It seems that children with developmental delay and/or neurological injury have increased rates of NSDP, although a causal relationship has not been demonstrated. Emerging evidence suggests that infants with DP are less active [19], have variable tone [20], and are delayed in some areas of development compared with their age-matched peers [17, 21, 22]. The association between neurological development and synostotic skull asymmetry has been a focus of research for several years [23–26], but until recently, it was presumed that plagiocephaly without synostosis was not associated with developmental delay [25]. Within the past few years, however, evidence has increased for a significant association, if not a causal pathway, between developmental delay and deformational (nonsynostotic) plagiocephaly [17, 20–22, 27].

Concerning clinically significant differences in gross motor development [22], infants with DP scored lower on items such as sitting up, rolling back to side, and crawling. Nevertheless, DP by itself is not a risk factor for delayed development in infants; rather the association between some developmental delays and DP indicates that there is an increased possibility of delay among infants with DP and developmental assessment is essential as part of the management of children with this condition [28].

Supine sleeping infants show delayed motor milestones in gross motor movements requiring upper body strength (roll, sit, pull to stand) in comparison to a prone-sleeping group at 6 months of age. No difference was found for the gross motor milestones using lower body strength such as walking. At 18 months, no significant differences were found [17, 18].

Several studies have demonstrated that children who adopt the supine sleep position are more likely to exhibit gross motor lags and may have delays in the acquisition of gross motor milestones when compared with infants who sleep in prone position [29, 30]. A change in findings for developmental screening of infants in pediatric practice was noted beginning 1 year after the American Academy’s recommendations regarding sleep position [31]. Empirical evidence is provided demonstrating that exposure to prone position while awake is positively associated with performance on gross motor assessments at both 4 and 6 months of age [32].

Infants born very preterm may develop deformational plagiocephaly. A positional preference of the head seems to be a normal aspect of these infants’ motor repertoire, with limited ability to predict persistence of an asymmetric motor performance. The decreased prevalence of deformational plagiocephaly between 3 and 6 months indicates an optimistic course. Infants with a history of chronic lung disease and/or slow gross motor maturation merit timely intervention [33].

Males with plagiocephaly at birth are a high-risk group for subtle developmental delay [34].

Head shape and developmental delay associated with deformational plagiocephaly usually improve by age 4 years [35]. Long-term follow-up controls demonstrate no persistence of motor delay in children with DP who have shown psychomotor delay before starting repositioning and physiotherapy [25, 36]. On the other hand, no child even showed a precocious psychomotor development [36].

Although DP seems to be associated with early neurodevelopmental delay, which is most evident in motor functions, a causal association should not be presumed. Although there may be adverse effects resulting from brain development in an asymmetric skull, it is also plausible that DP is merely a marker for other conditions that impede development [37]. Further well-controlled research to study the effect of skull deformation on brain development, the effect of brain development on skull shape, and the effect of positioning limitations on both DP and motor development should be required. Pediatricians should monitor closely the development of infants with this condition [22, 38].

More controversial is whether some intellectual differences can be detected between children with deformational plagiocephaly and those without cranial deformity.

Children with DP showed evidence of developmental disadvantage that persisted from infancy to the toddler years. Delays in motor development, which were particularly evident in infancy, were slightly attenuated, whereas differences in cognitive and language skills were as large or larger than those observed in the same children in infancy [34].

Early language acquisition in children with single-suture craniosynostosis (SSC) and in children with deformational posterior plagiocephaly was examined. A noticeable developmental risk for specific language impairment was found in children with nonsyndromic SSC, and a deviant language development was observed already in early infancy. Contrary to previous beliefs, a developmental risk for defective language development was found in deformational posterior plagiocephaly too [39].

Infants and toddlers with deformational plagiocephaly (DP) have been shown to score lower on developmental measures than unaffected children. To determine the persistence of these differences, the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III), was administered as a measure of child development in 36-month-old children with and without a history of DP. Preschool-aged children with a history of DP continue to receive lower developmental scores than unaffected controls [34]. These findings do not imply that DP causes developmental problems, but DP may nonetheless serve as a marker of developmental risk, and clinicians should screen children with DP for developmental concerns to facilitate early identification and intervention [40].

Infants with DP show differences in brain shape, consistent with the skull deformity characteristic of this condition, and shape measures were associated with infant development. Longitudinal studies, beginning in the neonatal period, are needed to clarify whether developmental effects precede or follow brain deformation. Little difference was found between infants with and without DP in total brain volume, volume of the cerebellum, or midsagittal areas of the cerebellar vermis and corpus callosum. As expected given the cranial deformation associated with DP, there were group differences in the shape of the brain and selected structures. Compared to unaffected controls, infants with DP had greater posterior deformation and flattening of the brain; the corpus callosum was shortened and positioned at a greater angle relative to a standard orientation; and the height and height–width ratio were greater for the cerebellar vermis. This finding is consistent with previous studies showing that corpus callosum size and shape differentiate typical from other groups of atypical children (e.g., those with prenatal alcohol exposure [41] and dyslexia [42]).

DP can also cause asymmetry of the face and the face that can lead to an asymmetry of the position of the eyes and to bilateral astigmatism for which it is very difficult to find suitable corrective lenses.

Visual field disturbances were also reported. DP is believed to affect the development of the visual field, but neither the laterality of field defect is related to the side of flattening nor a correlation between severity of visual defect and severity of plagiocephaly was found to be statistically significant or predictive of the magnitude of the disturbance. It is still controversial whether this is a real narrowing of the visual field rather than a delay of its development taking into account that a normalization can succeed with the acquisition of the following neurodevelopmental stages [43].

An increased prevalence of strabismus associated with DP was instead confirmed. Individuals with DP does not seem to show a higher prevalence of horizontal strabismus compared to the general population, although the prevalence of astigmatism in patients with DP seems to be superior to that of the general population [44].

Visual disturbances could also become an issue that requires corrective surgery to repair.

Consequences such as a persistent asymmetry of the face or of the head are less studied and still more controversial.

In patients with DP, the ipsilateral temporomandibular joint is pushed anteriorly, and the lower jaw develops asymmetrically [45]: repositioning assets and/or the use of the headband improves the shape of the skull but does not change the position of the temporomandibular joint or the asymmetry of the mandible [46, 47]. Some studies indicate possible occurrence of abnormal dental occlusion that may interfere with orthodontic treatment [4]. Hearing defects caused by recurrent ear infections due to a decreased drainage of the middle ear resulting from the displacement of the eustachian tube are reported [48]. Even if DP could correct in 6–12 weeks with treatment, the facial asymmetry could correct over a more prolonged period, up to 18 months [49]. No study, however, has examined children with deformational plagiocephaly in order to discover whether facial asymmetry persists into adolescence. If the facial asymmetry persists, it could have adverse psychosocial consequences, similar to strabismus, which has been shown to hamper an adolescent’s interpersonal relationships [50].

Some of the problems that can be experienced due to facial abnormalities include problems with chewing and eating, while head shape abnormalities can possibly cause temporomandibular joint syndrome.

Treatment usually cures deformation of the skull, but did not prevent the side effects on the temporomandibular joint that is pushed forward on the same side of the head flattening, pushing on the lower jaw that becomes asymmetrical [51].

Pediatricians should be urged to send all the children with DP to a specialist in child orthodontics to follow up mandibular growth and solve mild mandibular asymmetries. The dentist may teach children and their caregivers specific exercises to improve the tongue’s range of motion and to develop nasal breathing so strengthening masticatory muscles and leading to a correct balance of the dental arches, often avoiding the use of expensive and bulky orthodontic devices. Learn to perform lateral movements of the mandible; let the bone grow symmetrically.

Children should be examined by a dentist when they still have their deciduous dentition, between 3 and 4 years of age, in order to detect and correct early any mild dysfunction, reducing the economic and the social costs and enhancing children quality of life giving them a radiant smile.