DOI: 10.1148/rg.242035105
RadioGraphics 2004;24:507-522
© RSNA, 2004
The Infant Skull: A Vault of Information1
Ronald B. J. Glass, MD,
Sandra K. Fernbach, MD,
Karen I. Norton, MD,
Paul S. Choi, MD and
Thomas P. Naidich, MD
1 From the Department of Radiology, Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029 (R.B.J.G., K.I.N., P.S.C., T.P.N.); and the Department of Radiology, Evanston Hospital and Northwestern University, Evanston, Ill (S.K.F.). Recipient of a Certificate of Merit award for an education exhibit at the 2002 RSNA scientific assembly. Received April 14, 2003; revision requested June 3 and received July 18; accepted July 21. All authors have no financial relationships to disclose. Address correspondence to R.B.J.G. (e-mail: ronald.glass@mountsinai.org).
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Abstract
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The art of interpreting skull radiographs is slowly being lost as trainees in radiology see fewer plain radiographs and depend more heavily on computed tomography and magnetic resonance imaging. Nevertheless, skull radiographs still provide significant information that is helpful in finding pathologic conditions and appreciating their extents. Abnormalities in the skull may be reflected as variations in the density, size, and shape of the skull, as well as skull defects. Skeletal dysplasias may manifest as a generalized decrease in calvarial density (hypophosphatasia, osteogenesis imperfecta), a generalized increase in calvarial density (osteopetrosis), or a focal increase in density (frontometaphyseal dysplasia). Diffusely decreased or increased calvarial density is usually associated with a process that affects the entire skeleton. Therefore, correct differentiation among these dysplasias depends on other concurrent features. Decreased size of the cranial vault at birth generally implies an underlying insult to the brain, including fetal alcohol syndrome and the so-called TORCH infections (toxoplasmosis, rubella, cytomegalovirus infection, herpes simplex). Macrocephaly may result from skeletal dysplasia or an increase in the intracranial volume (eg, due to underlying anomalies of the brain such as hydrocephalus).
© RSNA, 2004
Index Terms: Infants, skeletal system, 10.10, 11.10 • Skull, abnormalities, 10.10, 10.143, 10.144 • Skull, diseases, 10.15, 10.1521, 10.1552, 10.1553, 10.16, 10.172, 10.593, 10.873 • Skull, injuries, 10.40 • Skull, radiography, 10.10, 11.10 • Skull, secondary neoplasms, 10.33
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Identify the diverse changes associated with local and systemic disease on radiographs of the infant skull.
- List the appropriate differential diagnoses for abnormalities of the infant skull.
- Discuss which abnormalities of the infant skull require further diagnostic work-up.
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Introduction
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Skull radiographs are most commonly obtained today as part of a diagnostic survey for dysplasia or abuse, for evaluation of abnormal head shape, and for birth trauma. Computed tomography (CT) provides a more detailed and definitive evaluation of the skull, with the further advantages of permitting three-dimensional reformations and evaluating the intracranial content. Abnormalities in the infant skull may signify any of a large number of diverse conditions. The spectrum of radiographic abnormalities in the skull can yield important diagnostic information in localized and systemic disease states (Table 1). This review highlights a number of conditions that affect the infant calvaria.
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Development
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The skull is divided into two distinct portions: the neurocranium, which surrounds the brain and special sense organs, and the viscerocranium, which forms the lower face and jaws. The neurocranium is further divided into the membranous neurocranium, which forms the cranial vault, and the cartilaginous neurocranium, which forms the skull base (1). In the newborn, the membranous bones of the vault are separated by the intervening sutures. Where the sutures intersect, they widen and assume the shape of fontanelles. The larger anterior fontanelle lies at the intersection of the sagittal, coronal, and metopic sutures and closes by the end of the second year. The posterior fontanelle lies at the intersection of the sagittal and lambdoid sutures and closes before the third month. The most significant growth of the skull occurs along the sagittal and coronal sutures (2).
At birth, the volume of the neurocranium is eight to nine times greater than that of the face (3). This ratio is 5:1 by 2 years, 3:1 at 6 years, and 2:1 in the adult. A lateral skull radiograph with the jaws closed reveals the relative areas in the midsagittal plane of the cranium. The ratio of cranium to facial bones is 4–4.5 at birth and decreases with age: 3–3.5 at 2 years, 2.5 at 6 years, and 1.5–2 in the adult (3).
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Methods of Radiographic Examination
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Skull radiographs of infants are obtained in the supine position. Radiographic views include the following: (a) A straight anteroposterior view is obtained to demonstrate the calvaria. (b) One or both lateral views are obtained to demonstrate the calvaria and skull base in the lateral projection; both lateral views are indicated in trauma and focal lesion evaluation. (c) An anteroposterior view with 30° caudal tilt (Towne view) is obtained to demonstrate the occipital bone and foramen magnum. (d) The axial submentovertex view for the skull base and basal foramina has been replaced by CT in most institutions.
The optimum CT technique for examining the skull will require a soft-tissue algorithm to demonstrate the brain and a bone algorithm with thin overlapping sections to enable three-dimensional reformation.
Abnormalities of the skull can manifest in diverse ways. Focal and diffuse changes in bone density as well as deformity of the calvaria may occur congenitally or be acquired during infancy.
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Variations in Skull Density
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Decreased Density: Generalized
In the neonate, severe thinning of the calvaria and decreased calvarial density may signify osteogenesis imperfecta, achondrogenesis, hypophosphatasia, or Menkes syndrome (in order of increasing rarity). Types of achondrogenesis include achondrogenesis type IB, a recessive lethal chondrodysplasia caused by mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene on chromosome 5 (4), and achondrogenesis type II, a lethal disorder caused by dominant mutations in the type II collagen gene (COL2A1) (5). A diagnosis of achondrogenesis is more likely when the patient also exhibits areas of absent ossification in the axial skeleton, micromelia, and hydrops. Menkes syndrome is a rare X-linked recessive disorder of copper metabolism caused by mutations on chromosome Xq13.3, which encodes a copper-transporting adenosine triphosphatase (ATPase) (6). Key differential features for Menkes syndrome are osteopenia, mental retardation, micrognathia, metaphyseal spurs that are most obvious in the femora, urinary tract abnormalities, and high serum copper levels.
Hypophosphatasia.—
Hypophosphatasia is a heterogeneous disorder characterized by low or absent serum alkaline phosphatase activity caused by deficient activity of tissue-nonspecific alkaline phosphatase (TNSALP). The gene for TNSALP is located at chromosome 1p34–36.1 (7). There are two modes of genetic transmission. The congenital form is inherited as an autosomal recessive and is lethal (8). The autosomal dominant form is milder and manifests later in life. Hypophosphatasia typically appears as decreased ossification of the skull and vertebrae or as isolated plates or islands of unusually thin calvarial bone (Fig 1). The skull may be boneless and represented by a caput membranaceum. Other skeletal changes of hypophosphatasia include short tubular bones that are poorly and irregularly ossified and frayed metaphyses that resemble those of rickets.
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Figure 1a. Hypophosphatasia in a male neonate. (a) Frontal radiograph of the skull shows that the cranium is irregularly ossified. (b) Frontal radiograph of the chest and abdomen shows platyspondyly, gracile ribs, and frayed proximal humeral metaphyses, which confirm the diagnosis.
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Figure 1b. Hypophosphatasia in a male neonate. (a) Frontal radiograph of the skull shows that the cranium is irregularly ossified. (b) Frontal radiograph of the chest and abdomen shows platyspondyly, gracile ribs, and frayed proximal humeral metaphyses, which confirm the diagnosis.
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Osteogenesis Imperfecta.—
Osteogenesis imperfecta is a bone dysplasia characterized by osteoporosis and osseous fragility. Dominant-negative mutations within the COL1A1 and COL1A2 genes cause molecular defects in type I collagen (9,10), resulting in decreased collagen matrix in the skin and bones (11). Four distinct subgroups of osteogenesis imperfecta are now defined, according to severity and inheritance (12). The autosomal dominant types I and IV are the least severe forms. The autosomal recessive type III is more severe and manifests in early infancy. The autosomal dominant type II is a lethal condition that manifests at birth. Most cases of type II osteogenesis imperfecta arise as new mutations (8). Diagnostic features of osteogenesis imperfecta include multiple intersutural (wormian) bones (13) along the lambdoid suture. Thin cortices, decreased ossification of the skull base, multiple fractures, and "accordion" deformity of the long bones and ribs are additional features of osteogenesis imperfecta and help differentiate osteogenesis imperfecta from abuse when fractures are first detected (Fig 2).
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Figure 2a. Osteogenesis imperfecta in a neonate. Lateral skull radiograph (a) and frontal chest radiograph (b) show markedly diminished ossification of the skull and vertebrae. Healing rib fractures are present.
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Figure 2b. Osteogenesis imperfecta in a neonate. Lateral skull radiograph (a) and frontal chest radiograph (b) show markedly diminished ossification of the skull and vertebrae. Healing rib fractures are present.
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Decreased Density: Localized
In the infant skull, the differential diagnosis for focal osteopenia is limited. Localized areas of defective ossification occur in the lacunar skull. True convolutional markings occur later, after sutural closure.
The term lacunar skull signifies a dysplasia of the membranous bone with well-defined lucent areas in the calvaria that correspond to nonossified fibrous bone (Fig 3) (14). The lacunae are bounded by normally ossified bone. The appearance resolves spontaneously by age 6 months and is not related to the degree of concurrent hydrocephalus. Lacunar skull is associated with neural tube defects, especially myelomeningocele with Chiari II malformation, and less commonly with encephalocele. The multiple well-defined areas of relative lucency in the cranium must be distinguished from the increased convolutional markings that develop with pansynostosis at an older age.
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Figure 3a. Lacunar skull in a neonate with lumbar myelomeningocele. (a) Lateral skull radiograph shows zones of poorer ossification and bands of denser ossification, which reflect disorganization of the membranous template of the calvaria. The posterior fossa is shallow. (b) Gross anatomic specimen of a lacunar skull. Scale is in centimeters.
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Figure 3b. Lacunar skull in a neonate with lumbar myelomeningocele. (a) Lateral skull radiograph shows zones of poorer ossification and bands of denser ossification, which reflect disorganization of the membranous template of the calvaria. The posterior fossa is shallow. (b) Gross anatomic specimen of a lacunar skull. Scale is in centimeters.
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Increased Density: Generalized
The differential diagnosis for increased bone density includes sclerosing bone dysplasias such as osteopetrosis, pyknodysostosis, and craniodiaphyseal dysplasia (in order of increasing rarity). Pyknodysostosis can be distinguished from the others by the thick calvaria, wide lambdoid sutures and fontanelles, and multiple wormian bones. Other diagnostic features of pyknodysostosis include short limbs, hypoplasia of the mandible, and an obtuse mandibular angle. Craniodiaphyseal dysplasia is thought to have dominant transmission (15). In the newborn, craniodiaphyseal dysplasia is characterized by severe osteosclerosis with overgrowth of the skull, facial bones, and mandible. Obliteration of the paranasal sinuses and basal skull foramina and thickening of the diaphyses appear later. Sclerosis in the remainder of the skeleton is less marked.
Osteopetrosis is a heterogeneous group of osteosclerotic bone dysplasias in which the entire skeleton is unusually dense. Impaired bone resorption results in abundant osteoid and narrow, fibrotic medullary spaces (8). Two modes of inheritance are known. Dominant osteopetrosis, which has a benign course and late manifestation, has been localized to chromosome 16p13.3 (16). Mutations in autosomal recessive osteopetrosis have been localized to the ATP6I gene, which mediates acidification of the bone-osteoclast interface (17). The malignant autosomal recessive form of osteopetrosis manifests at birth (Fig 4), and the intermediate autosomal recessive form manifests in the first decade of life (18). Sclerosis initially affects the basal bones; later, the calvaria becomes dense and thick. The facial bones are usually relatively less dense (19). In congenital osteopetrosis, hematologic derangements, due to the diminished hematopoietic compartment, arise early and result in early death. The bones are fragile and prone to fracture and show a high susceptibility to osteomyelitis (18). Neural and vascular foramina are narrow, causing cranial nerve palsies by neural compression.
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Figure 4. Osteopetrosis in a neonate. Lateral skull radiograph shows sclerosis, which is most pronounced in the skull base with relative sparing of the mandible. The cervical vertebrae are also sclerotic.
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Increased Density: Localized
In the neonatal skull, the differential diagnosis for focal sclerosis includes frontometaphyseal dysplasia and craniometaphyseal dysplasia (in order of increasing rarity). Craniometaphyseal dysplasia is a dominant bone dysplasia mapped to chromosome 5p15.2-p14.1 (20) in which the sclerosis is confined to the frontal bone, nasion, and mandible. In craniometaphyseal dysplasia, metaphyseal expansion is a late feature.
Frontometaphyseal dysplasia is an X-linked dominant syndrome that has been localized to mutations in the FNLA gene (21). This dysplasia is characterized by prominence of the supraorbital ridges, restricted thoracic expansion, sternal deformity, and joint contractures. The manifestations are more severe in males and variable in females (22). Sclerosis is limited to the frontal bone and the skull base. Premature synostosis of the sutures, as well as an anterior mandibular spur, have been described (23) (Fig 5). Other radiologic findings include widening of the metaphyses, arachnodactyly, "coat hanger" configuration of the ribs, and coxa valga.
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Figure 5. Frontometaphyseal dysplasia in a male neonate. Lateral skull radiograph shows sclerosis confined to the frontal bone and skull base. Note the anterior mandibular spur and partially fused coronal sutures.
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Variations in Skull Size
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Microcephaly
The term microcephaly signifies a head circumference that is more than 2 standard deviations below the mean for age or is below the third percentile. Primary microcephaly includes familial and autosomal dominant microcephaly and several chromosomal syndromes (24) (Table 2). The small cranial size typically reflects underlying damage to the developing brain (radial microbrain). Infants with trisomy 21 are typically microcephalic. In Rubinstein-Taybi syndrome, microcephaly is associated with severe developmental delay and broad distal phalanges of the thumbs and first toes. This syndrome arises from microdeletions of the CREB-binding protein gene (25). CREB-binding protein is an essential transcriptional coactivator. In trisomy 13, the microcephalic neonate also has mandibular hypoplasia, a dysgenetic corpus callosum, and ventriculomegaly. Microcephaly occurs in other much less common syndromes, such as bird-headed Seckel dwarfism, a rare autosomal recessive condition that has been mapped to two loci on chromosomes 3q22.1-q24 and 18p11.31-q11.2 (26). Infrequently, malformation that leads to reduced brain growth can result from acquired disease such as congenital TORCH infections (toxoplasmosis, rubella, cytomegalovirus, herpes simplex), maternal diabetes, and alcohol or hydantoin embryopathy. Lack of normal postnatal brain growth is associated with secondary pancraniosynostosis, resulting in a small head of normal shape.
Congenital TORCH infections are acquired transplacentally in utero or during birth. Congenital cytomegalovirus infection is associated with microcephaly, microgyria, and intracranial calcifications (Fig 6). Affected infants are small for dates and present with petechial rash, hepatosplenomegaly, chorioretinitis, deafness, and developmental delay. Babies who acquire a TORCH infection at birth are not yet microcephalic; microcephaly at birth signifies an earlier infection in utero. Congenital rubella is associated with cataracts, middle ear and cardiac malformations, and skeletal features such as metaphyseal linear "celery stalk" striations. Congenital rubella and other TORCH infections are now rare because of childhood immunization and prenatal screening.
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Figure 6. Congenital cytomegalovirus infection and microcephaly in a neonate. Semilateral skull radiograph shows intracranial calcifications that conform to the shape of the ventricles.
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Macrocephaly
The term macrocephaly signifies a head circumference that is more than 2 standard deviations above the mean or exceeds the 97th percentile by at least 0.5 cm. Macrocephaly may result from a variety of genetic defects or acquired causes of increased intracranial volume, such as hydrocephalus or subdural collections or any cause of raised intracranial volume (Table 3). Genetic causes include neurofibromatosis, achondroplasia, cerebral giantism (Sotos syndrome), and campomelic dysplasia. Cerebral giantism is characterized by a large dolichocephalic skull, large hands and feet, weight above the 90th percentile, and profound developmental delay. Pathognomonic signs of campomelic dysplasia are hypoplastic scapulae, short limbs with anterior angulation in the femora and tibiae, and hypoplastic fibulae. Macrocephaly is encountered in later infancy in patients with mucopolysaccharidoses, mucolipidoses, and other metabolic storage diseases, where abnormal metabolites deposit in the meninges, thicken them, and interfere with cerebrospinal fluid absorption.
Large head size is also seen in two dysmyelinating diseases: Alexander disease and Canavan disease. Alexander disease is a rare nonfamilial progressive neurologic degenerative disease with onset in early infancy, resulting in early childhood death. Alexander disease is characterized by the presence of abnormal intracytoplasmic proteinaceous inclusions in fibrous astrocytes (Rosenthal fibers) (27). Mutations in the glial fibrillary acid protein (GFAP) gene have been shown in patients with Alexander disease (28). Canavan disease, a severe autosomal recessive leukodystrophy with manifestation in early infancy, is characterized by axonal demyelination and spongiform degeneration, predominantly in the white matter (29). The disease is caused by aspartoacylase deficiency, which results in accumulation of N-acetyl-L-aspartate in the brain. The aspartoacylase gene has been localized to chromosome 17p13-ter (29).
Achondroplasia is an autosomal dominant rhizomelic dwarfism that affects endochondral bone. It is the most common nonlethal dysplasia. More than 90% of cases arise as spontaneous mutations affecting the gene encoding the fibroblast growth factor receptor 3 (FGFR3); these mutations occur on the paternal chromosome (30). The cartilaginous skull base is small. The membranous cranial vault is disproportionately large, with associated frontal bossing and depression of the nasion (Fig 7). In the neonate with achondroplasia, the head circumference is more than 2 standard deviations above the mean; it increases even further above the normal range in the first year (31). The posterior fossa is shallow, and all basal foramina are hypoplastic. Small jugular foramina impede venous flow (32), and the small foramen magnum impedes cerebrospinal fluid drainage, resulting in ventriculomegaly with increased head size. Skeletal abnormalities include short wide ribs, square iliac bones, a "champagne glass"–shaped pelvic inlet, short pedicles, narrowing of the lumbar interpediculate distances, and spinal stenosis.
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Figure 7a. Achondroplasia in a neonate. Frontal (a) and lateral (b) skull radiographs show that the cranial vault is large in relation to the small skull base. There is frontal bossing and a depressed nasion.
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Figure 7b. Achondroplasia in a neonate. Frontal (a) and lateral (b) skull radiographs show that the cranial vault is large in relation to the small skull base. There is frontal bossing and a depressed nasion.
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Abnormalities of Head Shape
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The skull shape can be altered by deformations or true sutural synostosis. In utero, deformation of the skull may result from faulty fetal packing or the syndrome of amniotic bands. Amniotic bands may cross the calvaria at any level to produce variable skull deformities or may cross the face, causing hypoplasias and clefting. Postnatally, head deformity commonly results from preferential sleep position (positional plagiocephaly) or premature sutural synostosis.
Faulty Fetal Packing
The term faulty fetal packing signifies concave depressions in the neonatal skull that are caused by prolonged extrinsic pressure from a malpositioned limb in utero (Fig 8). The skull deformity is not permanent and will resolve with time. Parietal bone compression has also been shown to occur from extrinsic pressure caused by uterine leiomyomas (33). A differential possibility for localized skull depression is compression applied during forceps delivery.
Positional Plagiocephaly
Calvarial deformation results from external pressure after birth when an infant is consistently placed in the same position for rest and sleep. This can be marked in very premature infants, whose heads become flattened and scaphocephalic when they are positioned on their side for mechanical ventilation. In 1992, the American Academy of Pediatrics recommended that neonates and infants be placed to sleep on their backs in order to decrease the incidence of sudden infant death syndrome. The long hours spent supine and the infants’ inability to change position caused persistent pressure against one portion of the skull (preferred sleeping position) and occipital flattening. The deformity may be bilateral and symmetric or one side may be substantially more flattened than the other, leading to secondary changes in the position and appearance of the ear. Posterior positional plagiocephaly has become increasingly common. Extreme cases come to radiologic evaluation to exclude possible unilateral or bilateral lambdoid synostosis. Normal outward pressure from brain growth, most marked in the first 2 years of life, provides sufficient stimulus for remodeling once the child is old enough to roll from side to side or sit up, even with support.
Craniosynostosis
Primary synostosis is subdivided into syndromic (familial or hereditary) and the more common nonsyndromic (isolated and sporadic). Premature fusion of the sutures may be isolated or form part of a syndrome, including Crouzon syndrome (premature synostosis, maxillary hypoplasia, shallow orbits), Apert syndrome (craniosynostosis with syndactyly of fingers and toes), and Pfeiffer syndrome (premature synostosis, broad thumbs and great toes, and mild soft-tissue syndactyly). The latter three syndromes are associated with fibroblast growth factor receptor 2 (FGFR2) mutations (34,35). FGFR2 mutations lead to increased numbers of precursor cells that are involved in the osteogenic pathway (31). Carpenter syndrome (premature synostosis, severe developmental delay, brachydactyly, syndactyly, thumb duplication) has been linked to the ATR-X gene (36).
Cloverleaf skull (kleeblattschaedel) develops when there is premature synostosis of all except the squamosal suture. This configuration may be seen with severe Apert or Crouzon syndrome or in association with thanatophoric dysplasia. Thanatophoric dysplasia is a sporadic lethal dysplasia caused by mutations in fibroblast growth factor receptor 3 (FGFR3), resulting in chronic FGFR3 hyperactivation and inhibition of bone growth (37). Additional diagnostic findings are short ribs, short curved long bones, and platyspondyly.
Normal skull growth occurs in a direction perpendicular to the axis of the sutures. The term premature cranial suture synostosis signifies premature closure of one or more of the cranial sutures. Secondary synostoses are encountered in a variety of unrelated conditions, including metabolic derangements such as hypophosphatasia and rickets, bone dysplasias such as mucopolysaccharidoses and thanatophoric dysplasia, and effects of fetal teratogens such as hydantoin. Secondary sutural closure occurs after ventriculoperitoneal shunting, when reduction in ventricular size reduces the expansile forces on the calvaria. When sutures fuse prematurely, head growth occurs along the axis of the fused suture. The altered skull shape is diagnostic. Because closure of the suture does not always occur along its entire length and may not involve the entire depth of the suture, the entire length of each suture must be evaluated (38). Radiographs obtained tangential to a palpable ridge or sutural bump may prove to be diagnostic in situations where standard radiographs are equivocal or show only an abnormal head shape but not suture closure. Synostosis may occur in utero and manifest at birth, but diagnosis is usually delayed until misdirected growth manifests as calvarial asymmetry.
Scaphocephaly and Dolichocephaly.—
These terms denote calvarial elongation in the anteroposterior diameter. This condition results from premature sagittal synostosis (Fig 9). This is the most common type of synostosis, accounting for up to 50% of cases, and is more common in males (2). Sagittal synostosis is frequently inherited as an autosomal dominant trait (39).
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Figure 9a. Sagittal synostosis in a neonate. (a) Lateral skull radiograph shows anteroposterior elongation of the cranium (scaphocephaly). (b) Frontal skull radiograph shows that the fused sagittal suture is sclerotic and "heaped up." (c) Photograph obtained during surgical exposure shows the prominent posterior sagittal ridge (arrowheads) along the line of closure.
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Figure 9b. Sagittal synostosis in a neonate. (a) Lateral skull radiograph shows anteroposterior elongation of the cranium (scaphocephaly). (b) Frontal skull radiograph shows that the fused sagittal suture is sclerotic and "heaped up." (c) Photograph obtained during surgical exposure shows the prominent posterior sagittal ridge (arrowheads) along the line of closure.
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Figure 9c. Sagittal synostosis in a neonate. (a) Lateral skull radiograph shows anteroposterior elongation of the cranium (scaphocephaly). (b) Frontal skull radiograph shows that the fused sagittal suture is sclerotic and "heaped up." (c) Photograph obtained during surgical exposure shows the prominent posterior sagittal ridge (arrowheads) along the line of closure.
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Brachycephaly.—
The term signifies abnormal calvarial widening in the transverse diameter. It typically arises when coronal or lambdoid synostosis limits anteroposterior growth. There is a slightly higher incidence of bilateral coronal synostosis in females (2). The ipsilateral frontal bone is flattened and the orbit is deformed with elevation of its superior lateral angle, resulting in the so-called harlequin eye (Fig 10). The midline of the face is skewed with respect to the midline of the skull base. The incidence of associated anomalies is higher with bilateral coronal synostosis than with sagittal synostosis (2).
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Figure 10a. Bilateral coronal synostosis in a 3-week-old neonate. (a) Frontal skull radiograph shows bilateral harlequin eye. (b) Lateral skull radiograph shows that the anteroposterior skull diameter is diminished. The coronal sutures are sclerotic, linear, and without normal interdigitations.
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Figure 10b. Bilateral coronal synostosis in a 3-week-old neonate. (a) Frontal skull radiograph shows bilateral harlequin eye. (b) Lateral skull radiograph shows that the anteroposterior skull diameter is diminished. The coronal sutures are sclerotic, linear, and without normal interdigitations.
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Plagiocephaly.—
Plagiocephaly, or asymmetry, usually occurs with unilateral coronal synostosis or asynchronous synostoses of multiple sutures bilaterally. Asymmetric growth results in displacement of the sagittal suture, nasal septum, and skull base to the affected side (Fig 11).
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Figure 11a. Unilateral coronal synostosis in a neonate. (a) Frontal skull radiograph shows right-sided harlequin eye. (b) Lateral skull radiograph shows sutural asymmetry. The normal suture has indistinct margins, whereas the fused right suture is sclerotic and linear.
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Figure 11b. Unilateral coronal synostosis in a neonate. (a) Frontal skull radiograph shows right-sided harlequin eye. (b) Lateral skull radiograph shows sutural asymmetry. The normal suture has indistinct margins, whereas the fused right suture is sclerotic and linear.
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Calvarial Defects
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Causes of calvarial defects include parietal foramina, cranium bifidum, abnormally large fontanelles, and cleidocranial dysplasia (Table 4).
Parietal Foramina
Parietal foramina result from delayed or incomplete ossification of the parietal bone. Parietal foramina typically occur as an isolated autosomal dominant trait or as part of a syndrome. The underlying genetic anomaly has been identified as chromosome 11p deletions with mutation of the ALX4 gene (40). The calvarial defects may be so large as to extend to the midline (Fig 12) and may be palpable. During the first few months of life, ossification along a midline bar may separate confluent parietal defects into paired parasagittal defects, which may persist into adult life.
Cranium Bifidum
The term cranium bifidum denotes an abnormal osseous defect through which there may be herniation of meninges and brain tissue. It occurs with midline malformations such as myelomeningocele, meningoencephalocele, or dermal sinus (Fig 13). Herniation through the calvaria may be the result of defective induction of the bone or failure of primary neural tube closure (41).
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Figure 13a. Frontal encephalocele and interhemispheric lipoma in a neonate. (a) Lateral skull radiograph shows a triangular area of lucency (arrowhead), which represents a lipoma of the corpus callosum. (b) Axial CT scan shows the lipoma as a triangular area of low attenuation (arrowhead). An anterior skull defect and soft-tissue mass (arrow in a) are most easily appreciated on the CT scan (b).
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Figure 13b. Frontal encephalocele and interhemispheric lipoma in a neonate. (a) Lateral skull radiograph shows a triangular area of lucency (arrowhead), which represents a lipoma of the corpus callosum. (b) Axial CT scan shows the lipoma as a triangular area of low attenuation (arrowhead). An anterior skull defect and soft-tissue mass (arrow in a) are most easily appreciated on the CT scan (b).
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Abnormally Large Fontanelles
Abnormally large fontanelles may arise in conjunction with suture spreading from elevated intracranial pressure or as part of skeletal dysplasias, such as osteogenesis imperfecta and cleidocranial dysplasia.
Cleidocranial Dysplasia
Cleidocranial dysplasia is an autosomal dominant syndrome affecting membranous bone. The locus for this dysplasia has been isolated to the short arm of chromosome 6. The abnormalities are caused by mutations in the CBFA1 gene, a transcription factor that activates osteoblastic differentiation (42). Cleidocranial dysplasia is characterized by widening of the fontanelles with broad lateral cranial diameter and multiple wormian bones along the lambdoid suture (Fig 14). The sutures and fontanelles close late. Associated skeletal anomalies include absent or hypoplastic clavicles, a widened pubic symphysis, multiple spinal anomalies, and hypoplastic middle and distal phalanges. Hearing loss occurs in 38% of those affected with cleidocranial dysplasia (42).
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Figure 14a. Cleidocranial dysplasia in an older child in whom the anterior fontanelle has remained widely patent. Frontal (a) and lateral (b) skull radiographs show frontal bossing, brachycephaly, wide biparietal diameter, and wormian bones along the lambdoid sutures. Concomitant ossicular abnormalities required use of a hearing aid.
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Figure 14b. Cleidocranial dysplasia in an older child in whom the anterior fontanelle has remained widely patent. Frontal (a) and lateral (b) skull radiographs show frontal bossing, brachycephaly, wide biparietal diameter, and wormian bones along the lambdoid sutures. Concomitant ossicular abnormalities required use of a hearing aid.
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Other Acquired Conditions
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Posttraumatic Abnormalities
The most common causes of abnormal head shape in the neonatal period are physiologic molding during birth and caput succedaneum.
Cephalohematoma.—
The term cephalohematoma signifies a traumatic subperiosteal hematoma of the calvaria (43). Because the cephalohematoma is bounded by the outer layer of the periosteum and the sutures, it cannot cross the midline. This restriction distinguishes it from subgaleal hematoma, which does cross the midline deep to the galeal aponeurosis. Cephalohematomas occur in approximately 1%–2% of live births, are almost twice as common in males than in females, and are more common in children of primiparous mothers. The incidence increases after forceps extraction (43). Cephalohematomas manifest as firm, tense soft-tissue masses that usually increase in size after birth. They resolve spontaneously. Most calcify peripherally and gradually incorporate into the calvaria. Cephalohematomas may be unilateral or bilateral (Fig 15).
Fractures.—
Fractures can occur from minimal applied force in the abnormal fragile bone associated with osteogenesis imperfecta. In normal bone, skull fractures are the result of trauma, whether from intentionally inflicted abuse or from accidental trauma, including injury sustained during birth and forceps extraction. Diastatic fracture lines are typically more lucent, more linear, and show no interdigitations, features that distinguish them from sutures (Fig 16). The metopic, mendozal, and interparietal sutures are most easily distinguished from fractures by their sutural interdigitations and characteristic anatomic locations. However, depressed skull fractures appear dense due to the overlapping bone fragments (Fig 17). Skull radiography will demonstrate horizontal linear fractures that are parallel to the axial plane of CT and therefore may not be detectable at CT. Acute fractures are accompanied by overlying soft-tissue swelling and hematoma, which become apparent on tangential views.
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Figure 16a. Bilateral skull fractures in a neonate who experienced an accidental fall. Frontal (a) and lateral (b) skull radiographs show fractures (arrowheads in a) that are sharply defined and slightly diastatic, with no element of compression.
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Figure 16b. Bilateral skull fractures in a neonate who experienced an accidental fall. Frontal (a) and lateral (b) skull radiographs show fractures (arrowheads in a) that are sharply defined and slightly diastatic, with no element of compression.
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Figure 17. Depressed skull fracture in a neonate. Lateral skull radiograph shows a depressed frontal fracture, which appears dense because the adjacent cortices overlap in the fracture zone.
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Skull fractures carry little prognostic value in predicting neurologic damage resulting from trauma (41). The skull is relatively commonly injured in abused children, representing 7%–30% of all abuse fractures (44). No pattern of skull injury is diagnostic of abuse. The diagnosis of abuse becomes more likely when there is a discrepant history of minor trauma in a child with complex, depressed, diastatic, or multiple fractures, particularly in the occipital bone (44). Associated distinguishing features in abuse include corner metaphyseal fractures and concurrent acute and healing fractures, usually with normal skull density. Osteogenesis imperfecta can be diagnosed when skull density is decreased and wormian bones are present (13,45).
Leptomeningeal Cyst.—
The term leptomeningeal cyst (growing skull fracture) signifies a well-defined bone defect that may arise when traumatic laceration of the dura exposes the bone to the pulsations of the cerebrospinal fluid within the subarachnoid space. Pulsatile pressure erosion then gradually widens the fracture line (Fig 18). Leptomeningeal cysts develop following 0.6% of skull fractures and are most common in children under 3 years of age (41). The differential diagnosis includes eosinophilic granuloma and infection. Calvarial involvement in eosinophilic granuloma is rare in young infants. When present, it manifests as solitary or multiple lucent areas in the calvaria. In eosinophilic granuloma, typical beveled edges do not occur in the infant cranium prior to development of the diploic layer. Osteomyelitis manifests as overlying soft-tissue edema and poorly defined infiltrating margins.
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Figure 18a. Evolution of a leptomeningeal cyst. (a) Lateral skull radiograph obtained at 9 weeks of age shows an acute parietal fracture. (b) Lateral skull radiograph obtained at 7 months of age shows that the fracture has healed except for a well-defined lucent defect in the parietal bone, which represents the calvarial defect at the site of a leptomeningeal cyst.
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Figure 18b. Evolution of a leptomeningeal cyst. (a) Lateral skull radiograph obtained at 9 weeks of age shows an acute parietal fracture. (b) Lateral skull radiograph obtained at 7 months of age shows that the fracture has healed except for a well-defined lucent defect in the parietal bone, which represents the calvarial defect at the site of a leptomeningeal cyst.
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Neoplasia
Advanced leukemia and neuroblastoma may both produce multiple, poorly defined osteolytic lucencies, which may coalesce. They thicken the bone, strip the dura away from the inner table, and may cause intracranial mass effect and induce sutural widening (Fig 19) (46). Metastatic deposits in the skull cause lytic destruction and expansion (Fig 20) and occasionally a characteristic "hair on end" appearance in the sphenoid bones. Localized areas of bone destruction in leukemia are frequently surrounded by normal bone and likely represent tumor metastases (47). Today’s efficacious chemotherapy usually prevents these diseases from reaching such an advanced stage. Associated features of metastatic disease include infiltration of the appendicular skeleton and hepatosplenomegaly in leukemia.
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Figure 19a. Acute leukemia in a 7-month-old female infant with proptosis. Frontal (a) and lateral (b) skull radiographs show that all of the sutures are wide due to raised intracranial pressure.
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Figure 19b. Acute leukemia in a 7-month-old female infant with proptosis. Frontal (a) and lateral (b) skull radiographs show that all of the sutures are wide due to raised intracranial pressure.
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Conclusions
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Recognition of abnormalities of the skull may assist in diagnosis of some dysplasias as well as diverse acquired conditions such as trauma and abuse. Diagnostic information obtained from skull radiographs can reveal valuable indicators of local and systemic disease conditions and can help direct and tailor further radiologic and laboratory work-up. Plain radiography of the infant skull provides much useful diagnostic information that cannot be obtained from cross-sectional imaging.
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Footnotes
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Abbreviation: TORCH = toxoplasmosis,
rubella,
cytomegalovirus,
herpes simplex
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References
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Abstract
LEARNING OBJECTIVES FOR TEST...
