MRI Signal Change of Calf Muscle after Sciatic Nerve Injury in Rabbit

ABSTRACT

The evaluation of peripheral nerve disorders has traditionally relied on clinical history, physical examination and electrodiagnostic studies. The electrodiagnostic study is currently the most popular procedure to analyse the nerve lesion, but it is painful and its result is operator dependent. The purpose of this study is to evaluate the significance of MRI signal change of denervated muscle in peripheral nerve as an adjuvant study of electrodiagnostic study. After the compression of sciatic nerves in 20 rabbits and severance of scitic nerve in 10 rabbits, the signal change of both T1WI(TR; 450 msec, TE; 15 msec) and T2WI(TR; 3,000 msec TE; 90 msec) of calf muscles were compared with EMG findings of the same muscles. Signal intensity ratio(SIR) of calf muscles was measured and compaired with the grade of abnormal spontaneous activity in the same muscles in needle EMG study. Serial studies were done on 4th day, 1 week, 2 weeks, 3 weeks, 4 weeks, 6 weeks, 8 weeks, 10 weeks after sciatic nerve injury. Among 25 rabbits showing abnormal spontaneous activity in needle EMG, the signal intensity of both T1WI and T2WI was increased in 13 rabbits. The signal intensity began to increase at 1 week in 10 rabbits and 2 weeks in 3 rabbits following nerve injury which was about 1 week later than appearance of abnormal spontaneous activity in needle EMG study. There were no signal intensity increase in rabbits which showed no abnormal spontaneous activity in needle EMG study. The signal intensity ratio and grade of abnormal spontaneous activity had a good correlation(Spearman's correlation coefficiency 0.635). The signal intensity of 3 rabbits which showed regeneration evidence in needle EMG study returned to normal. These findings suggest that MRI study of denervated muscle can be used as an evaluation method for severe peripheral nerve injury, howeverits value is doubtful in mild peripheral nerve injury.