Quantitative assessment and localization of the hollowing of the temple after craniectomy and cranioplasty-The frontozygomatic shadow.

Background: After cranioplasty, in many cases a not negligible soft tissue defect remains in the temporozygomatical area, also referred to as a hollowing defect of the temple.

Objective: To assess the precise localization and volume of the hollowing defect, to optimize future cranioplasties.

Methods: CT data of patients who received craniectomy and conventional CAD cranioplasty in our institution between 2012 and 2018 were analyzed. CT datasets prior to craniectomy and after cranioplasty were subtracted to quantify the volume and localization of the defect.

Results: Out of 91 patients, 21 had suitable datasets. Five cases had good cosmetic results with no defect visible, 16 patients had an apparent hollowing defect. Their average defect volume was 5.0 cm3 ± 4.5 cm3. The defect localizations were in the area behind the zygomatic process and just below the superior temporal line, covering an area of app. 3x3 cm2. Surgical attempts of temporal muscle restoration were more often found in reports of good results (p<0.01), but also in 50% of reports, whose surgeries resulted in hollowing of the temple. Mean time between the two surgeries was 112 ± 43 days. No significant differences between patients with and without hollowing defect were detected regarding time between the two surgeries, age or performing surgeon.

Conclusion: This work supplies evidence for the indication of a surgical corrective during cranioplasty in the small but cosmetically relevant area of the "frontozygomatic shadow". Based on our 3D data analysis, future focused surgical strategies may obtain better aesthetical results here.