Selective Fascicular Injury of the Median Nerve after Arterial Catheterization: A Case Report with Diagnostic and Interventional Insights from Ultrasonography

Proximal median neuropathy after arterial catheterization is rare and may present with misleading clinical features. We report a 50-year-old man who developed isolated index-finger flexion weakness following brachial arterial line insertion. Electrodiagnostic studies were contraindicated. Ultrasonography revealed focal median nerve enlargement with a fascicular-level intraneural hematoma. Ultrasound-guided hydrodissection using 5% dextrose water resulted in clinical improvement and hematoma reduction. This case highlights the diagnostic and therapeutic value of ultrasonography in identifying selective fascicular injury and guiding minimally invasive treatment when electrodiagnostic evaluation is not feasible.