Fig. 6.1
Superior view of normal skull including the major bones, sutures, and fontanels
The fontanels are fibrous connective tissues located between multiple cranial bones (Fig. 6.1). Newborns have six fontanels: the anterior and posterior fontanels and paired mastoid and sphenoid fontanels. The anterior fontanel, located between the frontal and parietal bones, is the most prominent of the fontanels and the one most commonly palpated when conducting pediatric physical examinations.
When examining an infant in your office, first locate the anterior fontanel to serve as a landmark to feel for the surrounding sutures. The lateral axes of the anterior fontanel make up the coronal sutures, the sagittal suture is located posterior to the anterior fontanel and the metopic suture extends anteriorly from the anterior fontanel dividing the frontal bone of the forehead. The lambdoid sutures are located in the posterior portion of the skull lateral to the posterior fontanel connecting the parietal bones with the occipital bone (Fig. 6.1).
The Anterior Fontanel
A common referral to pediatric neurosurgeons from primary care providers is for evaluation of a child’s anterior fontanel . It is easy to become fixated on the fontanel being either larger or smaller than you expect, however, the anterior fontanel can vary greatly in size and time of closure. An infant’s gender and race can also influence the size and closure rate of the anterior fontanel. At birth, fontanel size can range from 0.6 to 3.6 cm, with most averaging approximately 2.1 cm in size [2, 3]. Infants of African descent tend to have larger fontanels ranging from 1.4 to 4.7 cm [4]. While preterm infants can have smaller fontanels, the size is comparable to full-term infants once preterm infants reach term [5].
It is not uncommon for fontanels to increase in size after birth and this should not raise concern if developmental progress and head circumference is normal [6].
On average, the anterior fontanel closes by 13.8 months of age. Only about 1 % of infants have a closed anterior fontanel by 3 months of age and this percentage increases to 38 % by 12 months of age. Ninety-six percent of anterior fontanels are closed by 24 months [2]. Fontanels typically close sooner in boys than in girls [5]. While early fontanel closure is most often be a normal variation, it can be associated with craniosynostosis and abnormal brain development; therefore, it is imperative that morphology is appreciated and precise head circumference measurements are obtained to exclude a pathological development [2].
Referrals to pediatric neurosurgery are also seen for the opposite finding—for the delayed closure of the anterior fontanel. While this can be a normal variant, there are a few true medical conditions associated with an enlarged or delayed closure of the anterior fontanel including achondroplasia, congenital hypothyroidism, Down syndrome, increased intracranial pressure, familial macrocephaly, and rickets .
The most common causes of raised intracranial pressure associated with bulging anterior fontanels are meningitis, encephalitis, hydrocephalus, hypoxic-ischemic injury, trauma, and intracranial hemorrhage [2]. If any of these conditions are suspected, it is important that immediate referral be made so infants can receive proper care and begin treatment if necessary.
The Posterior Fontanel
The posterior fontanel , located at the junction of the occipital and parietal bones, is usually completely closed by 2 months of age, taking the name bregma. Its normal measurement ranges from 0.5 to 1 cm, but as with the anterior fontanel, it tends to be slightly larger in infants of African ancestry with an average size of 0.7 cm compared to an average size of 0.5 cm in Caucasian infants [2].
Plagiocephaly
The term plagiocephaly is derived from the Greek word plagios, meaning oblique and kephale, meaning head.
Deformational Plagiocephaly
Also known as positional molding, deformational plagiocephaly is a common cranial deformity in children and is by far, the most common cause of misshapen skull in infants. It is a term used to describe flattening on one side of the head (Fig. 6.2) [7].
Fig. 6.2
Right posterior deformational plagiocephaly. Anterior bossing of the forehead and displacement of the ear on the ipsilateral side are consistent with a deformation rather than synostotic condition
When the American Academy of Pediatrics introduced the Back to Sleep Program in 1992 to reduce the number of infant fatalities caused by sudden infant death syndrome (SIDS ), the number of referrals to pediatric neurosurgeons for deformational plagiocephaly dramatically increased. While this program has been successful at reducing the number of infant deaths attributed to SIDS by 40 % in the United States, as a result, there has been an exponential rise in asymmetric (plagiocephaly) and symmetric (brachycephaly) occipital flattening [8]. Recent studies estimate the prevalence of deformational posterior cranial flattening to be as high as 18–19.7 % in healthy infants [7, 9], but these calculations can vary, depending on how this entity is defined [7, 10].
Most cases of deformational plagiocephaly are caused by applied pressure to the back of the skull while an infant is sleeping in the supine position. Other predisposing factors of deformational plagiocephaly include muscular torticollis, prematurity, developmental delay, and intrauterine constraint due to multiple gestation pregnancies [7].
Diagnosis : Clinical Signs
The classic findings associated with deformational plagiocephaly include occipital flattening and contralateral occipital bulging with anterior shifting of the ipsilateral forehead (frontal bossing), ear, and cheek [7]. The shape that the skull creates from this molding, when evaluated from a vertex view, resembles a parallelogram [11, 12]. A more severe form of plagiocephaly is known as brachycephaly. The shape of a brachycephalic skull differs from plagiocephaly in that brachycephaly involves bilateral occipital flattening. This presentation does not involve ipsilateral frontal bossing or anterior displacement of the auricle.
Treatment for deformational plagiocephaly mostly relies upon behavior modification. A timely evaluation is optimal because interventions are time dependent; however, evaluation for plagiocephaly is usually not recommended before 3–4 months of age since many cases self-correct by this age [13]. After an infant receives a diagnosis of plagiocephaly, parents should be encouraged to have their child spend as little time as possible on the flattened side of the skull. This can be achieved by alternating the child’s sleeping position and repositioning the crib so the infant must turn toward the non-flattened side of the skull to look toward the room. Supervised “tummy-time” is also a way to improve a flattened skull [14]. Additionally, the use of baby carriers as opposed to car seats and strollers can aid in improving the flattened part of an infant skull. An infant’s skull is soft and malleable within the first 6 months; therefore, any type of repetitive positioning can influence the skull shape and ultimately result in plagiocephaly. Infants with muscular torticollis may benefit from physical therapy to address the cervical muscular contracture [10].
Helmet therapy is also a treatment option for plagiocephaly. It is not always warranted, but could be considered when the deformity is a serious cosmetic concern of the parents. However, there is minimal evidence to support the effectiveness of this method for treatment [15, 16]. There are no risks associated with helmet therapy, but mild transient skin irritation has been described as an adverse event [17].
The challenge for the pediatric primary care provider is to identify the child manifesting signs of a true cranial deformity due to premature suture fusion from amongst the majority of children being evaluated for positional plagiocephaly.
Scaphocephaly : Sagittal Synostosis
Sagittal synostosis is the most common synostosis identified in the pediatrician’s office and can even be identified in the nursery by observant practitioners. It is associated with frontal bossing, bilateral occipital/parietal narrowing posterior to the anterior fontanel and decreased vertical height of the posterior cranium: a long narrow head (Fig. 6.3). Head circumferences greater than the 90th percentile can also be associated with sagittal synostosis [7].
