Craniosynostosis Imaging 

Craniosynostosis is the premature fusion of the cranial sutures. The condition can occur as an isolated defect or as part of a syndrome and is recognized in 2 forms: simple and compound. In simple craniosynostosis, only 1 cranial suture is involved; compound craniosynostosis involves 2 or more sutures. (See the images below.)^{[1, 2]}

Preferred examination

Patients in whom craniosynostosis is suggested should undergo a careful clinical examination, with the clinician looking for abnormalities of the skull and extremities.

Plain radiography is the first radiologic step. Plain radiography quickly and simply identifies skull-shape abnormalities, which are seen in most patients with craniosynostosis. With this simple and inexpensive examination, usually all cranial sutures can be surveyed for patency. Conventional cranial computed tomography (CT) scans with bone windows or 3-dimensional (3D) CT scans are frequently obtained to confirm bony abnormalities and to delineate any associated intracranial anomalies. Three-dimensional CT is the criterion standard for the evaluation of craniosynostosis.

Limitations of techniques

The entire length of each suture is not always visible on plain radiographs, and some patients have only a small bony bar limiting growth at a particular suture. If the skull shape is entirely normal, craniosynostosis is unlikely.

CT scanning is considered to be expensive and may require that the patient be sedated.

Recent studies

Danelson et al investigated the possible benefits of employing 3D models in preoperative planning for craniosynostosis surgery, specifically, spring-mediated cranioplasty and cranial vault reconstruction.^[3]

In the study, models were created using image analysis software to isolate cranial vault bones from preoperative CT scans of the study's patients; this information was ultimately fed into a 3D printer, which built a reproduction of each patient's cranial vault. The models were particularly useful as templates for prebending the springs used in spring cranioplasty and permitted better quantification of the springs' force characteristics.

Plain radiographs are obtained easily and demonstrate osseous anatomy well. At a minimum, views should include anteroposterior (AP), Townes, and bilateral lateral films. Plain radiographs are useful for identifying the abnormalities of head shape (dolichocephaly, brachycephaly, and plagiocephaly) that are characteristic of the various forms of craniosynostosis. (See the images below.)

Plain radiographs can be used to identify prematurely fused sutures. Normal sutures are seen on plain images as serrated, nonlinear, lucent lines. Sutures in patients with craniosynostosis are usually straight with sclerotic heaped-up margins or are completely absent. The sclerotic margins may outline the sutures well and lead to the false impression that they are patent. Particular attention should be paid to the presence of this sclerotic margin and to focal sites of heaped-up margins, which are indicative of premature synostosis.

Plain radiographs can also be used to demonstrate overall morphology of the cranium and to identify the presence of localized problems (constricting bony bands restricting growth)

In addition, plain radiographs can be employed in identifying the presence of generalized problems (copper-beaten appearance, indicating elevated ICP). They can be used to identify other skeletal anomalies as well.

Preferred examination

Visualizing the length of all sutures is not always possible, and suture closure may be difficult to detect unless it is accompanied by an abnormal head shape.

False positives/negatives

Normal variations in the shape of the pediatric skull exist. For example, many formerly premature infants have long, narrow skulls resembling dolichocephaly but without sagittal synostosis. Many children also have asymmetrical flattening of the occiput caused by habitually lying on 1 side of the head, without underlying suture abnormalities; this is called positional molding. These 2 types of skull deformities are more common than craniosynostosis.

CT scans provide a more detailed method of visualizing intracranial pathology and detailed anatomy of the calvaria and brain parenchyma. In contrast to plain radiographs, the skull base is visualized well, and hard and soft tissues of the craniofacial skeleton can be studied in detail. (See the images below.)^{[3, 4]}

Neuroimaging is performed in children with isolated suture synostosis primarily to look for underlying brain damage or associated cerebral anomalies.

Infants with trigonocephaly may have midline anomalies (eg, holoprosencephaly).

Anomalies of the venous drainage and stenosis of the venous foramina at the skull base can occur with multisuture synostosis with syndrome- and nonsyndrome-related causes.

After abnormal or suggestive plain radiographic findings are noted, CT scans with bone windows with or without 3D reconstruction are frequently requested prior to surgical therapy.

Features such as shallow anterior fossa, deformed dystopic orbits, abnormal calvarial contour, and asymmetrical cranial base can be realistically depicted.

Degree of confidence

The sensitivity of CT scans, when combined with physical examination and plain radiography, approaches 100%.

False positives/negatives

Even on CT scans, the entire length of every suture may not be clearly visible. Once again, normal variations in skull shape may pose a problem.

MRI shows better definition of intracranial soft-tissue structures than does CT scanning. In addition, MRI is useful in the detection of hydrocephalus and cerebral developmental defects, such as myelination defects and deformities of the maxilla resulting in airway compromise.

If children with craniosynostosis have abnormalities of tone or have diminished movements, MRI should be performed, because it is the most sensitive method for detecting cortical and white matter abnormalities.

Degree of confidence

MRI is not a strong modality for evaluating bony abnormalities and thus cannot be used as the primary method of evaluating craniosynostosis. MRI is used primarily for assessing associated brainstem and soft tissue abnormalities.

The literature has shown some advancement in the prenatal detection of craniosynostosis by using 3D (versus 2D) ultrasonography. A case was reported by Krakow et al in which prenatal 2D ultrasonographic findings were consistent with craniosynostosis.^[5] After 3D ultrasonography, positional molding was suspected instead. Neonatal radiographs confirmed that the case was that of positional molding.

With 3D ultrasonography, the full length of the suture is visible, which is not possible with conventional ultrasonography. Ultrasonography can also be useful in detecting bony abnormalities associated with the syndrome-related causes of craniosynostosis.

Degree of confidence

Research is ongoing to determine the usefulness of ultrasonography as a tool in diagnosing craniosynostosis.

False positives/negatives

Ultrasonography is user dependent, and therefore, inexperienced personnel can miss the diagnosis of craniosynostosis.