A new method of quantifying the extent of tissue loss following spinal cord injury in the rat.

Many agents are being tested for their ability to limit the development of secondary tissue damage following trauma to the spinal cord by comparing the extent of trauma-induced tissue destruction between groups of animals receiving different treatments. However, the changes that occur following spinal concussion result in initial swelling of the cord and then progressive shrinkage. It is therefore impossible to determine the preinjury cross-sectional area of cord once it has been damaged, making accurate calculations of the extent of tissue destruction difficult. To overcome this problem, a method for predicting the preinjury cross-sectional area of damaged spinal cord was developed in the rat by establishing correction factors that related the cross-sectional area of a reference transverse section to the area of sections at other points along the cord. This method was used to calculate the volume of tissue destruction in groups of rats 48 h, 4 days, and 4 weeks after photochemically induced cord injury. The results were compared with the volume of tissue destruction obtained when calculated from measured rather than predicted cord areas. One month following photochemically induced injury, the spinal cord had shrunk significantly. This resulted in significant underestimation of the lesion volume when calculated from the measured area of injured cord. This demonstrates that the preinjury area of the cord must be established in order to calculate the full extent of tissue destruction and that it can be estimated accurately using the method described in this study.