[Extra-osseous and intra-osseous microvascularization of the sternum of the child].

The microvascularization of the sternum of the child has been studied by a method of India ink injection and by histology. Extra-osseous vasculature includes vascular pedicles and sternal vascular networks. Vascular anterior and posterior pedicles issue from internal mammary vessels. Sternal anterior and posterior networks are disposed on the faces of the sternum and are divided in a superficial one and a deep one; both are included in the perichondrium. In newborns and in young infants, vascular structures looking like baskets are affixed to the deep sternal network. It is unlikely that they intervene in the constitution of the adult pattern of the sternal vasculature. The early complete development of sternal networks contrasts with the existence of evolutive characteristics of the intra-osseous vasculature. Intra-osseous vasculature includes the cartilage canal vessels and the vessels of the ossification centers. Cartilage canals are provided with an axial artery, issued from the deep sternal network, which produces short capillaries which continue in peripheral sinuses. Cartilage canals permit the penetration of perichondral tissue deep in the cartilage of the developing sternum, allowing the formation of the ossification center. The ossification center is vascularized by centrifugal arteries, issued from the cartilage canal artery, and disposed in a radiant pattern. They continue, through a conical progressive dilatation, into a sinusoid network, which presents a convergent disposition towards the center of the ossification point. Vascular events precede ossification. Hematopoietic development is consecutive to the vascular events too. The slenderness of vascular pedicles contrasts in neonates with the wide development of the sinusoid network. Adipose tissue is rare in the bone marrow sternum of the child. Secondary evolution of the ossification center vasculature permits its connections with the deep sternal vascular network, with adjacent cartilage canals, and with adjacent ossification centers. Progressively, the number and the importance of the peripheral pedicles of the ossification centers increase. Thus, a multiple and centripetal vascular provision takes the place of the initial, unique, centrifugal one. These modifications correspond to the transition from the vascular pattern of an expanding structure (the ossification center) to the one which is adapted to the full expression of its hematopoietic function.