CEPHALOCELES

Occipital Cephaloceles

•Most common in European/North American Caucasians

•75% of cephaloceles, M:F = 2.4:1

•Typically contains dysplastic brain

Frontoethmoidal Cephaloceles

•10-15% of cephaloceles

•Southeast Asian predominance

•Frontonasal (40-60%)

○Through fonticulus frontalis into forehead

•Nasoethmoidal (30%)

○Through patent foramen cecum into nose

•Nasoorbital (10%)

○Through lacrimal bone/maxilla into orbit

Parietal Cephaloceles

•5-10% of cephaloceles

•Most are atretic

○Associated with falcine sinus, sinus pericranii

Skull Base Cephaloceles

•10% of cephaloceles

•Brain anomalies common (e.g., callosal dysgenesis)

Persistent Craniopharyngeal Canal

•Less than 1%, usually incidental finding

•Large complex lesions rare

○Associated with pituitary anomalies

○May have sphenoidal cephalocele

Craniosynostoses

Craniosynostosis Overview

Terminology

Craniosynostosis is also known as craniostenosis, sutural synostosis, and cranial dysostosis. The craniosynostoses are a heterogeneous group of disorders characterized by abnormal head shape. Craniosynostosis can be nonsyndromic (70-75% of cases) or syndromic.

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normally closes last. Craniostenosis occurs when osseous obliteration of one or more sutures occurs prematurely.

Skull distortion occurs from a combination of (1) restriction of skull growth perpendicular to the prematurely fused suture and (2) compensatory overgrowth at the nonfused sutures.

Clinical Issues

Craniosynostosis can be associated with neurological and/or vascular compromise. Severe deformities can be cosmetically disfiguring and socially stigmatizing. Precisely when the anatomical and functional anomalies become clinically relevant varies from patient to patient and thus requires a tailored approach to treatment.

Imaging

Imaging plays an essential role in recognition of craniosynostoses, identification of coexisting brain anomalies, preoperative treatment planning, and postoperative followup.

Craniosynostoses can be nonsyndromic or syndromic and may affect a single suture or multiple sutures. In this section, we discuss representative examples of each type.

Nonsyndromic Craniosynostosis

Terminology and Etiology

Nonsyndromic craniosynostoses (NCSs) are genetically determined lesions that occur in the absence of a recognizable syndrome.

The genetic component is believed to be suture specific. For example, genome-wide association studies have identified strong and reproducible associations between sagittal NCS and BMP2 and BBS9, whereas gene mutations are relatively rare in metopic NCS.

Coronal NCS has a stronger genetic component compared with other forms. Several diverse genes include FGFR3, TWIST1, EFNB1, and TCF12 (which are also associated with syndromic forms of craniosynostosis). The genetic basis of lambdoid NCS—the rarest type—is unknown.

Etiology

The calvaria normally expands during infancy and early childhood to accommodate the growing brain. This mostly occurs at narrow seams of undifferentiated mesenchyme—the cranial sutures—that lie between adjacent bones. Compared with most major embryonic structures such as the brain and cardiovascular systems, the cranial sutures form relatively late (at around 16 weeks of gestation).

Normal sutures permit skull growth perpendicular to their long axis. As long as the brain grows rapidly, the calvaria expands. As brain growth slows, the sutures close.

The normal order of closure is metopic first, followed by the coronal and then the lambdoid sutures. The sagittal suture

Pathology

Location. Approximately 60% of all single-suture craniosynostosis cases involve premature fusion of the sagittal suture, followed in frequency by those that involve the coronal (22%) and metopic (15%) sutures. Lambdoid craniosynostosis is very rare, causing just 2% of all cases.

Classification. Craniosynostosis is generally classified by head shape as scaphocephaly or dolichocephaly (long and narrow)

(41-18), brachycephaly (broad and flattened) (41-21), trigonocephaly (triangular at the front) (41-19), or plagiocephaly (skewed) (41-20).

Gross Pathology. Gross examination shows fibrous or bony sutural "bridging." Focal synostosis or diffuse bony "beaking" along the affected suture are typical findings.

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CRANIOSYNOSTOSIS: ETIOLOGY AND PATHOLOGY

Normal Suture Development

•Late (16 weeks' gestation)

•Metopic closes first, then coronal, then lambdoid

•Sagittal closes last

Pathology

•Location

○Sagittal (60%, most common single suture)

○Coronal (22%)

○Metopic (15%)

○Lambdoid (2%)

○Multiple (5%)

•Gross pathology

○Suture obliterated by diffuse or focal bony "beaking"

(41-18A) Lateral radiograph of a newborn shows pronounced scaphocephaly with unusually severe elongation of the calvaria in the anteroposterior plane . (41-18B) Bone CT in the same patient shows the elongated configuration of the skull. Note severe narrowing with almost complete obliteration of the superior sagittal suture.

(41-18C) Bone CT with 3D shaded surface display (SSD) in the same patient shows pronounced elongation of the skull. Note ridge of bone along the vertex that resembles the keel of a ship. (41-18D) Coronal 3D SSD in the same patient shows normal-appearing coronal and lambdoidsutures. The sagittal suture is completely fused and demonstrates the elevated midline ridge of bone , characteristic of scaphocephaly. (Courtesy K. Moore, MD.)

Clinical Issues

Epidemiology. The overall prevalence of craniosynostosis is estimated at 1:2,000-2,500 live births.

Sporadic (nonsyndromic) craniosynostoses are more common than syndrome-associated cases, accounting for 75% of all craniosynostoses. Between 85-90% of these involve only a single suture, whereas 5-15% are multisuture synostoses.

Demographics. Sex varies with craniostenosis type. Both scaphocephaly and trigonocephaly have a moderate male predominance (M:F = 3.1:1 and M:F = 2:1, respectively).

Presentation. Most craniosynostoses—even syndromic ones—are not detected during pregnancy. Affected infants generally present during the first year of life. The most common presentation is unusual head shape with craniofacial asymmetry.

Natural History. Severe deformities may lead to hydrocephalus, elevated intracranial pressure, compromised cerebral blood flow, and airway obstruction.

Treatment Options. Mild deformities are sometimes treated with physiotherapy and head repositioning or orthotic helmet. Severe skull deformities may require one or more surgeries to remodel the cranial vault.

Imaging

General Features. Digital radiographs are sufficient to identify simple single-suture craniosynostoses. However, in addition to identifying the deformity and affected suture, preoperative planning requires careful imaging assessment of calvarial and dural venous sinus anatomy. Delineating associated intraand extracranial abnormalities is especially important in evaluating patients with multiple or syndromic synostoses.

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CT Findings. Although the diagnosis of cranial synostosis can be made clinically or on plain film radiographs, thin-section CT scans with multiplanar reconstruction and 3D shaded surface display (SSD) are invaluable for detailed evaluation and preoperative planning. However, the radiologist should always rely heavily on "CT source data" rather than surface-rendered images to avoid false positive diagnoses!

Head shape generally predicts which suture(s) will be abnormal, but CT is required to determine whether part or all of the affected suture(s) is fused.

Scaphocephaly. Scaphocephaly, also known as dolichocephaly, is caused by sagittal suture synostosis. Patients with scaphocephaly demonstrate an elongated skull with decreased transverse and increased AP measurements. Forehead bossing is common. In severe cases, the sagittal suture is elevated, and the elongated ridge of bone resembles the keel of a ship (41-18).

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Brachycephaly. Brachycephaly is caused by bicoronal or bilambdoid synostosis. In such cases, the skull appears widened in the transverse dimension while shortened from front to back (41-21A). Craniofacial deformities such as bilateral "harlequin" orbits—peculiar bony deformities seen as elevation/elongation of the superolateral orbit walls—are common.

Trigonocephaly. Trigonocephaly is caused by synostosis of the metopic suture. The forehead appears wedge-shaped or triangular (41-19). Hypotelorism is common.

Plagiocephaly. In plagiocephaly, the calvaria is very asymmetric. Unilateral single or asymmetric multiple sutural fusions can produce this appearance. In unilateral coronal synostosis, the hemicalvaria is shortened and pointed; it may be associated with a unilateral "harlequin" eye (41-21B). If the lambdoid suture is fused, the skull assumes a more trapezoid appearance with occipital flattening and posterior ear displacement (41-20).

(41-20A) NECT scan in a

6m boy with plagiocephaly shows an asymmetric, flattened posterior skull bulging in the left posterior parietooccipital area .

(41-20B) 3D shaded surface display in the same patient shows synostosis of the left lambdoid suture with posterior bulging of the calvaria . The right lambdoid suture appears normal. (Courtesy K. Moore, MD.)

(41-21A) Newborn infant is shown with brachycephaly caused by bicoronal synostosis. Coronal suture is completely fused , while the lambdoid and sagittal sutures are open. (41-21B) The right coronal suture appears normal. The leftis ridged and fused. Note characteristic "uplifting" of the superolateral orbital rim, giving the classic "harlequin" appearance of unilateral coronal craniosynostosis. (Courtesy K. Moore, MD.)

Turricephaly. Turricephaly or "towering" skull is a more extreme deformity caused by bicoronal or bilambdoid synostosis.

Oxycephaly. The coronal, sagittal, and lambdoid sutures are all fused in oxycephaly.

Kleeblattschädel. Kleeblattschädel is also known as "cloverleaf" skull. Bicoronal and bilambdoid synostoses cause an unusual pattern of bulging temporal bones, towering skull, and shallow orbits (41-22).

MR Findings. MR is helpful to rule out coexisting anomalies. Hydrocephalus, corpus callosum dysgenesis, and gray matter abnormalities may be present but are more common in syndromic craniosynostoses. MRA or CTA is useful to delineate venous sinus drainage prior to surgical intervention.

CRANIOSYNOSTOSIS: IMAGING

Scaphocephaly

•Most common type: sagittal suture synostosis

•Elongated skull with midline bony ridge

Brachycephaly

•Bicoronal or bilambdoid synostosis

•Coronal → widened transverse dimension ± "harlequin" orbit

•Lambdoid → flattened occiput

Trigonocephaly

• Metopic suture synostosis, "quizzical eye"

Plagiocephaly

• Unilateral coronal or multiple sutures

"Cloverleaf" Skull

• Bicoronal + bilambdoid synostoses

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Syndromic Craniosynostoses

Syndromic craniosynostoses account for just 25-30% of all cranial synostoses. In syndromic disease, the craniosynostosis presents as one feature of a genetic syndrome due to chromosomal defects or mutations in genes within interconnected signaling pathways.

Compared with their sporadic, nonsyndromic counterparts, syndromic craniosynostoses are much more likely to be associated with additional craniofacial or skeletal anomalies, such as limb abnormalities, dysmorphic facial features, and skull deformity. In addition, brain malformations are common, and developmental delay is more frequent. In contrast to nonsyndromic craniosynostoses (in which the sagittal suture is most often affected), bilateral coronal synostosis is the most common pattern in these patients.

Nearly 200 inherited syndromes have been described in conjunction with craniosynostosis. More than 60 different

(41-22A) Syndromic craniosynostosis is demonstrated by this lateral radiograph in a newborn with Pfeiffer syndrome. Note the unusual "towering" configuration of the calvaria. (41-22B) AP radiograph shows the "towering" skull especially well. Also note the symmetrically protruding temporal fossae , which create the classic "cloverleaf" appearance of Kleeblattschädel skull.

(41-22C) Sagittal 3D SSD shows abnormal head shape with "towering" skull , frontal bossing, mandibular and facial hypoplasia , protruding temporal fossae . Premature closure of the squamosal, coronal, lambdoid, and sagittal sutures is present. Multiple "holes" are foci of thinned calvaria. (4122D) Frontal SSD shows widened metopic sutureand "harlequin" orbits with superolaterally pointed rims . (K. Moore, MD.)

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(41-23) CC agenesis with interhemispheric lipomaencases ACAs and extends through choroidal fissure into both lateral ventricles .

(41-24) Autopsy shows interhemispheric lipomaencasing both ACAs and extending into lateral ventricles . (Courtesy AFIP Archives.)

mutations have been identified, reflecting the extreme genetic heterogeneity of this disorder. Mutations in the FGFR2 gene account for several of the most severe syndromic craniosynostoses, including Apert, Pfeiffer, and Crouzon syndromes.

We first discuss acrocephalosyndactyly types 1-5, using the eponyms by which these syndromes are most commonly known. We then mention some of the rare acrocephalopolysyndactylies.

Apert Syndrome

Apert syndrome is also known as acrocephalosyndactyly type 1. Craniosynostosis with hypertelorism, midface hypoplasia, and cervical spine anomalies is common. Severe symmetric hand and foot syndactyly is present in most patients. Bilateral coronal synostosis is the most common calvarial anomaly.

Of all the syndromic craniosynostoses, patients with Apert syndrome are most severely affected in terms of intellectual disability, developmental delay, CNS malformations, hearing loss, and limb anomalies.

Intracranial anomalies occur in more than half of all Apert cases and include hydrocephalus, callosal dysgenesis, and abnormalities of the septi pellucidi (25-30% each). Cavum vergae and arachnoid cysts are seen in 10-12% of cases. Venous anomalies and Chiari 1 malformation are less common associations.

Acrocephalosyndactyly type2, also known as Apert-Crouzon or Crouzon syndrome, shows many of the same features seen in Apert syndrome. However, affected individuals more commonly have multiple suture calvarial involvement. Hypertelorism and exophthalmos are prominent features. Both types 1 and 2 acrocephalosyndactyly are associated with FGFR2 mutations.

Saethre-Chotzen Syndrome

Saethre-Chotzen syndrome is also known as acrocephalosyndactyly type 3. A specific mutation in TWIST1 has been associated with this disorder. Duplicated distal phalanges, cone-shaped hallux epiphysis, and syndactyly of the second and third digits are characteristic findings in the extremities.

Waardenburg Syndrome

Waardenburg syndrome (WS) is also known as acrocephalosyndactyly type 4. WS is characterized by pigmentation abnormalities and sensorineural hearing loss. Depigmented patches of skin and hair and vivid blue eyes or heterochromia irides are common.

At least six genes are involved in WS, including SOX10; mutations in these genes affect myelination. Central myelin deficiency with cerebral and cerebellar hypoplasia is common in the neurological variant of WS. Peripheral demyelinating neuropathy can result in Hirschsprung disease.

Pfeiffer Syndrome

Pfeiffer syndrome is formally known as acrocephalosyndactyly type 5. Multiple sutures are typically affected, and severe deformities such as a "cloverleaf" skull are common (41-22).

Carpenter Syndrome

(41-25) Coronal T1WI shows lipoma with extension through choroidal fissures into both lateral ventricles and the choroid plexi.

Carpenter syndrome is an autosomal-recessive acrocephalopolysyndactyly caused by biallelic mutations in RAB23. Craniosynostosis is a consistent and severe component. As the name implies, both polydactyly and syndactyly are