Craniofacial development initiates at approximately gestation day 25, following closure of the anterior neuropore. Neural crest cells migrate and induce formation of the branchial arches. The first branchial arch and neural crest ectomesenchyme give rise to 5 prominences that surround the stomodeum (the future mouth). The facial prominences (or processes) consist of a single midline frontal prominence (median nasal process), paired maxillary prominences, and paired mandibular prominences. The facial prominences progressively fuse by disintegration of the contacting epithelial surfaces, and the intervening grooves fill in by migration of cells and proliferation of mesenchyme. Formation of the palate involves fusion of the primary palate, which is derived from the median nasal process, and the palatine shelves, which are derived from the maxillary processes. Failure of appropriate fusion of the 7 embryonic facial prominences results in persistent facial or palatal clefts.

During fusion of the facial processes, complete lysis of the overlying epithelium occurs. Failure of complete epithelial lysis can result in trapping of epithelial elements between embryonic processes of bone. This epithelial tissue may undergo proliferation and cystic degeneration. This can result in a nasopalatine duct cyst, globulomaxillary cyst, or nasoalveolar cyst. The nasopalatine duct cyst is the most common developmental cyst of the maxilla. This results from entrapment of epithelial cells within the incisive canal during fusion of the horizontal palatal processes and the premaxilla. This cyst is usually asymptomatic. CT shows a well-circumscribed midline low attenuation lesion with sclerotic margins located along the course of the incisive canal between the nasal fossa and the alveolar process of the maxilla. The globulomaxillary cyst is due to entrapment of epithelium at the site of fusion of the median nasal process and the maxillary process. Radiographs and CT show an inverted pear shaped or oval radiolucency located between the maxillary lateral incisor and the cuspid. Displacement of the roots of these teeth is common.

Disorders of facial clefting can be isolated or syndromic. Hundreds of syndromes associated with facial clefting have been described. Facial clefting is usually classified as central versus lateral. The Pierre Robin sequence is an example of a central clefting syndrome. Restricted mandibular development causes failure of the tongue to descend away from the fusion line of the secondary palate. Lateral facial clefting syndromes typically result from deficiencies in the first and second pharyngeal arches. Examples include Treacher Collins syndrome and hemifacial microsomia. Children with velo-cardio-facial syndrome have deficiencies of the frontal nasal process, including palatal deficiency, a broad nasal bridge, a hypoplastic philtrum, and hypertelorism.

The most common type of facial clefting is a simple cleft involving the upper lip or palate. Lip clefting usually extends from the lateral border of the philtrum into the nostril, and is due to failure of the medial nasal prominence to merge with the maxillary prominence. Palatal clefts are caused by failure of fusion between the primary palatal process and the secondary process of the maxillary prominence. Typically, the cleft is located between the incisors and the canines. If there is failure of fusion between the secondary palatal shelves, a more extensive palatal cleft occurs. Bilateral complete clefts of the lip and palate result from lack of fusion of the primary and secondary palatal shelves and the maxillary and frontonasal processes.

Early during the embryonic phase, the developing frontal bones are separated from the nasal bones by a small fontanelle: the fonticulus frontonasalis. The prenasal space refers to the separation between the nasal bones and the deeper cartilaginous nasal capsule. The prenasal space extends from the base of the brain to the nasal tip. During the end of the second gestational month, a transient mid-line diverticulum of dura projects into the fonticulus frontonasalis and another dural diverticulum projects into the prenasal space. With normal development, these diverticula regress and there is obliteration of the fonticulus frontonasalis and prenasal space. As the frontal and ethmoid bones close at the midline of the skull base, a small ostium remains; the foramen cecum.

The dural diverticula adjacent to the developing nose contact ectoderm. As the diverticula regress, ectoderm can be drawn along and form a dermal sinus, superficial pit, or dermoid or epidermoid cyst. Nasal cephalocele and nasal glioma also are related to this developmental process, with abnormal persistence of a dural diverticulum or trapping of neural tissue extracranially as the base of the diverticulum closes. Persistent herniation of brain parenchyma into the dural projection results in a nasal encephalocele.

The skull develops from mesenchyme that surrounds the embryonic brain. The cartilaginous neurocranium (chondrocranium) undergoes endochondral ossification to form the bones of the skull base. The calvaria forms by intramembranous ossification in the mesenchyme surrounding the lateral and superior margins of the brain. Abnormal embryonic brain development can cause secondary anomalies of the calvaria, such as cephalocele and anencephaly. The sutures are dense connective tissue membranes between the growing calvarial flat bones. Premature closure of sutures (craniosynostosis) leads to various calvarial deformities. There are 6 fontanelles in the fetal calvaria; these are fibrous zones at the junction points between multiple sutures. The squamous portion of the temporal bone forms by way of intramembranous ossification in the maxillary prominence of the first branchial arch.

Congenital Depressions

Congenital calvarial depressions are indentations or grooves in the skull due to in utero extrinsic pressure on the fetal cranium. Potential causes include a prolonged abnormal fetal position, fetal head and neck tumor, and amniotic bands. Radiographs and CT demonstrate a localized skull depression without a fracture line or scalp swelling.

Parietal Foramina

Parietal foramina are clinically insignificant ossification defects in the parietal bones. The defects are symmetric, and vary in size from a few millimeters to several centimeters. Large parietal foramina are sometimes palpable. There is autosomal dominant hereditary transmission of parietal foramina in some families. Radiographs show symmetric ossification defects on each side of the sagittal suture. The defects have smooth, well-defined margins.¹

Cutis Aplasia Congenita

Cutis aplasia congenita is a localized failure of cutaneous development that can occur in the scalp, face, trunk, or limbs. Although most often an isolated lesion, cutis aplasia congenita can occur in association with various additional anomalies, such as limb deformities (distal phalangeal hypoplasia), hemangiomas, intracranial arteriovenous malformation, spinal dysraphism, and epidermolysis bullosa. Approximately 70% of patients with cutis aplasia congenita have a solitary scalp defect. The most common location is in the paramedian region of the vertex. Approximately 20% of these scalp lesions have an associated calvarial defect. The dura may or may not be intact when there is a skull defect. Cross-sectional imaging studies show localized thinning of the cutaneous tissues (Figure 26-1). A skull defect, when present, is usually well-defined. MR is the most sensitive imaging technique to assess for dural involvement.²

Microcephaly

Microcephaly is a nonspecific term that indicates an abnormally small head. By necessity, an abnormally small brain accompanies microcephaly; that is, microencephaly. The rare calvarial disorder of total craniosynostosis is the only important primary form of microcephaly. Secondary forms are much more common, with a small calvarial size due to microencephaly. The brain in patients with microcephaly, particularly when mild, is usually structurally normal aside from being somewhat small. Various brain malformations and destructive brain lesions can lead to microcephaly, however. The most common causes of congenital microencephaly are maternal factors (e.g., infection, malnutrition, or drug ingestion) and various primary developmental lesions of the brain. Acquired microencephaly and microcephaly can result from cranial irradiation, therapeutic shunting of severe hydrocephalus, or exposure to various toxins or drugs. Although there are no absolute criteria for initiation of an imaging evaluation of the child with suspected microcephaly, an occipitofrontal circumference of greater than 2 standard deviations from the mean has a substantial association with an underlying brain abnormality.

Macrocephaly

Macrocephaly, or enlarged head, carries a substantial differential diagnosis. Mild forms are often familial and of no clinical significance. Many infants with macrocephaly have prominent subarachnoid spaces; that is, “benign enlargement of the subarachnoid spaces.” Other potential causes include hydrocephalus, subdural hematoma or hygroma, and intracranial neoplasm. Enlargement of the head can occur with various rare brain malformations, such as primary megalencephaly and pituitary gigantism. Calvarial enlargement is a component of some bone dysplasias, including cleidocranial dysostosis, achondroplasia, and Hurler disease.

Craniosynostosis

The cranial and facial bone sutures are the principal sites of growth of the skull and facial bones. Craniosynostosis refers to premature fusion of a suture, whereas craniostenosis is the resultant fused bone. Normally, the metopic suture is the first of the cranial sutures to fuse, beginning at approximately 2 years of age and completed by 3 years. The other skull sutures progressively narrow during childhood as growth of the underlying brain slows, but closure does not begin until adulthood. Loss of a radiographically visible suture significantly precedes actual closure. For instance, there is no identifiable metopic suture on imaging studies in about one-third of normal 3-month-old infants despite physiological patency. Craniosynostosis occurs in approximately 1 per 2,000 births.^3,4

Craniosynostosis occurs in primary and secondary forms. Primary craniosynostosis is apparently due to an abnormality of the mesenchymal layer of the ossification centers in the calvaria. Most often, craniosynostosis occurs as a sporadic lesion, without associated anomalies. Craniosynostosis is, however, associated with numerous craniofacial syndromes, including Apert, Crouzon, Carpenter, and Pfeiffer syndromes.^5,6 Secondary forms of craniosynostosis can occur in patients with intracranial pathology that causes volume loss, such as shunted hydrocephalus or brain atrophy. Craniosynostosis can also occur in association with hyperthyroidism, abnormalities of calcium and phosphorus metabolism (e.g., rickets, hypophosphatasia, and hypercalcemia), and hematological disorders that cause bone marrow hyperplasia.

Standard skull radiographs are diagnostic for most instances of craniosynostosis; however, CT has greater sensitivity and specificity. CT also provides three-dimensional depictions of cranial deformities, which is often essential for planning reconstructive surgery. The imaging features of craniosynostosis include lack of a visible radiolucent suture line (partial or complete), ridging at the site of the fused suture, and cranial deformity.

Craniosynostosis results in various cranial deformities that relate to the specific sutures involved and the age at which fusion occurs. Recognition of these deformities is important for the radiographic detection of premature suture closure. Brachycephaly refers to a skull that is wide, tall, and foreshortened; this occurs with bilateral coronal synostosis. Scaphocephaly (dolichocephaly) indicates a narrow elongated calvaria (“hull” shaped) due to synostosis of the sagittal suture (Figure 26-2). Trigonocephaly describes a narrow triangular configuration of the forehead with a mid-line ridge (“keel”); this deformity results from premature fusion of the metopic suture (Figure 26-3). Plagiocephaly (“twisted skull”) refers to an asymmetric configuration of the cranium. Three types of plagiocephaly are recognized. Synostotic plagiocephaly is due to unilateral craniosynostosis (Figure 26-4). Compensational plagiocephaly refers to flattening of the forehead in response to premature fusion of the contralateral lambdoid suture. Deformational plagiocephaly lacks an underlying synostosis, and may be related to extrinsic compressive forces. Acrocephaly (tower skull) describes a deformity in which the anterior aspect of the cranium is higher than the posterior aspect, resulting in slanting from front to back; synostosis of multiple sutures is usually involved, and this skull shape frequently is associated with Apert syndrome. Oxycephaly refers to a skull that is tall and foreshortened in the anterior-posterior and lateral dimensions, with an obtuse or obliterated nasofrontal angle. This deformity is associated with late bilateral coronal synostosis or refusion following surgical treatment for coronal synostosis. Turricephaly indicates a skull with excessive upward growth (tower shape) due to early synostosis of the frontoparietal sutures; this deformity occurs in various craniosynostosis syndromes. Kleeblattschädel, or cloverleaf skull, indicates a trilobate appearance of the cranium due to premature fusion of multiple sutures.

Premature fusion of the sagittal suture is the most common form of craniosynostosis, accounting for approximately 60% of cases. Most affected patients are boys. Scaphocephaly is sometimes recognizable at birth in these children. Physical examination may demonstrate a palpable ridge along the closed sagittal suture. The elongation of the calvaria that commonly occurs in premature infants due to positional molding is distinct from true sagittal craniosynostosis. The radiographic features of sagittal craniosynostosis include elongation of the skull, sclerosis along the sagittal suture, and sclerotic bone bridging the suture (visible on frontal views) (Figure 26-5).

Approximately 20% of instances of craniosynostosis involve the coronal sutures. Coronal craniosynostosis is more common in girls than in boys. Children with unilateral coronal synostosis have forehead asymmetry, contralateral malposition of the ear, unilateral brow retrusion, contralateral frontal bossing, premature closure of the anterior fontanelle, and ridging of the affected suture. Bilateral coronal craniosynostosis results in brachycephaly and anterior displacement of the anterior fontanelle. The forehead is flattened, and there may be palpable ridges along the prematurely closed sutures. Frontal radiographs and anterior 3D CT images show an oval configuration of the orbit, with a characteristic “harlequin eye” appearance (Figure 26-6). There is undergrowth of the ipsilateral frontal bone, with a shallow anterior cranial fossa (Figure 26-7). Children with bilateral coronal craniosynostosis have hypertelorism.

Metopic synostosis accounts for less than 20% of surgical cases of craniosynostosis. At least three-quarters of these children are male. There is a relatively high association with brain anomalies, such as holoprosencephaly and dysgenesis of the corpus callosum. Children with metopic craniosynostosis have a palpable midline frontal ridge. Hypotelorism is usually identifiable clinically and radiographically. Imaging evaluation demonstrates an oval configuration of the orbital margins, with upward and medial angulation. On frontal skull views, this produces a “quizzical eye” appearance. CT shows midline pointing of the anterior cranial fossa (Figure 26-3), diminished interpterional width, diminished frontal bone height, anterior displacement of the coronal sutures, and a normal length of the frontal base (Figure 26-8).

Premature closure of multiple cranial sutures results in the cloverleaf skull malformation (Figure 26-9). The involved sutures are sclerotic. There is marked calvarial deformity due to outward bulging of the squamosal regions. The squamosa are thinned. Internal sclerotic ridging may be present. The orbits are shallow, resulting in exophthalmos.

Posterior Plagiocephaly

Posterior plagiocephaly is most often due to positional molding (posterior deformational plagiocephaly or positional plagiocephaly). True unilateral lambdoid synostosis accounts for only 2% to 3% of cases. Nonoperative therapy is sufficient for most patients with positional molding, but surgical correction is indicated in most instances of true unilateral lambdoid synostosis.^7–9

Positional plagiocephaly has become more common in recent years, apparently due to the encouragement of back sleeping for infants. Although the deformity is occasionally present at birth, the clinical presentation is much more common during the first few months of life. The deformity usually is unilateral or predominates on 1 side. Physical examination shows occipital flattening, ipsilateral anterior ear displacement, and mild ipsilateral frontal bossing. In extreme cases, the nasal root is displaced slightly away from the affected side.

The etiology of deformational plagiocephaly is unknown, and may be multifactorial. Suspected factors include intrauterine restraint, twin pregnancy, and postnatal positioning. This deformity is more common in boys. It is sometimes accompanied by torticollis. Torticollis due to fibromatosis of the sternocleidomastoid muscle may contribute to plagiocephaly by limiting neck mobility, but facial asymmetry in these children can occur without accompanying skull flattening. Deformational plagiocephaly may result in varying degrees of mandibular dysmorphology, which can cause symptomatic malocclusion or other mandibular symptoms later in life.

Treatment of deformational plagiocephaly is best initiated during infancy while the skull is still plastic. The simplest early treatment is counter positioning. Physical therapy is useful if there is torticollis. Helmet therapy can be initiated at approximately 6 months of age if positioning is ineffective. The helmets are designed to either passively prevent deformational force, or actively remold the cranial vault during growth. Assessment of the effectiveness of conservative therapy for deformational plagiocephaly is typically by clinical observation. Skull radiographs and 3D CT are reserved for patients with worsening deformity or those for whom surgical correction is contemplated.

With unilateral lambdoid synostosis, sutural ridging is palpable on physical examination; this finding is absent with deformational plagiocephaly. Unilateral lambdoid synostosis results in posterior parietal bossing contralateral to the flattened area of the skull and displacement of the ear posteriorly, whereas deformational plagiocephaly has ipsilateral frontal bossing and anterior displacement of the ear. Premature closure of the posterior fontanelle occurs in children with unilateral lambdoid synostosis, but not with deformational plagiocephaly.

Evaluation with standard skull radiographs allows confident exclusion of the diagnosis of unilateral lambdoid synostosis if the patent sutures are visible in their entirety. However, the radiographic findings are often inadequate for a true positive diagnosis. Apparent bridging of the suture on radiographs can result from an oblique orientation of the beam. Perisutural sclerosis is also an unreliable diagnostic sign at this location.¹⁰ The bony bridge of true lambdoid synostosis can be demonstrated with CT.⁷ Other findings on 3D CT include inferior canting of the base of the ipsilateral occipital bone, and ipsilateral deviation of the midline occipital bony structures (Figure 26-10). In contradistinction, 3D CT of children with posterior plagiocephaly shows a patent suture, no skull base tilt when viewed from behind, and no substantial deviation of the occipital midline structures. The diagnosis of synostosis is also possible with high-resolution sonography, if performed early in infancy. With positional plagiocephaly, a hypoechoic gap is visible between the occipital bones along the entire suture; true fusion is indicated by a bony bridge that obliterates the gap.^11–13

Cephalocele

A cephalocele is a developmental anomaly in which intracranial structures herniate through a congenital calvarial defect. Characterization of cephaloceles is according to the location of the defect and the structures that are herniated: meningocele, meningoencephalocele (meninges and brain; also termed encephalocele), and encephalocystomeningocele (meninges, brain, and ventricle). An atretic cephalocele contains meningeal tissue, but there is no open intracranial communication. Cranium bifidum (cranioschisis) refers to a midline calvarial defect through which intracranial structures herniate. A small calvarial defect that does not involve herniation of meninges is termed cranium bifidum occultum.

Cephaloceles occur in approximately 1 in 4000 to 5000 livebirths. This anomaly occurs more frequently in families with a history of spina bifida or another (CNS) malformation. Younger siblings of affected patients carry a 6% risk of a congenital CNS anomaly. Cephaloceles occur as part of the HARD ± E syndrome, which encompasses hydrocephalus, agyria, retinal dysplasia, and (in approximately 50% of patients) encephalocele.^14–21

In Europe and North America, the occipital region is the most common location of cephaloceles, occurring in 50% to 80% of patients. Frontal locations are more common in children in Southeast Asia and Russia. Nasal cephaloceles are particularly common in Southeast Asia. Occipital cephaloceles are more common in girls, whereas anterior cephaloceles are slightly more common in boys. Approximately 50% of cephaloceles are accompanied by other CNS anomalies.²²

Most cephaloceles are clinically apparent at birth, as a mass of the head or face. The lesion may be somewhat soft at palpation, due to the contained fluid. Anterior cephaloceles frequently are associated with substantial orbital and midline facial deformities. Those that extend into the nasal cavity sometimes cause respiratory symptoms due to airway obstruction. Small anterior or basal cephaloceles may not be clinically obvious; rarely, clinical detection is delayed until adulthood. These patients may present with cerebrospinal fluid (CSF) rhinorrhea or meningitis. A cutaneous marker for an underlying neural tube closure defect of the calvaria is termed the “hair collar” sign. This finding consists of a ring of long, dark, coarse hair surrounding a midline scalp nodule. Cephaloceles that do not contain nervous tissue and lack an accompanying brain anomaly carry a much better prognosis. The operative treatment of cephalocele includes repair of the defect and reconstruction of associated craniofacial deformities. Potential surgical complications that can necessitate imaging evaluation include CSF leak and wound infection.^23–25

The mechanism of formation of cephaloceles is incompletely understood. Most are likely due to a defect in the primary inductive process of neurulation. This mechanism accounts for coexistence of cephaloceles with cerebral and craniofacial malformations. The stage of gestation at which the insult occurs may affect the location of the defect and the likelihood of associated intracranial or facial anomalies. The initial stages of formation of the skull base and facial structures occur between gestation days 28 through 35, in a complicated process that involves the notochord, the neural tube, and the surrounding mesoderm. Maldevelopment at this stage of gestation could account for the coexistence of anterior cephaloceles with anomalies of the corpus callosum, holoprosencephaly, anomalies of the visual and olfactory structures, and facial clefts. Posterior cephaloceles may be related to defective induction and formation of the membranous cranial roof, which occurs between gestation days 38 and 45. Isolated cranial defects that lack associated brain anomalies likely are due to an event at a later stage of embryogenesis. Focal deficiency of formation of the chondrocranium can cause a calvarial defect. Coalescence of multiple ossification centers initiates ossification of the chondrocranium. Failure of proper union of these ossification centers can result in a persistent defect; this mechanism best explains some basal cephaloceles.

In general, MRI is most useful diagnostic imaging technique for evaluation of a suspected cephalocele. MR demonstrates the site of herniation, the contents of the sac, and any associated intracranial anomalies. Characterization of involvement of intracranial arteries and veins is important for surgical planning. CT optimally demonstrates detailed anatomy of the bony defect. Intrathecal contrast can be utilized in conjunction with the CT examination to document communication with the subarachnoid space. Communication with the subarachnoid space can also be assessed with radionuclide cisternography.

In the occipital region, meningoceles and meningoencephaloceles occur with approximately equal frequency. The size varies substantially between patients, ranging from a tiny defect to a large lesion that contains a large portion of the brain. A small cephalocele may be covered by normal appearing skin, whereas a thin membrane that is contiguous with the scalp is the typical covering of a large lesion (Figure 26-11). Occipital cephaloceles can be classified according to location: infratentorial, supratentorial, or combined (Figure 26-12).

An infratentorial occipital cephalocele sometimes occurs in conjunction with upper cervical spina bifida. Approximately 50% of infratentorial occipital cephaloceles are associated with Chiari III malformation. The defect in these patients is adjacent to the foramen magnum in the supraoccipital bone. Typically, there is only minimal herniation of brain tissue through the defect. There is, however, substantial distortion of the posterior fossa structures: caudal displacement of the cerebellum, vertical orientation of the medulla and pons, and compression on the fourth ventricle. Hydrocephalus is common in these patients.

An occipital cephalocele with combined infratentorial and supratentorial involvement is sometimes accompanied by hypoplasia or abnormal implantation of the tentorium (Figure 26-13). Any herniated brain tissue in these patients nearly always consists of supratentorial structures. When there is substantial herniation of supratentorial brain, the brainstem and cerebellum are displaced anteriorly and compressed. This may be associated with hydrocephalus.

Approximately 50% of children with a supratentorial occipital cephalocele have herniation of brain tissue through the defect. This most commonly consists of tissue from the occipital lobes (Figure 26-14). Hydrocephalus may occur in these patients. In general, supratentorial cephaloceles carry a more favorable prognosis than infratentorial or combined cephaloceles.

Anterior (sincipital) cephaloceles are predominantly comprised of 3 types of frontoethmoidal lesions: frontonasal, nasoethmoidal, and naso orbital cephaloceles. The interfrontal cephalocele can be considered as an additional type of frontoethmoidal cephalocele or as a separate subtype of anterior cephalocele. The skull defect of a frontoethmoidal cephalocele is located at the foramen cecum, where the frontal and ethmoid bones meet immediately anterior to the crista galli. The subtypes of this lesion are characterized by the external location of the hernia. Most patients with frontoethmoidal cephaloceles suffer secondary deformities due to interference with development of the facial skeleton. Maxillary hypoplasia is common. The nasal cartilages are deformed. The face may appear to be elongated. Lateral displacement of the orbits is sometimes present.^26,27

The frontonasal subtype of anterior cephalocele extends between the frontal and nasal bones (Figure 26-15). The associated soft tissue mass may be identified at the nasal root or the glabella. With a large lesion, there is inferior displacement of the nasal bones, ethmoid bone, and frontal processes of the maxillae. The frontal bones are displaced superiorly and the medial orbital walls are displaced laterally. When brain herniation occurs with a frontonasal cephalocele, it usually consists of the anterior-inferior portions of the frontal lobes, sometimes accompanied by the olfactory bulbs (Figure 26-16). The character of herniated brain varies between patients, ranging from a mass of dysplastic tissue to brain that is nearly normal structurally. Associated intracranial anomalies that can occur in these patients include hydrocephalus and holoprosencephaly.²⁸

The nasoethmoidal subtype of anterior cephalocele extends between the nasal bones and the nasal cartilage. The nasal cartilage, nasal septum, and ethmoid bone are displaced inferiorly and posteriorly. The medial walls of the orbits form the lateral borders of the bony canal that is created by the cephalocele. Hypertelorism may occur. The externally visible mass is usually below the glabella, typically off midline adjacent to the nasal cartilage; separate components on each side of the nose are occasionally present. Compromise of the nasal cavity may lead to symptomatic nasal obstruction. Intracranial anomalies are uncommon in children with nasoethmoidal cephalocele; dysgenesis of the corpus callosum has been reported in some patients.

The bony canal of a nasoorbital cephalocele is located between the ethmoid bone and the frontal process of the maxilla along the medial wall of the orbit. This lesion, therefore, is slightly off midline. The frontal process of the maxilla is displaced anteriorly and medially. The medial wall of the orbit and the lacrimal bone are displaced posteriorly and laterally. The cephalocele is identified clinically at the nasolabial fold, between the nose and the lower eyelid.

An interfrontal cephalocele is a rare lesion that occurs as a midline defect above the frontonasal suture. The cranial defect is located between the 2 frontal bones along the inferior portion of the metopic suture. With a large defect, a considerable length of the metopic suture may be involved. A variable volume of frontal lobe tissue protrudes through the defect; the brain herniation may be asymmetric. The herniated brain is frequently compromised due to a constricting ring at the defect.

Basal (sphenoidal) cephaloceles are rare. There are 4 main types of basal cephalocele: spheno orbital, sphenomaxillary, transethmoidal, and sphenopharyngeal (most common) subtypes. The sphenoorbital cephalocele protrudes through the superior orbital fissure into the posterior aspect of the orbit, causing proptosis. The sphenomaxillary cephalocele also passes through the superior orbital fissure, but then continues inferiorly through the inferior orbital fissure into the pterygopalatine space; further extension may occur into the infratemporal fossa. With the transethmoidal cephalocele, the hernia protrudes through the cribriform plate into the anterior nasal cavity or ethmoid sinuses.

Sphenopharyngeal cephaloceles extend through or between the sphenoid and ethmoid bones. The terminology of subtypes is according to the locations of the bony defect and the hernia sac. A transsphenoidal cephalocele involves a defect in the sella turcica, with protrusion of the hernia sac through the sphenoid sinus into the nasal cavity or epipharynx. Further extension into the oral cavity may occur in conjunction with a cleft palate (Figure 26-17). The intrasphenoid type is similar, but the hernia does not extend beyond the sphenoid sinus. The sphenoethmoidal cephalocele is the least common of the sphenopharyngeal lesions. This type has combined defects of the sphenoid and ethmoid bones, and protrusion of a hernia sac into the posterior nasal cavity. A cephalocele that involves the nasopharynx usually presents with nasal obstruction, CSF rhinorrhea, or (rarely) meningitis. In addition to cephalocele, the differential diagnosis of a nasal mass in a neonate includes nasal glioma, dermoid cyst, nasal polyp, vascular malformation, and hemangioma.²⁹

Facial malformations of variable severity occur in all children with a basal cephalocele. Hypertelorism is typical. Other orbital malformations that can occur in these patients include coloboma, ocular hypoplasia, optic nerve hypoplasia, and retinal defects. Pituitary and hypothalamic involvement may result in endocrine dysfunction. The most common associated brain malformation is dysgenesis of the corpus callosum. MRI typically demonstrates inferior extension of the third ventricle and the pituitary gland through the defect.

Parietal cephaloceles are usually clinically obvious (Figure 26-18). These lesions usually are located at the mid-line along the course of the sagittal suture. The interhemispheric fissure may communicate with the sac. The face and cervical spine are not affected. The prognosis is determined by the severity of associated intracranial anomalies. These patients may have dysgenesis of the corpus callosum or Dandy-Walker malformation.³⁰

Atretic cephaloceles apparently represent involuted true meningoceles or encephaloceles. The extracranial mass contains meningeal tissue and vestigial tissues (arachnoid, glial, or CNS rests). These lesions are typically located at the midline of the parietal or occipital region and usually communicate with the subarachnoidal space. Rarely, there is communication with the ventricular system. An anomalous vascular component is sometimes present, such as persistent vertical embryonic orientation of the straight sinus. Although many patients with atretic cephalocele are otherwise normal, a variety of brain anomalies can occur (e.g., gray matter heterotopias, ventriculomegaly, malposition of the tentorium, and cystic malformations of the posterior fossa). Cranial MR is mandatory for these patients to detect and characterize associated intracranial anomalies, some of which may not be clinically apparent in the young child or infant.^31–34

Lateral Facial Cleft

There are various classification systems for oblique facial clefts. Most commonly utilized is the Tessier classification system, which recognizes 15 types of craniofacial clefts, based on the pattern of involvement of the mouth, nose, orbit, and cranium. 3D CT imaging helps define the anatomy of the facial bones and skull in these children, and aids in preoperative planning.^35,36

Cleft Lip and Cleft Palate

Common cleft lip and cleft palate account for more than 98% of facial clefts. Cleft lip is due to failure of the medial nasal prominence to merge with the maxillary prominence. These clefts involve the palate, the lip, or both, and can be unilateral or bilateral. The cause of cleft palate is failure of fusion between the primary palatal process and the secondary process of the maxillary prominence. Although most often isolated, a substantial minority of individuals with cleft lip or cleft palate have an associated syndrome.

There is a broad spectrum of predisposing genetic and environmental factors for cleft lip and cleft palate. The offspring of an affected parent carries a risk of approximately 4%; maternal supplementation with vitamin B6 and folic acid during the first trimester of pregnancy substantially diminishes this risk. Maternal smoking during early pregnancy is a risk factor. Various teratogens have been implicated in the pathogenesis of cleft lip and cleft palate, including phenytoin, organic solvents, alcoholic beverages, and salicylates. Cleft palate is common in patients with DiGeorge syndrome; other potential craniofacial anomalies in these children are micrognathia, low set ears, telecanthus, and bifid uvula. There is an association of cleft palate with maternal diabetes mellitus type 1 and maternal rubella. Genes associated with orofacial clefting have been mapped at chromosomes 6p23, 2p13, and 19q13.2.^37,38

Clefts of the lip can be unilateral or bilateral, and complete or incomplete. A complete cleft of the lip extends to the floor of the nostril. Cleft lip results in aesthetic deformity and it interferes to some extent with feeding. The major functional impairments of cleft lip and palate, however, predominantly are related to involvement of the palate. Cleft palate is associated with feeding difficulties during infancy and speech impediments in older children. There is midfacial hypoplasia. Appropriate dental development is impaired.

Imaging studies of patients with cleft palate show a variable degree of midfacial hypoplasia. The ipsilateral hemimaxilla is small and the premaxillary segment tilts superiorly. Involvement of the nose is an important component of cleft lip and palate. With a unilateral cleft, the ipsilateral ala is displaced inferiorly and the alar-facial groove is absent. The nasal septum is deflected. With bilateral clefts, the malar cartilages are caudally displaced and separated. The columella is deficient.³⁹

Alveolar bone grafting is a common procedure in the management of cleft palate. The objectives of this procedure include the creation of a stable maxillary dental arch, enhancement of facial symmetry, and closure of oral-nasal fistulae. 3D CT imaging studies are useful for preoperative planning in these patients, and to assess viability of the bone graft after surgery.

Torus

Torus palatinus (maxillary torus) is a benign osseous expansion in the midline of the hard palate. This occurs in about one-quarter of the general population. A torus is composed of dense cortical bone. Imaging studies show a well-defined, radiodense mass along the inferior aspect of the palate at the midline. The nasal surface of the hard palate is not affected.

Torus maxillaris is a hyperostosis that arises from the alveolar portion of the maxilla, most commonly in the molar region. When located along the lingual surface of the dental arch, it is termed torus maxillaris internus; the torus maxillaris externus is located along the outer margin of the dental arch. A torus medullaris arises from the lingual surface of the mandible, most often adjacent to the apex of the second premolar.

Tori are clinically identifiable in approximately 2% of newborns. They become more frequent with increasing age. Typically, growth of the lesion continues during childhood and early adulthood, with stabilization occurring at about the time of skeletal maturity. Only rarely is a torus large enough to produce significant clinical problems.

Craniolacunia

Craniolacunia (Lückenschädel) is a congenital dysplasia of the skull that is associated with myelocele, meningocele, and Chiari II malformation. Although the associated anomalies may be accompanied by hydrocephalus, the pathogenesis of lacunar skull is unrelated to ventriculomegaly or increased intracranial pressure. Radiographs and CT show involvement of the membranous portion of the skull with multiple areas of thinning that are surrounded by well-defined thin sclerotic bands (see Figure 14-16 in Chapter 14). The appearance on skull radiographs has been likened to that of soap bubbles or beaten copper. The parietal and frontal bones are most prominently affected. The enchondral portion of the skull is not involved. Craniolacunia usually begins to fade soon after birth, and may completely disappear within the first several months of life.¹

Calvarial Thickening

Craniometaphyseal Dysplasia

Craniometaphyseal dysplasia is a rare autosomal recessive condition that is characterized by progressive enlargement of the metaphyses of the long bones and overgrowth of the craniofacial skeleton. These patients are usually tall for their age and the tubular bones may be palpably enlarged. Thickening of the skull base can result in symptomatic compression of the optic nerves and cranial nerves (e.g., diminished visual acuity, progressive hearing loss, and cranial nerve palsies).

Radiographs of the extremities of children with craniometaphyseal dysplasia show flask-shaped long bone metaphyses, due to metaphyseal flaring and lack of diaphyseal tubulation. There is diffuse calvarial thickening, with disproportionate involvement of the skull base (see Figure 57-29 in Chapter 57). The craniofacial overgrowth causes obliteration of the paranasal sinuses and compression of neural foramina.

Osteopetrosis

Osteopetrosis is a rare skeletal disorder that is characterized by generalized bone sclerosis and fragility due to defective bone resorption. The autosomal recessive type usually presents during infancy. Potential clinical manifestations include cranial nerve palsy due to osseous encroachment on neural foramina, pathological fractures, and compromised bone marrow function (anemia, thrombocytopenia, and sepsis). Manifestations of optic nerve compression are common. The autosomal dominant type of osteopetrosis tends to have milder clinical manifestations, and the clinical presentation occurs later in life. The predominant findings in these patients include pathological fractures and defective dentition.

The characteristic radiographic feature of osteopetrosis is increased radiodensity of the entire skeleton. Marked cortical thickening in the long bones leads to narrowing of the medullary portions. Calcified cartilage in the marrow spaces produces a unique “bone within bone” appearance on radiographs. The long bones are undertubulated, due to diminished osteoclastic activity. Sclerosis and amorphous thickening are present in the skull base; the membranous portion of the calvaria is not involved (see Figure 57-27 in Chapter 57). The optic canals, neural foramina, and internal auditory canals are narrow.

Wormian Bones

Wormian bones are accessory bones that occur in the sutures. Wormian bones are most common within the lambdoidal suture. This finding most often occurs as a normal developmental variation. However, multiple wormian bones can occur in association with several developmental disorders, including osteogenesis imperfecta (see Figure 57-24 in Chapter 57), cleidocranial dysplasia, hypophosphatasia, hypothyroidism, Menkes syndrome, and pyknodysostosis.

Neurofibromatosis Type 1

Skeletal system involvement with neurofibromatosis type 1 is predominantly due to a mesodermal dysplasia. Macrocephaly is common in these patients. The most common focal abnormality of the skull and face in children with neurofibromatosis type 1 is hypoplasia of the sphenoid, most often the greater wing. This can be associated with protrusion of intracranial structures into the orbit, that is, an orbital cephalocele. Occasionally, the sphenoid wing deformity is progressive. Other orbital deformities are also common in patients with craniofacial manifestations of neurofibromatosis type 1.

Bony orbital abnormalities in patients with neurofibromatosis type 1 are nearly always associated with a plexiform neurofibroma (most common) or optic nerve glioma. The osseous deformities may develop due to a secondary dysplasia, in which interaction of a plexiform neurofibroma with the developing skull is a major component. The most common imaging findings of the skull and facial bones in patients with a plexiform neurofibroma are enlargement of the orbital rim and sphenoid wing dysplasia (Figure 26-19). Other potential findings include expansion of the middle cranial fossa into the posterior orbit, bone erosion and decalcification by contiguous tumor, and enlargement of cranial foramina due to tumor infiltration of sensory nerves. Optic nerve glioma may result in an enlarged optic canal.^40–44

The most common abnormalities of the mandible in patients with neurofibromatosis type 1 are prominent bone density, an enlarged mandibular foramen, lateral bowing of the mandibular ramus, concavity of the medial surface of the ramus, increase in the dimensions of the coronoid notch, and a decrease in the mandibular angle.⁴⁵

Achondroplasia

Clinical manifestations of skull base involvement are common in children with achondroplasia. Achondroplasia is a bone dysplasia that results in short stature, dysmorphic features, congenital skeletal abnormalities, and neurological impairment. The underlying defect is abnormal enchondral ossification. In the skull, only the base is involved, and there is compensatory increase in the growth of the membranous bones of the cranial vault. This results in macrocephaly and a prominent bulging forehead.

Skull radiographs and CT of children with achondroplasia show a constricted appearance of the skull base. The foramen magnum is often small. Narrowing of the jugular foramina may lead to elevated intracranial venous pressure. The base of the occipital bone is elevated, resulting in a small posterior fossa.

Craniofacial Duplication

Craniofacial duplication is a rare form of conjoined twinning that presents as a spectrum from dicephalus to diprosopus to partial facial duplication to simple nasal duplication. The pathogenesis is believed to involve duplication of the notochord. Dicephalus consists of 2 heads and 1 body. Diprosopus is characterized by 2 faces, 1 head, and 1 body. Most neonates with the severe forms of craniofacial duplication are stillborn. For those infants who are viable, CT and MR are indicated to accurately characterize the duplicative anomalies in the skull, facial bones, and brain.^46–48

Median Facial Malformations

Median facial malformations usually occur in conjunction with anomalies of the brain such as holoprosencephaly. There are 5 major types of median facial malformations: cyclopia (type I), ethmocephaly (II), cebocephaly (III), hypotelorism with median cleft lip (IV), and hypotelorism with bilateral cleft lip (V). Types I through III are typically accompanied by alobar holoprosencephaly; type IV is accompanied by semilobar or alobar holoprosencephaly; and type V is associated with semilobar or lobar holoprosencephaly. Some patients with median facial malformations have normal brain development; this is sometimes considered to be a type VI deformity.

Cyclopia refers to a single midline orbit. The ocular structures may be absent, there may be a single malformed globe, or there may be dysplastic fused ocular structures. A proboscis is usually present above the orbit; this structure is duplicated in some patients. Otherwise, the nasal structures are absent, as are the median facial bones. Nearly all individuals with cyclopia have alobar holoprosencephaly. Cyclopia occurs in approximately 1 per 100,000 births, including stillbirths. About half of affected infants are stillborn. This anomaly is more common in female infants.^49,50

Ethmocephaly is characterized by severe hypotelorism, arhinia, and a single or double proboscis. The hypotelorism in infants with cebocephaly is somewhat less marked than in ethmocephaly. There is a proboscis-type nose with a blind-ending and/or single nostril. Patients with types IV and V median facial malformations have hypotelorism of varying severity and abnormal flattening of the nose.

Craniopharyngeal Canal

The craniopharyngeal canal (also termed persistent hypophyseal canal) is a small vertical midline defect in the sphenoid bone, inferior to the sella turcica. The estimated prevalence is 0.42%.⁵¹ The craniopharyngeal canal is hypothesized to represent a remnant of the Rathke pouch versus a remnant of a vascular channel formed during osteogenesis.

A larger defect at this site is termed a large craniopharyngeal canal or transsphenoidal canal. This defect can lead to herniation of intracranial structures such as the pituitary gland or the third ventricle into the nasopharynx. A transsphenoidal meningoencephalocele can occur. Some patients with a large craniopharyngeal canal have coexisting craniofacial anomalies, such as hypertelorism, midfacial cleft, cleft lip and palate, abnormal optic tracts, or orbital anomalies. Dysgenesis of the corpus callosum has been reported.^52,53

Craniofacial Syndromes

The craniofacial syndromes constitute a diverse group of anomalies, with varying combinations of craniosynostosis, facial clefting, and clefting of the palate and/or lip. There are approximately 70 defined genetic syndromes that involve craniosynostosis. Cleft lip and cleft palate are associated with over 400 syndromes.

Apert Syndrome

Apert syndrome (acrocephalosyndactyly type 1) is an autosomal dominant disorder that is characterized by craniosynostosis, midface hypoplasia, and syndactyly of the hands and feet. Most cases are sporadic. Advanced paternal age is a risk factor. Apert syndrome occurs in approximately 1 per 160,000 to 180,000 livebirths.^54,55

Patients with Apert syndrome typically suffer bilateral coronal synostosis during fetal development, although there is variability in suture involvement. There is also premature fusion of sutures in the skull base, resulting in shortening of the cranial base from the occiput to the anterior nasal septum. The most common calvarial deformity is that of acrocephaly, with a tall forehead that slopes posteriorly (see Figure 58-15 in Chapter 58). The occiput is flat. In infants with Apert syndrome, there is a wide midline defect due to separation of the metopic and sagittal sutures; this closes between the ages of 2 and 4 years.⁵⁶

The orbits are shallow in Apert syndrome, resulting in proptosis. Hypertelorism is also common. There is maxillary hypoplasia; mandibular growth is relatively normal, resulting in severe malocclusion. The palate is high and narrow, and clefting of the soft palate occurs in approximately 30% of patients. The ears are low set, and nearly all patients have some degree of conductive hearing loss. Occasionally, there is fixation of the stapes to the promontory.

All patients with Apert syndrome have bilateral complex syndactyly of the hands and feet; this serves to distinguish Apert syndrome from other craniofacial syndromes. The syndactyly of the hands involves both soft tissue and bone, and typically involves the index, middle, and ring fingers; simple syndactyly occurs at the fourth interdigital space. The thumb is foreshortened and curved laterally. The phalanges of the hand are foreshortened (brachyphalangism).

Children with Apert syndrome often have clinical manifestations of airway narrowing, due to the midface hypoplasia, narrowing of the nasal cavity, and a small pharynx. Fusion anomalies of the cervical spine can occur, most often at C5-C6. Hydrocephalus occurs in some patients. Other potential CNS abnormalities in Apert syndrome patients include dysgenesis of the corpus callosum, cortical dysplasia, heterotopic gray matter, and hypoplastic white matter. Cranial nerve dysfunction can occur due to foraminal stenosis in the skull base. Compromise of intellectual development, often mild, occurs in about half of patients with Apert syndrome.