Brachycephaly

Etiology

Positional (non-Synostotic)/Deformational Brachycephaly

The cranial sutures or fibrous joints that separate the cranium bones do not fuse or ossify at birth. This ensures the essential event of volumetric growth and development of the brain postnatally. As a result, a newborn skull retains its ability to mold in the initial months of life and is, therefore, susceptible to the deformational effects of external force. The frequent practice of placing an infant in a supine sleeping position can lead to a symmetrical flattening of the occipital bone, resulting in positional or deformational brachycephaly.[7] A unilateral flattening of the occipital bone in infants may result in deformational plagiocephaly, a related positional skull deformity. Positional brachycephaly may also be observed at the time of birth in some infants. This may be attributable to prolonged labor or intrauterine fetal head constraint due to factors such as abnormal intrauterine position, multiple gestations, oligohydramnios, and congenital or acquired structural anomalies of the uterus.[8]

Brachycephaly Due to Craniosynostosis (Synostotic Brachycephaly)

The skull consists of the neurocranium and the viscerocranium (splanchnocranium). The neurocranium forms a protective shell surrounding the brain and the brainstem, while the facial bones form the viscerocranium (or facial skeleton).[9] The neurocranium consists of the cranial vault (calvaria) and the chondrocranium (skull base). The bones that constitute the chondrocranium mineralize by endochondral ossification, which is the replacement of cartilage by the bone matrix. The calvaria bones originate from intramembranous ossification, which involves direct mineralization of mesenchymal connective tissue without needing a transitional cartilaginous component.

Premature abnormal mineralization of the cranial sutures, which can occur between the calvaria bones, results in craniosynostosis. Bilateral premature mineralization of the coronal sutures leads to bi-coronal craniosynostosis, referred to as anterior brachycephaly.[10] Unilateral premature mineralization of the coronal suture in infants results in anterior plagiocephaly, a related skull deformity. Genetic abnormalities such as fibroblast growth factor receptor type-2 (FGFR-2) and type-3 (FGFR-3), twist homolog-1 (TWIST1), and ephrin-B1 (EFNB1) gene mutations may predispose an infant to craniosynostosis.[11] Fibroblast growth factor receptor type-2 plays an integral role in the abnormality, although the exact etiology remains unclear. Fibroblast growth factors (FGFs) participate in the differentiation, cell proliferation, migration, and regulation of normal bone morphogenesis.[12] These mutations may be clinically syndromic or non-syndromic.[10] Clinical syndromes with craniosynostosis include Crouzon syndrome, Apert syndrome, Pfeiffer syndrome, Saethre-Chotzen syndrome, Antley-Bixler syndrome, and Muenke syndrome.[13][14]

Epidemiology

Positional brachycephaly or plagiocephaly is the most common head-shape abnormality, affecting between 20% and 50% of infants in the United States.[1][15][16] Approximately 20% of cases of positional plagiocephaly may be observed at the time of birth. In comparison, 80% of the cases present within the first 3 months of life as an acquired postnatal cranial deformation.[17] Positional plagiocephaly is more common in male children.[17] Up to 93% of infants with positional plagiocephaly will also have some degree of torticollis, which the average physician often underrates.[18] Synostotic brachycephaly, resulting from bicoronal synostosis, occurs in around 3% of non-syndromic synostoses and has a higher prevalence of around 0.5 per 10000 live births in syndromic synostosis.[19][20] Lambdoid craniosynostosis is relatively rare, with a reported incidence of 1% to 9% of cases of craniosynostosis.[21]

History and Physical

It is essential to differentiate between non-synostotic (brachycephaly or plagiocephaly) and synostotic (bi-coronal or bi-lambdoid synostosis) infant head shape abnormalities by taking a detailed history in combination with an astute physical examination. Important questions include:

• Family history of abnormal head shapes
• Prenatal exposure to teratogens
• When the abnormality was first observed
• History of intrauterine fetal head constraints
• Birth history

Physical examination should include measuring the infant's head circumference, palpating the sutures for evidence of ridging, and examining the fontanelles to assess elevated intracranial pressure. The infant's head should be assessed from the anterior view, posterior view, lateral view, and, importantly, from the vertex (top of the head). Anthropometric measurements using cranial calipers provide vital information on head length, width, and occipitofrontal transcranial diameters. A complete neurological examination should also be performed. Indices such as the cephalic index (ie, the ratio of maximum width to the maximum length of the skull) and the cranial vault asymmetry index (ie, the percentage difference between the diagonal dimensions of the skull) may provide helpful information on the degree of severity of an infant's head shape abnormality.

Positional brachycephaly is characterized by bilateral/symmetrical flattening of the occiput, widening of the posterior skull, bilateral temporal bossing, and a round face. There is usually evidence of sutural ridging (bi-coronal or bi-lambdoid craniosynostosis) with synostotic brachycephaly. In lambdoid craniosynostosis, there may be an associated sutural trough rather than an expected ridge. Bicoronal synostosis is often associated with turricephaly; the forehead appears somewhat towered with seemingly shallow orbits and a shortened nasal bone. Some infants with bicoronal synostosis resulting in brachycephaly may have peri-orbital findings, including Harlequin eye signs and exophthalmos.[10] 

The Harlequin eye sign is characterized by the affected side having a higher supra-orbital margin than the unaffected side. During the physical examination, it is essential to determine whether or not other craniofacial or systemic abnormalities are present, including mid-face hypoplasia, abnormal facies, or limb abnormalities, which may indicate the presence of an associated syndrome.[22] Patients with syndromic craniosynostosis may also present with elevated intracranial pressure (ICP), obstructive sleep apnea, hearing disabilities, visual impairment, dental malocclusion, ventricular dilatation, and Chiari malformations.[23] Determining whether urgent or elective treatment is required is also essential.[22]

Positional Plagiocephaly

Positional plagiocephaly produces a parallelogram head-shape deformity. The affected side will have occipital flattening and associated bossing of the ipsilateral frontal region and contralateral occipital region. The ear position will be pushed forward, and the mastoid will have a normal appearance. 

Posterior Plagiocephaly Secondary to Unilateral Lambdoid Craniosynostosis 

Posterior plagiocephaly produces a trapezoid head-shape deformity. Similar to positional plagiocephaly, the affected side will have occipital flattening. In contrast to positional plagiocephaly, there will be associated bossing of both the contralateral frontal and contralateral parietal regions. The ear position will be backward, and the mastoid will be bulging and positioned downward. 

Bilateral Lambdoid Craniosynostosis 

The presentation of bilateral lambdoid suture craniosynostosis is that of brachycephaly, with both ears displaced inferiorly and anteriorly.[21]

Bicoronal Craniosynostosis 

The presentation of bi-coronal craniosynostosis is turricephaly, with a towered forehead, seemingly shallow orbits, and a shortened nasal bone. 

Anterior Plagiocephaly

Anterior plagiocephaly is secondary to unilateral coronal suture craniosynostosis with contralateral forehead bossing. 

Evaluation

The physical examination is the most crucial aspect of the diagnosis of craniosynostosis. Radiological imaging studies are usually not required to diagnose positional plagiocephaly but may be helpful in unclear cases. Conversely, synostotic infant head shape abnormalities require radiographic evaluation of the abnormal sutures either by skull x-ray or computed tomography (CT scan of the head). CT imaging with 3-dimensional image reconstruction is the imaging modality of choice. Other imaging modalities, such as ultrasonography before fontanelle closure or magnetic resonance imaging (MRI), may also be employed if there is a concern for intracranial abnormalities, such as hydrocephalus. In synostotic brachycephaly (bi-coronal synostosis), CT imaging studies usually demonstrate the thickening of the sutures implicated. Skull x-rays will show a sclerotic margin along the suture of interest. In some instances, these sutures may not be visible. Genetic tests may be performed if affected infants present with additional features suggesting the presence of an underlying genetic syndrome. 

Treatment / Management

Positional (non-synostotic) brachycephaly or plagiocephaly are usually treated conservatively. The best management for positional plagiocephaly is prevention. Pediatrician counseling on tummy time beginning in infancy and early repositioning. If present, torticollis exercises should be utilized. Surgery is not indicated, given the absence of craniosynostosis. The parents of affected infants should be reassured, and attempts may be made to alternate the infant's head position for sleep (repositioning education). Other conservative treatment measures include massage therapy, physiotherapy (for torticollis), assistive devices, and helmet therapy. Helmets are expensive, require frequent visits to the orthotist every 2 weeks, and have their own complications, including pressure sores, subcutaneous abscess, and failure to correct the deformity.[24] Therefore, prevention and active repositioning should instead be the mainstay of therapeutic intervention in children. (B2)

Synostotic infant head shape abnormalities require surgical intervention, with the timing of surgery being crucial. Infants with signs or symptoms of raised intracranial pressure require urgent interventions. Surgical repair of uncomplicated bi-coronal synostosis is usually delayed until after the 6th month of life and is usually undertaken between 6 and 12 months old. Lambdoid synostosis should be repaired between the 2nd and 6th months of life. Established surgical management strategies include sub-total or complete cranial vault remodeling, cranioplasty (spring-assisted), and endoscopic suturectomy with postoperative helmet therapy. Early referral is advised as delayed referrals may result in more extensive surgical interventions with higher risks of complications. The best outcomes for endoscopic surgery are up to 6 months of age, while the bone is still the most malleable. The benefits of endoscopic surgery include less observed patient discomfort, less blood loss, and shorter hospital stays.[25] (B2)

Following endoscopic surgery, a helmet is often fitted 3 to 7 days following surgery and may be worn up to 1 year post-operatively.[26] Open surgical repair is usually employed between 4 to 12 months of age. All open cranial vault reconstructions begin with a bi-coronal skin incision. Lambdoid craniosynostosis requires bi-parietal craniotomies with barrel staving of the frontal and occipital bones. In cases of coronal craniosynostosis, anterior cranial vault remodeling with orbital rim advancement is used. This technique includes a bifrontal craniotomy, the creation of an orbital bandeau, and subsequent bifrontal advancement.[27]

Differential Diagnosis

Synostotic (bi-coronal or bi-lambdoid synostosis) brachycephaly in infants may be associated with multiple syndromic conditions. Following a standardized pattern of physical examination is essential to avoid overlooking any vital etiological clues. Some of the common syndromes included in the differential diagnosis are as follows:

• Crouzon syndrome: Bicoronal synostosis resulting in brachycephaly, proptosis, midface hypoplasia with a characteristic underbite (mal-occlusion), and an upturned nose.[28] Patients will usually have normal intelligence.
• Apert syndrome: Bicoronal synostosis with syndactyly of digits 2, 3, and 4.[29] Patients may have mental retardation and mid-face hypoplasia. 
• Pfeiffer syndrome: Craniosynostosis, abnormally broad and medially deviated thumbs and great toes, varying degrees of protruding eyes, and conductive hearing loss.[30]
  • Type 1: Turribrachycephaly, midface hypoplasia, high forehead, ocular hypertelorism, hypoplastic maxilla, and dental abnormalities. Intelligence is usually normal.
  • Type 2: Cloverleaf skull (or Kleeblattschadel-type craniosynostosis), hydrocephalus, ocular proptosis, beak-shaped nose, and neurological problems due to severe involvement of the brain.
  • Type 3: This is the same as type 2, except for the absence of a Cloverleaf skull. Additionally, natal teeth and an anterior cranial base are present.
• Saethre-Chotzen syndrome: Also called "acrocephalosyndactyly," craniosynostosis and or syndactyly of certain digits and characterized by a low-set hairline and facial asymmetry.[31] 
• Carpenter syndrome: Craniosynostosis, syndactyly of certain digits or polydactyly.[32] May have short stature and congenital heart defects. 
• Antley-Bixler syndrome: Craniosynostosis, proptosis, low set ears, mid-face hypoplasia, radiohumeral or radioulnar synostosis, arachnodactyly, and joint contractures.
• Muenke syndrome: Coronal craniosynostosis, carpal synostosis, hearing loss, developmental delay, cone-shaped epiphysis, and high narrow palate.
• Beare-Stevenson cutis gyrata syndrome: Craniosynostosis, cutis gyrata (furrowed and wrinkled appearance of skin and acanthosis nigricans), choanal atresia, abnormality of the pancreas, and aplasia/hypoplasia of the earlobes.
• Jackson-Weiss syndrome: Craniosynostosis, midfacial hypoplasia, broad great toes, or malformation or fusion of certain bones within the feet.

Prognosis

Positional (non-synostotic) brachycephaly or plagiocephaly are the most common infant head shape abnormalities encountered in the primary health care setting. Parental reassurance and management with conservative measures such as repositioning education are usually sufficient, with improvements evident in most infants as they attain their developmental milestones.[16] Refractory cases of positional brachycephaly should be referred for helmet therapy, and any instances of suspected craniosynostosis should be referred early for an opinion from an experienced craniofacial team. Early craniofacial referrals of synostotic brachycephaly may prevent the need for more extensive surgical interventions. Cosmetic outcomes following non-syndromic craniosynostosis repair are excellent for open and endoscopic approaches with low redo rates.[33]

Complications

Positional brachycephaly primarily raises aesthetic concerns. Reliable evidence of its effect on the neurological development of affected infants is lacking. Conversely, untreated synostotic brachycephaly may impede volumetric brain growth and development, is associated with elevated intracranial pressure in infants, and has a high incidence of intracranial hypertension in older untreated patients.[34] Cognitive and behavioral difficulties in those affected have been previously suggested to be related to elevated ICP.[10] However, no correlation was identified between both variables in several other studies.[35][36][37] The effect of craniosynostosis surgical repair on neurodevelopment remains widely debated.