## 4 Discussion
Discrepancies in the ml/Cr ratio were observed only in the frontal lobes, while for the NAA/Cr ratio they were observed in the occipital lobes. Hence, the preferred shooting position may have an influence on the localization of more prominent brain damage. A markedly increased ml/Cr ratio in the right frontal lobe may be the consequence of vivid glial proliferation associated with neuroinflammation related to chronic traumatic encephalopathy [18]. Neuronal loss, reflected as a decrease in the NAA/Cr ratio, is more uniform in the frontal lobes as the difference between the sides was not detected, and may be a result of generalized atrophy of frontal and temporal lobes characteristic of chronic traumatic encephalopathy [18]. Meanwhile, a significantly lower NAA/Cr ratio in the right occipital lobe in comparison to left side might be caused by a neuronal loss due to repetitive brain countercoup injury secondary to a blast wave generated from shooting. The cumulative peak overpressure affecting the head of a trainee equipped with a 0.50 caliber sniper rifle with 20'' long barrel during three days of training ranged from 160-300 psi. Furthermore, the average peak overpressure for the head generated by the same type of rifle was approximately 6 psi [19]. The maximum wind speed associated with a blast overpressure at the level of 5 psi is equivalent to around 260 km per hour [20]. Hence, a more prominent exposure to blast overpressure on the one side may result in significant brain damage, and frequent switching of the shooting position should be recommended as a potential factor which may decrease the risk of chronic traumatic encephalopathy. Nonetheless, further research which also includes the analysis of brain metabolites in the group of soldiers preferring a left shooting position is necessary to confirm this hypothesis. The most frequent findings In the neurocranium were asymmetry of the lateral ventricles (11.1%), dilated Virchow-Robin spaces (7.4%), and the enlargement of the subarachnoid spaces (7.4%) as well as the presence of cavum septum pellucidum and cavum vergae (5.6%). The prevalence of the lateral ventricles' asymmetry in the population is approximately 6% [21], while for cavum septum pellucidum and cavum vergae it is about 1-2% [22; 23]. The elevated frequency of these anomalies in military personnel in comparison to the general population was also observed by [PERSON] et al.--asymmetric ventricles were observed in 25.4% of cases, while the cavum septum pellucidum was present in 46.4% of cases [3]. The higher incidence of the lateral ventricles' asymmetry and the enlargement of the subarachnoid spaces may be associated with the neuronal loss secondary to brain injury. The neuronal loss may be asymmetric, as our results regarding the differences in the NAA/Cr ratio between sides indicate, leading to the different sizes of the lateral ventricles. In turn, the presence of the cavum septum pellucidum and cavum vergae (fluid-filled spaces between the laminae of the septum pellucidum, located in its anterior and posterior part, respectively), generally regarded as anatomical variants, are characteristic findings in subjects with chronic traumatic encephalopathy. The postulated mechanism of their formation is the presence of shearing forces acting on the septum pellucidum due to blast wave propagation in the lateral ventricles causing its fenestration [24]. Their frequent occurrence were also observed among such sport professionals as football players or boxers. The size of the cavum septum pellucidum correlates with decreased performance on a list learning task and worse scores on tests of estimated verbal intelligence [25]. In addition, the prevalence of dilated perivascular spaces is between 2% and 3% of healthy population and it generally increases with advancing age [26]. However, it is also associated with mild traumatic brain injury as the probable reflection of early and permanent brain alterations [27]. The increased incidence of dilated Virchow-Robin spaces in veterans was found in the [PERSON] et al.