• Clinical science

Craniosynostosis

Abstract

Craniosynostosis (CS) is the premature fusion of one or more cranial sutures. It is caused by a mutation in genes that code for fibroblast growth factor. Most affected infants are asymptomatic; CS is usually recognized based on an abnormal head shape in the first year of life. The shape of the skull is determined by which suture is prematurely fused, of which the sagittal suture (scaphocephaly) is the most commonly affected. When multiple sutures are involved, CS may cause hydrocephalus and/or cerebral constriction. Diagnosis is clinical, with skull x-ray and CT scan helping to assess the extent of fusion. Surgery is recommended in all infants for cosmetic reasons and to treat/prevent intracranial complications.

Epidemiology

  • Incidence: 1/2500 births
  • Potential risk factors
    • Hereditary (positive family history)
    • Advanced maternal age
    • Nicotine use during pregnancy
    • Use of clomiphene citrate (used for infertility treatment)

References:[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

  • Mutation in genes which encode for the fibroblast growth factor (FGF), FGF receptor, and/or transforming growth factor beta (TGF-β
    • Sporadic mutation (more common) or
    • Hereditary genetic defect
  • Altered FGF, FGF receptor, or TGF-β signaling between the dura mater and mesenchyma of the suture → premature fusion of the skull suture(s)

References:[3][4][5]

Pathophysiology

  • The skull is composed of 5 separate bones: 2 frontal bones, 2 parietal bones, and the occipital bone
  • In a newborn, these bones are separated by patent sutures and fontanelles.
    • Sutures: Most sutures begin to close by 12 years of age; complete suture closure occurs at ∼ 40 years of age.
      • Vertical sutures
        • Metopic suture: between the 2 frontal bones
        • Sagittal suture: between the 2 parietal bones
      • Horizontal sutures
        • Coronal suture: between each frontal and parietal bone
        • Lambdoid suture: between the occipital bone and each parietal bone
    • Fontanelles
      • Anterior fontanelle: at the junction where the 2 frontal and the 2 parietal bones meet; closes between 9–18 months
      • Posterior fontanelle: at the junction between the occipital bone and the 2 parietal bones; closes between 3–6 months
      • Anterolateral fontanelle: one on either side; at the junction of the frontal, parietal, temporal, and sphenoid bones; closes at 3 months
      • Posterolateral fontanelle: one on either side; at the junction of the parietal, temporal, and occipital bone; closes at 2 years
  • Function of patent sutures and fontanelles
    • Allow compression and/or overlapping of the skull bones during childbirth
    • Allow for growth of the brain
  • Premature closure of one or more sutures → craniosynostosis


References:[3][6]

Clinical features

  • Usually asymptomatic
  • Recognized as an abnormal head shape within the first year of life
Skull deformity due to premature fusion Suture/s involved Features

Scaphocephaly/dolichocephaly

(sagittal synostosis)

  • Sagittal suture
  • Most common type of CS (∼ 45%)
  • Long, narrow skull (boat-shaped)

Anterior plagiocephaly

(unilateral coronal synostosis)

  • Unilateral coronal suture
  • 2nd most common type of CS
  • Laterally twisted/oblique skull and face

Posterior plagiocephaly

(unilateral lambdoid synostosis)

  • Unilateral lambdoid suture
  • Least common type of CS
  • Twisted/oblique skull
  • Occipitoparietal flattening on the affected side
  • Low-set ears on the affected side
Trigonocephaly
  • Metopic suture
  • Common type of CS (∼ 25% of cases)
  • Triangular shaped head
  • Prominent occiput and parietal eminences
  • Close-set eyes (hypotelorism)
Brachycephaly
  • Bilateral coronal sutures
  • Short, broad, flattened skull

Oxycephaly

(turricephaly)

  • Bilateral coronal sutures (if left untreated)
  • Long skull (increased craniocaudal dimension)

Kleeblattschädel

(cloverleaf skull)

  • Multiple cranial sutures (esp. the metopic, coronal, and lambdoid sutures)


References:[1][7][8][9][10][11]

Diagnostics

  • Mainly a clinical diagnosis
  • Skull x-ray (AP and lateral views): bony suture bridges or lack of suture clarity
  • Cranial CT (with 3D reconstruction)
    • To assess extent of CS
    • To identify hydrocephalus
    • Helps plan surgical reconstruction

References:[1][9]

Differential diagnoses

The following conditions show patency of sutures similar to craniosynostosis on skull x-ray or ultrasound:

References:[10]

The differential diagnoses listed here are not exhaustive.

Treatment

  • Surgery: indicated in all patients either to minimize cerebral constriction or for cosmetic reasons
    • Strip craniectomy or cranial vault remodeling
    • Timing: controversial; mostly recommended at 3–9 months of age

References:[2][3]