Background and purpose: Compressive and entrapment neuropathies are diseases frequently observed on routine clinical examination. A definitive diagnosis based on clinical symptoms and neurologic findings alone is difficult in many cases, however, and electrophysiologic measurement is used as a supplementary diagnostic method. In this study, we examined to use protein tracers (Evans blue albumin or horseradish peroxidase) and gadolinium-enhanced MR imaging to determine the changes of blood-nerve barrier permeability in compressive neuropathies.
Methods: In dogs, the median nerve was compressed for 1 hour by using five kinds of clips with various strengths (7.5-90-g force). After clip removal, the combined tracers of Evans blue albumin and gadolinium or horseradish peroxidase was administered intravenously as a tracer. After the animals were euthenized, we compared gadolinium-enhanced MR images with Evans blue albumin distribution in the nerve under fluorescence microscopy. The horseradish peroxidase-injected specimens were observed by transmission electron microscopy.
Results: On enhanced MR imaging, intraneural enhancement was caused by 60- and 90-g-force compression after 1 hour. Marked extravasation of protein tracers in the nerve occurred where there was compression by 60- and 90-g-force compression, and capillaries in the nerve showed the opening of tight junction and an increase of vesicular transport under the electron microscopy. This situation indicated breakdown of the blood-nerve barrier, with consequent edema formation and was seen as enhancement on MR imaging.
Conclusion: Gadolinium-enhanced MR imaging can detect morphologic and functional changes of blood-nerve barrier in the nerve induced by mechanical compression.