Sagittal synostosis: I. Preoperative morphology of the skull

Making the Diagnosis in Sagittal Craniosynostosis-It's Height, Not Length, That Matters

INTRODUCTION

This study assesses the diagnostic reliability of a novel photogrammetric measurement to distinguish sagittal craniosynostosis (SS) from control and false positive cases (SNS).

METHODS

Head CTs from 2014-2020 were reviewed for patients with sagittal synostosis (SS, n = 177), presumed sagittal synostosis with normal imaging (SNS, n = 30), and controls (n = 100). Using preoperative clinical photographs and CTs, a measurement reflecting the anterior-posterior location of the vertex was measured using an angle drawn between the cranial vertex, nasion, and opisthocranion (VNO) in profile view, with the head in a neutral position.

RESULTS

Mean age at pre-operative head CT was 9.5 months for the SS cohort, 4.2 months for the SNS cohort, and 8.9 months for controls (p = .327). Mean age at pre-operative clinical photograph was 9.5 months for the SS cohort and 4.2 months for the SNS cohort (p = .149). Pearson correlations revealed no significant association between age and VNO angle. The average VNO angle measured on clinical photographs was 54.7° ± 3.8° for the SS group, 43.1° ± 2.2° for the SNS group, and 41.1° ± 3.7° for controls (p < .001). Receiver operating characteristic (ROC) analysis yielded a cut-off of ≥ 50° to identify SS. Diagnostic sensitivity and specificity were 96.6% and 99.2%, respectively. Three-rater analysis yielded an average ICC of 0.742 (p = .004).

CONCLUSIONS

Measurement of the VNO angle is a reliable screening tool to diagnose sagittal craniosynostosis, with an angle of 50° or more suggesting suture synostosis. This method relies on the relationship between the anterior displacement of the vertex and occipital bulleting to approach the diagnostic accuracy of CT imaging.

Occult Scaphocephaly: A Forme Fruste Phenotype of Sagittal Craniosynostosis

INTRODUCTION

Latent cranial suture fusions may present with mild or absent phenotypic changes that make the clinical diagnosis challenging. Recent reports describe patients with sagittal synostosis and a normal cranial index (CI), a condition termed normocephalic sagittal craniosynostosis (NSC). The goal of this study is to evaluate the shape and intracranial volume (ICV) in a cohort of NSC patients using quantitative cranial shape analysis (CSA).

METHODS

We identified 19 patients (7.5 ± 2.28 years) between 2011 and 2016, who presented to our hospital with NSC. Cranial index and CSA were measured from the computed tomography image. Cranial shape analysis calculates the distances between the patient's cranial shape and its closest normal shape. Intracranial volume was measured and compared to an established age-matched normative database.

RESULTS

Cranial index revealed 15 (78.9%) patients within the mesocephalic range and 4 patients (21.1%) in the brachycephalic range. Detailed CSA identified 15 (78.9%) patients with subtle phenotypic changes along the scaphocephalic spectrum (ie, subtle anterior and posterior elongation with inter-parietal narrowing) and 1 patient (5.3%) with isolated overdevelopment on the posterior part of the right parietal bone. Three patients (15.8%) had a CSA close to normal. Mean ICV was 1410.5 ± 192.77cc; most patients (78.9%) fell within ±2 standard deviations.

CONCLUSION

Quantitative CSA revealed that most of the patients with NSC had cranial shape abnormalities, consistent with a forme fruste scaphocephaly that could not be otherwise recognized by clinical observation or CI. Given these findings, we propose the term occult scaphocephaly to describe this condition. The associated incidence of intracranial hypertension is unknown.

Impact of extra-axial cerebrospinal fluid collection in frontal morphology after surgical treatment of scaphocephaly

Background

Infants with sagittal suture synostosis often present a pathologic dilatation of subarachnoid spaces. The impact of such subarachnoid spaces' enlargement in the morphology of the skull, especially on the forehead and on the surgical outcome, was analyzed.

Methods

Children less than 6 months of age undergoing a surgical correction of the scaphocephaly with Renier's H technique between 2003 and 2008 were included in the study. In these patients, preoperative and postoperative fronto-occipital diameter (FOD), biparietal diameter (BPD), temporal width (TW), and naso-frontal angle (NFA) were measured. Cranial index (CI) and the difference between preoperative and postoperative CI (ΔCI) were calculated. Preoperative cranio-cortical width (CCW) was measured to analyze the subarachnoid spaces' volumes. The children here considered were then divided into two groups: Group 1 with CCW within normal estimated value corrected for age and Group 2 with CCW larger than estimated normal value.

Results

About 159 children were enrolled (72.3% male). CCW was larger than expected in 95 children (59.8%). A positive correlation between CCW and BPD (P ≤ 0.001) and a negative correlation between CCW and NFA (P ≤ 0.001) were found. When comparing the two groups, the mean age at preoperative computed tomography (CT) scan was 121 days in Group 1 and 110 days in Group 2. The mean age at operation was 130 days in Group 1 and 123 in Group 2. The mean age at postoperative examination (RX or CT scan) was 53.4 months in Group 1 and 51.8 months in Group 2. Preoperatively, the mean BPD, TW, and CI were significantly larger in Group 2 (P ≤ 0.01), whereas the NFA was significantly narrower (P = 0.03). Postoperative analysis showed that ΔCI was statistically different between the two groups (Group 1: 10%, Group 2: 7%; P < 0.04). The duration of follow-up period ranged between 19 and 129 months.

Conclusion

Two main subtypes of forehead of infants with scaphocephaly may be distinguished. Indeed, the morphology of the forehead differs when a pathologic subarachnoid spaces' enlargement is present preoperatively and it also affects the postoperative evolution. Such observation highlights the importance of evaluating whether subarachnoid spaces are enlarged when planning a surgical correction in isolated sagittal suture synostosis.

The Management of Nonsyndromic, Isolated Sagittal Synostosis

AIM

Isolated sagittal synostosis is the commonest form of craniosynostosis. The reasons for surgery are to normalize the head shape and to increase the cranial volume, thus reducing the risk of raised intracranial pressure and allowing for normal brain development. It has been suggested that sagittal synostosis may impair neuropsychological development. This systematic review appraised the literature on the management of sagittal synostosis.

METHODS

A literature search was performed with the assistance of a professional librarian. Studies selected had to satisfy the criteria set by PICO (patients, intervention, comparison, and outcome). Cranial index and neuropsychological outcome were used as outcome measures. MINORS was used to assess the methodological quality of the selected articles. A score of 75% was deemed to be of satisfactory quality, and the quality of the evidence from the selected studies was graded using the GRADE system.

RESULTS

One hundred forty-eight articles were initially identified. Only 6 articles fulfilled the PICO criteria and scored a minimum of 75% on MINORS. Four studies compared 1 technique to another with documented cranial indices. Two studies compared 1 group to another and assessed the neuropsychological development. According to GRADE, the quality of evidence was deemed to be very low.

CONCLUSIONS

This systematic review assessed cranial index and neuropsychological outcome following surgery for isolated, nonsyndromic sagittal synostosis. The quality of the evidence in the published literature was noted to be of very low quality. There is a need for better-designed, prospective studies to guide surgeons involved in management of sagittal synostosis.

Skull base development and craniosynostosis

Abnormal skull shape resulting in craniofacial deformity is a relatively common clinical finding, with deformity either positional (positional plagiocephaly) or related to premature ossification and fusion of the skull sutures (craniosynostosis). Growth restriction occurring at a stenosed suture is associated with exaggerated growth at the open sutures, resulting in fairly predictable craniofacial phenotypes in single-suture non-syndromic pathologies. Multi-suture syndromic subtypes are not so easy to understand without imaging. Imaging is performed to define the site and extent of craniosynostosis, to determine the presence or absence of underlying brain anomalies, and to evaluate both pre- and postoperative complications of craniosynostosis. Evidence for intracranial hypertension may be seen both pre- and postoperatively, associated with jugular foraminal stenosis, sinovenous occlusion, hydrocephalus and Chiari 1 malformations. Following clinical assessment, imaging evaluation may include radiographs, high-frequency US of the involved sutures, low-dose (20-30 mAs) CT with three-dimensional reformatted images, MRI and nuclear medicine brain imaging. Anomalous or vigorous collateral venous drainage may be mapped preoperatively with CT or MR venography or catheter angiography.

Intracranial volume is normal in infants with sagittal synostosis

Premature sagittal synostosis results in an elongated, narrow skull shape, scaphocephaly. It has been unclear whether the intracranial volume (ICV) of these children is different from that of normal children. The aim of the present study was to precisely determine the ICV in a large cohort of children with premature sagittal synostosis and to compare it to the ICV of a sex- and age-matched control group. All patients (n = 143) with isolated sagittal synostosis registered in the Göteborg Craniofacial Registry until the end of 2012 with a preoperative CT examination were identified. For each case, a sex- and age- (±30 days) matched control was identified from children who had undergone CT for post-traumatic or neurological reasons. The ICV was measured in a semi-automatic MATLAB program with functions such as region growing, watershed, and thresholding in axial CT slices. The ICV was calculated using the Cavalieri principle. The mean (± SEM) values of ICV for children with sagittal synostosis and for corresponding controls were 866 ± 13 ml and 870 ± 15 ml, respectively. The mean ages of these groups were 173 ± 8 days and 172 ± 8 days, respectively. Subgroup analysis of sex and age at CT (≤180 days and >180 days) did not reveal any differences in ICV between cases and controls. Precise determination of ICV in addition to the use of adequate controls has made it possible to conclude that children with premature isolated sagittal synostosis have a normal ICV.

Isolated sagittal craniosynostosis: definition, classification, and surgical indications

Sagittal craniosynostosis (SC) remains the most common type of synostosis, accounting for about a half of all forms. It would result from a mesenchymal disorder involving the intramembranous ossification of the sagittal suture and leading to its early fusion. No specific data on the etiologic factors are currently available. The premature ossification of the sagittal suture can result in three main types of SC, according to the different segment prevalently involved: anterior, posterior, and complete SC. The diagnosis is easily obtained by clinical examination. However, a radiological work up (3D CT scan) may be necessary to rule out hidden venous or cranial anomalies possibly associated with most severe cases, or for the surgical planning. The most common indication for surgery is the improvement of the cosmetic appearance of the skull, since a cranial deformation may have a significant psychological impact on affected subjects. To relieve from raised intracranial pressure is a further indication to surgery. Although an increased intracranial pressure can be demonstrated in a minority of affected children at diagnosis, indeed, it can present later (usually after the second/third year of life) with chronic symptoms. The role of surgery in the preservation of cognitive functions in scaphocephalic patients does not seem to be relevant, since minor anomalies of the cerebral development associated with SC would occur independently from the cranial shape. On the other hand, the surgical correction may show a protective effect on some visual skills, like the ability to fix and follow, and the fixation shift.

Preoperative craniofacial dysmorphology in isolated sagittal synostosis: a comprehensive anthropometric evaluation

Although clinical descriptions of altered calvarial shape in isolated sagittal synostosis abound in the literature, systematic quantitative assessment of the total morphologic pattern of preoperative craniofacial dysmorphology remains limited in this population. To address this deficit, a retrospective study was undertaken of 256 preoperative patients younger than 6 years with isolated sagittal synostosis who were seen at the Dallas Craniofacial Center. Patients were examined using a battery of 23 anthropometric measurements of the head and face, from which 10 proportion indices were calculated. The measurements and proportions for each patient were compared with sex- and age-matched norms and converted to standard (Z) scores. The pooled data for each variable were analyzed using 1-sample t-tests. The patients were then separated into 2 age groups--younger than 6 months (n = 162) and 6 months or older (n = 94)--and compared via 2-sample t-tests to examine age-related differences. To further elucidate craniofacial growth patterns, standardized anthropometric measures were then correlated against age. Results indicated that the head was enlarged and elongated with compensatory transverse growth of the anterior cranial vault and reduction in the height of vertex. The face was enlarged, especially along the sagittal axis. The head and face were significantly larger relative to age in children younger than 6 months and show a general decrease in size relative to age in all dimensions except cranial length. The data indicate a complex pattern of dysmorphology, which involves the entire craniofacial complex, not just the cranial vault.

New insights into the relationship between suture closure and craniofacial dysmorphology in sagittal nonsyndromic craniosynostosis

Premature closure of the sagittal suture occurs as an isolated (nonsyndromic) birth defect or as a syndromic anomaly in combination with other congenital dysmorphologies. The genetic causes of sagittal nonsyndromic craniosynostosis (NSC) remain unknown. Although variation of the dysmorphic (scaphocephaly) skull shape of sagittal NSC cases has been acknowledged, this variation has not been quantitatively studied three-dimensionally (3D). We have analyzed the computed tomography skull images of 43 infants (aged 0.9-9 months) with sagittal NSC using anatomical landmarks and semilandmarks to quantify and characterize the within-sample phenotypic variation. Suture closure patterns were defined by dividing the sagittal suture into three sections (anterior, central, posterior) and coding each section as 'closed' or 'fused'. Principal components analysis of the Procrustes shape coordinates representing the skull shape of 43 cases of NSC did not separate individuals by sex, chronological age, or dental stages of the deciduous maxillary first molar. However, analysis of suture closure pattern allowed separation of these data. The central section of the sagittal suture appears to be the first to fuse. Then, at least two different developmental paths towards complete fusion of the sagittal suture exist; either the anterior section or the posterior section is the second to fuse. Results indicate that according to the sequence of sagittal suture closure patterns, different craniofacial complex shapes are observed. The relationship between craniofacial shape and suture closure indicates not only which suture fused prematurely (in our case the sagittal suture), but also the pattern of the suture closure. Whether these patterns indicate differences in etiology cannot be determined with our data and requires analysis of longitudinal data, most appropriately of animal models where prenatal conditions can be monitored.

Sagittal synostosis: II. Cranial morphology and growth after the modified pi-plasty

The aim of this study was to characterise the postoperative cranial growth and morphology after a modified pi-plasty for sagittal synostosis. The shape of the skull of 82 patients with isolated premature synostosis of the sagittal suture (SS group) operated on with a modified pi-plasty was studied longitudinally. Forty-five children with unilateral incomplete cleft lip (UICL), evaluated longitudinally at the ages of 2.4 and 23.2 months were used as controls. A standardised radiocephalometric technique was used for image acquisition. The radiocephalograms were analysed using a modification of a method developed by Kreiborg, which included the digitisation of 89 landmarks of the calvaria, cranial base, and orbit (43 in the lateral and 46 in the frontal projections), the production of mean shape plots for each group, and the intergroup comparison of a series of 78 variables (linear distance between selected landmarks, and angles defined by groups of three landmarks). Paired and unpaired t tests were used to assess the differences between the variables studied. These were accepted as significant for values of p<0.01 and were presented as coloured segments or areas in the respective plots. In a comparative analysis with the mean UICL lateral plots, the mean preoperative lateral plots of the study group (SS) showed that the anterior slope of the forehead was more pronounced and it was also more convex. The vertex area was located more anteriorly and was less convex. The occipital curvature was more prominent. Comparison of the mean frontal plots showed a deficiency in convexity and lateral projection of the upper parietal regions, and the line of maximum skull width was lower. The postoperative mean lateral plots of the study group showed a correction of the exaggerated anterior inclination of the forehead and a reduction of the abnormal occipital convexity. However, there was little change in the vertex region and it remained flatter than in the control group. In the mean frontal plots, the increase in convexity and in the lateral projection of the upper parietal areas led to a shape that was similar to that of the UICL group. The mean (SD) cephalic index changed from 64.9% (1.8%) to 71.4% (3.5%) (p<0.001). The longitudinal comparison between the mean postoperative plots at 3 and 5 years of age showed that there had been little change in cranial shape. In conclusion, after a modified pi-plasty for sagittal synostosis, significant objective changes in cranial shape towards normality were produced. The postoperative profile cranial shape was improved except in the vertex area, which remained flatter than normal. In the frontal projection an almost normal shape was obtained. The postoperative cranial shape obtained at 3 years of age had remained stable at the age of 5 years.