Plagiocephaly can be classified into two types, plagiocephaly that is followed by craniosynostosis and positional plagiocephaly in the absence of craniosynostosis [1]. In case of plagiocephaly not accompanied by craniosynostosis, the sutures of the skull are normal, and the growth of the skull is often not hindered [1-4]. However, the skull becomes asymmetrically distorted due to various reasons. The most common shape of the head is flattened on one side on the posterior part of the head [5-8]. When plagiocephaly is accompanied by craniosynostosis, deformation of the skull is caused by premature fusion of the sutures present in the skull. This condition is often surgically treated [9-13] and helmet therapy may also be performed [14-17].

In the late 1980s, the American Academy of Pediatrics (AAP) claimed that sudden infant death syndrome (SIDS) is closely related to the prone sleeping position [3,18]. In April 1992, the AAP recommended and enforced a campaign to encourage every parent to position the infants in the supine position when sleeping to prevent SIDS. Consequently, the incidence of SIDS decreased by more than 40%; however, the incidence of positional plagiocephaly increased by approximately 600% [18]. The incidence of positional plagiocephaly is increasing every year [19].

Positional plagiocephaly can be defined as deformation and flattening of one side of the head by continuous application of an external force. Such deformation and flattening processes mostly occur in the first few months after birth and are mainly affected by the position of the head [3,4]. The increasing number of patients with plagiocephaly and continued interest and demand of the parents have led to new treatments with the range gradually increasing as well. Positional plagiocephaly can be prevented when the parents fully understand the causes of the disease and show continued interest in infant welfare. Studies have reported that educating the parents on the posture and environment of the infant after birth is beneficial for the prevention of positional plagiocephaly [3,7,20]. If positional plagiocephaly is detected at a very early stage (before 2 months after birth) with congenital muscular torticollis, early physical therapy for congenital muscular torticollis is very effective in correcting positional plagiocephaly. Furthermore, maintaining a position that does not exert pressure on the conservatively flat part of the head or a placing the infant in the prone position may be helpful [21,22]. Following the report of helmet therapy by Clarren et al. [23] in 1972, several studies have advocated that helmet therapy is very effective as a supplementary treatment for infants with severe positional plagiocephaly.

Risk factors for positional plagiocephaly include first birth, assisted labor, multiple pregnancy, injuries from birth, congenital malformation, premature infants, boys, and especially congenital muscular torticollis and remaining in the prone position for a prolonged time [4,7,23,24].

The most common cause of the disease is the deformation of the head shape during birth that is not corrected due to infant being placed in the same sleeping position. During birth, the skull rapidly changes in shape due to the effect of gravity, fluidity of the cranial sutures, and plasticity of the brain. This allows the relatively large head to exit the narrow birth canal. In most infants, the deformed skull naturally corrects itself over time [1-4,7]. However, most infants sleep in the supine position and turn their heads in response to certain stimuli. In conditions, such as congenital muscular torticollis, the tense neck muscle causes the infants to hold their neck and head in a preferred position [21,22]. Maintaining the head in the same position for a prolonged period will cause flattening of the part of the head that is facing the floor, and the upper part of the face will begin to flatten thereafter. Both sides of the head will gradually deform, leading to an asymmetrical shape of the head [7]. When a part of the skull becomes flat, the infant’s head naturally turns towards the flat side and is pulled by gravity. The degree of flattening gradually worsens during the first 5–6 months after birth. Compensatory asymmetry of the skull is observed as the skull assumes the shape of a parallelogram. Consequently, the positions of the ear, lower jaw, and eye pit change, leading to facial asymmetry [7,25]. If one side of the back of the head is severely flattened, the occipital bone is pushed towards the opposite side on the back of the head, causing the opposite occipital bone to protrude prominently. Greater force of gravity is applied to regions with a larger surface area. As the frontal bone on the opposite side of the occipital bone flattened by gravity becomes flat, the ipsilateral frontal bone protrudes in a manner similar to the occipital bone. Therefore, the head tilts towards the flattened occipital bone and the position of the ears changes (Fig. 1) [3,7,25,26]. In cases of multiple pregnancy, the limited intrauterine space prevents fetal posture change. This can lead to the application of constant force on the fetus’s head, leading to positional plagiocephaly [3,7,19]. Positional plagiocephaly is often accompanied by congenital muscular torticollis, which may contribute towards the development positional plagiocephaly due to the neck position and tension in the neck muscles and ligaments [21,22].

Such progression of asymmetry terminates once the infant begins to move, change positions during sleeping, and stand. The deformity of the skull can be naturally corrected over a period of a few months. However, the degree of natural correction varies depending on the severity of asymmetry, and full correction is rarely observed. The uncorrected asymmetrical shape of the head shape at this point is mostly maintained throughout adulthood [3,7,25].

Plagiocephaly can mostly be diagnosed clinically and by physical examinations. Radiography of the skull is performed to determine craniosynostosis, and ultrasound, magnetic resonance imaging, and computed tomography can be performed to achieve a definitive diagnosis. Moreover, three-dimensional (3D) reconstitution of the skull after imaging may also aid in detecting craniosynostosis [7,25].

The simplest way to assess the severity of plagiocephaly is to use a diagonal caliper during physical examination, which measures the difference between the diagonal lengths on each side of the head. A diagonal caliper is a cost-effective tool; however, there may be errors between the measurements, which can reduce the accuracy of evaluating the severity of plagiocephaly. Moreover, the difference between the diagonal lengths may be reduced by the scalp or hair of the patient, and the error can be large when the patient markedly when the measurements are being recorded. A study reported that errors in the readings recorded by different examiners may be as high as 2.2 mm on an average and that imaging data can aid in reducing such errors when measuring the difference in the diagonal length [27,28].

Difference of 9–12 mm and more than 12 mm in the cranial vault asymmetry are defined as mild to moderate and severe asymmetry, respectively [27,28]. The cranial vault asymmetry index is used to determine the severity of positional plagiocephaly and can be calculated as shown below. An index >3.5 indicates severe asymmetry [27-29].

Plagiocephaly can be treated surgically or conservatively. Plagiocephaly, accompanied by craniosynostosis, is often surgically treated [9-13]. Positional plagiocephaly, which is not accompanied by craniosynostosis, is treated conservatively [14-17].

Conservative treatments involve a variety of treatments, such as change of positions [7], physiotherapy [30], massage therapy [7], and helmet therapy [30-33]. Promising outcomes can be achieved from conservative treatments when the treatments are initiated at an early stage of the disease due to the plasticity of the cranium and cranial sutures of the infants [7,30-33]. Furthermore, confirmation of other causes of positional plagiocephaly and treatment of possible congenital deformity are required. Performing physiotherapy for the tense neck muscles may be beneficial for congenital muscular torticollis [30].

Positional plagiocephaly is increasing in infants for various reasons. It can mostly be diagnosed clinically and by physical examinations, and treated surgically or conservatively. Most of positional plagiocephaly, which is not accompanied by craniosynostosis, is treated conservatively. The helmet therapy has controversy as to when to start and how long to maintain the therapy. However, for the patients with positional plagiocephaly, appropriate helmet therapy, in accordance with their ages, is a very effective treatment to change the shape and position of their head.