Cranial sutures are present throughout the skull, which is divided into 2 parts, the calvarium and the skull base, via an imaginary line drawn from the supraorbital rims to the base of the occiput (Fig 18-1). Cranial sutures normally fuse during the first 2 years of life. Craniosynostosis is the premature closure of one or more cranial sutures during the embryonic period or early childhood.
Bony growth of the skull occurs in osteoblastic centers located at the suture sites. Bone is laid down parallel and perpendicular to the direction of the suture (Fig 18-2). Premature suture closure prevents perpendicular growth but allows parallel growth. This growth pattern, called Virchow’s law, results in clinically recognizable cranial bone deformations.
A, Normal sutures and fontanelles of the fetal skull. B, Adult cranial base, complete with sutures.
(Illustration by C. H. Wooley.)
The following are types of abnormal head shapes in infants, listed in order of decreasing frequency:
Most often plagiocephaly (Greek, plagio, “oblique”; kephale, “head”) is deformational, the consequence of external compressive forces, occurring prenatally or during infancy. Deformational plagiocephaly due to intrauterine constraint (eg, oligohydramnios) is characterized by ipsilateral occipital flattening with contralateral forehead flattening. This condition may also be caused by unilateral coronal suture synostosis. On the synostotic side, the forehead and supraorbital rim are retruded (depressed), the interpalpebral fissure is wider, and the orbit is often higher than on the nonsynostotic side. The nonsynostotic side displays a protruding or bulging forehead, a lower supraorbital rim, a narrower interpalpebral fissure, and frequently a lower orbital position.
A, Normal sutures. Bone growth occurs at the suture, with bone laid down parallel and perpendicular to the direction of the suture. B, Virchow’s law. Prematurely fused sutures allow bone growth only in the parallel direction; perpendicular growth is inhibited. C, An example of Virchow’s law. Premature closure of the sagittal suture produces scaphocephaly (boatlike skull); the shaded area shows the normal skull shape.
(Illustration by C. H. Wooley.)
Brachycephaly (literally, “short head”) is frequently the result of bilateral closure of the coronal sutures. Limited growth along the anterior-posterior axis results in a comparatively short head. Most often, the forehead is wide and flat.
Scaphocephaly (literally, “boat head”) is usually a result of premature closure of the sagittal suture. There is anteroposterior elongation of the skull, along with bitemporal narrowing.
In patients with dolichocephaly (literally, “long head”), the skull shape is similar to that in scaphocephaly.
The skull shape is trilobar. Kleeblattschädel (“cloverleaf skull”) is typically the result of synostosis of the coronal, lambdoidal, and sagittal sutures.
Etiology of craniosynostosis
Early suture fusion can be sporadic and occur as an isolated abnormality (eg, sagittal suture synostosis and most cases of unilateral coronal suture synostosis), or it can be part of a genetic syndrome, associated with other abnormalities. Craniosynostosis syndromes are usually autosomal dominant conditions, often with associated limb abnormalities. Many of these syndromes have overlapping features, making accurate diagnosis based on clinical findings difficult. Identification of specific mutations may be diagnostic. Mutations in the fibroblast growth factor receptor genes (FGFRs) or in the TWIST gene are found in most patients with syndromic craniosynostosis.
Common systemic features of the craniosynostosis syndromes include fusion of multiple calvarial sutures and skull base sutures. Syndactyly (partial fusion of the digits) and brachydactyly (short digits), ranging in severity, are hallmarks of these syndromes, the exception being Crouzon syndrome. The following sections discuss the most common types of craniosynostosis syndromes. All are autosomal dominant.
Crouzon syndrome is the most common craniosynostosis syndrome. Calvarial bone synostosis often includes both coronal sutures, resulting in a broad, retruded forehead; brachycephaly; and a tower-shaped skull. The skull base sutures are also involved, leading to varying degrees of midfacial retrusion. There is marked variability of the skull and facial features, with milder cases escaping diagnosis through multiple generations. Hypertelorism and proptosis, with inferior scleral show, are the most frequent features of Crouzon syndrome (Fig 18-3). Hydrocephalus is common, but intelligence is usually normal. Typically, findings are limited to the head. Unlike in the other syndromes, patients with Crouzon syndrome do not have anomalies of the hands and feet; thus, the presence or absence of these anomalies in a patient can aid diagnosis.
Fusion of multiple calvarial sutures, most often both coronal sutures, and skull base suture fusion are usually found in patients with Apert syndrome. The skull shape and facial features of these patients resemble those of Crouzon patients. Apert syndrome, however, is associated with an often extreme amount of syndactyly (Fig 18-4), in which most or all digits of the hands and feet are completely fused (mitten deformity). Apert syndrome is likely to be associated with internal organ (cardiovascular and genitourinary) malformations and mental deficiency. Hydrocephalus is less common in this syndrome than in Crouzon syndrome.
Figure 18-3 Crouzon syndrome. This patient exhibits brachycephaly and a “tower” skull with forehead retrusion; proptosis; inferior scleral show; and a small, beaklike nose. Also visible is the emerging midfacial hypoplasia.
(Reproduced with permission from Katowitz JA, ed. Pediatric Oculoplastic Surgery. New York: Springer; 2002:fig 31-23.)
Figure 18-4 Broad forehead, midfacial retrusion, and marked syndactyly in a patient with Apert syndrome.
(Courtesy of Robert W. Hered, MD.)
Patients with Pfeiffer syndrome have craniofacial abnormalities resembling those of Apert patients but often have more severe craniosynostosis, resulting in a cloverleaf skull. There is a high risk of hydrocephalus. The syndactyly is much less severe, and patients have characteristic short, broad thumbs and toes.
The features of Saethre-Chotzen syndrome are much milder than those of other craniosynostosis syndromes; this syndrome is therefore underdiagnosed. Early suture fusion is not a constant feature but, when present, typically involves 1 coronal suture (plagiocephaly), resulting in facial asymmetry. Other common features are ptosis, low hairline, and ear abnormalities. Abnormalities of the hands and feet include brachydactyly and mild syndactyly (Fig 18-5). Intelligence is usually normal.
Ocular complications of craniosynostosis
Proptosis (or exorbitism) results from the reduced volume of the bony orbit. The severity of the proptosis in patients with craniosynostosis is not uniform and frequently increases with age because of the impaired growth of the bony orbit.
Because the eyelids may not close completely over the proptotic globes, corneal exposure may occur, with possible development of exposure keratitis. Aggressive lubrication may be necessary to prevent corneal drying. Tarsorrhaphy can reduce the exposure. Surgically expanding the orbital volume, thereby eliminating the proptosis, may be indicated in extreme cases.
In patients with extremely shallow orbits, globe luxation may occur when the eyelids are manipulated or when there is increased pressure in the orbits, such as occurs with a Valsalva maneuver. The globe is luxated forward, the eyelids closing behind the equator of the globe. The condition is very painful and can cause corneal exposure. It may also compromise the blood supply to the globe, which is a medical emergency. Physicians and patients (or their caregivers) should quickly reposition the globe behind the eyelids. The best technique for doing this is to place a finger and thumb over the conjunctiva within the interpalpebral fissure and exert gentle but firm pressure; this technique does not damage the cornea. For recurrent luxation, the short-term solution is tarsorrhaphy; the long-term solution is orbital volume expansion.
Figure 18-5 Patient with Saethre-Chotzen syndrome. Note the facial asymmetry, flat forehead, low hairline, mild left ptosis, lateral deviation of the great toes, shortened toes, and partial syndactyly of fingers 2 and 3.
(Courtesy of the March of Dimes.)
Patients with craniosynostosis show a variety of horizontal deviations in primary position; exotropia is the most frequent. The most consistent finding, however, is a marked V pattern (see Chapter 10). This V pattern is often accompanied by a marked overelevation in adduction, especially when 1 or both coronal sutures are fused, as occurs in unilateral coronal suture synostosis and Apert (Fig 18-6) and Crouzon syndromes. The apparent overaction (often pseudo-overaction) of the inferior oblique muscle on the side of the coronal suture fusion may be due to one of the following: orbital and globe extorsion, which converts the medial rectus muscle into an elevator when the eye is in adduction; superior oblique trochlear retrusion (because of superior orbital rim retrusion), which induces superior oblique underaction and secondary true inferior oblique overaction; anomalous extraocular muscle insertions or agenesis; or orbital pulley abnormalities (see Chapter 3).
Optic nerve abnormalities
Optic nerve damage may occur for several reasons in patients with craniosynostosis. Optic nerve function may deteriorate in patients with chronically elevated intracranial pressure (ICP), which may result from hydrocephalus or be caused by crowding of the intracranial contents due to synostosis. In patients with midfacial retrusion, sleep apnea may develop and can cause idiopathic intracranial hypertension. In rare cases, optic nerve damage can occur secondary to compression stemming from synostosis of the optic foramina. Optic atrophy may occur with or without antecedent papilledema. Because children with elevated ICP may not report headache, a common symptom of this condition, young patients with multiple fused sutures should be monitored for this complication.
Figure 18-6 Strabismus in a patient with Apert syndrome. Note the good alignment in primary position with marked overelevation in adduction and exotropia in upgaze (V pattern).
(Courtesy of John Simon, MD.)
Ocular adnexal abnormalities
Common ocular adnexal abnormalities include orbital hypertelorism, telecanthus, abnormal slant of the palpebral fissures secondary to superior displacement of the medial canthi, ptosis, and nasolacrimal abnormalities. Epiphora is common and may be secondary to nasolacrimal duct obstruction, poor blink secondary to proptosis, obliquity of the palpebral fissures, or ocular irritation from corneal exposure.
Surgical management of craniosynostosis
Reconstructive surgery for severe craniofacial malformation is frequently extensive and involves en bloc movement of the facial structures. The status of the visual system should be documented preoperatively and monitored postoperatively, with appropriate treatment as indicated. Procedures that involve moving the orbits may significantly change the degree or type of strabismus. Because of this, deferring treatment of strabismus until craniofacial surgery is completed may be appropriate.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.