Infants with misshapen skulls: When to worry

Infants with misshapen skulls: When to worry

By Annie Jill Rohan, NNP/PNP, Sergio G. Golombek, MD, andAlan D. Rosenthal, MD

With more babies being put to sleep in the supine position,pediatricians increasingly are seeing infants whose skulls are flattenedin back. You need to distinguish these children-- whose "flat heads"merit mainly parental reassurance--from the occasional child whose misshapenskull calls for referral and surgical intervention.

Pediatricians have taken a new interest in craniosynostosis of late.The Back to Sleep campaign has increased the number of babies whose skullsare flattened in back. This type of "flat head" is distinct fromtrue craniosynostosis, where one or more of the cranial sutures closes prematurelyor is absent. Most often noted at birth or in the first year of life, craniosynostosisis thought to affect 1 to 2.5 in 1,000 children.¹ Whereas synostosisimplies a congenital developmental malformation, skull deformations suchas positional "flat head" and secondary synostosis arise froman alteration in the normal forces acting on the growing cranium, most oftenin a healthy child. The cosmetic implications of these deformities is whatusually prompts parents and physicians to pursue treatment, though suchabnormalities occasionally threaten neurologic function.

Pediatricians need to differentiate congenital and secondary craniosynostosisrequiring intervention from an unshapely skull arising from sleep positionthat calls for no or little management--but lots of parental reassurance.We show you how by reviewing the normal development of the skull, describinghow craniosynostosis arises and the syndromes with which it is associated,and discussing various causes of skull deformation and secondary synostosis.Finally, we outline the surgical treatment patients with true synostosesmay require.

How the skull develops

The skull, a bony structure designed to protect the brain in utero andin infancy, molds to facilitate passage through the birth canal and alsomust accommodate expansion caused by rapid brain growth. The skull's numerousbones are "jointed" together by structures known as sutures, relativelyimmobile points between the skull bones that allow for growth and molding.Fontanels are the points at which the suture lines cross (Figure 1).

The pressure exerted by a growing brain pushes the skull bones apart,causing new bone to be laid down along suture lines. The sutures containosteogenic cells, blood vessels, and loose connective tissue; periosteumcovers the external surfaces of the cranial bones, and the internal surfacesare in contact with the outermost covering of the brain, the dura. Bonedeposited and resorbed at the sutures along the periosteal and dural bonesurfaces remodels the shape of the skull as the head enlarges. The rapidbrain growth of infancy is nearly complete by the end of the second yearof life; later osteoblastic activity is minimal, and rigid bone replacesthe fibrous sutures. The sutures are largely ossified by the time a childis 8, and bone union is completed by age 20.^2­4

Because suture lines project across many planes, the skull can grow inall directions, but at any given suture line, the skull grows perpendicularlyto the suture. Growth along the sagittal suture, for example, increasesthe width of the skull. Growth along the coronal suture increases the skull'santerior-posterior diameter.

When something goes wrong: Primary synostosis

In craniosynostosis, premature closure or absence of one or more of thesutures of the skull hampers normal growth in one or more directions, fosteringcompensatory growth along another open suture line. The aberrant growthcauses the skull to become misshapen in a way that is predictable, dependingon which suture is closed or absent. Where the sagittal suture is synostosedand growth in width is hampered, for example, the skull becomes elongatedand scaphocephalic. Similarly, where the coronal sutures are synostosedand anterior-posterior growth is restricted, the skull becomes widened andbrachycephalic. Synostosis of a unilateral coronal or unilateral lambdoidalsuture results in skull asymmetry, or plagiocephaly (Figure 2).

Rudolph Virchow, a pioneer in craniosynostosis in the 1800s, was thefirst to conceptualize these observations: A prematurely fused suture (thentermed "craniostenosis") restricts growth in a plane perpendicularto the fusion and enhances growth in a planeparallel to the fusion.⁴The names of the skull deformities caused by the fusion of various suturesappear in Table 1.

Synostosis involving more than one suture, which often is associatedwith a syndrome, poses a complex problem, as growth restriction is evenmore marked than when a single suture is closed or absent. These less commonforms of synostosis include kleeblattschädel, or "cloverleaf"deformity, and acrocephaly, or oxycephaly (pointed head). Without earlyintervention,multisutural conditions often cause rising intracranial pressureand subsequent neurologic impairment.

In the United States, male to female ratio is approximately 3:2--witha particularly high prevalence of sagittal synostosis in males-- and about85% of patients are Caucasian.^5,6 Three large surgical seriesreveal the incidence of the various forms of isolated craniosynostosis (notassociated with a syndrome), which account for approximately 90% of totalcases.^7­9As shown in Table 2, half the cases of isolatedsynostosis involve the sagittal suture; one third involve one or both coronalsutures; one tenth, the metopic suture; fewer than one tenth, the lambdoidalsutures. The remainder reflect combinations of sutures.

Several different classification systems have been proposed for craniosynostosissince Virchow first categorized the various forms based on the appearanceof the misshapen skull. As the specialty of craniofacial surgery has evolvedto include surgeons, ophthalmologists, dentists, geneticists, and otherprofessionals, many in the field prefer to classify the abnormalities accordingto their presumed pathogenesis. In such a system, synostosis is primaryor secondary, or it is related to a syndrome or not related to a syndrome.Syndrome-related forms of synostosis have been classified in various ways,including syndromes caused by single genes, chromosomally caused syndromes(Table 3), environmentally induced syndromes, and syndromes whose genesisis unknown.¹⁰

A combination of causes

The etiology of true sutural craniosynostosis is unknown, but many factorshave been implicated. Although we are aware of both environmental and geneticinfluences, no one theoretical mechanism can explain all cases. Accordingto some theories, secondary effects of cranial base abnormalities or mesenchymalblastema defects play a role. Metabolic conditions affecting bone formation,as well as hyperthyroidism, hypercalcemia, rickets, and mucopolysaccharidedisorders also have been implicated, as have the effects of intrauterineevents and positioning. Hematologic disorders such as thalassemia, sicklecell disease, and polycythemia are associated with many cases. Teratogenicagents such as phenytoin, valproic acid, methotrexate and retinoic acidalso have been suspected.^2,3,5,10

At least 60 recognized syndromes have been associated with craniosynostosis.The more common ones appear in Table 4; best known are Apert's, Pfeiffer's,and Crouzon's. Because of midface hypoplasia, orbital defects, and otheranomalies, variants of craniosynostosis in the setting of a syndrome requiremore individualized assessment and treatment than isolated craniosynostosis.In addition, the cranium of some children with these syndromes may lackadequate growth potential, requiring surgical revisions to prevent intracranialhypertension and its deleterious effects.^11­13

Apert's syndrome includes craniosynostosis and abnormalities of the face,hands, and feet. The degree of craniosynostosis varies, but coronal sutureson both sides are usually involved. The face is asymmetric with a hypoplasticor retruded structure, and the patient often has hydrocephalus. Syndactyly,which ranges from partial to complete fusion of most or all digits and toes,also is seen. Approximately one third of patients have a cleft palate. Many,but not all, patients are mentally retarded. Chromosomes are normal in Apert'ssyndrome, and while parent-child transmission is unusual, autosomal dominantinheritance has been established.^14,15

Pfeiffer's syndrome also includes facial and digital abnormalities, butcarries a much better prognosis for normal intelligence than Apert's syndrome.The synostosis also usually involves bilateral coronal sutures, but it ismore variable than in Apert's syndrome and can include the cloverleaf deformity.Broad, short thumbs are a characteristic feature. Chromosomes are normal,and inheritance is autosomal dominant.¹⁴

Crouzon's syndrome is characterized by synostosis of more than one suture,most likely the coronal and sagittal. Cleft palate or bifid uvula, hypertelorism,exophthalmos, auditory meatal atresia, and maxillary hypoplasia result frommidface abnormalities (Figure 3). Mental retardation is an associated finding,though normal intelligence is common. Inheritance is autosomal dominant,but up to half of all cases are fresh mutations.^14,15 Chromosome10 recently was linked with the syndrome.⁵

Deformational malformations and secondary synostosis

Whereas primary synostosis implies a congenital malformation, skull deformationsand secondary synostosis result from an alteration in the normal forcesacting on the growing cranium. Most deformational disorders can be correctedwithout surgery before the sutures fuse. Sometimes, however, deformationsprogress to secondary synostosis and in the rare instances where deformityis considerable, corrective surgery becomes an option. Secondary synostosisalso can result from an acquired disease affecting bone formation, suchas rickets. Conditions most often associated with secondary synostosis orskull deformations include the following:

Prematurity. Premature infants often develop deformational scaphocephalybecause of their impaired mobility and prolonged positioning on a firm mattress.Sometimes the scaphocephaly and loss of temporo-parietal convexity persistto adulthood. The use of donut-shaped head supports and waterbed mattresses,and careful positioning in newborn intensive care units, can minimize thedeformity. Typically, this type of mild scaphocephaly does not warrant otherforms of intervention.¹⁶

Ventriculo-peritoneal shunting. Secondary sagittal synostosis is welldocumented following shunting in infancy for hydrocephalus. In chronicallyhydrocephalic children the skull often thickens, the skull base alters,and the sagittal suture closes prematurely once the skull has been decompressedwith a shunt. Surgical correction is most likely to be required when massivehydrocephalus is present at birth (the head circumference is approximately50 cm, or four to five standard deviations above normal) or when ventriculardecompression is carried out at a very low birth weight. Correction posesa unique challenge because the condition often is diagnosed after the firstyear of life, when skull growth is almost complete.

Microcephaly. A lack of brain growth commonly produces secondary synostosisin children with microcephaly. Surgical correction is not usually indicated.In the 1890s and early 1900s, surgical treatment of craniosynostosis produceddisappointing results because many surgeons failed to differentiate betweenmicrocephaly and craniosynostosis.¹² This differentiation issimply accomplished by clinical exam--by carefully evaluating any childwith premature closure of a fontanel and suspected sutural fusion for headgrowth and signs of raised intracranial pressure. In microcephaly, a smallhead circumference indicates subnormal growth. In the child with synostosiswhose brain is growing normally, compensatory, albeit aberrant, head growthis a hallmark and head circumference remains normal. The rare case of synostosisinvolving many sutures with restricted compensatory head growth and a resultingsmall head circumference is characterized by intracranial hypertension andgross skull malformation.

Birth-relateddeformational malformations. Deformational plagiocephalyis the most common type of deformational skull malformation.¹⁷Characterized by forehead asymmetry and sometimes associated with torticollis,this abnormality results from compressive or restrictive forces acting ona coronal or a lambdoidal suture. Deformational plagiocephaly can resultfrom in utero positioning, the birth process, or subsequent positioning,and is estimated to occur in more than 40% of healthy newborns. Correctearly diagnosis is essential to identify those few cases that require surgeryand to treat the remainder effectively by nonsurgical means.¹⁶Proper positioning, specialized exercise, and helmeting are used to treatnonsurgical cases.

Recognizing typical "flat head"

Concurrently with an increase in supine infant positioning, the incidenceof lambdoidal synostosis is rising. It previously accounted for less than10% of craniosynostosis but now represents as much as 15% to 20% of thesemalformations in surgical series.⁶ It is unlikely that primarylambdoidal synostosis actually has increased, however. More likely, thesefigures reflect a failure to diagnose a deformational disorder or the failureof conservative treatment for deformational plagiocephaly.^18,19

The craniofacial distortion of deformational posterior plagiocephalyis the opposite of the distortion seen in synostotic posterior plagiocephaly,so the two are easy for the primary care provider to distinguish. Patientswith true synostosis often have occipital flattening and a thick ridge overlyingthe fused lambdoid suture; frontal and parietal bossing on the oppositeside represents compensatory growth, giving the skull a trapezoid shape.In addition, on the same side as the fused suture, the ear is lower andfarther back than normal. In contrast, the child with positional moldinghas an open suture, which often can be discerned on both exam and plainradiograph. These children, like those with true synostosis, have occipitalflattening overlying the affected suture. Frontal and temporal prominence,however, is found on the same side as the suture, with frontal flatteningon the opposite side, giving the skull a parallelogram shape. The ear onthe side of the affected suture is lower than normal but displaced forward,rather than posteriorly as in children with synostotic plagiocephaly.^18,19

Deformational plagiocephaly is partially self-correcting. Without intervention,mild deformities usually resolve completely or almost completely. When resolutionisn't complete, later hair growth makes the deformation barely perceptible.For more severe forms of deformational plagiocephaly, physical maneuverscan enhance molding of the misshapen cranium. Instruct parents to positiontheir sleeping child so that the head does not rest on the flattened side.This can often be achieved by moving a child's crib or his toys. To givethe infant a respite from lying on the back of the head, he can be placedon the stomach when he is awake and someone is with him. Physical therapyis indicated when the child also has torticollis. In the most serious cases,helmet molding has been shown to accelerate and improve final results, butthis requires an expert orthotist, constant use, and frequent modificationduring growth. Good results even in these more severe cases can usuallybe expected where treatment is initiated before the child is 6 months old.¹⁷

True craniosynostosis and surgery

The difficulty of diagnosing craniosynostosis varies. In some instances,especially single-suture abnormalities, diagnosis is made by physical examinationand confirmed with plain radiographs. In more complex abnormalities, advancedradiologic imaging is indicated. Computerized tomography (CT) allows moreaccurate diagnosis than plain radiography, and three-dimensional CT reconstructionis an even more powerful diagnostic tool (Figure 4). Magnetic resonanceimaging is less useful than CT in evaluating bone.

On plain radiographs, fused sutures have either a broad ridge of overgrowthof solid bone along a previous suture (sometimes misread as a patent suture),or the suture is completely obliterated, making it indistinguishable fromthe surrounding bone. Physical examination reveals immobile bone platessurrounding the affected suture. Where one expects a patent suture, noneis palpable or a bony ridge is in its place. The ridge is especially characteristicof the fused sagittal suture.¹¹

Unilateral coronal synostosis and metopic synostosis are often associatedwith pre- and postoperative ocular impairments, including dissociated movement,strabismus, amblyopia, and refractive errors. Consequently, an ophthalmologicexam should be incorporated in the work-up for these patients, with follow-uppostoperatively (Figure 5).

In an infant who is healthy and developmentally normal, however, theappropriateness of performing an extensive procedure is questionable. Whileraised intracranial pressure has been demonstrated in up to one third ofcases of single suture synostosis, many observers believe that because ofcompensatory growth, neurologic impairment is unlikely in these cases.^20,21Yet our society places great significance on physical appearance, and theimportance to psychosocial development of correcting a skull malformationshould not be ignored. Uncorrected cranial deformities have been shown tohave negative effects on peer acceptance, parent-child bonding, self-image,and coping.^9,22 The safety of surgical procedures is increasing,and advances in technique have improved cosmetic results. Use of the "craniofacialteam" also has contributed to the successful management of patientswith craniosynostosis. For more about surgery for this condition, see box"When surgery is necessary" .

Usually a benign condition

Incidence of true sutural synostosis has been stable for years, but manymore infants than in the past now have asymmetrical skulls because of thesuccess of the Back to Sleep campaign to reduce the risk of sudden infantdeath syndrome. The resulting "flat head" is benign and largelyself-correcting. Pediatricians who readily recognize the difference betweenpositional deformities and true synostoses can offer reassurance to parentswhen that is all that is required and refer those few children in whom substantialintervention is appropriate. With early diagnosis, cosmetic outcome in thesechildren is usually excellent.

MS. ROHAN is Clinical Instructor, Department of Pediatrics,State University of New York at Stony Brook, Stony Brook, NY.

DR. GOLOMBEK is Assistant Professor of Pediatrics at thesame institution.

DR. ROSENTHAL is Associate Clinical Professor of NeurologicalSurgery, Albert Einstein College of Medicine, Bronx, NY.

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Infants with misshapen skulls: When to worry.

Contemporary Pediatrics

1999;0:047.