Vascular pathogenesis of limb defects. I. Radial artery anatomy in radial aplasia.

Twelve human fetuses with radial aplasia were dissected to evaluate the vasculature of the arm. Three types of vascular patterns were found. In type I there was a single midline superficial vessel with no radial or ulnar artery. This pattern occurred in four perfused twins (acardia) with twins reversed arterial perfusion sequence, one fetus with clinical trisomy 18, and one with an unknown disorder with multiple field defects. In type II there was absence of the radial artery with or without persistence of the embryonic median artery; the other vessels were normal. This pattern was seen in three fetuses with unknown disorders associated with multiple malformations. In type III the radial artery was present but had an abnormal course. This pattern was found in three fetuses with thrombocytopenia-absent radius syndrome. From these dissections and the results of animal experiments on the embryology of the vasculature, the following conclusions can be drawn. Vasculogenesis precedes differentiation of mesenchyme into muscle and bone. The embryonic capillary net determines the adult vascular anatomy of the limb. Failure to form, malformations, or disruption of the capillary net results in anomalies of the adult vasculature and may lead to musculoskeletal defects. Failure to chondrogenesis does not disturb the capillary net, and normal arteries will develop. Absence of the radial artery found in association with radial aplasia implies that there was abnormal vasculogenesis or disruption of developing vessels, or both. Either can lead to this congenital musculoskeletal defect.

Vascular pathogenesis of transverse limb reduction defects.

Evaluation of four patients with unilateral transverse limb reduction defects indicates that some instances of this structural defect may be the result of an in utero vascular accident. Three of the four patients had microscopic evidence of fetal vascular occlusive disease on multiple sections of the placenta, suggesting that occlusion of the brachial artery was secondary to embolization from the placental vascular thrombi. The fourth, a 116 mm crown-rump long fetus, had a massive thrombus occluding the brachial artery, which was felt secondary to hypovolemia and hypoperfusion associated with fetal blood loss during placental abruption. Recognition of the disruptive vascular pathogenesis of some cases of unilateral transverse limb reduction defects explains their negligible recurrence risk. In such cases attention should be focused on careful gross and, microscopic evaluation of the placenta.