductus arteriosus and the inferior mesenteric artery remained unchanged during the period. No change was seen in the relative positions during the 7-8 month period.
3) Distances between the arising points of the left and right intercostal arteries were measured on the dorsal surface of the thoracic aorta. The distance was wider in the upper segment of the aorta than in the lower segments. A good correlation between the distance and fetal age (6-8 months) was recognized only in the upper segments.
4) Distances between arising points of adjacent upper and lower intercostal arteries were measured on the dorsal surface of the aorta. The distance between the arising points of the 9th and 10th intercostal arteries was the largest in both the left and right sides. In general, the distance in the upper segments was larger than in the lower segments.
5) The diameter of the common iliac artery, which is the terminal branch of the abdominal aorta, increased more rapidly than other main arteries.
6) The 3rd and 4th intercostal arteries were most frequently seen to arise from the thoracic aorta as a common trunk. Formation of a common trunk was less frequent in lower intercostal arteries.
7) The data obtained in the present study were discussed in comparison with those in adults.
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