Table 2.

Definitions for the Stages of Fusion of the Spheno-occipital Synchondrosis

Stage	Classification	Definition
Stage I	Open	The synchondrosis was completely open and appeared as a radiolucent band; absence of osseous core and no fusing sign on superolateral margin of the synchondrosis
Stage II	Incipient fusion	Fusion between the sphenoid and occipital bone on the right and/or left lateral margin, typically on the superior third of the synchondrosis
Stage III	Appearance of single osseous core	A single osseous core appeared within the synchondrosis, and the bilateral margins of the superior third of the synchondrosis were fused evidently; a radiopaque osseous core was isolated within the synchondrosis or connected with sphenoid or occipital bones
Stage IV	Appearance of additional osseous cores	Multiple complex osseous cores were observed within the synchondrosis; partially fused synchondrosis with presence of isolated and/or bony bridged osseous cores
Stage V	Fusion with ossifying vestige	The synchondrosis was almost fused but still visible as a mixed radiopaque and radiolucent ossifying vestige
Stage VI	Complete fusion	The synchondrosis was completely ossified and appeared like a single bone without radiolucent gaps