• Georg C Feigl and Thomas Pixner.
• Institute of Anatomy, Medical University Graz, Harrachgasse 21, 8010, Graz, Austria. georg.feigl@medunigraz.at
• Surg Radiol Anat. 2011 Nov 1;33(9):823-5.

IntroductionImage interpretation during ultrasound guided interscalene nerve blocks might be difficult and misleading due to rare anatomical variations of the sternocleidomastoid muscle.Case ReportDuring a routine dissection, we found a cleidoatlanticus muscle, which originated lateral to the regular cleidomastoid portion of the sternocleidomastoid muscle. This muscle separated from the sternocleidomastoid muscle at level of the dorsally crossing omohyoid muscle to fuse with the levator scapulae muscle's origin at the transverse process of the atlas.ConclusionAs 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.

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