Objective: To use magnetic resonance imaging (MRI) to characterize secondary injury immediately after spinal cord injury (SCI), and to show the effect of hypertonic saline on MRI indices of swelling, edema, and hemorrhage within the cord.
Design: A prospective, randomized, placebo-controlled study.
Setting: Research laboratory.
Subjects: Twelve adult Long-Evans female rats.
Interventions: Rats underwent a unilateral 12.5 mm SCI at vertebral level C5. Animals were administered 0.9% NaCl (n = 6) or 5% NaCl (n = 6) at 1.4 mL/kg intravenously every hour starting 30 minutes after SCI. Immediately after SCI, rats were placed in a 4.7T Bruker MRI system and images were obtained continuously for 8 hours using a home-built transmitter/receiver 3 cm Helmholtz coil. Rats were killed 8 hours after SCI.
Measurements and Main Results: Quantification of cord swelling and volumes of hypointense and hyperintense signal within the lesion were determined from MRI. At 36 minutes after SCI, significant swelling of the spinal cord at the lesion center and extending rostrally and caudally was demonstrated by MRI. Also, at this time point, a hypointense core was identified on T1, PD, and T2 weighted images. Over time this hypointense core reduced in size and in some animals was no longer visible by 8 hours after SCI, although histopathology demonstrated presence of red blood cells. A prominent ring of T2-weighted image hyperintensity, characteristic of edema, surrounded the hypointense core. At the lesion center, this rim of edema occupied the entire unilateral injured cord and in all animals extended to the contralateral side. Administration of HS resulted in increased serum [Na], attenuation of cord swelling, and decreased volume of hypointense core and edema at the last time points.
Conclusions: We were able to use MRI to detect rapid and acute changes in the evolution of tissue pathophysiology, and show potentially beneficial effects of hypertonic saline in acute cervical SCI.