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Abnormal head shape may be due to congenital or acquired conditions including birth injury, and is the most common reason for referral to a paediatric neurosurgeon.1 2 Birth injuries may present immediately or late, and imaging is rarely required in order to correctly identify the type of injury. However, an understanding of the underlying pathophysiological processes is helpful in order to appreciate potential complications that can occur in association with these injuries. When assessing an infant or child with an abnormally shaped head, it is important to differentiate between birth moulding, positional plagiocephaly and craniosynostosis which may require surgical treatment. The aim of this article is to explain the differences between these conditions, how they are best imaged and demonstrate some of the imaging findings. Definitions are given in box 1.
ANATOMY AND DEVELOPMENT OF THE SKULL IN INFANTS
The skull is formed from multiple separate bones that develop in the first weeks of embryonic life from mesenchyme enveloping the developing brain. The bones progressively ossify later in gestation. At birth the skull bones are separated by connective tissue sutures which allow movement and alteration in the shape of the skull vault during birth. The major sutures include the metopic suture located in the midline between the two frontal bones, the coronal suture between the frontal and parietal bones, the sagittal suture midline between the two parietal bones, and the lambdoid suture between the parietal and occipital bones. The fontanelles are widened, membranous areas at the intersection of sutures. In relation to the major sutures, the anterior fontanelle (AF) is situated between the metopic, sagittal and coronal sutures, with the posterior fontanelle (PF) found at the intersection of the sagittal and lambdoid sutures. Skull growth is primarily driven by growth of the underlying brain which proceeds rapidly to 90% of adult size in the first year of post-natal life, reaching 95% of adult size by 6 years of age. There is little brain growth after 7 years of age.2 The sutures serve as growth sites where new bone is deposited in response to separation of osteogenic cells at the edges of opposing bones. Except for the metopic suture, the major sutures remain unfused until at least 2 years of age allowing for continued brain growth, and are not usually completely obliterated by bone until the end of the fourth decade (table 1).
SCALP ANATOMY
The scalp is comprised of five layers of tissue: skin, connective tissue, aponeurosis, loose areolar tissue and periosteum (pericranium) overlying the skull bones.
BIRTH-RELATED SCALP SWELLINGS
Scalp swellings are common in neonates following vertex delivery and most resolve with conservative management. The most common birth injuries to the head are caput succedaneum and cephalhaematoma. Both are more common after prolonged or difficult labour, in primigravidas and following instrumented deliveries, although caput succedaneum and cephalhaematoma have been diagnosed in utero on antenatal ultrasound. These, and cephalhaematomas occurring in neonates born by caesarean section without labour, are postulated to be caused by fetal head positioning in utero or head compression by the uterine walls in association with oligohydramnios or prolonged rupture of the membranes (PROM).3 Caput succedaneum is a subcutaneous fluid collection usually occurring on the presenting part of the head. The swelling results from oedema and/or bruising secondary to the high pressure exerted on the tissues by the birth canal during labour. The swelling produced is not localised to a particular bone, in other words it can cross suture lines, and has a soft, boggy feeling with irregular margins. Similar swelling produced by the suction pressure of a vacuum cup is known as a chignon. Both sorts of subcutaneous swellings typically resolve gradually over hours to days following delivery and complications such as skin necrosis or hair loss are rare.4
Cephalhaematomas are relatively common, occurring in up to up to 2.5% of live births and are often associated with instrumented deliveries, especially vacuum extraction.5 The swelling is due to sub-periosteal haemorrhage caused by disruption of veins that bridge the diploic space (between the inner and outer tables of the skull) to communicate superficially with the overlying periosteum (pericranium). The same veins have deep communication with meningeal veins. Injury results from trauma to the skull as it is forcefully and repeatedly compressed against the pelvic bones with contractions during labour. The diploic veins of each skull bone are separate in the unfused skull so that the haematoma produced is contained by the ligaments that bind the periosteum to the skull at the edge of the sutures. Venous bleeding into the sub-periosteal space is slow, so most cephalhaematomas develop within the first 24–72 h after delivery. The size of the collection is usually limited by pressure within the sub-periosteal space creating a tamponade that prevents further bleeding.
Cephalhaematomas are firm and well-defined although overlying subcutaneous swelling can obscure their margins. They may be related to any of the cranial bones, although the parietal bone is the most common site. The majority of cephalhaematomas resolve within 1 month of life. Approximately 3–5% of all cephalhaematomas will calcify to a variable extent6: in those that persist beyond 1 month after delivery, progressive sub-pericranial ossification results in a calcified cephalhaematoma. Depending on their size, calcified cephalhaematomas can cause significant cosmetic deformity (fig 1) and large collections may be associated with depression of the inner table of the skull, encroaching on the intracranial space. These are both indications for surgery.6 7 Other complications of cephalhaematoma include infection, anaemia and hyperbilirubinaemia secondary to breakdown of haemoglobin in the collection. Although imaging of cephalhaematoma is rarely needed, ultrasound is useful for visualising the edges of a suspected cephalhaematoma which may be obscured by overlying subcutaneous oedema. Radiographs may be obtained if there is suspicion of an underlying fracture, although computed tomography (CT) is indicated if a depressed skull fracture or intracranial injury is suspected. CT is also useful for pre-surgical planning in patients with large calcified cephalhaematomas.
The sub-aponeurotic (sub-galeal) space is a large potential space between the scalp aponeurosis and pericranium, extending from the supra-orbital ridges to the nape of the neck and laterally to the ears. Within this space are sheets of highly vascularised connective tissue making it prone to bleeding. Haemorrhage can occur into this space during delivery or fluid may accumulate later within disrupted tissue planes. In fact, presentation with scalp swelling due to sub-aponeurotic fluid collection can occur as late as 18 weeks after delivery.8 Sub-aponeurotic haemorrhage is more frequent following vacuum extraction but may arise spontaneously or after minor trauma.9 Rarely, these collections can lead to significant volume loss requiring transfusion. Ultrasound of the scalp can demonstrate fluid in the sub-aponeurotic space, but most importantly can demonstrate the fluid crossing the cranial sutures, thus differentiating it from a cephalhaematoma. Radiographs or CT are indicated if a skull vault fracture or intracranial injury is suspected.
SKULL DEPRESSIONS IN INFANCY
Because the bones of the fetal and infant skull are generally very malleable compared with later in life, they can be relatively easily deformed or depressed by external pressure. Congenital skull depressions unrelated to birth trauma are described in infants delivered vaginally or by caesarean section, but are extremely rare. Causes include pressure on the soft fetal skull in utero by a bony prominence from the maternal pelvis or spine, a uterine fibroid, a fetal limb or a body part of a twin10; the condition is sometimes referred to as faulty fetal packing.11 Such skull depressions are usually asymptomatic but are occasionally associated with intracranial haemorrhage, usually over the surface of the brain. Treatment options for congenital depressions include surgical elevation, manual elevation using digital pressure at the sides of the depression, suction elevation with a breast pump or vacuum extractor or observation only with spontaneous resolution within 6 months.10 12 Acquired depressed skull fractures are usually related to obstetric manoeuvres or instrumentation during delivery. A “ping-pong” fracture is a particular type of fracture seen only in neonates and infants, so called because it consists of a depression in the skull vault without an associated cortical break (fig 2). Opinions vary as to what is the best management for these injuries, however non-surgical techniques such as suction elevation have been shown to be successful in patients with skull depressions of less than 2 cm.13
INFANTS WITH MISSHAPEN HEADS
Head shape varies greatly in the first 2 years of life, and many patients with abnormally shaped heads will improve spontaneously with growth and development.14 When faced with a child with a misshapen head in the clinical setting, one of the first distinctions to make is between birth moulding, positional/deformational plagiocephaly and craniosynostosis. Birth moulding is the change in head shape produced in order to allow the skull to pass through the birth canal. Increased pressure on the skull in the antero-posterior (AP) direction compared with side to side causes the parietal bones to temporarily move away slightly from the base of the skull (which the unfused sutures allow), and the frontal and occipital bones to override the parietal bones to a variable extent. Overriding of the skull bones is often palpable after birth but usually resolves in hours to weeks after delivery.
POSITIONAL OR DEFORMATIONAL PLAGIOCEPHALY
Positional or deformational plagiocephaly results from local pressure on a specific area of the skull. It typically affects the posterior skull and is a common presentation in paediatrics, but needs to be differentiated from early fusion of the lambdoid suture which is extremely rare but does not respond to conservative treatment and may require complex surgery. The incidence of deformational plagiocephaly has risen in recent years as a result of the American Academy of Pediatrics (AAP) Back to Sleep campaign,15 which has also been responsible for a decrease in the incidence of sudden infant death syndrome (SIDS).16 17 Other risk factors for deformational plagiocephaly include intrauterine crowding (eg, in PROM, twin pregnancy), decreased mobility (eg, prematurity, developmental delay, chronic illness) and abnormal postnatal head positioning, for example in patients with torticollis.
The skull shape is crucial in helping to differentiate deformational plagiocephaly from partial/unilateral lambdoid synostosis. In deformational plagiocephaly the skull assumes a rhomboid or parallelogram shape (best viewed from above), with associated bulging of the forehead on the same side as the occipital flattening. Furthermore, the ear on the same side also moves forward and inferiorly compared with the opposite ear. In true lambdoid synostosis the skull assumes a trapezoid shape with bulging of the mastoid on the same side as the occipital flattening and posterior displacement of the ear. These findings are associated with contralateral bossing of the frontal and parietal bones, not seen in deformational plagiocephaly.18 In cases of true craniosynostosis, a palpable bony ridge or prominence is usually felt along the fused suture and this will be absent in patients with positional plagiocephaly. In contrast, when the suture is unfused, slight movement can be appreciated when gentle firm pressure is applied using the thumbs on either side of the suture.
As with many conditions, prevention of deformational plagiocephaly is more desirable than cure and parents should be encouraged to vary their child’s head position from side to side during sleep and feeding, and allow the child to lie prone for at least 5 min per day beginning in the first 6 weeks of life. The amount of time spent in car seats and baby bouncers should also be limited. Re-enforcement of this advice is needed if occipital flattening starts to become apparent. It is important to thoroughly examine the cervical spine and neck muscles. Patients with signs of torticollis should be referred early for physiotherapy with close follow-up to identify those patients who are not responding to conservative management.16 19 Patients with congenital spinal abnormalities or a neurological cause for their torticollis may warrant early referral to paediatric neurosurgical services for further management.
Helmet treatment for deformational plagiocephaly may be tried if repositioning or physiotherapy is not effective. The aim of this treatment is to place mild pressure on prominent areas of the skull while allowing room for flattened areas to expand.2 The helmet is worn for 23 h per day and patients are followed up at least weekly to document changes, make adjustments and check the scalp for signs of irritation or pressure abrasion. Early referral is important since helmet therapy has been shown to be less effective after 1 year of age.20 Even in patients who do not respond well to conservative treatment, or where there is residual deformity due to deformational plagiocephaly, hair growth usually covers the area of flattening and surgical intervention is contemplated only in severe cases for cosmetic purposes. Although a benign condition, deformational plagiocephaly can have psychological and emotional consequences for the child if altered head shape and facial asymmetry persist throughout life.21
CRANIOSYNOSTOSIS
Craniosynostosis is defined as the premature closure of one or more cranial suture and this is the most common craniofacial malformation. The incidence of craniosynostosis is approximately 1 in 2000 to 1 in 3000 newborns.2 22 Of the total, approximately 15% are affected by syndromic craniofacial malformations involving more than one suture.23 24 Premature closure of sutures prevents separation of the bones and affects skull growth perpendicular to the affected suture, leading to typical skull deformations which progress without treatment.
The exact cause of primary craniosynostosis remains unclear, but suspected genetic and environmental factors have been extensively investigated. Environmental effects associated with an increased incidence include rickets (both vitamin D deficiency and resistance), chronic renal failure, hypothyroidism and hypophosphatasia, certain teratogens including anti-convulsant drugs, chemotherapeutic agents and multiple causes of abnormal fetal positioning in utero leading to constraint of the fetal skull. Mutations in fibroblast growth factor receptors (FGFR 1, 2 and 3) and the TWIST and MSX2 genes are the most frequently implicated genetic abnormalities in syndromic and multi-suture craniosynostosis.2 Craniosynostosis may be also be seen in association with mucopolysaccharidoses, other lysosomal storage diseases, and haematological disorders with marrow hyperplasia and bony overgrowth.25 Rarely, sutural closure occurs secondary to an abnormality of the underlying cerebrum leading to decreased brain growth or atrophy (fig 3). It may also occur as an uncommon complication following placement of a ventricular shunt to treat hydrocephalus, after which there is a reduction in outward pressure from the brain on the inner surface of the skull bones.
A full review of multisutural and syndromic craniosynostosis including Apert’s and Crouzon’s syndrome is outside the scope of this article, but these patients are a unique group with morphological and functional abnormalities not found in patients with isolated craniosynostosis affecting a single suture. This group of patients requires multidisciplinary care from specialties including paediatric craniofacial and neurosurgical teams, ophthalmology, otolaryngology, genetics and orthodontics in order to address the multiple issues that occur throughout their childhood and into adult life.
IMAGING STUDIES IN CRANIOSYNOSTOSIS
In most cases of suspected craniosynostosis, the history and clinical examination are sufficient to secure the diagnosis. However, when there is doubt, skull radiography is the initial modality of choice to determine whether the sutures remain patent or not. Signs of premature suture fusion include loss of visualisation of the suture or part of it, peri-sutural sclerosis and bony bridging; however, radiographs are often unreliable in the first 3 months of life when the low mineralisation of the skull makes it difficult to visualise the presence of sutural fusion.26 Radiographs may detect secondary signs of craniosynostosis such as “copper-beating” produced by excessive impressions from cerebral gyri on the inner table of the skull (fig 4). CT is the definitive investigation for evaluating the morphology of sutures and the overall effect of craniosynostosis on skull shape. It also enables the brain to be evaluated for gross structural abnormalities and ventricular size, although magnetic resonance imaging (MRI) is better for evaluating more subtle structural abnormalities, the brain parenchyma and craniocervical junction, which is particularly important in patients with multisutural or syndromic craniosynostosis. Depending on local protocols, a request for CT may be most appropriate after neurosurgical evaluation, in order that the examination may be scheduled to coincide with planned surgery and avoid unnecessary irradiation if surgery is not indicated. In patients with craniofacial syndromes, imaging has a more important role in planning surgical intervention. Ultrasound is not established as a tool for evaluating the sutures in suspected craniosynostosis.
SINGLE SUTURE CRANIOSYNOSTOSIS
Patients with premature closure of a single suture usually present with characteristic alteration in their head shape. Focal neurological deficits and raised intracranial pressure (ICP) in these patients are rare unless the synostosis is severe, although there is growing evidence that a significant number of children with single suture craniosynostosis have mild to moderate neurobehavioural impairment despite normal intelligence.22
Premature closure of the metopic suture restricts normal growth of the frontal cranial vault, leading to secondary parietal widening and characteristic trigonocephaly, with a pointed forehead and palpable bony midline ridge in the frontal region. If the fronto-nasal suture is also involved, hypotelorism also occurs (fig 5). Rarely this deformity is associated with frontal lobe malformations but is usually unrelated to any underlying brain abnormality. Treatment depends on the severity of the deformity. Mild cases are left alone and often improve over time. If the cosmetic deformity is unacceptable, surgical remodelling of the calvarium or an operation to reduce the prominence of the central ridge may be performed.
Scaphocephaly produced by premature fusion of the sagittal suture is the most common type of craniosynostosis, and 80% of affected patients are male. Skull growth is restricted in the transverse direction perpendicular to the affected suture, which is compensated for by elongation of the skull in the sagittal plane (fig 6). The head is elongated with frontal and occipital prominence and a bony ridge is often palpable along the midline between the AF and lambdoid suture. Surgery is performed to excise the affected suture or remodel the cranial vault depending on age at presentation.24
Anterior plagiocephaly may be a manifestation of coronal synostosis which is typically unilateral and occurs more commonly in girls. It is also the most commonly fused suture to be associated with a syndrome, especially when synostosis is bilateral; however, over 60% of all cases are sporadic.2 Unilateral coronal synostosis restricts forward growth of the cranial vault on the affected side and compensatory changes take place on the contralateral side which becomes prominent. The orbital rim on the affected side becomes recessed, but the fused suture also restricts growth of the adjacent sphenoid bone and the roof of the orbit formed by the greater wing of the sphenoid becomes elevated – the so-called “harlequin deformity” of the orbit (fig 7). Other compensatory changes include prominence of the temporal bone on the affected side and asymmetry of facial development with nasal deviation and alteration in the length of the zygomatic arch which results in flattening of the cheek on the affected side22 (fig 8).
Box 1 Definitions
Acrocephaly – pointed head.
Birth moulding – change in shape of the fetal head as it passes through the birth canal producing mild vertical elongation of the skull and overriding of the frontal and occipital bones with the parietal bones. Usually resolves within hours to weeks of birth.
Brachycephaly – short head.
Caput succedaneum – a subcutaneous fluid collection on the presenting portion of the infant’s skull, present at birth. Usually resolves over several days.
Cephalhaematoma – a sub-periosteal collection of blood caused by birth trauma. May be slow to resolve and can calcify.
Chignon – subcutaneous swelling occurring secondary to vacuum extraction.
Craniosynostosis – a medical condition resulting from premature closure/fusion of one or more cranial sutures, causing problems with normal skull growth. Brain growth may be secondarily affected and raised intracranial pressure can result.
Dolicocephaly – long head.
Fontanelles – membranous spaces in the skull formed at the intersection of sutures.
Oxycephaly/turricephaly – tower-shaped head.
Plagiocephaly – asymmetric head.
Scaphocephaly – keel-shaped head.
Suture – a type of fibrous joint only occurring in the skull, also known as a synarthrosis. Many are typically unfused at birth. Following fusion the adjacent bones are bound together by Sharpey’s fibres allowing little or no movement across the joint.
Sub-aponeurotic/sub-galeal haemorrhage or fluid collections – accumulate in the large potential space deep to the scalp aponeurosis and superficial to the periosteum.
Trigonocephaly – triangular-shaped head.
Bilateral coronal synostosis results in a broad, flattened forehead and wide brachycephalic cranial vault (fig 9). The orbital depth is frequently decreased resulting in exophthalmos and associated ocular problems. Surgical correction of coronal synostosis is usually undertaken by a craniofacial team including a paediatric neurosurgeon and currently involves cranial vault remodelling and fronto-orbital advancement.2 24 These patients should also be evaluated for the possibility of an associated syndrome.
Posterior plagiocephaly resulting from lambdoid synostosis is extremely rare compared with other forms of craniosynostosis and the more commonly encountered deformational plagiocephaly. In lambdoid synostosis there is characteristic flattening of the occipital bone and prominence of the mastoid bone on the affected side. Compensatory growth occurs in the parietal and occipital regions on the opposite side resulting in a trapezoid shaped skull (fig 10). Surgery to correct deformity resulting from lambdoid synostosis is only indicated in the most severe cases, primarily for cosmetic reasons.
TIMING OF SURGERY
Because brain growth is so rapid and dynamic, timing of surgery is thought to be important both functionally and aesthetically; however, it remains a subject for discussion amongst craniofacial and neurosurgeons.2 With advancing age, skull deformity increases in severity requiring more extensive surgery and it is generally accepted that earlier treatment, preferably before 1 year of age, is most appropriate in terms of a better functional and cosmetic outcome. Other reasons for performing surgery early include better re-ossification of the skull following surgery under 1 year of age. Furthermore, from 3–9 months of age the skull vault is still malleable and easy to shape.20 A satisfactory cosmetic outcome in these patients is also important in terms of psychosocial benefit in order to avert the potential psychological consequences of growing up with an abnormally shaped head.
SUMMARY
Birth related injuries rarely require imaging but it can be helpful in order to determine the cause of a scalp swelling in the neonatal period or later in infancy if there is uncertainty based on the history and clinical examination. Deformational plagiocephaly is a benign, preventable condition but can cause unacceptable cosmetic deformity and parental anxiety. Prevention strategies should be discussed at the same time as supine positioning for sleeping. Patients with suspected craniosynostosis warrant early referral to a paediatric neurosurgeon in order to achieve the best cosmetic and functional result if surgical treatment is required. Skull radiographs and CT are the imaging modalities of choice in suspected craniosynostosis. Patients with coronal synostosis should be evaluated for possible underlying syndromes and those with multisutural or syndromic craniosynostosis require management by a multidisciplinary team of clinicians.
REFERENCES
Footnotes
Competing interests: None.