Roentgen Determination of the Time of Closure of the Spheno-Occipital Synchondrosis

The spheno-occipital synchondrosis is the joint between the basal portions of the sphenoid and occipital bones in that portion of the skull base usually designated as the clivus. The articulation is similar to the cartilaginous junction between the epiphyses and metaphyses of long bones. A synchondrosis is a temporary union since the connecting cartilage becomes ossified with advancing age. While the times of union of epiphyses to primary centers of the skeleton have been widely studied, a paucity of information is available concerning the normal closure of the spheno-occipital synchondrosis.

Embryologic and Anatomic Considerations

In the human embryo the earliest evidence of the cranium is found in dense masses of mesenchyme which surround the cranial end of the notochord. Cartilage formation in the developing mesenchyme in this area is apparent at the beginning of the second month of embryonic life. During the ninth and tenth weeks of embryonic life, ossification centers begin to appear in the occipital area, but most of those in the sphenoid area develop much later.

Both the occipital and sphenoid bones are of mixed intracartilaginous and intramembranous development. In both bones the intramembranous portions are more laterally situated, while the primitive skull base is entirely intracartilaginous (Henderson and Sherman; Patten). The basilar portion of the occipital bone forms from two ossification centers which coalesce early during development. The body of the sphenoid develops from four centers, two for the presphenoid and two for the postsphenoid section.

At birth the body of the sphenoid exists as a unit formed by junction of the basal portions of the presphenoid and post-sphenoid segments of the bone which occurs at approximately the eighth month of fetal life (Goss). The basilar part of the occipital bone is also well developed at birth. During the early years of life bone growth along the synchondrosis is even but, with growth deceleration, relative narrowing appears along the superior aspect of the articulation.

Roentgenologic Investigation

Prior reports indicate lack of agreement in respect to the time of closure of the spheno-occipital synchondrosis. Observations as to the time of the beginning of ossification vary from puberty (Caffey) to the third decade of life (Pendergrass, Schaeffer, and Hodes). A particularly clear description of the method of closure from above downward has been given by Goss, although he differs with others as to the age of ossification.

As a result of these discrepancies, a study was undertaken, on a limited scale, to ascertain more accurately the appearance of the spheno-occipital synchondrosis at different ages and the time of closure. The subjects for examination were chosen at random, an attempt being made to obtain at least two persons with ages corresponding to each yearly interval between five and twenty-five years of age. A total of 47 persons are included in this report.