Since then, technological advances like increased frequency and variable sizes of footprints of linear transducers have escalated the use of ultrasound in peripheral nerve pathologies. Ultrasonographic findings of peripheral nerves were first reviewed by Fornage in 1988. Introduction of high-frequency ultrasound probe has made direct visualisation of peripheral nerves possible, thus providing anatomical details about the nerve. Conventionally, neuropathies have been diagnosed on the basis of clinical examination, Tinel’s sign and electrodiagnostic (nerve conduction velocity and electromyography) findings which provide information about the nerve involved and possible site of injury. Clinically, radial neuropathy presents as wrist drop with or without sensory loss along the posterior surface of arm, forearm, thenar eminence and dorsal aspect of radial three and a half digits, depending upon the site of injury. The prevalence of radial nerve palsy following fracture of the humerus shaft is 11.8%, while incidence of iatrogenic injuries is approximately 4.2%. The radial nerve has a long and tortuous course in the upper limb and lies in close proximity to the bone in the spiral groove, making it susceptible to injuries. Radial nerve pathologies include compressive syndromes, entrapment neuropathy, focal intrinsic lesions and peripheral nerve sheath tumours. MR imaging helps in confirmation of the ultrasound findings, differentiating similar appearing lesions and provides additional soft-tissue details.Altered echogenicity and signal intensity, discontinuity of the nerve, focal thickening and cause of compression can be assessed by imaging modalities.Knowledge of anatomical relations and course of the nerve is necessary to identify the nerve at pre-determined anatomical locations.Radial nerve injuries are assessed by clinical examination and diagnosed using electrodiagnostic and imaging studies.This pictorial review aims to illustrate a wide spectrum of causes of radial neuropathy and emphasises the importance of imaging modalities in diagnosis of neuropathies. MR imaging adds to soft-tissue details and helps in characterising the lesion. It yields unmatched information about anatomical details of the nerve. Technological advances in ultrasonography have allowed direct visualisation of the involved nerve with assessment of the exact site, extent and type of injury. Plain radiographs are used to identify fracture sites, callus or tumours as cause of compression. Diagnosis relies on clinical examination, electrodiagnostic studies and imaging findings. Involvement of only the posterior interosseous nerve (PIN) results in weakness of the wrist and digit extensors. Injury in the mid-arm is associated with loss of sensation in the dorsolateral aspect of the hand, the dorsal aspect of the radial three-and-a-half digits and in the first web space. Injury to the nerve distal to innervation of triceps brachii results in loss of extensor function with sparing of function of the triceps resulting in the characteristic ‘wrist drop’. Signs and symptoms of radial neuropathy depend upon the site of injury. The most common site of involvement is in the proximal forearm affecting the posterior interosseous branch while the main branch of the radial nerve is injured in fractures of the humeral shaft. Injury to the nerve can occur due to a multitude of causes at many potential sites along its course. The radial nerve has a long and tortuous course in the upper limb.
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