Comprehensive Craniomorphometric Analysis of 167 Patients With Metopic Craniosynostosis

Abstract

BACKGROUND: Metopic craniosynostosis is the second most common form of single suture synostosis, associated with a trigonocephalic head shape. Due to physiologic closure of the metopic suture in infancy, controversy persists regarding the most accurate method to assess severity. The goal of this study was to compare and validate previously described and newly developed measurements of severity for trigonocephaly. Additionally, a new severity scale was proposed to help guide clinical decision making. METHODS: Morphometric analysis using Materialise-Mimics was performed on preoperative CT scans of infants with metopic synostosis and control age-matched infants. Measurements included endocranial bifrontal angle (EBF), adjusted endocranial bifrontal angle (aEBF), frontal angle, anterior fossa angle, metopic index, horizontal cone angle, temporal depression angle, foramen ovale distance, and bitemporal/biparietal distance ratio. Volumetric and area analyses of the frontal cranium were conducted to determine the degree of restriction in the metopic cohort. Preoperative electroencephalogram (EEG) data were compared for a subset of metopic patients to assess whether the proposed severity scale has neurodevelopmental implications. Results were analyzed using an independent sample t test, Pearson’s correlation coefficient, and receiver operating characteristic curve analysis. RESULTS: Analyses were performed for 167 patients with metopic synostosis (mean age 7.2 ± 4.9 months), and compared with 44 control subjects (mean age 7.6 ± 7.6 months). The EBF, aEBF, frontal angle, anterior fossa angle, horizontal cone angle, and bitemporal/biparietal ratio were all significantly smaller in the metopic cohort compared with the control cohort (P < 0.05).The metopic index, temporal depression angle, and foramen ovale distance were not significantly different from the control cohort. Metopic skulls demonstrated a significantly decreased anterior cranium area (average, 2466.12 mm2; P < 0.001) and significantly increased anterior-posterior (AP) length (average, 4.00 mm; P = 0.003) and craniocaudal length of the anterior cranium (average, 6.41 mm; P = 0.01) compared with control skulls. There was a significant negative correlation between the anterior cranial area and both the vertical length and AP length. The frontal angle significantly correlated with the increases in vertical height and AP length, whereas the aEBF correlated with only the AP length. Other measurements did not significantly correlate with changes in anterior calvarium dimensions. Receiver operating characteristic curve analysis identified a frontal angle of 101.3° as the diagnostic threshold between operated metopic synostosis and normal skulls. Sixteen metopic subjects with existing EEG data were evaluated. Six patients with frontal angles more acute than the diagnostic threshold exhibited significantly attenuated EEG signals compared with controls (P = 0.037). Patients with frontal angles greater than the diagnostic threshold did not exhibit any significant change in their EEG compared with controls. CONCLUSIONS: In the largest radiographic series of metopic synostosis patients to date, this study examined the validity of measurements for severity of metopic craniosynostosis. The frontal angle provides the strongest correlation with growth compensation in the most severe cases of trigonocephaly. Furthermore, a severity classification using the frontal angle correlates with preoperative EEG analysis. The bitemporal/biparietal ratio, metopic index, cranial volumes, cranial base structures, and orbital structures should be reconsidered as measures of metopic severity as they are either nonconcordant with the anterior-cranium compensatory changes or not significantly different from control.