Sternalis muscle

The sternalis muscle (also known as rectus sternalis or parasternalis muscle) is a rare anatomical variant located in the anterior thoracic wall, lying superficial to the pectoralis major muscle. It typically runs vertically parallel to the sternum within the parasternal region and may be present unilaterally or bilaterally.

Anatomical features

The muscle demonstrates marked variability in its attachments:

1. Origin

Sternalis muscle may arise from the upper sternum, clavicle, or sternocleidomastoid fascia.

2. Insertion

Inferior attachments may involve the pectoralis fascia, rectus sheath, external oblique aponeurosis, or lower ribs and their costal cartilages.

Neurovascular Supply

1. Innervation

Primarily via intercostal nerves, with occasional contribution from pectoral nerves.

2. Blood supply

Likely derived from perforating branches of the internal thoracic vessels.

Function

The sternalis muscle is generally considered to be functionally insignificant.

Clinical Relevance

The sternalis muscle is most often identified as an incidental finding during imaging or cadaveric dissection. Its significance lies in its potential to mimic pathological masses, particularly in breast imaging (e.g., mammography and CT), where it may be mistaken for breast tumours or chest wall lesions.

From a surgical perspective, it may be encountered during breast or thoracic procedures and can occasionally be utilised as a muscle flap.

Therefore, awareness of this variant is essential for both radiologists and surgeons to prevent diagnostic errors and guide appropriate clinical management.