Bilateral supernumerary sternocleidomastoid heads with critical narrowing of the minor and major supraclavicular fossae: Clinical and surgical implications
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Extract: Anatomical variations of the sternocleidomastoid muscle are rare and concern its origin, insertion, and the number of heads. We report on a rare bilateral variant of the sternocleidomastoid muscle with aberrant and supernumerary muscular heads, observed in a cadaveric subject. On the right side of the neck, a typical sternomastoid head of the sternocleidomastoid muscle, and three aberrant clavicular heads of variable thickness, origin, and termination were noticed. On the left side, two sternomastoid heads were present; the medial one was of typical pattern, while the lateral was supernumerary. The cleidomastoid portion of the left sternocleidomastoid muscle was fused with the double sternomastoid segment. A strap-like muscle originating from the middle third of the clavicle and inserting onto the transverse process of the C3 vertebra was noticed. This is known as the cleidocervical muscle. On the right side of the neck, the posterior cervical triangle was diminished, the minor supraclavicular fossa was considerably narrow, whereas on the left, it was diminished in addition to a bilateral shortening of the major supraclavicular fossa minimizing space needed for potential surgical access. These findings are of prominent significance for anesthetists in ultrasound guided needle positioning in brachial plexus block, as well as in subclavian or external jugular vein catheterization, and in surgical interventions involving structures lying under the sternocleidomastoid muscle.
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