Pediatric Positional Skull Deformity
The mechanical difference between an infant’s head and a water balloon is only a matter of kinetics. A water balloon laid on a table conforms to the contour of the table instantly. The infant head laid on a firm mattress takes weeks to conform, but if the infant is sufficiently immobile, the result is the same.
Flattening of the posterior aspect of the skull in early infancy is by far the most common reason for referral of new patients to the pediatric neurosurgeon; it is more common than craniosynostosis by an order of magnitude. The literature mentions this condition by a number of names: posterior plagiocephaly, nonsynostotic occipital plagiocephaly, posterior positional plagiocephaly, and others. Use of the term positional skull flattening is particularly suitable for communication with families because it avoids jargon and conveys a mechanism.
Positional skull flattening is not difficult to recognize. Like the various forms of craniosynostosis, positional flattening causes a characteristic pattern of deformity that the trained eye can distinguish without radiological investigations. Gravity exerts a deforming force on the entire skull, not just on the dependent, flattened surface. The contralateral frontal aspect of the skull often becomes somewhat flattened as well, and prominences develop in the contralateral occipital region and the ipsilateral frontal region. Viewed from above the skull looks like a parallelogram.
The ipsilateral frontal prominence is occasionally the feature of the deformity that families find most distressing even though the posterior flattening is more severe. Other components of the facial skeleton may become deformed: The ear ipsilateral to the flattening is displaced anteriorly compared to the other ear. The nose feels the tug of gravity and rotates in the plane of the face. Like the ipsilateral ear the ramus of the mandible on the side of the flattening may be pushed forward, and the jaw may be asymmetrical. Concerns have been expressed about the possibility of dental malocclusion later in childhood, but the actual prevalence of this problem is unknown. The differential diagnosis of positional skull flattening is synostosis of the lambdoid suture. Fortunately for the busy primary physician, because lambdoid synostosis is so vanishingly rare, for practical purposes all predominantly posterior skull deformities in infants are positional.
Infants are occasionally born with posterior flattening, which implies earlier immobilization of the fetal head in a tight place somewhere, most likely against the sacral promontory. More often the head is round (or normally molded) at birth and becomes flat in the first couple months of life as the infant lies supine for naps in compliance with the recommendations of the American Academy of Pediatrics’s "Back to Sleep" campaign. Conjunction of developmental immobility with a degree of congenital torticollis leads to asymmetrical flattening, which is the implication of the term plagiocephaly. Once flattening develops, it perpetuates itself, as the infant must overcome an even greater moment of inertia to rotate the head off the flat surface. In the second half of infancy, with the developmental acquisition of independent sitting and active rolling from supine to prone, the deformity ceases to progress. Subsequent brain expansion remodels the skull and reduces the flattening somewhat, and the asymmetry that persists is mitigated further by disproportionate enlargement of the neck muscles and the facial skeleton and by hair growth. Whether even the most severe positional skull flattening ever leads to significant deformity in developmentally normal school age children is doubtful.
The best treatment is prevention. In the first few months, sleep position should be varied by propping the infant slightly to one side or the other with a folded towel or blanket. The infant who has already developed flattening should be propped to the opposite side. Behavioral interventions to encourage active rotation of the head off the flattened aspect can be helpful as well. For instance, most right-handed parents carry small infants in the crook of the left arm so that the infant must rotate the head to the right to gaze at the parent’s face. Likewise, most right-handed parents lay infants down with the head to the parent’s left, forcing the infant to rotate the head to the right to look out into the room. Probably not coincidentally, the great majority of asymmetrical infant heads are flattened on the right side. These right-handed routines should be varied. Infants quickly learn to defeat positional manipulations beyond 4 or 5 months of age. Asymmetrical positional flattening is almost always associated with a degree of congenital torticollis, and passive range of motion exercises for the neck are useful at any age. These exercises can be taught and reinforced by a physical or occupational therapist, and they should be performed several times daily, as with diaper changes.
Externally applied forces cause positional flattening, and externally applied forces can be utilized to correct the deformity. The "orthotic helmet" is a padded polypropylene band that is custom fabricated to fit snugly over the prominent aspects of the infant skull and to leave daylight over the flattened aspects. The infant wears the helmet continuously with interruptions only for bathing, and over the course of several months, as the brain grows, the head expands into the daylight and becomes more rounded. Minor adjustments in the fit of the helmet are required on a roughly bi-weekly basis to prevent pressure injuries to the scalp. Data suggest that orthotic helmet therapy is no more effective than positioning and exercises in the management of mild to moderate deformities, and the frequent visits to the orthotist are a burden to families from remote communities, so the author reserves this intervention for the most severely affected patients. The Food and Drug Administration has recently decided to require safety and efficacy data from every manufacturer of orthotic helmets, and as many regions like Oregon are served by only a single orthotist for whom fabrication of helmets is a sideline, the long-term availability of this therapeutic option is in doubt.
Surgical interventions have virtually no place in the management of positional skull flattening. "Unipolar" or "bipolar release" of the sternomastoid muscle has been recommended for congenital torticollis caused by scarring and contracture due to birth injury. The distinction between functional and contractural shortening of the sternomastoid is not very clear in practice, so the indications for surgery have always been indefinite, and the superiority of surgical release to physical therapy or to the untreated natural history of this condition has never been demonstrated. The surgical treatment of posterior skull flattening has a dubious history as well. In the 1980s and early 1990s surgeons at a few centers were advocating a variety of synostectomies and reconstructive procedures for posterior plagiocephaly under the diagnostic label of "lambdoid synostosis." The Center for Disease Control actually investigated an epidemic of lambdoid synostosis in the Rocky Mountain region, concluding discretely that there were disagreements about the use of this diagnostic term. As the nature of posterior plagiocephaly has become better understood, and as the generally benign natural history has been appreciated, surgical indications have all but disappeared.
