Secondary bicoronal synostosis after metopic craniosynostosis surgical reconstruction.

Re-synostosis after standard surgical procedures for nonsyndromic craniosynostosis is a rare event, which can occur at the same suture or rarely in adjacent sutures. Here, we report 2 patients with primary metopic craniosynostosis who developed bicoronal synostosis in previously opened sutures several months after surgery.

Introduction

Craniosynostosis is defined as premature fusion of one or more cranial sutures, which can present as an isolated defect (nonsyndromic) or as a part of a syndrome with other anomalies (syndromic).[1] The incidence of craniosynostosis was estimated to be one per 1800–2200 births.[23] Although nonsyndromic craniosynostosis constitutes >85% of cases, over 150 genetic syndromes associated with craniosynostosis have been identified.[4]

Sagittal suture is the most common suture involved in craniosynostosis, followed by coronal and metopic suture involvement; true lambdoid involvement is rare.[1]

Potential risk factors for nonsyndromic craniosynostosis include positive family history of craniosynostosis, white maternal race, clomiphene citrate consumption for infertility,[5] advanced maternal age, maternal smoking, male infant sex, maternal residence at high altitude and certain paternal occupations.[15]

The exact incidence of recurrence after standard craniosynostosis surgical procedures is unknown. It seems that the rate of recurrence is higher in syndromic compared to nonsyndromic patients who have only one suture involvement.[6]

An increase in re-synostosis rate had been reported when the first operation occurred after 1-year-old.[6] On the other hand some authors reported that fronto-orbital reconstruction in nonsyndromic unicoronal synostosis at younger than 6 months of age has the highest incidence of re-synostosis, so operation at 6–12 months has the least need for secondary surgery.[7] In addition, one large-scale study recommended the age between 9 and 12 months as the appropriate age for craniosynostosis surgery.[8] Postoperative calvarial growth restriction due to fibrosis of newly formed bone and pericranium that replaces the removed suture might cause re-synostosis.[910] Secondary coronal synostosis after corrective craniotomy of craniosynostosis involving sutures other than coronal sutures occurs in almost 10% of cases, with 1% requiring surgical intervention.[11]

This article discusses two cases of bicoronal synostosis that developed in previously opened sutures after primary metopic craniosynostosis surgery.

Case Reports

Database of patients with craniosynostosis treated in the Children's Hospital Medical Center in Tehran was retrospectively reviewed. Re-synostosis at the same suture was observed in sagittal, unicoronal and bicoronal synostosis patients. Re-synostosis in the suture other than the first suture was very rare and found only in 2 patients with previous metopic craniosynostosis. Among 63 metopic craniosynostosis patients operated on during the recent 5 years, two children were found with re-synostosis in both coronal sutures.

Case 1

A 3-month-old girl with metopic synostosis was managed with bifrontal craniotomy and bicanthal advancement procedure. Her postoperative period was unremarkable with a regular increase of head circumference, but an obvious decreased growth of head was found 6 months later. Brain computed tomography (CT) scan confirmed bicoronal synostosis and closed fontanel. She underwent a second operation with bicanthal advancement and bifrontal craniotomy [Figure 1]. Both coronal sutures were closed and anterior fontanel was ossified in bulge shape due to underlying high intracranial pressure (ICP). During the second surgery scar and adhesions subsequent to previous surgery were released. In this procedure at area of closed coronal sutures enough space is prepared that makes the skull can grow in a near normal manner.

Figure 1

Photography of patient with typical skull deformity related to metopic synostosis (a), brain computed tomography (CT) scan confirmed the closed metopic and open coronal sutures (b). Postoperative CT shows the new deformity with closed coronal sutures (c)

Case 2

A 7-month-old girl with metopic synostosis was admitted for cranial reconstruction procedure. She had acceptable head growth and then developed bicoronal synostosis 7 months after first surgery [Figure 2]. Brain CT scan and intraoperative findings confirmed bicoronal synostosis. She underwent a second operation with bicanthal advancement and bifrontal craniotomy that was associated with removing the closed sutures and making enough space at the previous coronal suture location. Skull reconstruction was done with bioabsorbable plate and screw to provide an acceptable appearance too.

Figure 2

Photography of patient (a) and brain computed tomography (CT) scan (b) confirm typical trigonocephaly related to metopic synostosis. Photography before the second surgery shows the new deformity of the skull related to coronal sutures consisted of bony bulging of fontanel area, increased height and decreased anteroposterior diameter of the skull (c)

Both children had uneventful neurosurgical operation and were being followed regularly without any new problem.

Discussion

Two children with nonsyndromic metopic craniosynostosis who underwent surgical correction at our institution developed symptomatic, postoperative increased ICP and unacceptable fronto-orbital appearance. Both children underwent a substantial correction of the pathology and achieved acceptable cosmetic outcomes.

Delayed intracranial hypertension and cranial restenosis occur in 10.8–36.8% of children after primary procedure of syndromic cranial synostosis, but reported only in 1.0–5.7% of children after surgery of single-suture, nonsyndromic cranial synostosis.[12] Some studies reported higher risk of secondary synostosis and delayed intracranial hypertension in sagittal suture synostosis and when primary surgery was performed at younger age (<5 months).[13]

Furthermore, a significant higher rate of symptomatic craniocerebral disproportion was found in children who underwent initial craniosynostosis surgery at an age older than 1-year.[14]

The exact etiology of cranial synostosis is mainly unknown, but there are three theories that predominantly explain the pathology.

The most popular theory of premature suture fusion indicates osseous pathology in the early phase of pregnancy caused by genetic or metabolic causes. The second theory points toward last phase of the pregnancy, when the head of the fetus could be constrained in the pelvis. The last theory considers brain malformation causing craniosynostosis.[15] It is not clear whether the primary abnormality is presented in whole cranium or only in the fused calvarial suture. In syndromic craniosynostosis, especially when the mid face is involved, it seems that the primary abnormality is caused by an underlying genetic disorder, frequently related to the fibroblast growth factor receptor gene which involves all parts of cranium.[1617]

In contrast, nonsyndromic, single suture synostosis may occur as a result of the continued influence of congenitally abnormal skull growth despite surgical repair, or compressive uterine forces that act on the individual sutures.[10] McCarthy et al. reported a series of 104 children with all types of single-suture craniosynostosis that eight of them had isolated sagittal synostosis, and 2 patients underwent a second operation due to progressive turricephaly.[18]

In another study containing 89 patients with single-suture sagittal synostosis, four children needed second surgery for intracranial hypertension due to new synostosis of other calvarial sutures.[19] In another recent report, there were a total of 143 patients with nonsyndromic single-suture sagittal synostosis from which 2 patients (1.5%) required a second surgery for symptomatic calvarial growth restriction.[14]

The reasons contributed to recurrent synostosis of previously open sutures remain conjectural. It has been suggested that dura mater and pericranium have osteogenic features, and dura mater seems to be the source of central new bone, while pericranial contact appears to increase peripheral new bone formation.[20] Coagulation of dura in the area of sagittal sinus may have a harmful effect on bone formation; probably resulting in an uneven bone formation due to a combination of areas of poor ossification with areas of excessive bone formation.[1421]

Another possible theory for recurrent stenosis in these cases is that the patients underwent surgery at early age, progressive stenosis in the coronal sutures may have occurred after the initial operation as a result of the underlying disorder that caused the first synostosis. It is possible that even isolated craniosynostosis reflect a series of underlying genomic disorders, which may predispose patients to symptomatic suture restenosis and potential involvement of previously open sutures. Progressive cranial synostosis and delayed intracranial hypertension have been reported in children with single-suture synostosis who have not undergone surgery.[22]

While the etiology of restenosis after primary synostosis repair is uncertain, it is suggested that even children with nonsyndromic, single suture synostosis should be followed for the 1st year after primary cranial vault repair to evaluate patency of the sutures.[12] The child should be evaluated for symptoms associated with increased ICP. Microcephaly or decreased head growth according to the age may be a late-occurring but insensitive indicator of recurrent synostosis.[23] Therefore, head circumference measurement is a useful part of the systematic surveillance protocol.

We recommend detailed neurologic examination and head circumference measurement as well as a routine annual funduscopic evaluation by an ophthalmologist familiar with these patients. In addition, brain CT scan may show various signs of postoperative cranial restenosis and delayed intracranial hypertension.