lunedì 14 maggio 2007

Sagittal synostosis


3-D CT images demonstrate sagittal synostosis. Markedly increased anteroposterior diameter of the head (dolichocephaly) with flattening of the superior contour is noted. The sagittal suture is fused (Figure 1 and Figure 2), with widening of both the coronal (Figure 2) and lambdoid sutures (Figure 1 and Figure 2).

Diagnosis: Sagittal synostosis

Premature fusion of the cranial sutures is termed craniosynostosis. Approximately 80-90% cases involve isolated defects, while the remaining cases are part of a recognized syndrome. In the isolated cases, the sagittal suture is affected most often (55%), followed by the coronal (20%), lambdoid (5%), and metopic (5%) sutures. Syndromes associated with synostosis include Crouzon disease and Chotzen and Apert syndromes.

The anterior fontanel represents the intersection of the metopic, coronal, and sagittal sutures. It normally closes in children by the age of 20 months. The posterior fontanel, located at the junction of the lambdoid and sagittal sutures, closes by the age of 3 months. Skull growth is restricted in the plane perpendicular to the prematurely fused suture and enhanced in the plane parallel to it.

Sagittal synostosis produces a long and narrow skull, called scaphocephaly or dolichocephaly. The AP diameter of the skull is increased, whereas the transverse diameter is decreased. Actual head volume is normal and there is no increase in ICP, no hydrocephalus, and no neurologic deficit.

Coronal synostosis can occur bilaterally or unilaterally and is called brachycephaly and plagiocephaly (twisted and asymmetric skull), respectively. Brachycephaly results in a short, wide skull, with a shortened AP diameter with a flattened occiput and forehead. It has a higher incidence of neurologic complications, including increased ICP, optic atrophy, and mental retardation.

Lamboid synostosis produces a marked flattening and underdevelopment of the posterior fossa and overgrowth of the bregma may occur, resulting in a tall tower like shape called oxycephalic or turricephalic skull.

Metopic synostosis occurs in utero. It is rare, and results in a pointed forehead and hypotelorism called trigonocephaly, and has an increased risk for associated anomalies of the forebrain.

The most severe form is called the kleeblattschädel deformity or cloverleaf skull, in which the coronal, sagittal, and lambdoid sutures are all affected. The skull resembles a cloverleaf shape, and patients typically have a bulging forehead, proptotic eyes, and severe neurologic impairment.

The signs of craniosynostosis on plain radiography include bony bridging across the suture that produces beaking or heaping up of bone as well as sclerosis, straightening and narrowing of the suture.

The diagnostic value of the CT scan outweighs that of plain radiography because the sutures can be identified more accurately. In addition, CT helps in evaluating the brain for structural abnormalities (eg, hydrocephalus, agenesis of the corpus callosum) and in excluding other causes of asymmetric vault growth (eg, brain hemiatrophy, chronic subdural hematoma). Three-dimensional surface CT reconstructions can help the surgeon to accurately delineate the craniofacial deformity and plan surgical management.

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