SUMMARY:High-resolution MR imaging of peripheral nerves is becoming more common and practical with the increasing availability of 3T magnets. There are multiple reports of MR imaging of peripheral nerves in compression and entrapment neuropathies. However, there is a relative paucity of literature on MRN appearance of diffuse peripheral nerve lesions. We attempted to highlight the salient imaging features of myriad diffuse peripheral nerve disorders and imaging techniques for MRN. Using clinical and pathologically proved relevant examples, we present the MRN appearance of various types of diffuse peripheral nerve lesions, such as traumatic, inflammatory, infectious, hereditary, radiationinduced, neoplastic, and tumor variants.ABBREVIATIONS: CIDP ϭ chronic inflammatory demyelinating polyneuropathy; CMT ϭ CharcotMarie-Tooth; fat sat ϭ fat saturated; FLAIR ϭ fluid-attenuated inversion recovery; FLH ϭ fibrolipomatous hamartoma; GBS ϭ Guillain Barré syndrome; CMT/HSMN ϭ Charcot-Marie-Tooth/hereditary motor and sensory neuropathy; MMN ϭ multifocal motor neuropathy; MPNST ϭ malignant peripheral nerve sheath tumor; MRN ϭ MR neurography; NF1 ϭ neurofibromatosis type 1; NL ϭ neurolymphomatosis; SE ϭ spin-echo; SNR ϭ signal-to-noise ratio; SPACE ϭ sampling perfection with application-optimized contrasts by using different flip angle evolutions; SPAIR ϭ spectralattenuated inversion recovery; STIR ϭ short-tau inversion recovery; T1WI ϭ T1-weighted imaging; T1WIFS ϭ T1-weighted fat-saturated imaging; T2WI ϭ T2-weighted imaging; T2WIFS ϭ T2-weighted fat-saturated imaging H igh-resolution MR imaging of peripheral nerves is becoming more common and practical with increasing availability of 3T magnets. These magnets provide high SNR, which can be used for a quicker acquisition time as well as higher image contrast and resolution. There have been multiple reports of MR imaging of peripheral nerves in compression and entrapment neuropathies.1-3 However, there is a relative paucity of literature on the MRN appearance of diffuse peripheral nerve lesions. 4 These lesions seen on MR imaging present a diagnostic dilemma because a long list of pathologies could be causing them. We attempt to highlight the salient imaging features of myriad diffuse peripheral nerve disorders and to describe a diagnostic approach to these lesions on the basis of the available literature and our experience in this area. Various clinical and pathologically proved relevant examples of these pathologies are illustrated. . T1WI demonstrates fat planes delineating the normal nerve (perineural fat). C, Axial STIR SPACE at the level of the thighs shows an abnormal sciatic nerve. Notice the enlarged size and T2 hyperintensity of the fascicles. The dark rim of perineural fat is also disrupted. Also note posterior compartment denervation muscle edema (arrows).

SUMMARY: MR imaging of peripheral nerves has been described in relation to abnormalities such as nerve injury, entrapment, and neoplasm. Neuroma formation is a known response to peripheral nerve injury, and here we correlate the MRN appearance of postinjury neuroma formation with intraoperative findings. We also present the MR imaging features of surgical treatment with a synthetic nerve tube and nerve wrap on postoperative follow-up imaging.ABBREVIATIONS: MRN ϭ MR neurography; NIC ϭ neuroma in continuity; SPACE ϭ sampling perfection with application optimized contrasts by using different flip angle evolutions; SPAIR ϭ spectral adiabatic inversion recovery; STIR ϭ short tau inversion recovery P eripheral nerve injuries and entrapments may lead to formation of NIC, neuroma in completely severed nerves, and amputation neuroma. These lesions also demonstrate unique MRN appearances. This article presents MRN and surgical correlations of various posttraumatic neuromas with relevant case examples.

It has been proposed in the literature that the Neuber relation be modified to read Kε/Kt×(Kσ/Kt)m=1 in order to improve its predictive capability when plane strain loading conditions exist. Kε, Kσ, and Kt are respectively the strain, stress, and elastic concentration factors. The exponent m is proposed to be 1 for plane stress and 0 for plane strain. This paper reports the results of biaxial notch root strain measurements on three sets of double-notched aluminum specimens that have different thicknesses and root radiuses. Elastoplastic strains are measured over gage lengths as short as 150 micrometers with a laser-based in-plane interferometric technique. The measured strains are used to compute Kε directly and Kσ using the uniaxial stress-strain curve. The exponent m can then be determined for each amount of constraint. The amount of constraint is defined as the negative ratio of lateral to longitudinal strain at the notch root and determined from elastic finite element analyses. As this ratio decreases for the three cases, the values of m are found to be 0.65, 0.48, and 0.36. The modified Neuber relation is an improvement, but discrepancies still exist when plastic yielding begins at the notch root.

A preceding paper reported the results of biaxial strain measurements at the roots of notched aluminum specimen subjected to monotonic tension loading. The specimens had different amounts of constraints at the notch root, and it was shown that a modified version of the Neuber relation gave some improvement in its predictive capability. Several of those specimens were also subjected to fully reversed cyclic loading until microcracks formed at the notch roots, and the results of those biaxial strain measurements are reported here. The modified Neuber relation in the cyclic form was used to predict the strains at the notch roots. Reasonably close agreement between the predicted and the measured load-strain loops was found for all three levels of constraint.

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