Both CT and high-frequency ultrasound have been shown to be reliable diagnostic tools used to differentiate normal cranial sutures from suture synostosis. In nonsynostotic plagiocephaly, overlapping of the bony plates and the so-called “sticky suture” is still controversial and is believed to represent a pathological fusion process. Synchrotron–microcomputed tomography (SRmCT) studies were undertaken to determine whether positional head deformities can be assumed to be true suture pathologies.
Morphological features and growth development of 6 normal cranial sutures between the ages of 3 and 12 months were analyzed histologically. Additionally 6 pathological sutures, including sagittal synostosis and nonsynostotic plagiocephaly (NSP), were compared with the group of normal sutures by histological and SRmCT studies. Synchrotron-microcomputed tomography is a special synchrotron radiation source with a high photon flux providing a monochromatic x-ray beam with a very high spatial resolution. Morphological characteristics of the different suture types were evaluated and bone density alongside the sutures was measured to compare the osseous structure of the adjacent bony plates of normal and pathological sutures.
Histologically jointlike osseous edges of the normal sutures were seen in the 1st month of life and interlocking at the age of approximately 12 months. During this 1st year, bone thickness increases and suture width decreases. The SRmCT studies showed that: 1) sutures and adjacent bones in NSP are comparable to normal sutures in terms of their morphological aspects; 2) bone densities in the adjacent bony plates of NSP and normal sutures are not different; 3) thickening of the diploe with ridging of the bone in sagittal synostosis is associated with significantly higher bone density; 4) synostotic sutures are only partially fused but vary in their extent; and 5) nonfused sections in sagittal synostosis behave like normal sutures without any signs of pathological bone formation.
Sutures in patients with NSP were found without any morphological irregularities or different osseous structures alongside those compared with normal sutures. Thus, a true suture pathology or osseous change of the adjacent bony plates is highly unlikely in NSP. Even though the number of specimens is limited in this series, cranial suture fusion seems to start at one undetermined point and spread along the suture, whereas other parts of the same suture are not involved according to morphological aspects and bone density measurements of the adjacent bones. This theory may represent a dynamic fusion process completed over time but just starting too early.