Sternalis muscle also called rectus sternalis, rectus thoracis, or episternalis is an anomalous muscle of the anterior chest wall with unknown anatomical function. It is regularly observed in lower animal but infrequently in humans. Presence of this muscle can create confusion with tumours of the anterior chest wall during routine mammography. Although less is known about its origin and innervations, knowledge about this muscle can have many clinical implications. A case of unilateral sternalis muscle detected during mastectomy, in a female with carcinoma of the right breast, is being reported with a brief review of the literature and highlighting its clinical significance.
Sternalis muscle is an uncommon anatomical variant of anterior chest wall muscles [
A 39-year-old female patient presented to the Surgical Outpatient Department of AIIMS, Bhubaneswar, with a right breast lump of approximately 3 cm in diameter. On evaluation she was found to have a T2N1M0 carcinoma in her right breast. After a detailed workup she was posted for modified radical mastectomy of the right breast. During mastectomy a thin ribbonlike muscle was found in the parasternal area with its fibres oriented craniocaudally, parallel to the sternum and perpendicular to the fibres of the right pectoralis major muscle (Figure
(a) Intraoperative photograph showing a thin fleshy ribbonlike muscle of size approximately 10 cm × 3 cm present in the right parasternal region perpendicular to fibres of the pectoralis major muscle. PM: pectoralis major, SM: sternalis muscle. (b) MRI of anterior chest wall (post-MRM) showing a unilateral sternalis muscle (white arrow) in transverse section.
In 2001, Jelev et al. defined the characteristics of the muscle as (1) location between the anterior thoracic fascia and pectoral fascia, (2) origin from the sternum or infraclavicular area, and (3) its insertion into the rectus sheath, lower ribs, costal cartilages, or external oblique aponeurosis [
Since its discovery different theories have been proposed to explain its embryological origin although the consensus is still lacking. Most of the authors support its origin from one among the adjacent muscles such as pectoralis major, rectus abdominis, sternocleidomastoid, or panniculus carnosus [
During routine mammography sternalis muscles can be mistaken for a tumour in the craniocaudal view during initial investigation or as a recurrence during follow-up in the postoperative period. Presence of this muscle can be confirmed by computed tomography (CT) or magnetic resonance imaging (MRI) and craniocaudal view in mammography [ It may be confused with hernia of the major pectoralis muscle by the examining clinician [ During radiotherapy the depth at which internal thoracic nodes are irradiated may vary in presence of this muscle [ Presence of sternalis muscle can cause changes in electrical activities during electrocardiography [ It may interfere with submuscular pocket dissection when a submammary approach is used during augmentation mammoplasty [ During oncological procedures it is important to excise this muscle as part of breast tissue lies deep in it [ It can also be used to cover prosthesis in the most medial part during augmentation mammoplasty [ If detected preoperatively sternalis muscle can be used in reconstructive surgery [
The last few decades have witnessed a lot of advances in medical science in the form of new diagnostic and therapeutic modalities. Because of this there is high probability that sternalis muscle will be detected more frequently than before. Although well known to anatomist it is relatively unfamiliar among surgeons and radiologists. Presence of this muscle can cause diagnostic dilemma which can be confirmed by CT or MRI scan. If detected preoperatively it can be used in various reconstructive procedures during surgery. When detected intraoperatively during mastectomy for carcinoma of the breast, it should ideally be removed for complete clearance of the breast tissue.
Written and informed consent was taken from the patient for publication of this case report.
The authors declare that there is no conflict of interests regarding the publication of this paper.
Dr. Prakash K. Sasmal and Dr. Susanta Meher collected the data and prepared the paper. Dr. Tushar S. Mishra, Dr. Satyajit Rath, Dr. N. Deep, and Dr. Prabhas R. Tripathy critically revised the final version of the paper.