Plagiocephaly

Etiology

More than 95% of cases of nonsyndromic craniosynostosis are sporadic.[6] Positive family history is present in 8-15% of patients with nonsyndromic coronal synostosis.[7] In lambdoid synostosis, the incidence of positive family history is 0% to 6%. Closure of the coronal suture starts at approximately 24 years of age, while lambdoid starts at 26 years of age. Craniosynostosis is the premature closure of a suture forming an osseous bridging and usually causing an abnormal skull shape.

Intrauterine deformational forces include a fetus's odd position, irregular uterus shape, compression of the fetus' head when descends into the pelvis, or due to multiple fetus pregnancy. Postnatal deformational forces most commonly occur due to prolonged position of the head for long periods. The etiology of craniosynostosis can be multifactorial due to intrinsic bone abnormalities, genetic mutations, and environmental factors.[8] Craniosynostosis can be associated with metabolic conditions such as hypophosphatemia, rickets, and hyperthyroidism, pre-term delivery, low birth weight, exposure to teratogens, valproic acid, and shunted hydrocephalus. Experiments in mice have shown that fetal head constraint induces upregulation of transforming growth factor (TGF) beta receptor 1 and 2 and fibroblast growth factor receptor 2 (FGFR2) at the coronal suture, thus causing coronal synostosis.[9] The genetic mutations associated with unilateral coronal synostosis include the twisted family basic helix-loop-helix transcription factor TWIST, FGFR2, and FGFR3.[10]

The incidence of deformational plagiocephaly increased after the "Back to Sleep" campaign started in 1992, which promoted a supine position to prevent sleep-related infant deaths; however, the incidence of sudden infant death syndrome has decreased.[11] Potential risk factors for deformational plagiocephaly include assisted delivery with forceps, vacuum extractor, first-born child, male sex, the supine position at sleep, limited neck rotation, low level of activity, and lack of tummy time.[11][12] Tummy time is the awake time of the baby spent in the prone position. There is a high association with congenital muscular torticollis. Due to the torticollis, the infant may hold the neck and head in a preferred position for a prolonged period causing flattening of a part of the head.[13]

Epidemiology

The incidence of anterior plagiocephaly is around one out of 10,000 live births.[14] It occurs in 13% to 16% of children with craniosynostosis. The incidence of unilateral coronal craniosynostosis is four to seven times that of bilateral coronal synostosis. The male to female ratio is 1 to 2. Unilateral lambdoid synostosis represents 1 to 5% of craniosynostosis.[15][16] The approximate occurrence of lambdoid synostosis is one in 33,000 births.

The prevalence of deformational plagiocephaly is 15 to 20% of infants.[17] However, a higher incidence of as much as 46.6% had been reported.[18] The prevalence is slightly higher in males at between 1 and 3 to 1 and usually diagnosed before four months of life. Before 1992, the incidence of deformational plagiocephaly was one in 300 infants. However, since the "Back to Sleep" campaign by the American Academy of Pediatrics, now called "Safe to Sleep," the incidence of deformational plagiocephaly has increased 400% to 600%.[16][19][20][21]

Secondary craniosynostosis can occur in systemic diseases such as rickets and hypothyroidism in newborns with microcephaly and following shunt placement for hydrocephalus.[22]

History and Physical

In synostotic anterior plagiocephaly, the forehead is flattened, and the supraorbital margin is high.[22] The forehead is pushed forward on the opposite side. There can be a deviation of the nasal septum to the normal side. Strabismus is seen in 50% to 60% due to dysfunction of superior oblique muscle secondary to changes in orbital roof and trochlea.[23] Deviation of mandible and change of occlusion may also be seen. A bony ridge can be palpated along the fused suture. In synostotic posterior plagiocephaly, frontal and occipital bossing occur on the opposite side.[22] There is a downward displacement of the ipsilateral ear and mastoid. When viewed from above, the skull resembles a trapezoid.

It is often challenging to distinguish deformational plagiocephaly from synostotic posterior plagiocephaly clinically.[16] Deformational plagiocephaly is more common. There are some points to differentiate deformational plagiocephaly from lambdoid synostotic plagiocephaly.[23] Lambdoid synostosis is present at birth; whereas, deformational plagiocephaly usually occurs some weeks after birth. History of a preferred sleeping position is noted in deformational plagiocephaly. The bony ridge along the suture and bulging mastoid are present in lambdoid synostosis. Frontal bossing is ipsilateral in deformational plagiocephaly; while, it is contralateral in lambdoid synostosis. There is contralateral occipital bossing in deformational plagiocephaly. Displacement of the ipsilateral ear is anterior in deformational plagiocephaly and posterior in synostosis. However, some authors have noted that ear position is not a very reliable sign to distinguish them.[16][24] The shape of the skull is a parallelogram in deformational plagiocephaly and trapezoid in lambdoid synostosis.

Increased intracranial pressure (ICP) features can be present in 15-20% of children with coronal or lambdoid synostosis.[25] However, the clinical features such as headache, vomiting, altered sensorium, and bulging fontanelle may not be found in many patients. Papilledema is the most reliable sign of intracranial hypertension in children with craniosynostosis, with a specificity of 98%.[26] Chronically raised ICP can lead to blindness due to optic atrophy and subnormal intelligence.[25]

Evaluation

Computed tomographic (CT) scan with three-dimensional (3D) reconstruction is the principal imaging modality for evaluating craniosynostosis.[16][27][28] A 64-slice multidetector CT scan helps in assessing vault and skull base with reasonably low radiation.[29] Premature fusion of a suture restricts the growth perpendicular to the affected suture.[30] There will be compensatory overgrowth along the other patent sutures. The CT findings of a prematurely fused suture are peri-sutural sclerosis, bony bridging, or the absence of the suture. In deformational plagiocephaly, the CT shows a patent lambdoid suture, and the frontal bossing is ipsilateral, as opposed to lambdoid synostosis. There is no significant distortion of the anteroposterior axis of the skull base in deformational plagiocephaly.[31] The chondrocranium is symmetric in deformational plagiocephaly.

The findings in unilateral coronal synostosis are a shallow ipsilateral anterior cranial fossa, contralateral frontal bossing, and an elevated roof and lateral wall of the ipsilateral orbit called the "harlequin eye" sign. The findings of unilateral lambdoid synostosis are ipsilateral occipitoparietal flattening, contralateral frontal and occipitoparietal bossing,  a unilateral small posterior cranium, and a tilted skull base. There is an ipsilateral deviation of the posterior fossa in the endocranial skull base view of unilateral lambdoid synostosis. Morphometric analysis of the skull base with the help of 3D CT can differentiate the three causes of plagiocephaly.[32] The skull base asymmetry is in the anterior and middle cranial fossae for coronal synostosis and in the posterior and middle cranial fossae for lambdoid synostosis.

Lambdoid synostosis can cause crowding of the posterior fossa and herniation of the caudal part of the cerebellum into the foramen magnum resulting in Chiari malformation.[25] Hydrocephalus and syringomyelia can also be associated; these are better appreciated in brain magnetic resonance imaging (MRI). However, a conventional MRI will not show the sutures satisfactorily. A new gradient-echo sequence is known as "Black Bone" MRI can show a patent suture as a hyperintensity signal, but it will be absent if the suture is closed.[33]

Anthropometric measurements help to assess the severity of plagiocephaly.[19] These are taken with calipers. The change observed in deformational plagiocephaly is the difference between the diagonal occipital-frontal transcranial diameters. This is the transdiagonal difference and will quantify the degree of asymmetry in deformational plagiocephaly. The severity of deformational plagiocephaly can be assessed by the difference between the diagonal lengths on each head's side.[13] A difference of 9 to 12 mm is defined as mild to moderate, and if more than 12 mm as severe asymmetry. An index named cranial vault asymmetry index can be calculated as 100 times the difference between cranial diagonal diameters divided by the shorter cranial diagonal diameter. A value greater than 3.5 indicates severe asymmetry.

Treatment / Management

Conservative treatment should be adopted for patients with deformational plagiocephaly and mild unilateral synostosis.[22] Meticulous evaluation by physical examination and diagnostic evaluation should be done to rule out synostosis before adopting a conservative approach for posterior plagiocephaly.[34] The treatment of deformational plagiocephaly is conservative with modification of sleep posture, counter positioning, physiotherapy for torticollis, tummy time, and helmet.[1][4][35] A helmet can be used for those who are not showing improvement with repositioning techniques. Helmet therapy for deformational plagiocephaly was introduced in 1979 by Clarren et al., who used a fiberglass model.[36] The helmet functions as a molding device. Currently, the helmet is custom-made for each child.[5] The optimal age for helmet therapy is 5-6 months, and it is not effective after 18 months of age.[4] Helmet therapy can cause contact dermatitis and pressure sores.[5] However, there is a lack of Class I evidence supporting the use of a helmet in deformational plagiocephaly.[37] If the deformity is severe, the Congress of Neurological Surgeons recommends helmet therapy if used during the appropriate period of infancy.[38](A1)

Surgical treatment is indicated in nonsyndromic craniosynostosis to reduce the morphologic abnormality, prevent increased ICP, and prevent psychosocial issues. Surgical aims are to achieve sufficient intracranial volume for brain growth and correct the skull's shape.[15] The steps are the removal of the fused suture and remodeling of both hypoplastic and compensatory growth abnormalities.[4] The optimal age for surgery is between 6 and 12 months of age, the most active phase of the brain and head development.

The surgical options are open craniotomy with reconstruction or endoscopic suturectomy. The procedures are fronto-orbital remodeling for anterior plagiocephaly and occipital advancement for posterior plagiocephaly.[39] The surgical techniques described are open calvarial reconstruction, strip craniectomy with implantation, barrel stave osteotomy, endoscopic suture release, and cranial distraction osteogenesis.[8][16][40] In an open procedure, the fused suture is identified, the bone flap with the suture is removed and remodeled, and fixation is done with resorbable plates.[22] In cranial distraction osteogenesis, distractors are applied to the osteotomised sites, and slow incremental distraction is done over weeks.[40] Some patients have associated torticollis with synostotic posterior plagiocephaly.[16][27]  Release of sternocleidomastoid may have to be done for associated refractory torticollis.[16] Successful surgery can resolve preoperative papilledema that is present in two-thirds of the patients with posterior synostotic plagiocephaly.[28](B2)

The cranial bones are flexible until the age of six months and can be easily manipulated by the endoscopic approach.[22] Open surgery is preferred after six months. A shorter operative time, less blood loss, and faster recovery are the advantages of endoscopic surgery. Nowadays, endoscopically assisted minimally invasive procedures are done more often.[41] However, a remodeling helmet should be used after the endoscopic procedure. Improvement in ophthalmic outcomes with a reduction in amblyopia, astigmatism, and strabismus has been observed in children with unilateral coronal synostosis after endoscopic strip craniectomy and helmet therapy.[42](B2)

Differential Diagnosis

The principal differential diagnosis in plagiocephaly determines if it is deformational (positional) or synostotic due to a suture's premature closure. Anterior plagiocephaly is due to coronal synostosis. Posterior plagiocephaly should be differentiated as synostotic or deformational. 

Facts noted in history are the presence at birth, preferred sleep position, and improvement with time.[23] Craniosynostosis is congenital, whereas deformational plagiocephaly usually develops in the neonatal period. History of a preferred sleep position will be present in cases of deformational plagiocephaly. The deformity in synostosis worsens with time. The deformities caused by position improve as the child develops head control.

The child with unilateral lambdoid synostosis has a thick ridge over the fused suture, with compensatory contralateral parietal and frontal bossing.[43] There is an ipsilateral occipitomastoid bulge, with a posteroinferior displacement of the ipsilateral ear. These characteristics are opposite to the findings in the children with deformational plagiocephaly. In the view from above, the shape of the head will be trapezoid in lambdoid synostosis and parallelogram in deformational plagiocephaly. A 3D CT will confirm the diagnosis. Torticollis is most commonly associated with deformational plagiocephaly. Chiari malformation can be present with lambdoid synostosis.

Prognosis

In deformational plagiocephaly, satisfactory outcomes can be achieved with conservative treatments if the treatments are initiated at an early stage of the disease.[13] The plasticity of the skull is good in infancy. Physiotherapy can improve congenital muscular torticollis.

There is evidence that nonsyndromic single suture synostosis can result in persistent neuropsychological deficits. Surgical intervention improves motor and cognitive function, especially in severe craniosynostosis. Long-term follow-up after surgery often found normal academic and social function.[28] If untreated or uncontrolled, craniosynostosis can lead to raised ICP and cognitive impairment.[25] Surgical correction of synostotic plagiocephaly produces significant improvements in the skull's shape and achieves high parent satisfaction.

Complications

Deformational plagiocephaly usually corrects with frequent repositioning of the baby; however, it can produce cosmetic deformities if not treated adequately. Untreated unilateral coronal plagiocephaly may cause strabismus, astigmatism, amblyopia, and mandible malalignment.[42]

Surgical complications after synostotic plagiocephaly correction are usually relatively few and minor and do not produce permanent sequela.[16][28] The following complications are associated with the surgical treatment of isolated and syndromic craniosynostosis.[22][39][40][44] Those patients with craniofacial syndromes are more prone to complications. Blood transfusion is reduced with the use of an endoscopic procedure compared to an open procedure.[41]

• Excessive blood loss
• Venous air embolism
• Consumption coagulopathy
• Cerebrospinal fluid leak
• Dural tears
• Hyperthermia
• Hypoactivity
• Wound infection local
• Epidural abscess
• Ear infections
• Subcutaneous hematoma
• Epidural hematoma
• Residual plagiocephaly
• Reoperation

Helmet therapy can lead to complications, although very rare.[13] 

• Inadequate correction 
• Pressure damage to the skin at the site of application 
• Scalp erosion, ulcer, and temporary hair loss
• Contact allergic dermatitis