Craniosynostosis

Craniosynostosis is the premature fusion of one or more cranial sutures, occurring before the cessation of brain growth.

• Incidence: Approx 1 in 2,000 to 2,500 live births.
• Virchow’s Law: The primary principle governing the skull deformity.
  • Skull growth is restricted in the plane perpendicular to the fused suture.
  • Compensatory overgrowth occurs at the patent sutures parallel to the fused suture to accommodate brain expansion.

Classification

Craniosynostosis is classified based on etiology and the number of sutures involved.

1. Based on Etiology

• Primary (Isolated): Due to intrinsic defect in the suture (genetic/developmental). Most common.
• Secondary: Due to underlying systemic pathology or mechanical constraint.
  • Metabolic: Hyperthyroidism, Rickets, Hypophosphatasia, Mucopolysaccharidosis.
  • Hematologic: Thalassemia, Sickle cell anemia (marrow expansion).
  • Mechanical: Microcephaly (failure of brain growth), shunted hydrocephalus (over-drainage).
  • Teratogens: Valproate, Phenytoin, Fluconazole.

2. Based on Complexity

• Simple: Involvement of a single suture (e.g., Sagittal).
• Complex: Involvement of two or more sutures (e.g., Bilateral Coronal, Pansynostosis).

3. Based on Clinical Association

• Non-Syndromic: Isolated anomaly (approx 75-85% of cases).
• Syndromic: Associated with other extracranial anomalies/genetic syndromes (approx 15-25% of cases).

Syndromes Associated with Craniosynostosis

Most syndromic cases are Autosomal Dominant and involve mutations in Fibroblast Growth Factor Receptors (FGFR) or Transcription factors (TWIST).

Major Craniosynostosis Syndromes (The "Big 5")

Other Syndromes

• Muenke Syndrome (FGFR3): Uni/bilateral coronal synostosis, sensorineural hearing loss.
• Antley-Bixler Syndrome: Brachycephaly + radiohumeral synostosis.
• Baller-Gerold Syndrome: Craniosynostosis + radial aplasia.

Clinical Characteristics of Common Types

Clinical features depend on the specific suture fused. The diagnosis is primarily clinical, supported by skull shape.

1. Sagittal Synostosis (Scaphocephaly / Dolichocephaly)

• Frequency: Most common type (40-55%).
• Suture: Sagittal (midline longitudinal).
• Pathology:
  • Restricted lateral growth (width).
  • Compensatory AP growth (length).
• Clinical Features:
  • Head Shape: Elongated, narrow skull ("Boat shaped").
  • Forehead: Frontal bossing (prominent forehead).
  • Occiput: Prominent ("Bullet" occiput).
  • Palpation: Midline bony ridge over the sagittal suture.
  • Neurology: Usually normal ICP; low risk of cognitive delay.

2. Metopic Synostosis (Trigonocephaly)

• Frequency: 2nd or 3rd most common.
• Suture: Metopic (midline frontal).
• Pathology:
  • Restricted lateral growth of the forehead.
  • Compensatory biparietal widening.
• Clinical Features:
  • Head Shape: Triangular forehead (viewed from above).
  • Eyes: Hypotelorism (decreased distance between eyes).
  • Eyebrows: Lateral up-slanting ("Spock" eyebrows) or pinching.
  • Palpation: Prominent midline vertical ridge on the forehead (Keel-shaped).
  • Differentiation: Distinguish from benign metopic ridge (no hypotelorism/trigonocephaly).

3. Unilateral Coronal Synostosis (Anterior Plagiocephaly)

• Frequency: 20-25%.
• Suture: One coronal suture (left or right).
• Pathology:
  • Restricted AP growth on the affected side.
  • Compensatory growth on the contralateral side.
• Clinical Features:
  • Forehead: Flattened/recessed on the affected side; bossing on the contralateral side.
  • Eyebrow: Elevated and recessed on the affected side.
  • Nose: Root deviates towards the unaffected side; Tip deviates towards the affected side.
  • Radiology Sign: "Harlequin Eye" deformity on X-ray/CT (elevation of the lesser wing of sphenoid).
  • Ear: Ipsilateral ear may be anteriorly displaced.

4. Bilateral Coronal Synostosis (Brachycephaly)

• Frequency: Often syndromic (Crouzon/Apert).
• Suture: Both coronal sutures.
• Pathology:
  • Total restriction of AP growth.
  • Compensatory vertical and lateral growth.
• Clinical Features:
  • Head Shape: Short, wide skull.
  • Occiput: Flat ("Turricephaly" or Tower skull if significant vertical growth occurs).
  • Face: Flat midface, supraorbital recession.
  • Complications: High risk of raised ICP and hydrocephalus.

5. Lambdoid Synostosis (Posterior Plagiocephaly)

• Frequency: Very rare (must distinguish from positional plagiocephaly).
• Suture: Unilateral lambdoid.
• Clinical Features:
  • Occiput: Flattened on the affected side.
  • Ear: Displaced posteriorly and inferiorly on the affected side (Key differentiator from positional molding where the ear moves anteriorly).
  • Trapezoid Sign: Viewed from above, head shape is trapezoidal.

Summary of Deformities