Craniosynostosis

Definitions and Epidemiology

Definitions

• Craniosynostosis: premature fusion of 1 ⩲ cranial sutures, causing an abnormal shaping of the skull 
• Scaphocephaly: elongated skull with frontal bossing, often due to fusion of sagittal sutures 
• Plagiocephaly: flattening of half of the forehead with raising of ipsilateral eyebrow due to unilateral coronal suture fusion
• Trigonocephaly: triangular-shaped forehead with prominent midline ridge caused by fusion of the metopic suture
• Brachycephaly: shortened skull that is wider and taller than normal due to bilateral coronal suture fusion
• Oxycephaly: tall cranium due to inadequately treated brachycephaly
• Acrocephaly: elevation of the anterior skull due to combined fusion of lambdoid, sagittal, and coronal sutures

Classification

• Simple versus complex:
  • Simple: A single suture fuses.
  • Complex or compound: Multiple sutures fuse.
• Primary versus secondary:
  • Primary: premature closure due to abnormalities of skull development
  • Secondary: closure due to failure of brain growth and expansion

Epidemiology

• Incidence:
  • 1 in 2,000 live births in the United States
  • 1 in 2,500 live births worldwide
  • No gender or racial predilection
• Scaphocephaly (sagittal suture) is the most common.
• 85% of cases are simple.
• 10%–20% of cases are associated with genetic syndromes.
• Complex cases tend to be associated with other malformations.

Etiology and Pathophysiology

Etiology

Nonsyndromic:

• Genetic mutations:
  • Caused by gene mutations of fibroblast growth factor (FGF), FGF receptor, or transforming growth factor beta (TGF-β)
  • Alters communication between the dura mater and mesenchyma of suture
  • Can be hereditary
• Environmental influence:
  • Advanced maternal age
  • Nicotine use in pregnancy
  • Clomiphene citrate in pregnancy

Syndromic:

• Crouzon syndrome:
  • Most common
  • Bilateral coronal craniosynostosis
  • Midfacial abnormalities
  • Hydrocephalus
  • Exophthalmos 
  • Airway obstruction
  • Mutation localized in GFR2 gene
• Apert syndrome:
  • Coronal craniosynostosis
  • Hand, elbow, hip, and knee deformities 
  • Exophthalmos
• Carpenter syndrome:
  • Lambdoid and sagittal craniosynostosis
  • Limb abnormalities (syndactyly) 
• Pfeiffer syndrome:
  • Unicoronal craniosynostosis
  • Facial deformities
  • Limb abnormalities
  • Exophthalmos
  • Hearing loss

Pathophysiology

• Skull is made up of 5 separate bones:
  • 2 frontal bones
  • 2 parietal bones
  • Occipital bone
• In infants → bones are separated by open sutures and fontanelles (anterior and posterior). 
• During childbirth → skull bones overlap and compress at sutures and fontanelles to allow delivery of head through vaginal canal.
• After birth → sutures remain open to allow for brain growth.
• Craniosynostosis is due to inappropriate closure of sutures.

Clinical Presentation

Aside from an abnormally shaped head, most patients are asymptomatic. Careful exam should be performed to evaluate for signs of increased intracranial pressure including developmental delay.

Diagnosis and Management

Diagnosis

Diagnosis relies on clinical observation, but imaging may be used to further characterize anatomy for classification or surgery

• Ultrasound of the head is preferred due to lack of radiation: can give a prenatal diagnosis
• CT scan of the head
• X-rays of skull
• DNA testing to look for underlying genetic disorders

Management

Molded helmet:

• For mild cases
• Reshapes head

Surgical intervention: 

• Goals:
  • Give brain room to grow
  • Release developing intracranial pressure (pseudotumor cerebri)
  • Correction of appearance
• Needed in:
  • Hydrocephalus
  • ↑ intracranial pressure
• Options available include:
  • Shunting
  • Ventriculoperitoneal shunting 
  • Ventriculopleural shunting

Prognosis

• Simple cases: 5% risk of recurrence
• Complex cases: up to 50% risk of recurrence
• Recurrence is ↑ in presence of genetic syndromes

Complications

• Permanent facial deformity
• Poor self-esteem
• ↑ intracranial pressure can lead to:
  • Developmental delay
  • Cognitive impairment
  • Lethargy
  • Seizures
  • Death

Differential Diagnosis

• Positional plagiocephaly: a common occurrence in infants that presents as a flat spot on a baby’s head that is caused by the baby spending too much time lying on their back. Positional plagiocephaly does not affect brain development or create increased intracranial pressure. The condition is treated by changing the position of the head and/or using a helmet in severe cases. 
• Infant torticollis: contracture of the sternocleidomastoid muscle due to abnormal fetal positioning or birth trauma. Typically noted by one month of age when the head is tilted to one side. The condition can be associated with facial asymmetry. Treatment is physical therapy and reassuring parents as the condition typically resolves by 6 months of age.