There are four key suture lines in the growing skull, namely, metopic, sagittal, coronal, and lambdoid. These are shown in Fig. 26.1. They allow progressive growth of the skull to accommodate rapid brain growth in the early years of life. In addition, there are two corresponding fontanelles, which are spaces between the bones of the skull where ossification is incomplete to facilitate birth passage. The fusion of cranial sutures occurs earliest in the metopic suture between the two frontal bones. This closes between 6 and 8 months of age. The remaining three sutures remain open until the third decade (sagittal 22 years, coronal 24 years, and lambdoid 26 years). The fontanelles usually close within the first 12 months with the posterior fontanelle closing between 3 and 6 months, and the anterior fontanelle closing between 9 and 12 months.1,2 Fig. 26.1 Cranial sutures in the human fetus. Premature closure produces growth restriction perpendicular to the line of the suture and compensatory overgrowth parallel to it. Bones Sutures Metopic Coronal Squamosal Sagittal Lambdoid Occipital Temporal Parietal Frontal
2. Carson BS, Dufresne CR. Craniosynostosis and neurocranial asymmetry. In: Defresne CR, Carson BS, Zinreich SJ, eds. Complex Craniofacial Problems. New York: Churchill Livingstone; 1992 Cranial growth usually occurs through two processes, suture growth and appositional growth. Appositional growth involves bone resorption on the inner surface and deposition on the outer surface of the skull. Suture growth usually occurs perpendicular to the cranial sutures and premature suture fusion will result in predominantly parallel growth. This is known as Virchow’s law and explains the deformities observed with fusion of a given suture. Only one-third of craniosynostoses are syndromic. In cases that are syndromic, genetic mutations in the FGFR2, FGFR3, and TWIST1 genes may be identified. Various theories exist regarding abnormal suture fusion and include the cranial base theory and the intrinsic suture theory. The cranial base theory states that synostoses result from abnormal tension exerted by the cranial base through the dura, but this does not account for isolated synostoses. The intrinsic suture biology theory proposes that synostoses result from the osteoinductive properties of dura mater, which contains osteoblast-like cells.1–3
3. Knoll B, Persing JA. Craniosynostosis. In: Bentz ML, Bauer BS, Zuker RM, eds. Pediatric Plastic Surgery. 2nd ed. St Louis: Quality Medical Publishing; 2008 Elevated intracranial pressure (ICP) is associated with craniosynostosis either due to cephalocranial disproportion or other factors such as intracranial venous congestion, hydrocephalus, or upper airway obstruction. Early clinical findings that suggest a raised ICP include headache, irritability, nausea, vomiting, and sleeping difficulties. Later findings include mental impairment, delayed development, and visual disturbances. Fundoscopic examination may show papilledema and examination of the fontanelles may show tense bulging, sometimes known as the volcano sign. Raised ICP may be measured directly or indirectly. Transorbital ultrasound can be used to measure optic nerve sheath diameter, which will increase (not decrease) with raised ICP. Visual evoked potentials measure the latency time of an encephalographic response to visual stimuli and will also be increased with raised ICP and axonal injury. Other modalities used to assess raised ICP include plain radiographs which may show late signs of a copper-beaten appearance or thumb printing from pressure of the gyri on the inner table.1–4
4. Xu W, Gerety P, Aleman T, Swanson J, Taylor J. Noninvasive methods of detecting increased intracranial pressure. Childs Nerv Syst 2016;32(8):1371–1386 No universal definition exists for raised ICP in children. Fundoscopy is a useful tool for assessing raised ICP in many cases, but it should be interpreted with caution in children. Across all age groups it has a specificity of 98% and a sensitivity of 100%. However, in children younger than 8 years of age, the sensitivity is around 22%. A Chiari malformation is not a vascular malformation, but it can result in a raised ICP. It is present when the cerebellar tonsils are displaced downward through the foramen magnum. This malformation may be a cause of hydrocephalus and neurodevelopmental injury. It is commonly seen in patients with Crouzon or Pfeiffer syndrome. Cephalocranial disproportion refers to a decreased intracranial volume and restriction of brain growth. It is one cause of raised ICP; others include intracranial venous congestion, hydrocephalus, and airway obstruction. The incidence of elevated ICP is affected by the number of sutures involved in craniosynostosis. The incidence of elevated ICP with single suture involvement is 13 and 42% when multiple sutures are involved.1–4
Plain radiographs are useful to show an absence of suture lines and are usually the only imaging modality required for patients with craniosynostoses. In syndromic cases, however, CT can be helpful to diagnose associated abnormalities, to plan surgery, and to monitor hydrocephalus. MRI is typically unnecessary except in patients with selected syndromes such as Apert or Pfeiffer, when associated brain abnormalities are suspected. Radiographs may show other signs of synostosis. For example, a copper-beaten appearance on radiograph is also known as Luckenschadel and is a characteristic late sign (with a low specificity) of raised ICP in craniosynostosis. Other late findings are cortical thickening, fingerprinting, and loss of cisternae.1,2
The appearance described is known as trigonocephaly where the head shape is “keel shaped” or triangular. This is caused by premature fusion of the metopic suture. A spectrum of deformities occurs with this condition, including bitemporal narrowing, hypotelorism, bilateral supraorbital retrusion, medially slanted lateral orbital rims, and epicanthal folds. ICP elevation is present in up to 10% of such cases. Unilateral coronal synostosis is associated with ipsilateral frontal flattening and contralateral bossing. Lambdoid synostosis is associated with ipsilateral occipital flattening and a mastoid bulge with downward cant of the posterior skull base on the affected side. Sagittal synostosis is associated with a boat-shaped head rather than triangular. Bilateral coronal synostosis will result in a broad flat head termed “brachycephaly.”1,2
Sagittal synostosis represents half of all synostoses. They are four times as common in males and clinically present with an increased anteroposterior (AP) cranial diameter and decreased biparietal width. This appearance is described as scaphocephaly, meaning “boat shaped.” Coronal synostoses represent approximately one-third of all synostoses, and they are usually unilateral. Metopic synostoses are a little less common than coronal synostoses, and affected babies develop trigonocephaly. The least common form is lambdoid, which is extremely rare (Fig. 26.2).1
A harlequin deformity results from a lack of descent of the greater wing of the sphenoid on the affected side. It is seen on radiographs of patients with a unilateral coronal synostosis. Physical findings in unilateral synostosis include an anterior plagiocephaly that involves ipsilateral frontal and occipitoparietal flattening, contralateral frontal and parietal bossing, and posterior displacement of the ipsilateral ear (Fig. 26.3). The nasal root is constricted and deviated to the affected side. The chin tends to point to the contralateral side due to an anteriorly displaced ipsilateral glenoid fossa.1–3
condition? The characteristic head shape in deformational plagiocephaly is a parallelogram appearance (see Fig. 26.2). Deformational plagiocephaly can be mistaken for either posterior (lambdoidal) or anterior (unilateral coronal) synostoses, but is not a true craniosynostosis. It is relatively common with an incidence of 1 in 300 and occurs secondary to external forces applied through the baby’s head. It has recently become more common and this may be due to the fact that infants are increasingly nursed in a supine position in order to minimize risk of sudden infant death syndrome. A triangular head shape is characteristic of metopic synostosis. A boat-shaped head is associated with a sagittal synostosis. A square, broad head shape is associated with a bicoronal synostosis. A trapezoidal head shape is associated with anterior or posterior plagiocephaly (lambdoidal or coronal synostoses, respectively).1–3
Deformational plagiocephaly is distinguished from a true craniosynostosis by the presence of a parallelogram configuration with flattening of the occiput (Table 26.1, also see Fig. 26.2). The nasal root will be unaffected in this condition and therefore remain in the midline. In contrast, the nasal root will be moved toward the ipsilateral side in a true craniosynostosis. The cheek, chin, ear, and brow position are all affected in both deformational and synostotic conditions. In general, the direction of their movement is opposite in each of two conditions.1,2 Table 26.1 Anatomic Features That Differentiate Synostotic and Deformational Plagiocephaly Anatomic Feature Synostotic Ipsilateral superior orbital rim Up Down Ipsilateral ear Anterior and high Posterior and low Nasal root Ipsilateral Midline Ipsilateral cheek Forward Backward Chin deviation Contralateral Ipsilateral Ipsilateral palpebral fissure Wide Narrow Anterior fontanel deviation Low contralateral High none
Turribrachycephaly is where there is excessive skull height and vertical forehead secondary to an untreated brachycephaly, such as can occur in bicoronal synostosis. Oxycephaly refers to a pointed head with a retroverted forehead secondary to a pansynostosis. Kleeblatschadel refers to a cloverleaf deformity secondary to involvement of all sutures except squamosal. Posterior plagiocephaly occurs secondary to lambdoid synostosis. Scaphocephaly (or dolichocephaly) is secondary to premature fusion of the sagittal suture.1–4
Crouzon syndrome is the most common syndromic craniosynostosis that occurs in 1 in 25,000 live births. It most commonly involves the coronal sutures but may involve other sutures including the sagittal and metopic. It is an autosomal dominant condition and ICP is elevated in approximately 65% of cases. Crouzon patients have normal extremities and this is a key finding that helps to differentiate this condition from some other synostotic conditions. Midface hypoplasia with exorbitism and turribrachycephaly are typical findings. This results in a class III malocclusion (not I) in most cases, with an anterior open bite and high arched palate.1–3
Apert syndrome is an autosomal dominant condition that affects 1:100,000 to 1:160,000 live births. The presence of a complex symmetrical syndactyly distinguishes this syndrome from other craniosynostoses which may have the other features described. Apert syndactyly has three distinct subtypes and was classified by Upton1 in 1991. Type I is a spade hand with the thumb and little finger separate and a syndactyly of the second and third web spaces. Type II is a mitten hand with the thumb free and syndactyly between the second, third, and fourth web spaces. Type III is a rosebud hand with all digits involved in the syndactyly (Fig. 26.4). Raised ICP is seen in more than three quarters of patients with Apert syndrome and ventriculoperitoneal (VP) shunts are often required. Many, but not all, patients have decreased intelligence. Apert syndrome is associated with bicoronal synostoses with significant turribrachycephaly and midface hypoplasia; therefore, patients have some features in keeping with both Crouzon and Pfeiffer syndromes.2 Cleft palate is also a feature of many different craniosynostotic syndromes so it is not a good differentiating factor.
Patients with Pfeiffer syndrome usually have a normal mental status, although this may be decreased in the most severe cases. Pfeiffer syndrome is a rare craniofacial condition involving synostoses in conjunction with extremity deformities and hydrocephalus. Incidence is 1:100,000 and is a result of mutations in the FGFR genes. Three different subtypes have been described according to clinical features and syndrome severity.1 Type I features include brachycephaly, midface hypoplasia, finger, toe abnormalities, and normal intelligence. Type 2 features a cloverleaf skull, proptosis, and major finger/toe abnormalities. Developmental delay may be present. Type 3 patients are similar to type 2 but without the cloverleaf skull.
Saethre-Chotzen syndrome occurs in 1:25,000 to 1:50,000 live births. It was described by Saethre in 1931 and then by Chotzen the following year. It is inherited in an autosomal dominant fashion and is associated with the TWIST-1 gene mutation. Patients have asymmetrical brachycephaly, eyelid ptosis, prominent crus helicis, deviated nasal septum, narrow palate, and a low hairline. Mental status is usually normal in these patients.1
The greatest risk for infants undergoing craniosynostosis surgery is major bleeding, especially given the low circulating volume they have. This is typically just 70–80 mL per kg. So the total circulating volume for a 10-kg infant would, for example, be just 700 mL. There is a large surface area of raw bone following surgery which tends to bleed most in the initial 24 hours post surgery. Patients are, therefore, closely monitored following surgery Fig. 26.4 A, Typical type I or spade-shaped hand. B, Type II or mitten hand. C, Type III or rosebud hand. A B C A B C with neurologic examination every 2 hours and hemoglobin/hematocrit and sodium reassessed every 6 hours for 24 hours. Transfusions are commonly given if hematocrit falls below 21%. The primary goal of synostosis surgery is not to address the abnormal head shape and appearance, instead it is to facilitate normal or optimal brain growth, while minimizing risk of developing raised intracranial pressure (ICP) and its consequences. Improvements in appearance are secondary goals. The approach to treatment is significantly different for nonsyndromic than for syndromic patients because the number of sutures involved is usually different and there are other considerations that need to be taken into account. Single-suture nonsyndromic patients usually require only a single open vault procedure, whereas syndromic patients typically have multiple sutures involved and hence require multiple complex procedures. Furthermore, they are at increased risk of other complications of craniosynostosis such as raised ICP. The timing of surgery is controversial and there are advantages and disadvantages of early versus later scheduling for surgery. For example, early surgery (6–12 months) has the advantage of more malleable bones, faster bone regeneration, and spontaneous healing. However, there is risk of recurrence, needing repeated surgery further down the line. In contrast, later surgery (after 12 months) means that bones are stronger and better able to hold fixation devices solidly, but the deformity is more advanced, the bones are less malleable, and healing may be less effective.1–3
The management of an isolated scaphocephaly involves treating a sagittal suture craniosynostosis. This may be undertaken with an extended strip craniectomy, a spring-assisted cranioplasty, or open vault reconstruction. The extended strip craniectomy has the advantage of being able to be performed endoscopically thereby minimizing scar incision length, blood loss, operative time, and recovery. It is used primarily for isolated sagittal synostoses in infants younger than 4 months of age.1 Wedge osteotomies are made adjacent to the coronal and lambdoid sutures to allow for transverse expansion. Helmet molding is used postoperatively for up to 18 months. The spring-assisted cranioplasty is another approach that can be useful for management of the sagittal suture or other sutures where there is symmetrical synostosis present. It uses continuous force generated by a spring across the osteotomy/ craniectomy site. It does, however, require a second procedure for device removal. LeFort midface advancement is part of the management of syndromic cases with multiple synostoses. It is used to advance the midface rather than address a sagittal suture synostosis. It may be performed in childhood or delayed until skeletal maturity. Fronto-orbital advancement is used to expand intracranial volume and reshape the cranial vault with advancement of the frontal bone. It is indicated for use in bilateral coronal synostoses (brachycephaly). It is also useful to protect the globes from compression and provide an aesthetic improvement of the face in such cases. Posterior vault expansion with or without distraction osteogenesis is also used to increase intracranial volume in syndromic cases of synostoses such as severe turribrachycephaly and occipital flattening. Biparieto-occipital craniotomies are used for the management of lambdoid craniosynostoses.