A 34-year-old female presents with a history of a bicycle fall directly onto her left upper arm 3 days before. She now exhibits an incomplete wrist drop (partial "fall hand").
The presented MRI images include coronal T2-weighted, fat-saturated on the left and transaxial T1-weighted (plain on the top and contrast-enhanced, fat-saturated on the bottom).
What are the MRI findings, and which is your final diagnosis?
Radial nerve contusion (neurapraxia) secondary to direct trauma
A mild humeral bone marrow edema is associated.Imaging findings:
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The coronal T2-weighted, fat-saturated images demonstrate diffuse hyperintense signal changes along the course of the radial nerve, consistent with nerve edema. The transaxial T1-weighted fat-saturated images further reveal increased contrast enhancement of the radial nerve, suggesting post-traumatic inflammation.
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Coronal views depict patchy areas of bone marrow edema within the humeral diaphysis on T2-weighted, fat-saturated images, likely resulting from contusion.
The clinical presentation of incomplete wrist drop alongside the imaging findings strongly points to a radial nerve contusion (neurapraxia) secondary to blunt trauma. Neurapraxia is the mildest form of nerve injury in the Seddon classification, characterized by transient loss of conduction without axonal disruption. The presence of nerve edema and enhancement on MRI supports this diagnosis. It is important to note that normal (unaffected) peripheral nerves can also present with slight hyperintensity in T2-weighted images. Only contrast enhancement is able to definitively indicate a contusion or compression of a peripheral nerve. Other potential causes of wrist drop, including fractures, compartment syndrome, or compressive neuropathies, should be ruled out.
Neurapraxia usually resolves spontaneously with conservative treatment, including immobilization and physical therapy. Repeat imaging may be warranted in cases of delayed recovery to exclude nerve entrapment or neuroma formation.
