Abstract
Peripheral neuropathies account for the most frequent disorders seen by neurologists, and causes are manifold. The traditional diagnostic gold-standard consists of clinical neurologic examinations supplemented by nerve conduction studies. Due to well-known limitations of standard diagnostics and atypical clinical presentations, establishing the correct diagnosis can be challenging but is critical for appropriate therapies. Magnetic resonance neurography (MRN) is a relatively novel technique that was developed for the high-resolution imaging of the peripheral nervous system. In focal neuropathies, whether traumatic or due to nerve entrapment, MRN has improved the diagnostic accuracy by directly visualizing underlying nerve lesions and providing information on the exact lesion localization, extension, and spatial distribution, thereby assisting surgical planning. Notably, the differentiation between distally located, complete cross-sectional nerve lesions, and more proximally located lesions involving only certain fascicles within a nerve can hold difficulties that MRN can overcome, when basic technical requirements to achieve sufficient spatial resolution are implemented. Typical MRN-specific pitfalls are essential to understand in order to prevent overdiagnosing neuropathies. Heavily T2-weighted sequences with fat saturation are the most established sequences for MRN. Newer techniques, such as T2-relaxometry, magnetization transfer contrast imaging, and diffusion tensor imaging, allow the quantification of nerve lesions and have become increasingly important, especially when evaluating diffuse, non-focal neuropathies. Innovative studies in hereditary, metabolic or inflammatory polyneuropathies, and motor neuron diseases have contributed to a better understanding of the underlying pathomechanism. New imaging biomarkers might be used for an earlier diagnosis and monitoring of structural nerve injury under causative treatments in the future.
Highlights
Peripheral neuropathies are among the disorders that are most frequently seen by neurologists and can manifest as mono, multifocal- or polyneuropathies
In the same pilot study, T2 relaxometry was applied in the PNS for the first time and the two quantitative imaging markers T2app and ρ were calculated, showing highly specific alterations for each group: while asymptomatic variant transthyretin gene (varTTR)-carriers were characterized by an increase of ρ only, manifest ATTRv amyloidosis was characterized by an increase of both ρ and T 2app
The results demonstrated that a decreasing sciatic nerve magnetization transfer ratio (MTR) correlated with increasing clinical severities in ATTRv amyloidosis as determined by the Neuropathy Impairment Score of the Lower Limb (NIS-LL)
Summary
Peripheral neuropathies are among the disorders that are most frequently seen by neurologists and can manifest as mono-, multifocal- or polyneuropathies. In a more recent study conducted in healthy volunteers of different ages, results excluded a significant MTR gradient along the sciatic and tibial nerve at the lower extremities, making MTC imaging a more reasonable technique that does not require standard values for each and every nerve segment when applied in different peripheral neuropathies [63].
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