My purpose / interest in the origin of “skull shapes” in humans is the question of “malformation vs. deformation”. Why? Because two ideas are afloat in the “pop-knowledge-verse” that raise a conflict: Specifically, the attribution of a “dolichocephalic” (long-headed) human group or subspecies, which is based on this skull morphology, and the medical attribution of this morphology as specific to the “uterine environment” and birth difficulties (both deformation and malformation) . This distinction between malformation vs. deformation vs. intentional deformation raises problems in the analysis of individual fossil skulls and more recent human skulls as “types” (even species), when the researcher assumes “misshapen skulls” are “normal” skulls that represent a population.
Ochsner J. 2001 Oct; 3(4): 191–199. PMCID: PMC3116745
Misshapen Heads in Babies: Position or Pathology?
Daniel R. Bronfin, MD, Medical Director, Craniofacial Team, Department of Pediatrics, Ochsner Clinic and Alton Ochsner Medical Foundation, New Orleans, LA
A newborn’s skull is highly malleable and rapidly expanding. As a result, any restrictive or constrictive forces applied to a baby’s head can result in dramatic distortions. These changes can be mild and reversible deformations, or severe, irreversible malformations that can result in brain injury. This paper reviews the anatomy and physiology of normal and abnormal brain and skull growth, the etiology of cranial deformation, the types of craniosynostosis most commonly seen in infants, and the importance of early diagnosis and treatment.
At birth, the shape of a newborn’s skull is highly variable due to its inherent plasticity, intrauterine constraint, and the tortuous journey through the birth canal. Variations from the typical oval shape that usually result from the vaginal delivery process will generally return to normal in a relatively short period of time. If this does not occur, the possibility of a rapidly progressive, irreversible, and, in rare circumstances, life threatening cranial malformation needs to be considered.
Historical Perspective: “Intentional Cranial Deformation”
Man’s fascination with misshapen heads dates back to prehistoric times. Archaeologists have found artistic renderings of the imposing heads of Neanderthals who lived 45 000 years ago. (Really?) Hippocrates described in detail a people referred to as the “Macrocephales.” Even in modern times, the television series “Saturday Night Live” entertained viewers with their comic series “The Coneheads.”
Of particular historical interest is the practice of intentional cranial deformation, “the process of dynamic distortion of the normal vectors of infantile neurocranial growth through the agency of externally applied forces”(1). Taking advantage of the rapid head growth and malleable skull unique to the newborn period, individuals have applied constrictive devices (wooden boards, stones placed in a crib, ties, manual molding) over the past centuries to intentionally and permanently deform a child’s skull. (Examples and figures – see original text)
Abnormal Development: Malformation vs. Deformation
There are two very distinct processes of morphogenesis through which the human skull is misshapen: malformation and deformation. Malformation refers to an intrinsically altered developmental process that interferes with cell migration and differentiation through genetically programmed biochemical processes or through extrinsic chemical interference (teratogens). In essence, this process represents an error in the normal development of a part. (Examples: See original text)
In general, cranial deformations are common, mild, and typically reversible, while cranial malformations are relatively rare, progressive, and often irreversible anomalies which, if not aggressively treated in a timely manner, can result in severe cosmetic and functional impairment.
One out of three infants will have some degree of deformational molding. Fetal head constraint is more common in primigravidas (preterm), large for gestational age babies, and when there is cephalopelvic disproportion, oligohydramnios, multiple births, or prolonged courses of labor.
Caput succedaneum (Figure 5) is due to edema of the skin and subcutaneous tissues of the scalp resulting in a “conehead” appearance, which normally resolves in less than 6 days. A cephalohematoma is a traumatic subperiosteal hemorrhage that does not cross a suture line. This deformity is initially soft and, with time, becomes firm as it calcifies; it generally requires up to 4 months to resolve entirely.
Babies born breech (Figure 5 left; Figure 6 right ) typically have craniofacial and limb deformations resulting from their in utero position. These babies characteristically have a long, narrow head, (“dolichocephaly” or “type 1”), with a prominent occipital shelf, redundant skin over the neck, overlapping lambdoidal sutures, and an indentation below their ears (from shoulder compression). These babies are also more likely to have a head-tilt, or torticollis, after birth due to fetal constraint. Developmental dysplasia of the hips and calcaneovalgus (club) foot deformity are also more commonly seen in this population and may or may not be reversible without intervention.
Postnatal deformation can also occur in the neonatal intensive care nursery when high-risk babies are kept paralyzed and intubated on their side for extended periods. These babies have long and narrow heads due to their relatively large heads and poor neck muscle tone; the skull bones are soft and thin and the skull is flattened by gravity alone. It is also important to note that neurologically impaired infants with hypo- or hypertonia may have a greater degree of positional deformity of their heads due to limited mobility when prone.
The other, and far more ominous, type of abnormal cranial development is craniosynostosis, or premature fusion of one or more cranial sutures. This malformation occurs in 1 in 2500 neonates as opposed to the 1 in 3 babies with a deformational anomaly. Craniosynostosis is classified as simple (1 suture) versus compound (2 or more sutures), and isolated (no other major malformations) versus syndromic (one of multiple associated anomalies).
The mechanism of skull malformation caused by a fused suture(s) in a developing skull was initially described by Virchow in 1851 (4). He pointed out that cranial growth restriction will occur in the plane parallel to a prematurely fused suture and enhanced in the perpendicular planes (Figure 9). Thus, if the sagittal suture were fused early, one would expect the skull to be restricted in the transverse dimension and to overcompensate in the anterior-posterior dimension in response to the growing brain resulting in dolichocephaly (type 1).
The original paper contains more info on what can go wrong in human fetal development and birth, and early infancy. A reminder of the consequences of obligatory bipedalism and a big brain. Examples of Malformation-Deformation in the fossil record may tell us a great deal about the ease or difficulty of human birth in a species or group.