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Magnetic resonance imaging evaluation of acute crush injury of rabbit sciatic nerve: correlation with histology.

OBJECTIVE
To investigate the relation between the quantitative assessment of magnetic resonance imaging (MRI) features and the correlation with histology and functional recovery by using the rabbit sciatic nerve crush model.


METHODS
In New Zealand, 32 rabbits were randomly divided into 2 groups (group A and B); all rabbits underwent crushing injury of their left sciatic nerve. In group A (n = 16), the sciatic nerves were crushed by using microvessel clamps with a strength of 3.61 kg. In group B (n = 16), the sciatic nerves were crushed with a strength of 10.50 kg. Right sciatic nerves were served as controls. Serial MRI of both hind limbs in each rabbit was performed before and at the time point of 1, 2, 4, and 8 weeks after crushed injury. The MRI protocol included T1-weighted spin-echo (T1WI), 3 dimension turbo spin-echo T2-weighted (3DT2WI), T2-weighted turbo spin-echo images with spectral presaturation with inversion recovery (T2WI/SPIR), balanced fast-field echo (B-FFE) and short-time inversion recovery (STIR) sequences. The coronal image of the sciatic nerve was obtained. The nerve and muscle signal ratio (SIR) on each sequence was measured. The function recovery was observed and pathological examination was performed at each time point.


RESULTS
A signal intensity increase of the distal segment of crushed sciatic nerves was found on 3DT2WI, T2WI/SPIR, B-FFE, and STIR, but not on T1WI images. Of 32 crushed nerves, 30 nerves showed high signal intensity. The correct diagnostic rate was 93.75% with false negative-positive of 6.25%. The SIR of the crushed sciatic nerve at distal portion was higher than those of the control nerves; there was a statistically significant difference (P < 0.001). The SIR of the distal portion of crushed nerves was higher than that of the proximal nerve portion; there was a statistically significant difference (P < 0.001). Whereas, the SIR at proximal nerve portions of crushed nerve was similar to control nerves (P > 0.05). The SIR between group A and group B was not found statistically significantly different (P > 0.05). The SIR of crushed nerves at distal portion increased at one week after the crush injury, subsequently further increased, and reached a maximum at 2 weeks. The pathological examination revealed myelin swelling and axonal fragmentation of crushed nerve. Abduction function of injured hind limb was deficit. From 4 to 8 weeks following the crush, the SIR decreased, correspondingly, nerve regeneration was revealed on pathology including extensive Schwann cells proliferation and the immature myelin formation. The abduction function gradually recovered. There was no abnormal finding on MRI for control and sham-operated nerves.


CONCLUSION
The SIR of injured nerve at distal portion increased on MRI. The evolution of SIR after injury was correlated with the degeneration and regeneration of nerve and the function recovery of lower extremities. Assessment of peripheral nerve injury by using SIR could reveal acute nerve injury, as well as aid in monitoring the recovery process. The pathophysiological basis for the SIR is predominantly the results of axon breakdown and myelin regeneration