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)
Appearance
Term
Cause
oval in transverse plane, normal length, symmetrical
normocephaly
normal closure of the sutures
anterior half of skull triagonal in transverse plane, often with ocular hypotelorism
trigonocephaly
premature closure of the metopic suture
round in transverse plane, with flattened occiput
brachycephaly
premature closure of both coronal sutures
oval in transverse plane but increased length, symmetrical
dolichocephaly
premature closure of the sagittal suture
ovoid in transverse plane but asymmetrical
plagiocephaly
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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