Craniosynostosis, Selected Craniofacial Syndromes, and Other Abnormalities of the Skull

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Chapter 20

Craniosynostosis, Selected Craniofacial Syndromes, and Other Abnormalities of the Skull

Thomas L. Slovis, Arlene A Rozzelle and William H McAlister

The basic clinical and radiologic features of craniosynostosis result either from lack of sutural formation or from premature fusion of contiguous portions of calvarial bones across the membranous sutures between them. The prevalence of premature sutural closures is displayed in e-Table 20-1.¹ Normal sutures permit growth of the skull in a direction perpendicular to their long axes. With normal endocranial stimulus to growth, cessation of growth in one suture is compensated by increased growth in others, with resulting craniofacial deformity (e-Table 20-2; Figs. 20-1 through 20-4).

Figure 20-1 A schematic drawing of a child’s skull with sagittal synostosis, in which growth of the skull is restricted in a plane perpendicular to the fused suture and elongated in a plane parallel to that fused suture. (From Sulica RL, Grunfast KM. Otologic manifestations of craniosynostosis syndromes. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:211.)

Figure 20-2 Premature synostosis of both coronal sutures.
Schematic representation as seen in Apert syndrome. The suture is obliterated except for short, open terminal segments and open segments near the sagittal suture and anterior fontanel. The metopic, sagittal, lambdoid, and temporoparietal sutures all are widely open. The calvaria is shortened in the anteroposterior direction and elongated in the craniocaudal plane. A, Frontal aspect. B, Lateral aspect.

Figure 20-3 Schematic drawings of premature synostosis of the sagittal suture.
A, Lateral aspect. B, Superior aspect.

Figure 20-4 Premature synostosis of the sagittal suture with elongation of the calvaria in the occipital-frontal direction, a decrease in the transverse axis of the calvaria, and relative (to length) decrease in vertical height.
The sagittal suture is ridged externally. A and B, Frontal (A) and lateral (B) projections in a 2-day-old neonate. A sutural bone is present in the region of the posterior fontanel (arrows). The coronal, lambdoid, and squamosal sutures are normally wide, as is the squamocondyloid synchondrosis at the base of the occipital squamosa. C and D, On frontal (C) and lateral (D) projections, similar changes are evident in the more mature skull of an 11-month-old girl.

e-Table 20-1

Prevalence of Individual Premature Suture Closure per 1 Million Live Births

Modified from Cohen Jr MM. Epidemiology of craniosynostosis. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:113.

e-Table 20-2

Calvarial Configurations in Primary Craniosynostosis

Suture	Calvarial Configuration	Descriptive Terms
Sagittal	Long, narrow head	Scaphocephaly or dolichocephaly
Bilateral coronal	Short, wide head; hypertelorism; proptosis; small anterior fossa	Brachycephaly or bradycephaly
Metopic	Frontal wedging or keel-shaped head	Trigonocephaly
Bilateral lambdoid	Shallow posterior fossa, prominent bregma	Turricephaly
Unilateral coronal	Unilateral frontal flattening, uptilting of orbit and tilting of nasal septum	Plagiocephaly
Unilateral lambdoid	Unilateral posterior flattening	Plagiocephaly
All sutures	Small, round head	Microcephaly

From Vannier MW. Radiologic evaluation of craniosynostosis. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:148.

The deformity of the shape of the head is present before the bony sutural changes are seen. Only a portion of the bony suture needs to be closed to have craniosynostosis (e-Fig. 20-5). The suture-associated dura mater is responsible for determining the development of the cranial suture. The dura supplies osteoinductive growth factors (e.g., transforming growth factor-β or fibroblast growth factor-2) and cellular elements. Abnormal head shape secondary to abnormal suture development can be diagnosed in utero at 13 weeks’ gestational age.^2,3 Craniosynostosis is associated with genetic abnormalities (e-Box 20-1) and is a secondary finding in many systemic disorders (e-Box 20-2).⁴

e-Figure 20-5 Severe craniosynostosis of the scaphocephalic type caused by premature synostosis of only a short segment of the sagittal suture of a 2-week-old infant.
A, In lateral projection, deformity resulting from the craniostenosis is clearly seen, but the sagittal suture itself is invisible (superior black arrows). Coronal (black arrows) and lambdoid sutures (white arrow) are widened. B, In frontal projection, the sagittal suture is visible in its entirety and is open except for a short segment (arrows) only a few millimeters long.

e-Box 20-1

Genes Bearing Known Mutations for Craniosynostosis

• Jackson-Weiss syndrome

• Beare-Stevenson cutis gyrata syndrome

• Nonclassifiable and variable craniosynostosis

• FGFR3

• Thanatophoric dysplasia, type I

• Thanatophoric dysplasia, type II

• Crouzonodermoskeletal syndrome

• FGFR3-associated coronal synostosis syndrome

(Muenke craniosynostosis)

• TWIST

• Saethre-Chotzen syndrome

• MSX2

• Boston-type craniosynostosis

From Cohen Jr MM. History, terminology, and classification of craniosynostosis. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:107.

e-Box 20-2

Conditions with Secondary Craniosynostosis

• Metabolic disorders

• Hyperthyroidism

• Rickets (various forms)

• Mucopolysaccharidoses and related disorders

• Hurler syndrome

• Morquio syndrome

• β-glucuronidase deficiency

• Mucolipidosis III

• α-mannosidase deficiency

• Hematologic disorders

• Thalassemia

• Sickle cell anemia

• Polycythemia vera

• Congenital hemolytic icterus

• Iatrogenic disorders

• Hydrocephalus with shunt

• Atrophy of brain

Modified from Cohen Jr MM. Sutural pathology. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:55.

Specific head shapes are associated with sutural synostoses (e-Fig. 20-6). The normal head has an egg shape, being widest in the parietal area posterior to the ears with a narrower, gently rounded forehead (Fig. 20-7).

Figure 20-7 A normal three-dimensional computed tomography scan of the head in a 7-month-old infant.
A, Frontal view clearly shows the anterior fontanel and coronal sutures. The metopic suture has closed. B, Lateral view shows the lambdoid and squamosal sutures and the normal coronal sutures. C, Bird’s eye view reveals the anterior fontanel and the coronal, sagittal, and lambdoid sutures. D, Posterior view shows the posterior sagittal suture and the lambdoid sutures. The normal head is egg shaped, widest at the biparietal area (C).

e-Figure 20-6 Trigonocephaly in a newborn.
A photograph of the head and face and three views of the skull—frontal, lateral, and superior. Note the ridge on the forehead. It appears similar to a keel of a boat. (From Welcker H. Untersuchungen über Wachstum und Bau des menschlichen Schädels. Leipzig: W. Engelmann; 1862.)

Sagittal synosotosis is characterized by a long and narrow head (see Figs. 20-3 and 20-4). The back is usually narrower than the front, and anterior or posterior bossing may exist. Metopic synostosis (trigonocephaly) results in a triangular shape of the whole forehead (not just a rounded forehead with a ridge superimposed) (Fig. 20-8; see e-Fig. 20-6).

Figure 20-8 Trigonocephaly.
Frontal projection shows the characteristic orbital hypotelorism and narrowing of the forehead. The metopic suture is invariably closed.

Unicoronal synostosis results in flattening of the ipsilateral forehead, flattening of the ipsilateral occipital area, the “harlequin eye” (the sphenoid is drawn up toward the closed suture and is thickened), ipsilateral temporal bulging and cheek protrusion, contralateral forehead bossing, and deviation of the nose away from the synostosed side (Fig. 20-9). Features that distinguish unicoronal synostosis from anterior deformational plagiocephaly are listed in e-Table 20-3.

Figure 20-9 Premature synostosis of the caudal segment of the right limb of the coronal suture in a 3-week-old infant.
A, In frontal projection, arrows are directed at the caudal ends of the right and left limbs of the coronal suture. The roof of the right orbit is lifted into a more oblique position, as is the right wing of the sphenoid. B, In lateral projection, the right limb of the coronal suture stops abruptly a few centimeters below the anterior fontanel. The lifting of the right orbital roof also is well seen (two lower arrows).

e-Table 20-3

Features that Differentiate Unilateral Coronal Synostosis from Anterior Deformational Plagiocephaly

Features	Synostotic	Deformational
Ipsilateral superior orbital rim	Up	Down
Ipsilateral ear	Anterior, high	Posterior, low
Nasal root	Ipsilateral	Midline
Ipsilateral malar eminence	Forward	Backward
Chin deviation	Contralateral	Ipsilateral
Ipsilateral palpebral fissure	Wide, low	Narrow, high
Anterior fontanel deviation	Contralateral	None

Modified from Cohen Jr MM, MacLean RE. Anatomic, genetic, nasologic, diagnostic, and psychosocial considerations. In: Cohen Jr MM, MacLean RE, eds. Craniosynostosis. New York: Oxford University Press; 2000:126.

Bicoronal synostosis causes a brachycephalic head (i.e., the head is wide and short). The supraorbital rims and forehead are recessed with bitemporal and upper forehead bulging (Fig. 20-10).

Figure 20-10 Bilateral coronal synostosis.
A, Frontal view shows the elevated orbital roofs. B, The height of the skull is increased from caudad to cephalad and decreased in the anteroposterior dimension. The coronal suture is not seen. C, Other lateral projection showing the absence of a complete coronal suture. The head is tall (towering) and short in the anteroposterior direction.

Lambdoid synostosis results in ipsilateral occipital flattening with compensatory bulging at the superior and inferior axes where the suture should have been (e-Fig. 20-11). The features differentiating unilateral lambdoid synostosis from posterior deformational plagiocephaly are listed in e-Table 20-4.

e-Figure 20-11 Premature closure and ridging of the caudal two thirds of both lambdoid sutures and flattening of the occipital squamosa in a 1-month-old infant.
The uppermost segment of the lambdoid suture is still open, and a small sutural bone is visible at the lambda itself. The sides of the occipital squamosa are straight, rather than convex, and the squamosa is narrower than is normal. A and B, Anteroposterior (A) and left lateral (B) projections.

e-Table 20-4

Features that Differentiate Unilateral Lambdoid Synostosis from Posterior Deformational Plagiocephaly

Features	Synostotic	Deformational
Contralateral posterior bossing	Parieto-occipital	Occipital
Forehead	Contralateral frontal bossing	Ipsilateral frontal bossing
Ipsilateral occipitomastoid bossing	Present	Absent
Ipsilateral ear	Anterior, anteroinferior, posterior, or symmetric	Anterior
Skull base and face	Ipsilateral inferior tilt	Normal*
Head shape, vertex view	Trapezoid-shaped or parallelogram-shaped depending on severity	Parallelogram
Head shape, posterior view	Parallelogram	Normal
Lambdoid suture	Unilateral synostosis^†	Patent suture

^*Ipsilateral face prominent.

^†Bulges at inferior and superior axes of location where suture should be.

Synostosis of multiple sutures occurs in 14%, and the resultant head shape depends on which sutures are closed.¹ The kleeblattschädel (“cloverleaf skull”) anomaly may result when all sutures except the squamosal are closed, resulting in severe temporal and vertex bulging with exophthalmos (Fig. 20-12). Unusual minor synostosis may exist, causing abnormal skull appearance.^5–8