Two unilateral sternalis muscles with distinct fascial compartmentalization: anatomical evidence and potential...

The sternalis muscle is an uncommon anatomical variant of the anterior thoracic wall. Its presence is clinically relevant due to potential misinterpretation in imaging and unexpected findings during surgical procedures.

During routine cadaveric dissection, two sternalis muscle variants were identified in the anterior thoracic walls of two male cadavers aged 75 and 39 years, respectively. A detailed morphological, topographic, and morphometric analysis was performed.

Two unilateral sternalis muscles were identified in the right parasternal region of the anterior thoracic wall, located superficial to the pectoralis major and separated from it by a distinct fascial plane allowing blunt dissection. The first (75-year-old donor) muscle measured approximately 71 mm in length, with a width ranging from 8 to 14 mm. The second specimen demonstrated a larger muscular structure measuring approximately 132 mm in length, with a maximal width of 39 mm and a proximal tendinous attachment to the manubrium sterni measuring approximately 11 mm. Inferiorly, both muscles blended with the anterior rectus sheath without a clearly defined distal tendon. In the second specimen, small segmental vascular branches arising from the internal thoracic system were identified.

These cases provide anatomical evidence of a reproducible fascial- muscular organization of the sternalis muscle and highlight its potential surgical relevance.