High-resolution Ultrasonography and Magnetic Resonance Imaging of Ulnar Nerve Neuropathy Beyond the Guyon Tunnel: Examination

Purpose or Learning Objective: Ulnar nerve (UN) neuropathy is the second most common upper limb neuropathy with an incidence of ~ 30 per 100,000 person-years. In most cases it affects both motor and sensory axons, leading to a mix of sensitive and motor impairment. Atypical syndromes with selective involvement of the superficial sensory branch (SSB) and deep motor branch (DMB) of UN are found in a minority of patients and may represent a clinical challenge due to unusual symptoms and confounding electrodiagnostic results. We aimed to (1) assess the prevalence of DMB and SSB damage in a consecutive series of patients’ electrophysiologic evidence of UN mononeuropathy; and (2) illustrate ultrasonography (US) and magnetic resonance imaging (MRI) findings and determine the value of these modalities in the diagnostic work-up of these conditions.

Methods or Background: We prospectively recruited a consecutive series of patients submitted to the Radiology Unit of the IRCCS Ospedale Policlinico San Martino during the diagnostic work-up of UN neuropathy. We excluded patients who had symptoms, imaging, or electrophysiologic evidence suggesting nerve damage. US was performed in all patients with two different machines depending on availability (iU22 platform, Philips Healthcare, Bothell, WA, USA, and i800 Aplio platform, Canon Medical Systems, Ōtawara, Japan). US systems were equipped with 17–5 MHz, 18–4 MHz, and 24–8 MHz linear transducers or a 22–8 MHz hockey-stick probe. MRI was performed on a 3-T unit equipped with 64-channel head radiofrequency coils (Magnetom Prisma, Siemens, Erlangen, Germany).

Results or Findings: Among a total of 166 patients included in this study, 15 (9%; 7 men; mean age: 57 years) were definitively diagnosed with SSB and DMB neuropathy. Imaging identified two entrapment neuropathies, four compressions by ganglion cysts, seven traumatic injuries, and two tumors. Thirteen (86.6%) patients with SSB/DMB neuropathy had already been examined with electrodiagnostic tests; US was requested due to the inconclusiveness of previous evaluations. In 12 (80%) cases, US led to a definite diagnosis; 3 (20%) patients underwent MRI to integrate US results.

Conclusion: SSB and DMB neuropathies are frequently overlooked conditions. Even if electrophysiology is currently considered the first-line test, it commonly leads to inconclusive results and needs to be integrated with other modalities. US and MRI have great potential in the diagnostic work-up of SSB and DMB neuropathies because they are able to directly demonstrate these submillimetric branches along their entire course and to characterize specific pathologic conditions.

Publication History

Article published online:
26 May 2023