Studies of vertebral coronal cleft in rhizomelic chondrodysplasia punctata.

Dissection and serial section-reconstruction preparations from vertebrae with coronal cleft of a 2 5/12-year-old girl with rhizomelic chondrodysplasia punctata are described. The cartilage plate between the dorsal and ventral vertebral ossification centers, abnormal thickness of which is the explanation of the radiologic coronal cleft, shows differences in thickness, with dorsal and ventral midline extensions and with small foci of communication of the cancellous bone of the dorsal and ventral ossification centers of the vertebral body bilaterally. Although the process in coronal cleft is in some ways similar to that of radiologic "retarded epiphyseal closure," the explanation of the coronal clefts in rhizomelic chondrodysplasia punctata appears to be overproduction of cartilage in the zone between the dorsal and ventral vertebral body ossification centers, plus reduced removal of cartilage cells from this zone. No evidences of persistence of notochord cells were seen microscopically in sections of the coronal clefts.