## 3 Results  
The proposed procedure was performed on a 27-year-old woman with a wide cranial vault lacuna in the upper part of the skull and slightly crossing the sagittal plane, as shown in Figure 6.  
The patient underwent surgery in 2000 when she was nine-year-old for a low-grade brain neoplasm and, again, four years later for a tumor recurrence. In both cases, the cranial void was closed by performing an autograft cranioplasty. A major wound infection a few months after the second surgery necessitated the removal of the autograft. In 2012 and 2014, two further cranioplasties were attempted, in both cases with methyl methacrylate allografts. Both attempts failed due to wound-closure breakdown with subsequent prosthesis exposure. When the patient was seen in April 2018, the defect was covered by a sunken skin flap with dystrophic and very thin skin. The scalp conditions were so critical that a new cranioplasty was not possible without risking skin necrosis. In particular, there was significant atrophy of the scalp, with a thin and fragile skin flap, especially on the boundary of the defect (see Figure 7). Figure 6: Preoperative scalp/skull conditions of the patient. Figure 7: CT image of the patient. The defective skull and the skin are clearly visible. The two arrows indicate areas where the skin is particularly fragile and thin. As a consequence, careful skin assessment and surgical planning were required to avoid additional and more serious complications. The procedure started with the segmentation of the patient's diagnostic images CT images are particularly suitable because cranial bones and scalp appear with two well-identifiable grayscale intensity windows, as shown in Figure 7. The CT imaging acquisition parameters were slice thickness equal to 2 mm with a spacing of 1 mm. The pixel spacing was equal to 0.48 mm \(\times\) 0.48 mm. To perform the required analyses, it is unnecessary to reproduce scalp anatomy in details describing all its layers. Still, it is instead important to duplicate its overall geometry and consistency. Consequently, all the scalp is segmented (and then modeled) as a single body. The segmentation was carried out using the threshold method in Materialise(r) Mimics software. The same software also allows automatically obtaining and exporting the STLs from the segmentation masks. The defective skull was then restored by applying the procedure presented by the authors in [12]. It is a semi-automatic template-based approach that can restore unilateral or quasi-unilateral (i.e., single defect slightly passing the sagittal plane, as in this case) cranial defects, ensuring to maximize symmetry and continuity with the healthy surrounding bones. Such procedure exploits the contralateral anatomy to provide a reliable template to guide the reconstruction of the missing bone. Unlike existing mirroring-based approaches, the contralateral part is only used as a reference to guide a subsequent reconstruction based on surface approximation/interpolation. The procedure automatically mirrors the contralateral points within the defect boundary around the skull's symmetry plane. The symmetry plane is automatically computed through the method proposed by [PERSON] et al. in [13]. The method only requires as input the 3D model of the skull in STL format and can find a good approximation of its symmetry plane in a fully automatic way also in the case of a large defective area. The points retrieved from the mirrored counterpart are defined as approximation centers for the reconstructive surface to ensure a symmetrical reconstruction as far as possible without over-constraining the surface, which is essential to obtain a smooth patch. The points on the defect boundary are defined as interpolation centers to ensure the continuity on the boundary between the patch and the surrounding bone. The points on the boundary are automatically retrieved by the algorithm starting from a seed point manually selected by the user.