Craniosynostosis

A congenital anomaly of the skull characterized by premature fusion of one or more cranial sutures.

(Figure)

(Figure)

Craniostenosis.

Estimated to be approximately 1:200,000 live births. Sagittal and lambdoid craniosynostosis (the most common type) are approximately four times more common in males than in females, whereas unicoronal craniosynostosis is more common in females. For the other forms, the distribution is about equal between the two genders.

A positive family history is present in up to 40% of cases, with genetic syndromes accounting for at least 50% of those cases. The most common syndromes include Apert Syndrome and Crouzon Syndrome. Both autosomal dominant and autosomal recessive inheritance have been described, but sporadic occurrence also is common. Genetic mutations that may be responsible for craniosynostosis include mutations in the fibroblast growth factor receptors (FGFR1, FGFR2, FGFR3), the TWIST, and MSX2 genes.

The etiology is unknown but may involve abnormal cranial suture development resulting in failure of growth perpendicular to the affected suture and overgrowth of skull parallel to the affected suture. Environmental factors etiologically linked to craniosynostoses include rickets and hyperthyroidism. Drugs that may be involved in craniosynostosis include phenytoin, retinoids, valproic acid, aminopterin/methotrexate, fluconazole, and cyclophosphamide. In some cases, local intrauterine factors related to constraint of the fetus (e.g., abnormal positioning in utero, multiple pregnancy, oligohydramnios) have been linked to craniosynostosis. The developing brain is the driving power behind skull growth and forces the skull to compensatory growth in directions perpendicular to the fused suture along adjacent open sutures.

The diagnosis may be suspected clinically if special attention is paid to the head circumference (percentiles), shape and presence of any deformities, size of the fontanelles, palpable ridges over affected sutures with absent movement of the bone on either side of the suture on palpation, neurologic behavior and development of the infant, the pupils and their reaction to light, and funduscopic evaluation for papilledema. Radiologic examinations (e.g., computed tomography scanning and/or magnetic resonance imaging) confirm the diagnosis. True craniosynostosis must be differentiated from birth molding (present at birth and resolving within days or weeks) and positional plagiocephaly without synostosis (a frequent finding resulting from local pressure on a specific area of the skull (same position), typically the occipital region leading to occipital or lambdoid plagiocephaly.

It must be differentiated between syndromic and nonsyndromic craniosynostosis. Nonsyndromic cases account for approximately 50% of all craniosynostoses and are commonly limited to synostoses of a single suture (sagittal, metopic, or coronal) and usually not associated with increased intracranial pressure, whereas syndromic craniosynostosis refers (most commonly) to patients with Acrocephalosyndactyly Syndromes (i.e., Apert, Crouzon, Pfeiffer, and Saethre Chotzen syndromes). Hydrocephalus, increased intracranial pressure, and developmental delay may occur secondary to craniosynostosis and are more common with bicoronal, combined coronal and sagittal, and total craniosynostosis. The anatomical classification is based on the suture(s) affected:

Sagittal craniosynostosis: Accounts for 40% of all craniosynostoses and most cases of single suture craniosynostosis. It results in dolichocephaly or scaphocephaly (decreased biparietal diameter and increased anteroposterior diameter) with frontal and occipital bossing if left untreated. The vast majority of patients are males. Increased intracranial pressure and mental retardation are rare.

Unicoronal craniosynostosis: This type of craniosynostosis is responsible for approximately 15% of all cases of craniosynostosis and is more common in females. Left uncorrected, plagiocephaly with marked craniofacial asymmetry develops with flattening of the forehead and the cheeks on the affected side, proptosis, ipsilateral elevated supraorbital ridge, and malalignment of the eyes. The orbital asymmetry may cause amblyopia. Frontal bossing occurs on the unaffected side. Increased intracranial pressure is not common.

Bicoronal craniosynostosis: 20% of all craniosynostoses leading to brachycephaly (decreased anteroposterior diameter) with a flattened, wide forehead and characteristic deformities of the orbits (shallow) leading to eye (proptosis) and nasolacrimal duct complications. Associated anomalies include choanal atresia, hypoplasia of the maxilla (and midface), high arched palate, increased intracranial pressure, and developmental delay. This type of craniosynostosis typically is found in Apert and Crouzon syndromes.

Lambdoid craniosynostosis: Responsible for up to 3% of craniosynostoses and affects males about four times more often than females. This form of craniosynostosis has to be carefully distinguished from deformational, nonsynostotic plagiocephaly, which is much more common than previously thought and explains why older studies report a significantly higher overall percentage for lambdoid craniosynostosis. Bilateral involvement results in brachycephaly with anterior and inferior displacement of the ears, while in unilateral cases flattening of the occiput and ipsilateral forehead bulging result in rhomboid skull and the same ear displacement as in bilateral craniosynostosis.

Metopic craniosynostosis: Approximately 4% of all craniosynostoses. The metopic suture is the first suture to close, which normally occurs soon after birth. Premature closure leads to trigonocephaly (keel shaped, pointed forehead). Hypotelorism may occur if the frontonasal suture also is affected. In severe cases, the forehead appears narrow with compensatory widening of the skull posterior to the coronal sutures. This is occasionally associated with mental retardation secondary to cerebral malformations, such as arrhinencephaly or even holoprosencephaly.

Coronal and sagittal craniosynostosis: Approximately 10% of all craniosynostoses. Typically, acrocephaly (cone-shaped head) develops.

Lambdoid and sagittal craniosynostosis: Approximately 1% of all craniosynostoses. Occipital plagiocephaly typically results.

Multisuture craniosynostosis: Results in oxycephaly (short and narrow head) with underdeveloped paranasal sinuses, shallow orbits, increased intracranial pressure, and mental retardation. Most often, the sagittal and coronal sutures are affected. Involvement of all sutures except the metopic suture leads to Cloverleaf Skull (Kleeblattschädel). In all these cases, increased intracranial pressure and mental retardation are common.

Total craniosynostosis: May be responsible for up to 10% of all craniosynostoses and lead to microcephaly and increased intracranial pressure.

It is important to identify associated syndromes and risks related to them preoperatively. Raised intracranial pressure is not uncommon and often underestimated and should be taken into consideration for the anesthetic plan. Upper airway obstruction is a common feature, and careful evaluation of the airway is required with regard to airway management. Obtain a complete blood count, serum levels of electrolytes, and coagulation parameters preoperatively. If craniosynostosis repair is planned, ensure packed red cells are available in the operating room before skin incision is made.

Surgical treatment of craniosynostosis can be an anesthetic challenge with a high complication rate. Mental retardation may lead to poor cooperation upon separation from the parents or during induction of anesthesia. Difficult airway management should be expected. Maintaining spontaneous ventilation and oxygenation during attempts to control the airway is strongly recommended. Be prepared to use alternative techniques to manage the airway (e.g., laryngeal mask, fiberoptic intubation). A surgeon familiar with surgical airway management and the necessary equipment should always be present in the operating room. Specific anesthetic measures are required in case of increased intracranial pressure. Careful protection of the eyes must be provided in case of proptosis because of the high risk for corneal damage. Current surgical technique for craniosynostosis consists of total cranial vault reconstruction, which carries a high risk of major blood loss (often significantly more than one circulating blood volume). Large-bore intravenous access with the possibility for rapid transfusion is mandatory. However, vascular access in these patients often is challenging. Accurate evaluation of blood loss usually is difficult. Invasive hemodynamic monitoring with the possibility of regular intraoperative blood work sampling (complete blood count, blood gas analysis, serum electrolytes, and coagulation parameters) is required. Depending on the patient's positioning, the risk of venous air embolism should be kept in mind and the need for central venous access considered. For this reason, nitrous oxide should not be used in these patients. To reduce the amount of homologous blood transfusions, preoperative hemodilution, intraoperative cell saver techniques, and induced arterial hypotension have been used. However, arterial hypotension should not be tolerated in patients with increased intracranial pressure in order to maintain cerebral perfusion pressure. Ventilation should aim at normocapnia or mild hypocapnia. Hypothermia in these usually small patients is not uncommon because of massive transfusion and the prolonged operative time. Although mild hypothermia might offer some degree of cerebral protection, moderate hypothermia must be avoided. Postoperative ventilation may be necessary in the presence of significant facial edema associated with the surgical procedure. Securing the endotracheal tube with a suture rather than a tape is preferable because accidental extubation could be fatal (facial edema!).

Sedative premedication in patients with increased intracranial pressure should be used with caution and under supervision of trained personnel only. Hypotensive anesthesia is most often achieved by using volatile anesthetics, opioids, and/or sympathodrenergic receptor blocking drugs. Avoid nitrous oxide secondary to the risk of venous air embolism. Avoid muscle relaxants until the airway has been secured. Avoid ketamine and succinylcholine in case of increased intracranial pressure.