Scaled cortical impact in immature swine: effect of age and gender on lesion volume.

The piglet scaled cortical impact model creates a focal contusion using a skull-mounted, spring-loaded blunt indentation device scaled to achieve identical tissue strains in subjects with different brain sizes. Preliminary data showed that contusion size increased proportional to subject age. This study details the results from a new, larger series of subjects of three ages, and compares the effect of age and additional host and physiologic variables on injury response. Sixty-seven subjects, including infant (5- to 7-day-old), "toddler" (1-month-old), and early adolescent (4-month-old) swine underwent scaled cortical impact under strict anesthetic protocols. Serum glucose, testosterone, and 17beta-estradiol levels were measured. Lesion size was measured at 1 week post injury, as the ratio of the lesion area over the area of the contralateral hemisphere. Adolescent subjects had lesions over eight times larger than infants (p < 0.0001). Lesion volumes were larger in toddlers than in infants, most significantly for males (p < 0.05). Adolescent subjects were warmer on average, but there was no correlation between temperature and lesion volume within any age group. Serum glucose did not differ among ages. Infant males had the highest levels of circulating sex steroids. In this model, age was the most robust predictor of lesion size. Temperature had an effect, but did not explain all the variability seen among age groups. There was an interaction among gender, hormone levels, and lesion size in younger subjects. Characterization of these variables allows use of this model for treatment trials for subjects at different stages of maturation.