Uncommon Variation in Musculature of the Chest wall

Deepthi Simhadri

doi:10.4172/2161-0940.1000113

Abstract

Occasionally a vertical strip of muscle is seen at the lateral border of sternum, which is named as ‘Rectus sternalis (sternalis) muscle’. This muscle is considered as part of the vertical strip of muscles (strap muscles present from chin to pubis). A rare case of unilateral right sided sternalis muscle was found during routine dissection of human male cadaver at Kamineni Institute of Medical Sciences, Narketpally. The early detection of this variant muscle is necessary for assessing in radiological examination. Here by we report a case of right unilateral rectus sternalis muscle. Knowledge of variations occurring in the muscular system is of great importance to the surgeons and professionals who works with imaging. An unusual variation in chest wall rectus sternalis, it can be confused for a mass on mammography, but confusion revolved by computerised tomography/magnatic resonance imaging. It has unclear embryonic origin, perhaps a remnant of the panniculus carnosus. It is an unusal muscle found occasionally in the anterior part of the thorax. This variation was found in a male cadaver during routine dissection, it belongs to a muscle of pectoral group. It was found in 8% of population. This muscle is called as rectus sternalis, rectus means straight; it lies parallel to the lateral border of sternum on right side, absent in left side. It is an accessory muscle of the chest wall; it is useful for reconstruction of the neck, chest, abdomen, and perhaps even other places. At last, sternalis may be nothing more than misplaced developed muscle tissue, arising from variable sources in a localised region at the anterior thorax, and serving no apparent function but to be fuddle diagnosticians. Therefore, familiarity of the sternalis only broadens the surgeon’s knowledge of variations of chest wall anatomy but also provides reconstructive operations (when present) for wounds in the chest wall as well as adjacent regions. It may be bilateral (or) unilateral. It is a rare variation.

Highlights

The muscular part of the chest wall is derived from myotome
Folan-Curran reviewed the literature and found that 55% of the sternalis muscles were innervated by branches of the internal and external thoracic nerves, 43% by branches of the inter-costal nerves and 2% both from the inter costal and thoracic nerves
According to Jelev et al [8] (Figure 3) Classification of rectus sternalis: Type-A: The rectus sternalis muscle lies on rightside, at lateral border of sternum, left side is absent

Summary

Introduction

The muscular part of the chest wall is derived from myotome. In the abdominal region, the muscles arrange into three layers. Superficial to the pectoralis major, some muscle fibres may pass vertically from the lower costal cartilages and rectus sheath to blend above with the sternocleidomastoid, (or) to be attached to the upper sternum (or) costal cartilages. These fibers may constitute the sternalis muscle (or) the rectus sternalis [2]. A superficial variant slip (or) slips may arise from the lower costal cartilages and rectus sheath to blend with sternocledomastoid muscle (or) to attach to the sternum (or) costal cartilages Its caudal end blends with fascia of rectus abdominis, 4 cm lateral to midsternal line at the level of 7th to 8th costal cartilages, this was innervated by anterior cutaneous branches of second inter costal nerve (Figures 1 and 2)

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Discussion

Conclusion