Decompressive craniotomy allows expansion of the swollen brain outside the skull, resulting in axonal stretch, which might lead to neural injury and consequently cause unfavorable outcome for the patients. The aim of this study was to assess and quantify the axonal deformation at both pre- and post-craniotomy period in order to provide more insight into the mechanical effects on the axonal fibers upon such a treatment.
Displacement fields representing the structural changes in whole brain were obtained by a nonlinear image registration method based on the three-dimensional CT imaging data sets of a patient both before and after decompressive craniotomy. Axonal fiber tracts together with their orientations were extracted from diffusion weighted (DW) images from a healthy brain and adapted to the patient’s brain by image registration. The deformation of the brain tissue in the form of Lagrangian finite strain tensor for the entire brain was then calculated from the displacement field. Based on the obtained brain tissue strain tensor and the axonal fiber tracts, 1st principal strain was extracted at axonal fibers. Furthermore, other axonal deformation measures, i.e., axonal strain, and axonal effective shear strain were also quantified.
Greatest axonal fiber displacement (up to 12 mm) was found predominantly located in the treated part of the craniotomy, accompanied by a large axonal deformation, e.g., 1st principal strain up to 0.49. This indicated the extent of axonal fiber stretching due to the neurosurgical intervention. Other strain measures, such as axonal strain and axonal effective shear strain also showed an increased level at the treated part for post-craniotomy compared to that found in the pre-craniotomy period.
The distortion (stretching or shearing) of axonal fibers at the treated part of the craniotomy may influence the axonal fibers in such a way that the neurochemical events are jeopardized. It is suggested that such a quantitative model may clarify some of the potential problems with such a treatment. Also, by further development of the technology it is quite possible to judge the outcome of strain levels already before the decompressive craniotomy is performed. This may have the possibility to optimize the size as well as the area of craniotomy.
2012. Vol. 20, no 4, 509-513 p.