# Craniosynostosis: Evaluation and Surgical Correction

## Overview

Craniosynostosis is the premature fusion of one or more cranial sutures, occurring in approximately 1 in 2000 to 2500 live births. The premature fusion restricts growth perpendicular to the fused suture and causes compensatory growth parallel to it, a principle known as Virchow's law. Cases are classified as single-suture non-syndromic, which accounts for 80 to 85 percent, or multi-suture, which may be syndromic or non-syndromic. The primary goals of treatment are to normalize head shape, prevent or treat elevated intracranial pressure, and optimize neurocognitive development.

## Anatomy of Cranial Sutures

The metopic suture runs between the two frontal bones and normally closes by 9 to 12 months of age. The sagittal suture separates the two parietal bones and is the longest suture. The coronal sutures lie between the frontal and parietal bones bilaterally. The lambdoid sutures separate the parietal and occipital bones bilaterally. The squamosal sutures run between the parietal and temporal bones. The anterior fontanelle, located at the junction of the metopic, sagittal, and coronal sutures, normally closes by 18 to 24 months. The posterior fontanelle at the junction of the sagittal and lambdoid sutures closes by 2 to 3 months.

## Cranial Vault Growth

The brain grows rapidly, reaching 65 percent of adult volume by age one and 90 percent by age three. Sutures serve as growth centers, with growth occurring perpendicular to each suture line. Premature fusion eliminates growth perpendicular to the affected suture, and compensatory expansion occurs at the remaining open sutures in directions parallel to the fused suture.

## Classification by Suture

### Sagittal Synostosis (Scaphocephaly/Dolichocephaly)

Sagittal synostosis is the most common type, representing 40 to 55 percent of cases with a 4:1 male predominance. The head shape is elongated in the anteroposterior dimension with a narrow biparietal dimension. A palpable midline ridge along the sagittal suture is characteristic, along with frontal bossing and an occipital bullet shape. The cephalic index, calculated as width divided by length times 100, falls below 75, indicating dolichocephaly, compared to the normal range of 76 to 80. Elevated ICP is uncommon in isolated sagittal synostosis.

### Metopic Synostosis (Trigonocephaly)

Metopic synostosis is the second most common type at 15 to 25 percent and appears to be increasing in incidence. It produces a triangular-shaped forehead with a midline frontal ridge, hypotelorism with narrowed interorbital distance, and lateral orbital recession creating a "quizzical" brow appearance. It must be distinguished from a normal metopic ridge, which represents physiologic closure without trigonocephaly. An interfrontal angle less than 120 to 125 degrees on CT supports the diagnosis.

### Unilateral Coronal Synostosis (Anterior Plagiocephaly)

Unilateral coronal synostosis is the third most common type at 15 to 20 percent with a female predominance. It produces ipsilateral forehead flattening with contralateral frontal bossing, harlequin deformity with elevation of the ipsilateral orbit on radiograph, nasal root deviation toward the affected side, and anterior displacement of the ipsilateral ear. It must be distinguished from positional plagiocephaly.

### Bilateral Coronal Synostosis (Brachycephaly)

Bilateral coronal fusion produces a short anteroposterior dimension with a wide biparietal dimension. Severe cases develop turricephaly, a tower-shaped head. This pattern is common in syndromic craniosynostosis including Apert and Crouzon syndromes and carries a high risk of elevated ICP.

| Suture | Skull Shape | Frequency | Key Features |
|--------|------------|-----------|--------------|
| Sagittal | Scaphocephaly (dolichocephaly) | 40-55% | Elongated AP, narrow biparietal, midline ridge |
| Metopic | Trigonocephaly | 15-25% | Triangular forehead, hypotelorism, quizzical brow |
| Unilateral coronal | Anterior plagiocephaly | 15-20% | Ipsilateral forehead flattening, harlequin eye |
| Bilateral coronal | Brachycephaly | Variable (often syndromic) | Short AP, wide biparietal, turricephaly |
| Lambdoid | Posterior plagiocephaly | 1-3% | Occipital flattening, ear displaced posteroinferiorly |

### Lambdoid Synostosis (Posterior Plagiocephaly)

Lambdoid synostosis is rare, representing only 1 to 3 percent of craniosynostosis cases. It produces ipsilateral occipital flattening with contralateral occipital bossing, and critically, the ipsilateral ear is displaced inferiorly and posteriorly, which is the opposite of positional plagiocephaly. Ipsilateral mastoid bulging is also characteristic.

### Positional Plagiocephaly vs. Lambdoid Synostosis

Positional plagiocephaly is approximately 100 times more common than lambdoid synostosis, occurring in roughly 1 in 60 infants versus 1 in 100,000. Key distinguishing features include ear position: in positional plagiocephaly the ear shifts anteriorly on the flat side, while in lambdoid synostosis it shifts posteriorly and inferiorly. The skull base is normal in positional plagiocephaly but tilted and asymmetric in synostosis. CT shows open sutures in positional cases and a fused lambdoid in true synostosis. Positional plagiocephaly is treated with repositioning and helmeting, while lambdoid synostosis requires surgery.

## Syndromic Craniosynostosis

### Apert Syndrome

Apert syndrome results from an FGFR2 gain-of-function mutation and features bilateral coronal synostosis combined with complex syndactyly of the hands and feet. Additional features include midface hypoplasia, hypertelorism, and shallow orbits. There are high rates of elevated ICP, Chiari malformation, and hydrocephalus. Cognitive impairment is common.

### Crouzon Syndrome

Crouzon syndrome is also caused by FGFR2 mutations and features bilateral coronal synostosis with midface hypoplasia. The absence of limb anomalies distinguishes it from Apert syndrome. Exorbitism, proptosis, and maxillary hypoplasia are characteristic. ICP elevation is variable.

### Pfeiffer Syndrome

Pfeiffer syndrome results from FGFR1 or FGFR2 mutations and is classified into three types. Type I is the mildest. Types II and III are most severe, with Type II featuring the cloverleaf skull deformity known as Kleeblattschadel and Type III having severe proptosis without the cloverleaf deformity. All types feature bilateral coronal synostosis with broad thumbs and great toes.

### Muenke Syndrome

Muenke syndrome is caused by the FGFR3 P250R mutation and presents with unilateral or bilateral coronal synostosis. The phenotype is mild and may be difficult to distinguish from non-syndromic cases. Sensorineural hearing loss is common.

### Saethre-Chotzen Syndrome

Saethre-Chotzen syndrome results from TWIST1 mutations and features bilateral coronal synostosis with a low-set hairline, ptosis, small ears, and brachydactyly.

## Diagnostic Workup

### Clinical Examination

Assessment includes head shape evaluation from all angles including vertex, anterior, posterior, and lateral views. Palpation identifies ridging at the fused suture. Head circumference and growth trajectory are documented. Ophthalmologic examination assesses for papilledema indicating elevated ICP. A full dysmorphology examination evaluates hands, feet, and facies to identify syndromic features. Developmental milestones are assessed.

### Imaging

CT scan with three-dimensional reconstruction is the gold standard for confirming suture fusion, showing absent lucency with bony bridging at the fused suture. Three-dimensional CT demonstrates skull shape and suture status. Low-dose protocols minimize radiation. Skull radiographs can show suture closure but have limited sensitivity. Ultrasound provides a non-radiation alternative in infants for assessing suture patency. MRI is not used for suture assessment but evaluates brain parenchyma, Chiari malformation, and hydrocephalus in syndromic cases.

### ICP Assessment

Direct ICP monitoring is indicated in multi-suture or syndromic cases. Papilledema on fundoscopy suggests chronically elevated ICP. A copper-beaten or thumbprinting pattern on skull radiographs indicates chronic ICP elevation.

## Surgical Treatment

### Timing

Endoscopic strip craniectomy is ideally performed at 2 to 4 months of age, before 6 months. Open vault remodeling is typically performed at 6 to 12 months of age. Earlier intervention allows more brain-driven remodeling, while later intervention permits more definitive reshaping. Syndromic cases may require multiple staged procedures.

### Endoscopic Strip Craniectomy with Postoperative Helmeting

The technique uses small 2 to 3 centimeter incisions over the fused suture. An endoscope-assisted suturectomy removes a strip of bone along the fused suture, and barrel-stave osteotomies in adjacent bone provide immediate width correction for sagittal cases. Blood loss is minimal, typically less than 50 milliliters, with operative time of 45 to 90 minutes. Postoperatively, a custom molding helmet is worn 23 hours per day for 6 to 12 months to guide skull growth.

Advantages include less invasiveness, less blood loss, shorter hospital stay of 1 to 2 days, and lower transfusion rates. Disadvantages include the requirement for early diagnosis before 4 to 6 months, strict helmet compliance, and less immediate correction since it relies on brain growth. This approach works best for sagittal and metopic synostosis diagnosed early, with expanding use for coronal synostosis.

### Open Cranial Vault Remodeling

For sagittal synostosis, options include Pi plasty with lateral barrel-stave osteotomies, total vault remodeling where biparietal bone flaps are removed, reshaped, and reattached with absorbable plates, and spring-assisted cranioplasty using internal spring devices to gradually expand the vault after osteotomies.

For metopic synostosis, frontal-orbital advancement and remodeling involves a bifrontal craniotomy, removal and reshaping of the frontal bone and supraorbital bar, anterior advancement of the bar, and widening to correct the trigonocephaly and hypotelorism, with fixation using absorbable plates and sutures.

For coronal synostosis, frontal-orbital advancement is the standard approach. Unilateral cases require asymmetric advancement, advancing the recessed side and setting back the bossed side. Bilateral cases involve symmetric advancement of the entire forehead.

For lambdoid synostosis, posterior vault distraction or remodeling is performed, though approaches are less standardized given the rarity of the condition.

General principles of open surgery include awareness that blood loss can be significant, reaching 50 to 100 percent of blood volume in infants, necessitating type and crossmatch with cell saver availability. ICU monitoring is standard postoperatively. Absorbable fixation is preferred in infants because rigid titanium plates may restrict growth or migrate intracranially. Hospital stay is typically 3 to 5 days.

### Posterior Vault Distraction Osteogenesis

This emerging technique for syndromic cases or posterior deformities involves osteotomy followed by placement of internal distraction devices. Gradual distraction over 6 to 8 weeks expands the vault, followed by a second surgery for distractor removal. The advantage is achieving greater expansion than single-stage remodeling.

### Midface Advancement

Le Fort III or monobloc osteotomy with distraction is performed for syndromic cases after cranial vault procedures, typically at age 6 to 12 years. It addresses midface hypoplasia, exorbitism, and airway obstruction. The complication rate is high, and these procedures are performed at specialized craniofacial centers.

<image>Clinical photographs showing anterior and vertex views of an infant with sagittal craniosynostosis (scaphocephaly), demonstrating the elongated dolichocephalic head shape with a palpable midline sagittal ridge, narrow biparietal dimension, frontal bossing, and occipital bullet deformity</image>

<image>Three-dimensional CT reconstruction of an infant skull with right unilateral coronal craniosynostosis, showing the fused right coronal suture with ipsilateral forehead flattening, contralateral frontal bossing, harlequin eye deformity with elevation of the right lesser sphenoid wing, and nasal root deviation toward the affected right side</image>

<image>Intraoperative photograph during fronto-orbital advancement and remodeling for metopic craniosynostosis, showing the bifrontal bone flap and supraorbital bar removed and reshaped on the back table, with the dura exposed and the original trigonocephalic bone pieces being recontoured and widened before replating with absorbable fixation</image>

## Clinical Pearls

Positional plagiocephaly is approximately 100 times more common than lambdoid synostosis; distinguish them clinically by ear position, with anterior shift in positional and posterior or inferior shift in synostotic cases. Endoscopic strip craniectomy is time-sensitive and ideally performed before 4 to 6 months of age; after 6 months, open vault remodeling becomes the preferred approach. Blood loss in open cranial vault remodeling can approach or exceed the infant's total blood volume, making meticulous surgical hemostasis and prepared blood products essential. Multi-suture and syndromic craniosynostosis carry a much higher risk of elevated ICP than single-suture cases, and these children need long-term monitoring including fundoscopy. A palpable metopic ridge alone is not craniosynostosis; true metopic synostosis presents with trigonocephaly, hypotelorism, and orbital recession, and the condition should not be over-diagnosed or over-treated based on a normal variant. Absorbable plates and sutures are preferred for fixation in infants because titanium plates can migrate intracranially through the growing skull or restrict growth at fixation sites. Genetic testing is indicated for all multi-suture synostosis and suspected syndromic cases, as FGFR and TWIST mutations have specific implications for recurrence risk and associated anomalies.

## References
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