Longitudinal enlargement of the lesion after spinal cord injury in the rat: a consequence of malignant edema?

Study design: Experimental animal study. Objectives: Quantitative analysis of secondary changes in lesion size after experimental spinal cord injury (SCI) in the rat, with special emphasis to the formation of dorsal column lesions. Setting: Slovakia. Methods: After SCI in the rat, animals survived for different periods ranging from 5 min to 7 days. Their whole spinal cords were cut transversally into 1 mm thick slabs. On each slab, the lesion profile was outlined. The overall shape of the lesion was reconstructed from a series of consecutive profiles and its length was measured. Results: Immediately after injury, a spindle-shaped hemorrhagic contusive lesion was observed, with the length of similar to 15 mm. After a quiescent phase lasting for at least 1 h, there was a dramatic secondary enlargement of the lesion and its length increased up to 40 mm between 1 and 48 h. The fully developed lesion consisted of the spindle-shaped epicenter and long cranial and caudal protrusions located in the midline between dorsal columns. Conclusion: We propose that secondary enlargement of the lesion can be explained by posttraumatic swelling. The expanding tissues are pushed out in longitudinal axis along the mechanically weakest parts of the spinal cord. Additional data that support this hypothesis are presented. Our findings indicate that malignant posttraumatic edema might have an important role in pathomechanisms of secondary injury after SCI.