Safety of cranial fixation in endoscopic brow lifts.

Introduction: The endoscopic brow lift technique relies on brow mobilization and often soft fixation to the underlying calvarium. While the endoscopic brow lift has been used safely, there are anecdotal reports of cerebrospinal fluid leak. We sought to measure calvarial thickness to improve the safety of cranial fixation.

Methods: A retrospective review was performed of T2 weighted MRIs of the face of 28 patients. Calvarial thickness was measured on 10 coronal planes, from 3 centimeters (cm) anterior to 6 cm posterior to coronal suture. Fifteen points were measured on each coronal plane, starting in the midline and extending laterally for 7 cm. There were a total of 150 calvarial measurements per patient, covering the surface area used in endoscopic brow lifts. Statistical comparison was performed using analysis of variance.

Results: Cranial thickness ranged from 1.1 to 13.6mm, with a mean of 6.1mm. The skull was thickest 2-4 cm posterior to the coronal suture, and thinnest 1cm anterior to the coronal suture. The cranium thins as it extends laterally, with an average thickness of 5.0mm at seven centimeters from midline. Average skull thickness for males was 5.96 versus 6.16 in females. There was no relationship between age and skull thickness.

Conclusion: Cranial thickness increases medially and posteriorly, and is larger for females compared with their male counterparts. Given the risk of CSF leak, surgeons need to be aware of how cranial thickness varies by location along the skull.