Development of traumatic brain edema in old versus young rats

Age is an important factor of mortality and morbidity following traumatic brain injury. The causes for the adverse effect of old age remain obscure. The aim of this study was to clarify whether age affects the development of posttraumatic brain edema. In Wistar rats, a cortical freezing lesion was applied to the parietal region in ketamine-xylazine anesthesia. 18 young rats (4-6 months) were compared to 15 old animals (36-40 months). In the early peritraumatic and late posttraumatic period blood pressure was monitored. 24 hours after trauma, the brains were removed and hemispheric swelling, water- und electrolyte-contents were measured. In addition, the brains of 3 animals of each group were histologically evaluated. In the old age group, 3 animals died during the 24 hours observation period (mortality 20%), whereas all young rats survived (p < 0.01). The cortical freezing lesion resulted in a hemispheric swelling of 6.9 +/- 0.5% in young, and 10.4 +/- 0.8% in old animals (p < 0.001). Accordingly, the increase of cerebral water content due to the lesion was significantly more pronounced in the group of old rats, i.e. 2.05% in old versus 1.50% in young animals (p < 0.01). The increase of swelling and edema in the old age group could not be attributed to arterial hypertension. On the contrary, mean arterial blood pressure was significantly lower in old animals. Histological examinations did not reveal significant differences between the two groups. Edema generation following a standardized cryogenic lesion is markedly enhanced in old versus young rats. This might be one factor among others for higher mortality and morbidity following traumatic brain injury in old versus young individuals.