Discussion and Conclusion

The stereotactical phenomena explain common neurological signs

The stereotactical phenomena explain why the initial and reversible loss of consciousness (IRLC) is the most common posttraumatic neurological sign, even if the involved structure - the ascendant reticulate matter (ARM) - is placed in the deep cerebral regions. It can also explain why, after the IRLC, most patients don't have any focal neurological deficit (motor, sensitive or visual) related to the superficial cerebral structures' lesions or functional impairement. The functional recovery is faster for the neuronal circuits with less infrastructure lesions and if the superficial lesions were more important than the deep ones, the recovery of the focal deficits would be longer than the recovery of the consciousness.

The stereotactical phenomena also explain the high incidence of the memory disturbances after a head trauma as the result of the periventricular neuronal circuits' functional impairment or lesions. At our best knowledge, this is the first theory to explain these clinical phenomena. The isolated functional impairment of the ARM could also be explained by the fact that the consisting neuronal fibres are less resistant because nonmyelinated. This argument is not applicable to the myelinated neuronal fibres whose functional impairment or lesions generate the frequent posttraumatic memory disturbances.

The stereotactical phenomena explain the deep cerebral lesions

The stereotactical approach can also explain the preferential localisation of the DAI in corona radiata, corpus callosum, fornix and upper brainstem (8). These anatomical regions correspond to geometrical centres of different skull vault segments. Deep traumatic cerebral hematomas can also be better understood as they occur close to the geometrical centre of the skull vault.

The stereotactical phenomena explain the importance of the contrecoup cerebral lesions

The stereotactical phenomena explain why the cerebral contrecoup lesions (CCL) are often more important than the direct lesions (DL). The bend spoke of the lateral skull segment is approximately equal to the bi-parietal skull diameter. According to the stereotactical theory the CCL are the consequence of the pressure waves' stereotactical summation toward the geometrical centre of the implied skull vault segment. Thus, up to a critical energy lateral impact, the CCL occur before the DL.

The stereotactical phenomena explain why the cerebral contusions (direct or contrecoup) are often located in the temporal and the frontal lobes. These cerebral regions correspond to small bend spoke segments of the skull and contain their geometrical centre - where maximal stereotactical summation occurs.

The stereotactical phenomena are supported by prviously reported experimental data

In older experiments Gurdjian noted significant differences between the DAI localisation after head impacts on primates and dogs. The primates' brains had predominant DAI in the upper brainstem while the dogs' DAI was concentrated in the lower brainstem regions (9). These differences are unexplained by the current biomechanical theories, but they can be easily understood according to the stereotactical approach by the difference between the shape of the animals' skull vaults and their geometrical centre localisation. According to the stereotactical approach, the DAI is concentrated in the geometrical centre of the skull vault and, as the primates' skull vault is more incurved, their geometrical centre is placed higher than the dogs' one.

Other stereotactical phenomena

The radiosurgery uses the stereotactical principle in order to avoid massive irradiation of the superficial structures when a deep cerebral lesion (tumour, malformation) has to be irradiated. The total irradiation doze, aimed to destroy the deep lesion, is spatially fractionated in many convergent beams. Thus, the superficial structures receive only small fractions of the total irradiation doze and are preserved.

Sounds are also pressure waves. Microphones with parabolic reflective surfaces and the concert halls' architecture use the stereotactical principle in acoustic applications.

Conclusion

The stereotactical phenomena can explain common posttraumatic neurological signs and cerebral lesions. Its complementarity with the other biomechanical theories could allow us to integrate the TBI biomechanics in a common concept in order to better understand the TBI pathophysiology and also related pathological entities like boxers' chronic encephalopathy or even Alzheimer's disease (10). Further experimental and especially human observational research in TBI biomechanics is needed.


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