Anatomic and HRCT Demonstration of Midline Sternal Foramina

The sternum is derived from a pair of vertical mesenchymal bands, called sternal bars, that develop ventrolaterally in the body wall. Chondrification occurs in these bars craniocaudally in the median plane to produce cartilaginous models of the manubrium, body segments (sternebrae), and the xiphoid process. Fusion of the bars at the inferior end of the sternum is sometimes incomplete (1, 3). This fusion defect can also be seen occasionally between the third and fourth body sternebrae. This imperfect union is known as midline sternal foramen. This condition is seen more frequently in the lower part of the sternum, as mentioned above, but may occur even in the manubrium (2, 4). It may be an isolated malformation or may be accompained by displacement of the heart or other midline abnormalities (2).