Radiation-free 3D head shape and volume evaluation after endoscopically assisted strip craniectomy followed by helmet therapy for trigonocephaly

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Abstract

Introduction

Radiation-free 3D post-operative sequential follow-up in craniosynostosis is hindered by the lack of consistent markers restricting evaluation to subjective comparison. However, using the computed cranial focal point (CCFP), it is possible to perform correct sequential image superposition and objective evaluation. We used this technique for mean volume and shape change evaluation of the head utilizing 3D photos after endoscopically assisted trigonocephaly surgery.

Methods

We performed a mean head shape and volume evaluation on age grouped 3D photos (n = 86) of children who underwent endoscopically assisted strip craniectomy with helmet therapy. We used CT-scans of healthy children as reference. We performed a mean shape evolution analysis and calculated the anterior fossa to total volume ratio (A/T-ratio). The volume- and A/T-ratio pattern were compared with the reference group.

Results

The mean anterior fossa volume evolved from 336 ml (33.4% A/T-ratio) pre-surgery to 664 ml (36.0% A/T-ratio) at 37–48 months post-surgery. Both groups have a near similar volume- and A/T-ratio pattern over time. The first 18 months show a predominant growth around the resected metopic suture. Between 18 and 24 months we observed mostly anterior orbital rim growth. From 24 months till 36–48 months the head grows predominantly at the temporal area. The least outward growth was observed at the temporal bones.

Conclusion

Using a novel technique we were able to objectively evaluate head shape and volume using stereophotogrammetry after endoscopically assisted strip craniectomy. The A/T-ratio and volume growth pattern of endoscopically treated patients is near identical to that of the normal reference group.

Introduction

Craniosynostosis is the premature fusion of cranial sutures occurring at 1 in 2000 to 1 in 2500 live births (Slater et al., 2008). Treatment for craniosynostosis comes with different approaches. Trigonocephaly has two main approaches; the open cranial vault reconstruction and (endoscopic) suturectomy with spring- or/helmet therapy (Keshavarzi et al., 2009, Hinojosa, 2012, Ozlen et al., 2011, Jimenez and Barone, 1998, Barone and Jimenez, 1999). Objective comparison, follow-up and evaluation of these approaches remain difficult. Modern clinical diagnosis of head shapes and follow-up after surgical craniosynostosis interventions usually rely on the use of CT-scans, cranial x-rays and in the past few years also three dimensional (3D) photogrammetry (Marcus et al., 2007, Marcus et al., 2009, Saber et al., 2012, Delye et al., 2015, Le et al., 2014, McKay et al., 2010, Wilbrand et al., 2012). 3D photogrammetry using 3D photo systems were introduced as a radiation-free alternative but are limited to capturing soft tissue surfaces lacking the bony structures used in traditional follow-up. However it is possible to use 3D photos for objective follow-up. A common reference point for skull comparison is the sella turcica since its relative position is assumed to be more or less stable during skull growth (Björk, 1955). A new method to determine a similar reference point, the computed cranial focal point (CCFP), was proposed using a 3D surface from a 3D photo (De Jong et al., 2015). The CCFP has a fixed location relative to the sella turcica. This allows orienting 3D photos of the head in the sella turcica-nasion plane anchored to the sella turcica for radiation-free longitudinal follow-up.

It is possible to perform radiation-free longitudinal follow-up using 3D photos and we want to initiate this practice by describing our methodology for this follow-up as well as the results for the endoscopically assisted craniosynostosis surgery. At our institute we have a database of 3D photos of patients who underwent this surgery. Using the CCFP for registration of 3D photos we are able to perform longitudinal evaluations. We evaluate the head shape changes over time to determine the growth pattern in these patients that underwent this surgery. Furthermore we look at the longitudinal volume change of the anterior fossa and the total head for this patient group. The anterior fossa volume is of interest due to being the volume in the affected region of the head. We compare these volume changes in CT-scans with a reference group of children that did not undergo this surgery.

Section snippets

Materials and methods

Since December 2010 we have used 3D photography in our craniosynostosis follow-up using a 3DMDhead System (3dMD Limited, London United Kingdom) in RadboudUMC, Nijmegen, the Netherlands. In our follow-up database we selected all 3D photos of children that underwent endoscopically assisted metopic craniosynostosis surgery with helmet therapy that had a pre-surgery 3D photo and at least one post-surgery 3D photo. 26 patients were identified that met these criteria, of which we evaluated the head

Volume analysis

The mean total and mean anterior head volumes above the sella turcica-nasion plane of the 3D photos can be seen in [Table 3] and [Fig. 2]. The mean total volume starts at 942 ml and increases to 1846 ml (96.0% incline). The mean anterior volume starts at 308 ml and increases to 664 ml (116.0% incline). The volumes are based on the outer skin layer as observed by the 3D camera.

The mean total and mean anterior head volumes above the sella turcica-nasion plane of the CT-scans can be seen in [

Discussion

With the use of the CCFP and 3D photos it is possible to perform a longitudinal radiation free follow-up of head shape and volume. The current population on which this was performed consisted of patients that underwent endoscopically assisted metopic suture craniosynostosis surgery. We started in December 2010 to create full head 3D photos of children with craniosynostosis pre- and post-surgery over time. So far only 27 patients could be used in the follow-up with a total of 86 usable 3D photos

Conclusion

We performed a retrospective study to evaluate the head shape and volume changes over time after endoscopically assisted metopic craniosynostosis surgery. We have been able to analyze the volume changes over time above the sella nasion plane thanks to the use of the CCFP (De Jong et al., 2015). The mean total and anterior head volume growth pattern was almost equal to the reference group. A total mean volume increase of 96.0% and an anterior mean increase of 116.0% was observed in the surgery

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