Posterior Skull Height Following Posterior Vault Remodeling: A Complement to Cephalic Index to Assess Sagittal Craniosynostosis

PURPOSE: Cephalic index (CI) is the most common measurement to quantify dolicocephaly in sagittal synostosis (SS), but it is considered unreliable as an outcome measure. Posterior skull height (PSH) has recently been suggested as a better outcome measure of SS reconstruction. Posterior vault reconstruction (PVR) addresses the dolicocephaly and skull height deformity observed in SS and thus, is an ideal intervention to compare and contrast PSH and CI as outcome measures. This study aims to define PSH and changes post-PVR by craniometric analysis and measure the correlation to aesthetic improvement in SS patients.

METHODS: Non-syndromic SS patients undergoing PVR from 1994-2017 with pre- and postoperative computed tomography (CT) scans were included. PVR was performed with or without switch cranioplasty. Mimics (Materialise Inc., Leuven, Belgium) was used to measure CI, PSH (defined as opisthion and basion to the cortex orthogonal to the Frankfort horizontal), and posterior bossing angle (PBA) (outer cortex-opisthion-opisthocranion). Surgical residents and laypeople were surveyed to correlate PSH and CI to aesthetic outcomes. Respondents rated patients on the visual analogue scale (VAS) (0 = no deformity; 100 = severe deformity) and recommended surgery if necessary. Independent t-tests and linear and logistic regressions were used as appropriate.

RESULTS: Of 397 SS patients, 87 patients underwent PVR, and 26 met inclusion criteria for CT imaging. Thirteen subjects with adequate photographs were included in the aesthetic assessment survey. Postoperative CI and PSH were significantly increased (CI: 69.55±4.07 to 76.32±4.07; from opisthion: 121.74±7.32 to 125.46±7.04 mm; from basion: 118.85±7.20 to 121.11±6.88 mm; p<0.0001 for all). Postoperative PBA was significantly reduced (47.8°±6.3° to 40.9°±5.3°, p<0.0001). Changes in CI, PSH, or PBA did not vary by surgical technique. Increasing CI was associated with improving VAS (coefficient = -0.97, R²=0.059, p<0.0001). An increase in PSH >5mm measured from the basion was associated with improvements in VAS (ΔVAS=-14.4, R²=0.038, p=0.002).

CONCLUSION: Posterior skull height and cephalic index are significantly increased post-PVR in SS patients. Improvements in PSH and CI are associated with improved aesthetic outcomes. Clinically-relevant assessment of sagittal synostosis likely requires 3D measurements such as the combination of the cephalic index and posterior skull height.