Normal Cranial Development and Head Shape
Head growth of the fetus and infant is largely determined by brain growth. The brain reaches 90% of adult size by 1 year of age; it is 95% of its ultimate adult size by 6 years of age and growth is complete by age 7. Skull anomalies may originate prenatally or may develop postnatally during the first 2 years of life.[3]
Figure 1 illustrates the boney anatomy of the normal skull sutures and fontanelles. The newborn infant's skull is incompletely ossified and the cranial sutures are normally open at birth, fusing by the end of the second year of life.[3] The size of the diamond-shaped anterior fontanelle has a wide range of normal, from 1 to 4 cm by 1 to 2.5 cm, and usually closes before 2.5 years of life. The triangular-shaped posterior fontanelle is small and typically closes by 2 to 3 months of life.
Infant skull anatomy. Reprinted with permission from Furdon SA, Benjamin K. Physical assessment. In: Verklam MT, Walden M, eds. Core Curriculum for Neonatal Intensive Care Nursing. St Louis, Mo: Elsevier Saunders; 2004.
Normal human cranial shapes vary; a combination of genetic and environmental factors, such as infant sleep position and cultural head binding practices, may influence head shape. Head shape is best appreciated by evaluating the head from the down. Table 1 illustrates and defines the head shapes often seen during infancy. Figure 2 shows normal variations in human head shape into adulthood. Each head shape has a unique profile, frontal appearance, and appearance when viewed from the . Although head shape is determined during infancy, it impacts facial features and appearance across the lifespan.
Head shape variations persist into adulthood. Reprinted with permission from Mooney MP, Siegel MI. Understanding Craniofacial Anomalies: The Etiopathogenesis of Craniosynostoses and Facial Clefting. New York, NY: Wiley-Liss, 2002.
Cranial index (CI), an objective measure used to quantify head shape, is the width of the head divided by the length multiplied by 100% (Fig 3). The normal CI ranges from 76% to 81% in prone sleeping infants; the normal CI for supine sleeping infants is 86% to 88%. A CI of > 81% indicates a shortened anterior-posterior dimension and widening between the biparietal eminences, is termed brachycephaly. Dolichocephaly, a narrow elongated head, is defined as a CI < 76%. Cranial index is heavily influenced by infant sleep position due to the malleability of the skull. A 2-month-old infant may have spent > 700 hours sleeping on a firm surface, leading to changes in the skull shape.[4] During infancy, increased supine positioning is a frequent cause of occipital flattening, also called deformational brachycephaly.[5]
Measuring cranial index is an objective method of evaluating various head shapes in newborns.
The normal head shape of American infants has changed from mildly dolichocephalic to mildly brachycephalic. Although normalcy is redefined, societal or parental expectations do not change immediately. Some parents become concerned, perceiving their infant's head shape as abnormal. Although some parents may respond to reassurance, others search for solutions, such as head-molding helmets or more invasive options such as surgery.
Adv Neonatal Care. 2005;5(6):329-340. © 2005 W.B. Saunders
Cite this: Impacting Infant Head Shapes - Medscape - Dec 01, 2005.
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