Current contribution of diffusion tensor imaging in the evaluation of diffuse axonal injury / Contribuição atual da imagem por tensor de difusão na avaliação da lesão axonal difusa

ABSTRACT Traumatic brain injury (TBI) is the number one cause of death and morbidity among young adults. Moreover, survivors are frequently left with functional disabilities during the most productive years of their lives. One main aspect of TBI pathology is diffuse axonal injury, which is increasingly recognized due to its presence in 40% to 50% of all cases that require hospital admission. Diffuse axonal injury is defined as widespread axonal damage and is characterized by complete axotomy and secondary reactions due to overall axonopathy. These changes can be seen in neuroimaging studies as hemorrhagic focal areas and diffuse edema. However, the diffuse axonal injury findings are frequently under-recognized in conventional neuroimaging studies. In such scenarios, diffuse tensor imaging (DTI) plays an important role because it provides further information on white matter integrity that is not obtained with standard magnetic resonance imaging sequences. Extensive reviews concerning the physics of DTI and its use in the context of TBI patients have been published, but these issues are still hazy for many allied-health professionals. Herein, we aim to review the current contribution of diverse state-of-the-art DTI analytical methods to the understanding of diffuse axonal injury pathophysiology and prognosis, to serve as a quick reference for those interested in planning new studies and who are involved in the care of TBI victims. For this purpose, a comprehensive search in Pubmed was performed using the following keywords: "traumatic brain injury", "diffuse axonal injury", and "diffusion tensor imaging".

RESUMO O traumatismo cranioencefálico (TCE) é a principal causa de morbimortalidade entre adultos jovens. Aqueles que sobrevivem são frequentemente deixados com sequelas funcionais nos anos mais produtivos de suas vidas. O principal aspecto fisiopatológico do TCE é a lesão axonial difusa (LAD), cada vez mais destacada pois está presente em 40 a 50% dos casos que necessitam de internação hospitalar. LAD é definida como a injúria axonial extensa caracterizada pela axoniotomia completa assim como pelas reações secundárias a axoniopatia, que são demonstradas por métodos de neuroimagem como áreas de edema e micro-hemorragia. Entretanto, os achados da LAD são frequentemente subestimados em estudos de neuroimagem convencional. É neste contexto que imagens por tensor de difusão (DTI) ganharam ênfase, já que permitem obter informações sobre a integridade da substância branca que não eram obtidas por sequências convencionais de ressonância magnética (RM). Existem artigos extensos sobre os fundamentos físicos e as aplicações de DTI em pacientes vítimas de TCE, no entanto, estes assuntos permanecem ainda nebulosos a alguns profissionais da área de saúde. Deste modo, propomos uma revisão didática sobre a contribuição do estado da arte de diferentes métodos analíticos de DTI no entendimento do processo da fisiopatologia e prognóstico da LAD, servindo assim como uma ferramenta acessível para aqueles interessados em planejamento de novos estudos e aqueles envolvidos no tratamento de vítimas de TCE. Uma pesquisa abrangente foi realizada no Pubmed com as seguintes palavras-chave: "traumatismo cranioencefálico", "lesão axonial difusa", "imagem por tensor de difusão".

Effects of nimodipine on cerebral hemodynamics, and prognosis of diffuse axonal injury patients

To evaluate the effects of nimodipine on hemodynamic state, vasospasm, and short time prognosis of diffuse axonal injury [DAI] patients. In a prospective, clinical trial double blind study, 40 DAI patients with Glasgow coma scale of 5-8 were selected and randomly divided into 2 equal groups. The first group was treated with 60 mg of nimodipine every 4 hours immediately after admission, and the control group did not receive this treatment. Mean blood flow velocity [MFV] and pulsatility index of both middle cerebral arteries were measured using transcranial Doppler on the 1st, 3rd, and 10th days of admission. Glasgow outcome scale was evaluated one month after admission. This study was performed from June 2003 to June 2004 at Imam Medical Center, Tabriz, Iran. There were significant differences in MFV among the 3 transcranial Doppler, which demonstrated hemodynamic changes in these patients. Nimodipine did not have any significant difference on MFV between the treatment and control groups. In the nimodipine group, 45% had good prognosis [30% in the control group] and nobody had vasospasm on the 10th day Doppler study [15% in the control group], although it did not show any statistical significant difference between them. Nimodipine improved the prognosis and decreased vasospasm, however, there was no statistical difference. Therefore, we suggest further studies in a larger number of DAI patients