The design of the PSI is based on the preoperative CT-scan of the patient`s head with the skull defect, the imaging data set is uploaded and processed with IPlanNet software by BrainLab®. With the help of the software, a 3D model of a negative mould of the PSI is designed and printed. In the operation room, the PSI is fabricated under sterile conditions using the PSI mould. The design of the PSI mould with the help of IPlanNet is demanding and takes some few hours depending on the complexity of the case to be designed. In certain cases the accuracy of the fabricated PSI mould is not optimal, so that the surgeon intraoperatively has to adapt for the inaccuracy to achieve the best cosmetic and functional results at the expense of the operation duration, a known risk factor for postoperative wound infection and other perioperative complications.