Sonography images demonstrated a lesion encased the swollen median nerve. (A) The transverse sonogram shows a round hypoechoic halo with well-defined margins and posterior acoustic enhancement completely surrounded the swollen median nerve. The brachial artery was partially encased, while the basilic vein and ulnar nerve were unaffected. (B) The longitudinal sonogram shows the mass extended along the median nerve. The swollen nerve shows hypoechoic echotexture lesion with discernible fascicles. The adjacent biceps brachii muscle with inhomogeneous-reduced echogenity is noted. (C) Avascularity could be visualized on the color Doppler image inside the mass. (D) Slightly increased vascularity is observed on color doppler sonography in biceps brachii muscle adjacent to the lesion.