International Journal of Health Sciences and Research www.ijhsr.org ISSN: 2249-9571 Case Report Accessory Pectoralis Muscle Intervening Between Pectoralis Major and Minor Muscles - A Case Report Jyothsna Patil, Naveen Kumar, Swamy Ravindra S, Somayaji SN, Satheesha Nayak B, Mohandas Rao KG Melaka Manipal Medical College (Manipal Campus), Manipal University, Manipal. India Corresponding Author: Naveen Kumar, Department of Anatomy, Melaka Manipal Medical College (Manipal Campus) Manipal University, Manipal. India. Received: 07/12//2013 Revised: 06/01/2014 Accepted: 13/01/2014 ABSTRACT Pectoral region is known to show the presence of accessory muscles. Functionally these muscles are regarded as insignificant, but their presence sometime causes confusions in the interpretation of radiologic procedures. One such anomalous accessory pectoralis muscle we would like to report here. This muscle was found between pectoralis major and minor muscles of left pectoral region, separated from them by a thin layer of fascia. It originated from the outer surface of left 4th rib and upper aspect of its costochondral junction. It fused with the deeper fibers of pectoralis major muscle near its insertion. Existence of such accessory muscles is rarely noted during diagnostic imaging techniques, prior knowledge of its occurrence is important for surgeons to achieve suitable dissection planes during surgery of the chest wall. Key words: Accessory pectoralis, sternalis, pectoralis quartus, pectoralis intermedius INTRODUCTION and lateral pectoral nerves of brachial In normal description pectoralis plexus. major and pectoralis minor contribute to the Frequent variations pertaining to formation of the chest wall. The pectoralis pectoral region includes axillary arch of major muscle is a thick triangular muscle Langer in which a slip originating from the that usually arises from the medial half of anterior border of latissimus dorsi and the clavicle, the sternum, and the first 6 inserting into the biceps fascia. Slightly costal cartilages. From these origins it variant form of such muscle but arising from combines to form a tendon that inserts to the pectoralis major itself and similar insertion lateral lip of bicipital groove of the humerus. is regarded as chondrohumeralis (Lama et The pectoralis minor is a thin muscle lying al, 2010). Presence of this accessory slip deep to the major; arises from upper margins may compress the axillary neurovascular of outer surfaces of 3rd to 5th ribs near their structures leading to associated clinical costal cartilages and inserted into medial complications. At times, there may be border of upper surface of coracoid process accessory muscular slips that lie on the as a flat tendon (Standring et al, 2005). Both anterior thoracic wall with or without the muscles are innervated by the medial causing clinical complications. In the International Journal of Health Sciences & Research (www.ijhsr.org) 198 Vol.4; Issue: 2; February 2014 present case we are reporting an accessory DISCUSSION pectoral muscle intervening between Several cases of additional muscle in pectoralis major and minor muscles with the pectoral region have been reported. atypical attachments makes it unique among These include the following: a sternalis other similar accessory muscles reported in muscle, which runs parallel to the sternum the literature. (Loukas et al, 2004); a pectoralis quartus muscle which arises from the rectus sheath CASE REPORT (Bonastre et al, 2002), runs parallel to the During routine dissection of pectoral pectoralis major muscle and inserts into the region for medical undergraduate students, tendon of the pectoralis major. we observed an accessory slender muscular Nonexistence of pectoralis major muscle slip lying deep to pectoralis major muscle either as an isolated anomaly or in and superficial to pectoralis minor muscle. association with congenital syndromes as A thin layer of fascia separated this muscle. classically referred to Poland syndrome was It was separated from pectoralis minor and reported in the literature in 1962 (Katherine major muscles by a thin layer of fascia. It et al, 2012). However, patients diagnosed as originated from the outer surface of left 4th Poland syndrome with normal pectoralis rib and upper aspect of left 4th costochondral musculature but with malformated breast junction (Figure). As this muscle took its structure has been reported by Spear et al origin proximal to the origin of pectoralis (2004). Such case has been described as minor on the 4th rib, its origin was deep to anterior thoracic hypoplasia. A rare case of pectoralis major muscle. However, as it agenesis pectoral muscle associated with extended obliquely upwards and laterally it malformation of the ear was reported by intervened between pectoralis major and Cilingir et al (2004) minor muscles before fuse with the deep Accessory pectoral muscles exhibit surface of pectoralis major muscle distally. their presence in two forms. Either they are This unilateral accessory muscle was about present anterior to pectoralis major as 15 cm long and encountered on left anterior superficial muscles of pectoral region, or chest wall of an adult male cadaver aged intervene between pectoralis major and about 60 years. minor muscles. Accessory pectoral muscles of superficial group is often termed as sternalis muscle which runs vertically, parallel and lateral to the sternum, anterior to pectoralis major. This accessory muscle is sometime regarded as the variant form of pectoralis major muscle when it gets its nerve supply from pectoral nerve. Rarely, it is innervated by intercostal nerves. In such condition it is considered as an aberrant abdominal muscle (O’Neil & Folan, 1998). Accessory pectoral muscles intervening between pectoralis major and minor muscles are of several varieties. Figure 1: Dissection of left pectoral region showing the Pectoralis minimus, an anomalous slip, lie presence of accessory pectoralis muscle (APM) originating deep to pectoralis major and superomedial to from left 4th rib and blending with the pectoralis major muscle (reflected upwards). pectoralis minor. Presence of this muscle International Journal of Health Sciences & Research (www.ijhsr.org) 199 Vol.4; Issue: 2; February 2014 usually causes vascular symptoms with the asymptomatic but its presence might be hyperextension of arm. This is because encountered during certain clinical thoracoacromial vessels lie deep to this approaches. As these muscular variations are variant slip of muscle (Rai et al, 2008). rarely noted during diagnostic imaging Pectoralis quartus, exists as a long flat techniques, prior knowledge of its presence tendon originating from costochondral is important for surgeons to achieve suitable junction of 5th and 6th rib pass under the dissection planes during surgery of the chest pectoralis major to insert into the inter- wall. tubercular groove of the humerus (Arican et al, 2006). Pectoralis intermedius in contrary REFERENCES to this arises from 3rd and 4th ribs and Standring S, Ellis H, Healy C, merges with the tendon of short head of Johnson D, Williams A (2005) Grays biceps brachii (Arican et al, 2006). Loukas anatomy. 39th Ed. 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