Craniosynostosis

Nov 27, 2021 7 min read
Craniosynostosis

Craniosynostosis is the premature fusion of one or more cranial sutures. It most commonly involves the sagittal suture. It can be isolated or part of a syndrome.

In This Article on Craniosynostosis

  1. Definition
  2. Genetics
  3. Physiology and Anatomy  
  4. Describing an Abnormal Head Shape
  5. Raised Intra-Cranial Pressure
  6. Radiological Investigations
  7. Syndromic Craniosynostosis
  8. Treatment
  9. Author and References


5 Key Points on Craniosynostosis

1. What is Craniosynostosis?

Craniosynostosis is the premature fusion of one or more cranial sutures. It can be an isolated abnormality or part of a syndrome.

2. What causes Craniosynostosis?

The majority of conditions are non-syndromic/isolated craniosynostosis. The most common genetic mutation is FGFR. Risk factors include family history, male gender and intra-uterine pathology.

3. When do cranial sutures normally fuse?

The first cranial suture to fusion is the metopic at ~6-9 months. Other fusion times are sagittal at 22 years (most common), coronal at 24 years, lambdoidal at 26 years.

4. What is Virchow's Law?

Virchow's Law states that premature suture fusion results in cranial growth predominantly parallel to sutures. It does not occur perpendicular.

5. What are the indications for treatment?

The indications and goals of treatment is to correct abnormal headshape/skull deformity, treat or prevent raised intracranial pressure, expand the intracranial volume, and protect the airway and cornea.


Definition of Craniosynostosis

Craniosynostosis is the premature fusion of one or more cranial sutures. It can be an isolated abnormality or part of a syndrome.


Genetics of Craniosynostosis

The incidence of craniosynostosis is ~1 in 2500 births. The majority are non-syndromic/isolated craniosynostosis with only ~20% have genetic aetiology.

The common genetic mutations are related to FGFR. Other genetic causes include TWIST, TCF12, ERF, EFNB1, RAB23, POR, IL11RA. This is described in the table below.

Genetic Mutations in Craniosynostosis, FGFR1, FGFR2, FGFR3, TWIST1, POR, RAB23, mutations, genetic, craniosynostosis, syndrome, Pfieffer, Crouzen, Apery, Muenke, Saethre-Chotzen, Antley-Bixlery, Carpenter, clinical features
Genetic Mutations in Craniosynostosis

There are specific risk factors for developing craniosynostosis. These include:

  • Family history
  • Advanced maternal age
  • Use of clomiphene citrate for infertility
  • Pregnancy-related issues: smoking, hydrocephalus, hypothyroidism.
  • Male gender


Physiology of Craniosynostosis

Cranial Growth

The cranium grows as the brain and CSF volume increases. This growth occurs via:

  1. Apposition: deposition of bone from the innner surface to the outer surface
  2. Sutural: perpendicular to the sutures.

Virchow's Law

Virchow's Law states that premature suture fusion results in cranial growth predominantly parallel to sutures. It does not occur perpendicular.

Virchow's Law for Craniosynostosis, Virchow's Law, Craniosynostosis
Virchow's Law for Craniosynostosis

This means that each fusion pattern has a characteristic skull shape. This is discussed in more detail in the Clinical Features section.

Theories

  • Suture abnormality realting to the osteoinductive properties of the dura mater
  • Abnormalities in the skull base results in abnormal tension on the cranial base exterted through the dura mater.


Anatomy of Craniosynostosis

The skull is constructed of 2 frontal bones, 2 parietal bones, and one occipital bone. In newborns, these bones are separated by patent sutures and fontanelles. The function of these fontanelles and patent sutures:

  • Allow for brain growth
  • Overlapping of skull bones during labor

The normal cranial suture anatomy can be visualized below.

Cranial Sutures, Skull Anatomy, Anatomy, Skull, Sutures, Fontanelles, Metopic Suture, Coronal Suture, Saggital Suture, Squamosal Suture, Lambdoidal Suture, Posterior Fontanelle, Anterior Fontanelle
Anatomy of Craniosynostosis

The premature fusion of one or more sutures leads to craniosynostosis. The normal timeline of cranial suture and fontanelle fusion is depicted below.

Cranial Sutures, Skull Anatomy, Anatomy, Skull, Sutures, Fontanelles, Metopic Suture, Coronal Suture, Saggital Suture, Squamosal Suture, Lambdoidal Suture, Posterior Fontanelle, Anterior Fontanelle
Timeline of Cranial Suture Fusion

Craniosynostosis usually begins during pregnancy or the first year of life. It's usually complete by 3 years of age. Important dates in "normal" fusions and closures

  • Posterior Fontanelle: 3-6 months
  • Metopic: 6-8 months
  • Anterior Fontanelle: 9-12 months.
  • Sagittal: 22 years (most commonly involved)
  • Coronal: 24 years
  • Lambdoidal: 26 years
  • Squamosal: approximately 60 years


Abnormal Head Shapes

Craniosynostosis results in an abnormal head shape. The condition can be described in relation affected suture or the resultant shape.

Each pattern of fusion has a characteristic skull shape because of Virchow's Law. For example, the fusion of the sagittal suture makes the skull grow parallel to this suture, which results in an elongated shape.

This is described in more detail below.

Clinical Features of Craniosynostosis, Scaphocephaly, Plagiocephaly, Trigonocephaly, Bracycephaly
Clinical Features of Craniosynostosis

It can be difficult to remember the shapes of each condition. The best way is to understand Virchow's Law.

Abnormal Skull Shapes in Craniosynostosis
Abnormal Skull Shapes in Craniosynostosis, Scaphocephaly, Plagiocephaly, Trigonocephaly, Bracycephaly

Another way is also to understand the translations of the words. These are detailed below.

Make it easier to remember!!

It is worth noting, synostosis can also cause specific facial features because of the connection between the face and the skull base. For example:

  • Midface hypoplasia
  • Recession of front-orbital rim leading to ocular issues.
  • Palpable ridges from thickening of closed sutures
  • Bulging fontanelles (Volcano Sign)


Raised Intracranial Pressure

Premature fusion of the cranial sutures can result in raised intracranial pressures >15mmHg. There is an increased risk with multiple suture synostosis.

Causes in Craniosynostosis

  • Cephalocranial disproportion: a decrease in intracranial volume and a restriction in brain growth
  • Intracranial venous congestion
  • Hydrocephalus
  • Upper Airway obstruction
  • Chiari Malformation

Clinical Features

  • Head: headaches, irritability, seziures
  • Eyes: papilloedema, optic atrophy
  • Abdomen: Vomiting


Investigations

Craniosynostosis is mainly a clinical diagnosis recognized by an abnormal head shape during the first year of life. Investigations are used for diagnosis, pre-operative planning and monitoring.

Radiology

There are different radiological investigations at the clinicians disposal.

Skull x-ray

  • AP, lateral and Townes projection and C-spine.
  • May demonstrate bony suture bridges or a lack of suture clarity.  
  • Harlequin Sign is seen on AP view for Coronal Synostoses
  • "Thumb printing" from gyri pressure on inner table.

Cranial CT with 3D reconstruction

  • Better understanding of suture fusion, intracranial volume and morphology.
  • Should be considered to plan for surgery
  • Can assess for the presence of hydrocephalus

Radiological Features of Craniosynostosis, Scaphocephaly, Plagiocephaly, Trigonocephaly, Bracycephaly
Radiological Features of Craniosynostosis on CT with 3D reconstructions

Transorbital ultrasound

  • Measure the diameter of the optic nerve sheath.
  • Increased ICP in cases such as craniosynostosis usually leads to the increased diameter of the optic nerve sheath.

MRI

  • Not routinely used
  • Can be considered for specific syndromes or concerns for specific pathologies, such as anomalous venous drainainge.

Additional Investigations

Adjunctive investigations can help in certain circumstances. These include

  • Fundoscopy:  assess for papilledema
  • Direct Intraparenchymal monitoring: ICP monitoring


Syndromic craniosynostosis

The majority of synostosis are non-syndromic. Generally speaking, the syndromic conditions have similar features, which include:

  • Autosomal dominant (except Carpenter and Antley-Bixter)
  • Abnormal Facies
  • Limb Abnormalities.

Crouzon syndrome (Most Common)

  • Genetics: Autosomal dominant FGFR2 mutation
  • Clinical features:  hydrocephalus, bicoronal synostosis, exorbitism, midface hypoplasia, and conductive hearing loss

Apert syndrome:

  • Genetics:  Autosomal dominant (although most cases are sporadic)
  • Clinical features: ICP elevation, parrot-beak deformity, severe midface hypoplasia, cleft palate, and upper & lower limb complex syndactyly.

Pfeiffer syndrome:

  • Genetics: Autosomal dominant FGFR2 (most common & severe) or FGFR1.
  • Clinical features: obstructive sleep apnea, broad thumbs/toes.

Saethre-Chotzen syndrome:

  • Genetics: Autosomal dominant mutation in TWIST-1 gene
  • Clinical features: low frontal hairline, ptosis of eyelids, and prominent crus helicis. Midface hypoplasia is less common.

Muenke syndrome:

  • Genetics: Autosomal dominant mutation with variable expression.
  • Cinical Features: Developmental delay and sensorineural hearing loss.
  • NB: not all patients with Muenke syndrome suffer from craniosynostosis


Treatment of Craniosynostosis

The treatment of craniosynostosis is centred on a multi-disciplinary team involving a plastic surgeon, ENT, orthodontist, speech therapist, child psychologist, and nurses.

Indications for Treatment

  • To correct abnormal headshape/skull deformity
  • Treat or prevent raised intracranial pressure
  • Expand the intracranial volume
  • Protect the airway and cornea.

Timing of Treatment

There is no consensus on when to do surgery. Most guidelines agree on 3-12 months. However, this is depedendent on factors such as: rasied ICP, syndromic, single vs multiple sutures.

Treatment Options

The goal of this article is not to perform a deep-dive on specific surgical techniques. Nonetheless, it is important to be aware of the following options:

  • Cranial Vault Remodelling and Reconstruction
  • Sagittal Strip Craniectomy.
  • Fronto-orbital advancements
  • Midfacer/Le-Fort III advancements
  • Orthognathic Surgery
  • Facial Contouring
  • Skeletal Distraction


References

Primary Contributor:

Dr Abdulrahman Abdulaziz Alghamdi, King Fahad University Hospital.

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2.     Brah TK, Thind R, Abel DE. Craniosynostosis: Clinical Presentation, Genetics, and Prenatal Diagnosis. Obstet Gynecol Surv. 2020 Oct;75(10):636-644. doi: 10.1097/OGX.0000000000000830. PMID: 33111964.

3.     Kirmi O, Lo SJ, Johnson D, Anslow P. Craniosynostosis: a radiological and surgical perspective. Semin Ultrasound CT MR. 2009 Dec;30(6):492-512. doi: 10.1053/j.sult.2009.08.002. PMID: 20099636.

4.     Dempsey RF, Monson LA, Maricevich RS, Truong TA, Olarunnipa S, Lam SK, Dauser RC, Hollier LH Jr, Buchanan EP. Nonsyndromic Craniosynostosis. Clin Plast Surg. 2019 Apr;46(2):123-139. doi: 10.1016/j.cps.2018.11.001. Epub 2019 Jan 30. PMID: 30851746.

5.     Sawh-Martinez R, Steinbacher DM. Syndromic Craniosynostosis. Clin Plast Surg. 2019 Apr;46(2):141-155. doi: 10.1016/j.cps.2018.11.009. PMID: 30851747.

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