Isolated synostotic plagiocephaly (ISP) is a congenital disorder caused by a premature unilateral closure of either the coronal or lambdoid suture. Premature coronal and lambdoid synostosis result in anterior and posterior ISP, respectively. ISP must be rigorously differentiated from syndromic and positional plagiocephaly forms. Diagnosis rests on clinical observations and imaging techniques. Genetic testing may also be considered.
ISP-associated cranial deformities can lead to severe consequences such as increased intracranial pressure. Hence, early surgical corrections are usually indicated to prevent long-term cranial and cerebral damage.
Isolated synostotic plagiocephaly (ISP) presents as an oblique head as a consequence of an anomalous unilateral fusion of the coronal or the lambdoid suture . In both cases, a palpable ridge will develop over the site of premature suture fusion . Unilateral coronal synostosis is associated with anterior ISP while posterior ISP is caused by an early fusion of the lambdoid suture . ISP affects approximately 1/100000 infants .
The genetic role in ISP is still in the focus of medical research. Rare mutations in the FGFRs, TWIST1, LRIT3, ALX4, IGFR1, EFNA4, RUNX2, and FREM1 genes may play a role for isolated ISP   .
Anterior ISP-associated deformities include a flattening of the frontal bone and of the ipsilateral orbital rim in combination with a contralateral frontal bossing. In 50-60% of cases, strabismus is found as a consequence of anatomical changes in the orbital roof. Anterior ISP can also lead to a deviation of the skull base, a positional change of orbits, eyebrow and ear asymmetries, as well as mandibular deviations with malocclusion   .
Posterior ISP leads to a trapezoid head shape with occiput flattening and malpositioned ears. Moreover, early lambdoid suture synostosis is linked to debilitating changes in the posterior fossa. Most notable findings in this context include an Arnold-Chiari malformation type 1 and a fusion of the jugular foramen. Thus, posterior ISP predisposes the patient for intracranial hypertension  .
ISP diagnosis relies on clinical findings and a thorough analysis excluding other potential causes of plagiocephaly. Plagiocephaly is clinically diagnosed by the typical formation of a parallelogram defined by ear and maxilla positions .
Positional plagiocephaly (PP) often occurs concomitantly with torticollis and produces stronger facial asymmetries   ; ISP is most easily identified by the posterior malpositioning of the ear on the affected side. On the other hand, PP produces anteriorly malpositioned ears . Syndromic plagiocephaly is usually accompanied by developmental retardation .
The use of computed tomography (CT) imaging is only indicated in case of an ISP suspicion, particularly if infant repositioning does not improve cranial asymmetry over weeks. CT findings can also be used in preparation for a surgical intervention aimed to avert an increased risk of intracranial hypertension (ICH) or to correct the plagiocephaly-caused malocclusion. If ICH has already developed, appropriate immediate countermeasures are indicated  .