A previously unclassified variant of sternalis muscle.

PURPOSE: We propose an addition to the Snosek et al. classification to include a subtype variant of sternalis muscle: mixed type and triple subtype.

METHODS: Dissection of the anterior thorax of a 96-year-old female cadaver revealed bilateral sternalis muscles with an undocumented variant of the right sternalis muscle.

RESULTS: The left sternalis muscle presented as a simple type-left single using the Snosek et al. classification scheme. The right sternalis muscle revealed a previously undocumented classification type. It consisted of three bellies and two heads, with the lateral head formed by two converging bellies and the medial head formed from the superficial medial belly.

CONCLUSIONS: The unique presentation of right sternalis muscle can be classified by expanding the Snosek et al. classification scheme to include triple-bellied subtypes. This presentation is classified as a mixed type-right triple, with single bicipital converging and single bicipital diverging. Documentation of sternalis muscle variations can prevent misdiagnoses within the anterior thorax.