Surgical and radiologic anatomy : SRA
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Image interpretation during ultrasound guided interscalene nerve blocks might be difficult and misleading due to rare anatomical variations of the sternocleidomastoid muscle. ⋯ As this muscle crosses at a level, where ultrasound guided interscalene blocks are performed, this unusual structure might lead to misinterpretation of the confusing ultrasound image, resulting in misguided needle positioning and consecutive inefficiency of the block technique.