Nonsyndromic Bicoronal Craniosynostosis

Introduction

Premature closure of both coronal sutures is most commonly seen in association with craniofacial syndromes and is known as syndromic bicoronal craniosynostosis (SBCS). A smaller subgroup of patients affected with this condition who do not have an associated or well-known syndrome are known as nonsyndromic bicoronal craniosynostosis (NSBCS). The classical phenotypic presentation includes brachycephaly, turricephaly, supraorbital recession bilaterally, exorbitism, slight hypertelorism, bulging temporal fossa ( Figs. 11.1–11.3 ), mild bilateral proptosis, and a prominent and bulging forehead, as well as bilateral inferior displacement of the exocanthia in relation to the endocanthia. These cohort of NSBCS patients are otherwise normal. There is variability in their clinical presentation but all share a common set of findings as listed previously. These patients certainly differ from the syndromic type of bicoronal synostosis and can be relatively easily differentiated. In all of these patients, the systemic findings of syndromic types such as polysyndactyly, broad thumbs and great toes, Kleeblattschädel, very large anterior fontanelles, severe bilateral proptosis, and significant midfacial hypoplasia are absent. As with any other type of synostosis, the earlier that the premature closure of the suture takes place, the more prominent and severe the clinical findings. Given the early success that we achieved treating single suture nonsyndromic coronal synostosis, we began to use the same technical principles to the management of these nonsyndromic bicoronal patients. In a similar fashion, we were pleasantly surprised by the rapid, steady, and consistent improvement of the presenting deformities. Presented in this chapter are our surgical approach technique and the results of treating the cohort of patients.

In 2019, Vinchon reviewed a total of 195 cases of patients with bicoronal craniosynostosis for a period that extended between 1978 and 2019. The incidence of syndromic patients was 53.3%. Of the cohort group, 12.3% had familial features and 3.5% had other associated extracranial anomalies suggestive of a syndrome. Of the total group, 31.3% were classified as nonsyndromic. It was found that the incidence of hydrocephalus and cerebellar tonsillar herniation and mortality was significantly lower in the NSBCS group. An estimated incidence of 1:20,000 live births has been calculated for this group of patients. Our own series concurs with their results as we have not had any cases of hydrocephalus or Chiari and all patients have grown and developed normally. That, however, is not the typical case with syndromic patients. ^,

Imaging

In contrast to single suture nonsyndromic patients, we obtain imaging in all of our patients in order to make an accurate diagnosis and look for any additional intracranial abnormalities. A set of plain radiographs are obtained and will clearly show sclerosis and closure of both coronal sutures. Additionally, in anteroposterior (AP) radiographs, the “bilateral harlequin sign” will be visible ( Figs. 11.4 and 11.5 ). Although this sign is not present in all cases, it can serve as confirmation of the bilateral synostosis. Most helpful and accurate for making the diagnosis is a computed tomography (CT) scan with three-dimensional (3-D) reconstruction imaging ( Fig. 11.6 ). It will be very evident that only the coronal sutures are closed and all other sutures are open. Common features seen will include the foreshortened anterior cranial fossa with widening of the forehead. Abnormal orbital axial deviation can be seen, as well as recessed supraorbital rims. Brachycephaly and turricephaly are also common features found in these scans. Magnetic resonance imaging (MRI), we believe, is optional to make the diagnosis, but should be done if the patient presents with any clinical signs of cerebellar or brain stem compression. This, however, has not been the case in any of our patients. The MRI scans that were obtained have all been normal. Nevertheless, a low threshold for scanning should be had, particularly if concerned with the possibility of a Chiari type presentation.

Patient Positioning

Following general anesthesia induction, endotracheal intubation, and placement of one or two peripheral intravenous lines, the patient’s head is placed on a padded pediatric cerebellar horseshoe headrest in the neutral position and with the neck also in a straight and neutral position ( Fig. 11.7 ). Corneal protectors, with ophthalmic lubricating ointment, are placed under the eyelids for protection of the eyes and corneas. The location of the anterior fontanelle is marked with a skin marker as well as the location of both stenosed coronal sutures. As done with the unicoronal synostosis, the area of the stephanion is located on each side and the incision site is also selected in a similar fashion. The proposed location of the osteotomy is marked on the skin. A precordial doppler is placed over the left side of the chest. The operating room table is then turned 180 degrees away from the anesthesia machine so that the surgeon can have full access to the head and face. The head, face, and orbital areas are prepped with povidone-iodine solution and allowed to properly dry for maximal effectiveness. Draping of the sterile field and table set up are done the same way as previously described in Chapter 8 .