"Does my baby's flat head mean he has to wear a helmet?" That question, recently posed by a concerned parent, is typical of the inquiries pediatricians hear regularly about head shape abnormalities. How would you respond to this parent's concern?
Here we offer a practical, objective approach to determining which patients with odd head shapes require further evaluation and treatment.
CAUSES OF HEAD SHAPE ABNORMALITIES IN INFANTS
Odd head shapes develop because the bones of the newborn skull are moveable and malleable. The bones are able to move because they are adjoined by fibrous sutures (junctures between 2 bones) and fon- tanelles (junctures between more than 2 bones) that remain unossified throughout the first years of life to facilitate vaginal delivery and allow expansion of the growing brain. The anterior fontanelle, easily palpated at the top of the head, typically closes by 18 to 24 months of age. The posterior fontanelle is more difficult to appreciate on physical examination and often closes in the first few months of life.
The major forces that misshape the head include:
• External pressure, either applied to the skull during the birthing process or resulting from uterine constraint in cases of multiple births (molding).
• Gravitational forces applied to the skull during early infancy (deformational or positional plagiocephaly).
• Early fusion of one or more of the sutures (craniosynostosis [Figure 1]).
Molding. In utero, molding can result from uterine crowding, such as occurs when multiple fetuses share the same womb. During parturition, the strong forces applied to the skull as it is squeezed through the birth canal cause the bones that make it up to override one another; this process can "mold" the head into various shapes. Difficult deliveries that require the use of forceps or vacuum extraction can result in severe molding. In addition, the calcification of a healing cephalohematoma can produce a distinct lump on the skull, usually on one of the parietal convexities. When discovered by a concerned parent (usually when the child is 1 to 2 months old), such a lump often prompts a visit to the pediatrician. Reassure parents that a cephalohematoma poses no long-term risk.
Because molding secondary to the birthing process typically resolves in hours to weeks, persistent or progressive shape deformities beyond that time should raise suspicion for deformational plagiocephaly or craniosynostosis.
|Figure 1 – A normal newborn’s skull consists of several plates of bone that are joined by fibrous sutures that facilitate vaginal delivery and expansion of the growing brain. In craniosynostosis, one or more of the sutures close prematurely, causing problems with normal brain and skull growth and resulting in an abnormal, asymmetric appearance. There are numerous types of craniosynostosis, each of which involves a different suture or combination of sutures and results in a distinctive head shape. Three of the more common types are shown here. (Reprinted with permission from University of Utah Health Sciences Center.20)|
Deformational plagiocephaly. Posterior-type deformational plagiocephaly is caused by constant gravitational forces applied to the occiput when the infant remains for prolonged periods in the same supine position--the sleep position promoted by the American Academy of Pediatrics (AAP) Back to Sleep campaign (Figure 2).1 Various degrees of brachycephaly (ie, a shortened, broad head) occur in most children who sleep solely on their backs.2
Any condition that is associated with abnormal bone formation or muscle tone (especially torticollis) can also cause deformational plagiocephaly. Dolichocephaly (ie, a long, narrow head with bitemporal narrowing) can develop in preterm infants who have large heads and weak neck muscles.3
|Figure 2 – The incidence of occipital plagiocephaly has risen dramatically since the AAP suggested the supine sleep position.|
(Reprinted with permission from Losee JE et al. Plast Reconstr Surg. 2005.1)
Craniosynostosis. Exactly why sutures fuse early is not known, but genetic and environmental fac- tors--such as single gene mutations, teratogen exposure, and fetal constraint--probably play a role.4 Craniosynostosis may also be an asso- ciated feature of several genetic syndromes, including Apert, Crouzon, Dubowitz, and Treacher Collins- Franceschetti syndromes.
Crouzon syndrome is associated with various facial and skull deformities, exophthalmos, and hydrocephalus. Apert syndrome is also associated with significant craniofacial deformities, hydrocephalus, and exophthalmos, along with mental retardation and syndactyly. Dubowitz syndrome5 is associated with marked microcephaly and facial anomalies (as well as other features); Treacher Collins-Franceschetti syndrome6 is associated with severe craniofacial abnormalities and hearing loss.
When craniosynostosis occurs, the growth of the skull is impeded in a plane that is perpendicular to the fused suture, but the skull continues to grow in the parallel plane. Brain growth occurs in the direction of the open sutures. Different head shapes result (see Figure 1) depending on which suture or combina- tion of sutures has fused:
• Trigonocephaly (a triangular-shaped head) arises from metopic craniosynostosis.
• Scaphocephaly arises from sagittal craniosynostosis.
• Turricephaly (a tower-shaped head) arises from coronal plus sagittal craniosynostosis.
• Brachycephaly arises from bilateral coronal craniosynostosis.
• Posterior plagiocephaly (trapezoidal-shaped head) arises from lambdoid craniosynostosis; this is a very rare form of craniosynostosis.