Synostosis is the fusion of bones during development and occurs along the suture lines of the skull. If the synostosis occurs prematurely, the normal expansion of the cranial vault may be prevented, resulting in abnormal shape or asymmetry. The growth inhibition occurs at right angles to the closed suture. and is affected by the order and timing of closure relative to the closure of the other sutures.


Sutures in the skull:

(1) metopic (single, midline)

(2) coronal (paired)

(3) sagittal (single, midline)

(4) lambdoidal (paired)

(5) squamosal (paired)




oval in transverse plane, normal length, symmetrical


normal closure of the sutures

anterior half of skull triagonal in transverse plane, often with ocular hypotelorism


premature closure of the metopic suture

round in transverse plane, with flattened occiput


premature closure of both coronal sutures

oval in transverse plane but increased length, symmetrical


premature closure of the sagittal suture

ovoid in transverse plane but asymmetrical


premature closure of one coronal (anterior asymmetry) or one lambdoidal (posterior asymmetry)

outline of skull small in the transverse plane; cranial vault higher but narrower than normal

turricephaly (oxycephaly, acrocephaly)

coronal and sagittal synostosis, forcing the skull to grow vertically


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