The ulnar nerve is a branch of the C8 and T1 nerve roots and arises from the medial cord of the brachial plexus. It supplies the intrinsic muscles of the hand and assists the median nerve in functioning of the flexors. Also known as the musician’s nerve, it is the second most common nerve involved in compressive neuropathy following the median nerve. Common sites of entrapment include cubital tunnel at the elbow, the ulnar groove in the humerus and the Guyon’s canal at the wrist. Patients present with altered sensation in the ulnar fourth and the fifth digit and the medial side of arm with loss of function of intrinsic muscles of the hand, the flexor carpi ulnaris and ulnar fibres of flexor digitorum superficialis in more severe cases. Diagnosis relies on clinical examination, electrodiagnostic studies and imaging findings. Plain radiographs are used to identify fracture sites, callus, or tumours as cause of compression. Technological advances in ultrasonography have allowed direct visualisation of the involved nerve with assessment of exact site, extent and type of injury. It yields unmatched information about anatomical details of the nerve. MR imaging adds to soft tissue details and helps in characterising the lesion. This pictorial review aims to illustrate a wide spectrum of causes of ulnar neuropathies as seen on ultrasound and MRI and emphasises upon the importance of imaging modalities in the diagnosis of neuropathies.

PurposePeripheral neuropathies are a group of disorders which affect the peripheral nervous system which have been conventionally diagnosed using electrodiagnostic studies. This study was carried out to assess the role of imaging in diagnosing peripheral mononeuropathy as exact anatomical localisation of the pathology is possible using high-resolution ultrasound and MR neurography, the modalities assessed in this study.MethodA hospital-based prospective analytical study was carried out in a resource-limited setting on 180 peripheral nerves in 131 patients with symptoms of peripheral mononeuropathy after taking IRB approval. Each patient underwent high-resolution ultrasound examination and MR neurography, findings of which were then compared and statistically analysed assuming electrodiagnostic findings as the gold standard.ResultsOverall, the diagnostic accuracy was highest for the proton density fat-saturated MR sequence (93.89%) followed by high-resolution ultrasound (80%). The sensitivity was highest for proton density fat-saturated sequence while the T1 MR sequence had the highest specificity. Combined diagnostic accuracy of both modalities was calculated to be 93.33% with a negative predictive value of 80%. High-resolution ultrasound and MRI equally detected the cases with nerve discontinuity, while neuromas were better identified on MRI.ConclusionWith the advent of higher frequency probes and improved MR field strength, imaging of peripheral nerves is possible with better accuracy. Imaging assessment of nerves allows anatomical delineation with identification of exact site of involvement. This comparative study demonstrates the role of imaging in diagnosing peripheral nerve pathologies with the accuracy of MRI as high as 93.89% which may serve as an imaging gold standard. High-resolution ultrasound, being quicker, cost effective and a comparable accuracy of 80% can serve as a reliable screening tool. This study incorporates a larger study group and compares HRUS with MRI, taking NCV as gold standard, which has not been done in the preceding studies. With this study, we conclude that these two imaging modalities are not mutually exclusive. Rather, they complement each other and can be used in conjunction as an imaging yardstick for diagnosing peripheral neuropathies.Electronic supplementary materialThe online version of this article (10.1186/s13244-019-0787-6) contains supplementary material, which is available to authorized users.

The radial nerve has a long and tortuous course in the upper limb. Injury to the nerve can occur due to a multitude of causes at many potential sites along its course. 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. Signs and symptoms of radial neuropathy depend upon the site of injury. 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’. 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. Involvement of only the posterior interosseous nerve (PIN) results in weakness of the wrist and digit extensors. Diagnosis relies on clinical examination, electrodiagnostic studies and imaging findings. Plain radiographs are used to identify fracture sites, callus or tumours as cause of compression. Technological advances in ultrasonography have allowed direct visualisation of the involved nerve with assessment of the exact site, extent and type of injury. It yields unmatched information about anatomical details of the nerve. MR imaging adds to soft-tissue details and helps in characterising the lesion. 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.Teaching Points• Radial nerve injuries are assessed by clinical examination and diagnosed using electrodiagnostic and imaging studies.• Knowledge of anatomical relations and course of the nerve is necessary to identify the nerve at pre-determined anatomical locations.• Altered echogenicity and signal intensity, discontinuity of the nerve, focal thickening and cause of compression can be assessed by imaging modalities.• MR imaging helps in confirmation of the ultrasound findings, differentiating similar appearing lesions and provides additional soft-tissue details.

Fibroma of tendon sheaths (FTS) is an uncommon soft tissue tumour which arises from the synovial sheath of tendons. We report a histologically proven case with intrarticular 'fibroma of tendon sheath' originating from the joint capsule of the knee, an even rarer entity, in a middle-aged female presenting with knee pain, swelling with limited range of motion. MRI and arthroscopy studies revealed an intraarticular mass originating from the synovial membrane with lobulated contours. Open excision was performed because of the large size of the mass, making it inaccessible arthroscopically. The patient is symptom free since the surgery done 15 months back.