Traumatic brain injuries (TBIs) have a devastating global epidemiological importance since they contribute to the mortality and morbidity in the society with a considerably large extent. After TBI the injured brain tissue tends to swell leading to the increment of the intracranial pressure (ICP) which can cause serious neurological damage and death. Therefore, a main goal of the neurosurgical procedure is the reduction of ICP which is possible via decompressive craniectomy (DC). However, its optimal execution regarding the size and the location of the skull opening is controversial. In this paper the reconstruction of DC is performed by finite element (FE) simulations. The applied modelling strategy is presented and patient-specific FE models are constructed with different levels of anatomic details which can predict the post-operative response of the brain tissue for a given pre-operative state. These models are validated by reconstructing real life DC case, where the predicted displacements and ICP are compared to their observed value measured by neurosurgeons. Results confirm the applicability of the above described modelling procedure, implying that such models can be used to optimize DC in the future based on the biomechanical response of the highly deformable brain tissue.