Neurosurgery - Cases and Frontosphenoidal Craniosynostosis: An Uncommon Cause of Anterior Plagiocephaly

Frontosphenoidal craniosynostosis is an extremely rare and often misdiagnosed cause of anterior plagiocephaly. Careful clinical examination and radiological features allow to differentiate between this entity and other forms of frontal asymmetry. This study aims to describe the impact of premature fusion of the frontosphenoidal suture in the development of orbital and cranial morphology, to compare it with the effect caused by coronal synostosis and to detail the surgical procedure used to correct both. We report three patients diagnosed with anterior plagiocephaly caused by frontosphenoidal synostosis and compare it with the clinical features and surgical implications of a patient affected by unilateral coronal craniosynostosis. Isolated frontosphenoidal synostosis must be taken into account in the differential diagnoses of frontal plagiocephalies. Key clinical features such as the displacement of the supraorbital edge, morphology of the temporal region on the affected side and deviation of the nasal root and chin can help to differentiate it from coronal craniosynosotosis and, consequently, to select proper surgical techniques.

the forehead and orbital dystopia, the most common underlying cause being usually an unilateral coronal suture synostosis. Differential diagnoses done mainly with anterior deformational asymmetries [1]. However, frontal craniosynostosis could be related to isolated involvement of other components of the coronal ring such as frontosphenoidal suture [2]. In 1995, Francel and collegues reported the first case of isolated frontosphenoidal craniosynostosis [3] and so far, only isolated case reports [2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and small retrospective studies have been published in the literature [19,20]. Both forms of monosutural craniosynostosis -coronal and frontosphenoidal -may lead to a similar but subtly distinct phenotype and radiological presentation. Therefore, it is capital to differentiate these entities to select the most appropriate surgical correction. We report three patients with a diagnosis of frontosphenoidal craniosynostosis and compare them with the more frequent: coronal craniosynostosis. The aim of this paper is to describe and identify the differences between the two craniofacial deformities and to detail the surgical procedures to correct them.

Introduction
Forehead and orbital deformities represent a common finding in simple suture craniosynostosis. Plagiocephaly is described as a unilateral flattening of  amblyopia. CT scan revealed a left frontosphenoidal suture fusion and a patency of the right frontosphenoidal suture as shown in the Figure 3.

Case 3
A five-months-old male patient was sent by his pediatrician to evaluate anterior facial asymmetry. On clinical examination, he had a left frontal flattening, a nasal tips lightly offset toward flattening, but no harlequin´s eye. No ophthalmological problems were reported. CT scan showed closure of the left frontosphenoidal suture with a descent and retrusion of the ipsilateral orbit, while the right frontosphenoidal suture and both coronal sutures were patent as shown in the Figure 4.
Genetic studies were not carried out in any of the three patients as they were all considered isolated craniosynostosis.

Surgical Technique
In our three patients, a left-sided advancement of a fronto-orbital bandeau was performed with frontal reshaping in "shell" variant [21] or with a Tessier bone bender as shown in Figure 5 and Figure  6. In frontosphenoidal craniosynostosis the orbital rim displaced downward and backward compared to a suspected diagnosed of anterior plagiocephaly was done and then, referred to a Neurosurgery specialist. Under physical examination, the patient showed retrusion and downward displacement of the orbital rim, moderate flattening of the forehead, a deviation of the nasal root towards to the non-synostotic side and ipsilateral hollowing of temporal squama. CT imaging was performed demonstrating as shown in Figure 1 a widely patent frontoparietal suture and a clearly synostotic frontosphenoidal suture. Postoperative medium-term CT follow-up and clinical evaluation showed progressive improvement and subsequent stability of orbital displacement and frontal projection as shown in the Figure 2.

Case 2
A 7-5 months-old male patient came to our consultation referred for anterior plagiocephaly with a suspected diagnosis of coronal synostosis. The patient was the first-born from a non-consanguineuos young couple. Antenatal and obstetrical history was otherwise irrelevant. He presented to our examination with a left frontal flattening with a ipsilateral downward eyebrow and supraorbital rim. Nasal tip was desviated to the left side and the chin centered on the midline. Ophtalmological examination excluded strabismus or  reported in literature [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] with the exception of two retrospective series comprising 12 and 17 years that reported only 12 patients [19,20]. This report adds another three patients to the clinical series and faces the unique challenges regarding appropriate diagnosis and surgical treatment of these patients.
The phenotype of frontosphenoidal craniosynostosis is milder compared to unilateral coronal synostosis. This difference is explained by the time and the area where the synosotosis occurs. Synostosis of the coronal suture usually as often happens around 16 weeks of embryological development. This fusión promotes the absence of the coronal suture and therefore, permits only the peripheral growth of the frontal and parietal bone. Fixation of the frontal bone to the parietal bone restricts the growth of the orbit in an antero caudal direction, leading to cranial displacement of the healthy side. So, the aim of surgical correction consists of advancement of the orbital edge and achievement of a elevation of the lateral canthus of the affected side together with a symmetric frontal bone flap on the synostotic side to create a normal-looking forehead. Bandeau reshaping and advancement in conjunction with the frontal bone were tailored to the magnitude of the craniofacial deformity in each individual patient, and unaffected side was used as a template for accurate surgical correction. The different bony segments were fixed with resorbable plates and screws. The surgery was well tolerated in all cases and the patients had an uneventful postoperative course.

Discussion
Frontoorbital craniosynostosis is a rare form of anterior craniosynostosis. Mostly, case series are  Given the phenotypic differences between frontosphenoidal craniosynostosis and coronal synostosis, we tailor our surgical approach to correct the specific deformities of each entity [5,12]. This is opposite to prior studies that suggested the same techniques for both craniosynostosis [14,24]. In Figure  7, we show the typical harlequin deformity described in coronal synostosis, with horizontal narrowing and elevation in the coronal plane of the affected orbit as compared to the non-affected side. In this manner the pathological orbit can be corrected advancing and descending the superolateral-edge.
Regarding the surgical approach, we describe a unilateral correction of synostotic side in contrast to what most authors have reported so far [5,6,11,[13][14][15]17,20]. Plooji and Mittermiller presented a patient, who underwent a unilateral procedure with good cosmestic outcomes [8,18]. Based in our results, we believe that this variation in the technique provides a satisfactory and stable correction of preoperative deformities as long as there is no contralateral compensatory craniofacial malformation.

Conclusion
Unilateral frontosphenoidal craniosynostosis is an infrequent cause of anterior plagiocephaly. Differential diagnosis with coronal synostotsis may be difficult and could result in delayed and improper treatment. Unilateral fronto-orbital advancement constitutes an option for surgical correction in frontosphenoidal craniosynostosis in the absence of compensatory deformity on the non-synostotic side. supraorbital rim. Conversely, the milder presentation of frontosphenoidal craniosynostosis is due to the fact that the fusion of this suture takes place several weeks later, around the 21 st week of embiological development. The premature fusión restricts the growth of the frontoorbital border and orbital roof in an anterocaudal direction. Thus, the resulting cranial deformity is characterized by a downward displaced orbital edge and a descent of the pterion and orbital roof [6].
Surgical correction of craniofacial deformity is indicated due to the ophthalmological implications of ocular malposition (astigmatism, amblyopia, strabismus) [22,23] and not so much because of the risk of developing intracranial hypertension, sleep apnea or optic atrophy which are typically associated with synostosis of other cranial vault sutures [23]. A skullmolding helmet has been reported for the treatment of this condition. However, this therapy ultimately failed and required surgical treatment [6,11,18].
In our three cases, the surgical technique consisted of unilateral fronto-orbital advancement and frontal remodeling to achieve symmetry with the nonsynostotic side. Before starting bone osteotomies, the cranial vault was carefully examined looking for a new forehead and orbit with adequate and harmonic shape. The osteotomies performed during harvesting of fronto-orbital bandeau incorporated the fused frontosphenoidal suture, but the classic tonguein-groove procedure was not necessary because resorbable fixation material provides adequate stability as other groups have reported [1]. This technical variation helps to reposition the supraorbital bandeau when a rotation in coronal plane is required to confer an elevation to lateral canthus of the orbit. Otherwise, we observed a pathological pterion with a rough appearance and vertical displacement, which leads to deeper osteotomies just like Lloid and coworkers has described [16]. The orbital rim is smoothed and shaped as necessary prior to repositioning. pterion is