Pectoral Region Introduction .
The pectoral region lies on the front of the chest. It essentially consists of structures which connect the upper limb to the anterolateral chest wall. Breast lies in this region.
Surface Landmark of Pectoral Region .
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| Surface landmarks: Shoulder, axilla, arm and elbow regions (anterior aspect) . |
The following features of the pectoral region can be seen or felt on the surface of body.
[1]. The clavicle lies horizontally at the root of the neck, separating it from the front of the chest. The bone is subcutaneous and therefore, palpable throughout its length.
[2]. Medially, it articulates with the sternum at the sternoclavicular joint and laterally with the acromion process at the acromioclavicular joint.
[3]. Both the joints are palpable because of the upward projecting ends of the clavicle . The sternoclavicular joint may be masked by the sternocleidomastoid muscle.
[4]. The jugular notch (interclavicular or suprasternal notch) lies between the medial ends of the clavicles, at the superior border of the manubrium sterni.
[5]. The sternal angle (angle of Louis) is felt as a transverse ridge about 5 cm below the jugular notch . It marks the manubriosternal joint. Laterally, on either side, the second costal cartilage joins the sternum at this level.
[6]. The sternal angle thus serves as a landmark for identification of the second rib. Other ribs can be identified by counting downwards from the second rib.
[7]. The epigastric fossa (pit of the stomach) is the depression in the infrasternal angle. The fossa overlies the xiphoid process, and is bounded on each side by the seventh costal cartilage.
[8]. The nipple is markedly variable in position in females. In males and in immature females, it usually lies in the fourth intercostal space just medial to the midclavicular line; or 10 cm from the midsternal line. In fact, the position of the nipple is variable even in males.
[9]. The midclavicular line passes vertically through the middle of clavicle, the tip of the ninth costal cartilage and the midinguinal point.
[10]. The infraclavicular fossa (deltopectoral triangle) is a triangular depression below the junction of the lateral and middle thirds of the clavicle.
[11]. It is bounded medially by the pectoralis major, laterally by the anterior fibres of the deltoid and superiorly by the clavicle.
[12]. The tip of the coracoid process of the scapula lies 2–3 cm below the clavicle, overlapped by the anterior fibres of the deltoid. It can be felt on deep palpation just lateral to the infraclavicular fossa. [13]. The acromion process of the scapula (acron = summit; omos = shoulder) is a flattened piece of bone that lies subcutaneously forming the top of the shoulder.
[14]. The posterior end of its lateral border is called the acromial angle, where it is continuous with the lower lip of the crest of the spine of the scapula.
[15]. The anterior end of its medial border articulates with the clavicle at the acromioclavicular joint. [16]. The deltoid is triangular muscle with its apex directed downwards. It forms the rounded contour of the shoulder, extending vertically from the acromion process to the deltoid tuberosity of the humerus.
[17]. The axilla (Latin armpit) is a pyramidal space between the arm and chest. When the arm is raised (abducted), the floor of the axilla rises, the anterior and posterior folds stand out and the space becomes more prominent.
[18]. The anterior axillary fold contains the lower border of the pectoralis major, and posterior axillary fold contains the tendon of the latissimus dorsi winding round the fleshy teres major.
[19].The medial wall of the axilla is formed by the upper 4 ribs covered by the serratus anterior. The narrow lateral wall presents the upper part of the humerus covered by the short head of the biceps and the coracobrachialis.
[20]. Axillary arterial pulsations can be felt by pressing the artery against the humerus. The cords of the brachial plexus can also be rolled against the humerus.
[21]. The head of the humerus can be felt by pressing the fingers upwards into the axilla.
[22]. The midaxillary line is a vertical line drawn midway between the anterior and posterior axillary folds.
Superficial fascia .
[1]. The superficial fascia (Latin a band) of the pectoral region is visualized after the skin has been incised. It contains moderate amount of fat and is continuous with that of surrounding regions.
[2]. The breast, which is well developed in females, is the most important of all contents of this fascia. The fibrous septa given off by the fascia support the lobes of the gland and the skin covering the gland.
Contents of Superficial Fascia .
In addition to fat, the superficial fascia of the pectoral region contains the following.
1. Cutaneous nerves derived from the cervical plexus and from the intercostal nerves .
2. Cutaneous branches from the internal thoracic and posterior intercostal arteries.
3. The platysma (Greek broad).
4. The breast.
Cutaneous Nerves of the Pectoral Region .
[1]. The medial, intermediate and lateral supraclavicular nerves are branches of the cervical plexus (C3, C4). They supply the skin over the upper half of the deltoid and from the clavicle down to the second rib.
[2]. The anterior and lateral cutaneous branches of the second to sixth intercostal nerves supply the skin below the level of the second rib.
[3]. The intercostobrachial nerve of T2 supplies the skin of the floor of the axilla and the upper half of the medial side of the arm .
[4]. It is of interest to note that the area supplied by spinal nerves C3 and C4 directly meets the area supplied by spinal nerves T2 and T3. This is because of the fact that the intervening nerves (C5–C8 and T1) have been ‘pulled away’ to supply the upper limb.
[5]. It may also be noted that normally the areas supplied by adjoining spinal nerves overlap but because of what has been said above there is hardly any overlap between the areas supplied by C3 and C4 above and T2 and T3 below .
Cutaneous Vessels .
[1]. The cutaneous vessels are very small. The anterior cutaneous nerves are accompanied by the perforating branches of the internal thoracic artery.
[2]. The second, third and fourth of these branches are large in females for supplying the breast. The lateral cutaneous nerves are accompanied by the lateral cutaneous branches of the posterior intercostal arteries .
Platysma .
[1]. The platysma (Greek broad) is a thin, broad sheet of subcutaneous muscle. The fibres of the muscle arise from the deep fascia covering the pectoralis major; run upwards and medially, crossing the clavicle and the side of the neck and are inserted into the base of the mandible and into skin over the posterior and lower part of the face.
[2]. The platysma is supplied by a branch of the facial nerve. When the angle of the mouth is pulled down, the muscle contracts and wrinkles the skin of the neck. The platysma may protect the external jugular vein (which underlies the muscle) from external pressure .
Breast .
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| Extent of the breast . |
[1]. The breast is the most important structure present in the pectoral region. The breast is found in both sexes, but is rudimentary in the male. It is well developed in the female after puberty.
[2]. It forms an important accessory organ of the female reproductive system and provides nutrition to the newborn in the form of milk. Its shape may be hemispherical, conical, pyriform, pendulous or flat.
[3]. The breast lies in the superficial fascia of the pectoral region. It is divided into four quadrants, i.e. upper medial, upper lateral, lower medial and lower lateral.
[4]. A small extension of the upper lateral quadrant called the axillary tail of Spence, passes through an opening in the deep fascia and lies in the axilla . The opening is called foramen of Langer.
[5]. Its base is circular and extends vertically from the second to the sixth ribs & Horizontally from the lateral border of the sternum to the midaxillary line.
[6]. The deep surface of the breast is related to the following structures in that order .
1 The breast lies on the deep fascia (pectoral fascia) covering the pectoralis major.
2 Still deeper there are the parts of three muscles, namely the pectoralis major, the serratus anterior, and the external oblique muscle of the abdomen.
3 The breast is separated from the pectoral fascia by loose areolar tissue called the retromammary space. Because of the presence of this loose tissue, the normal breast can be moved freely over the pectoralis major.
Structure of the Breast.
The structure of the breast may be conveniently studied by dividing it into the skin, the parenchyma, and the stroma. The parenchyma is known as the mammary gland.
Skin .
It covers the gland and presents the following features.
[1]. A conical projection, called the nipple, is present just below the centre of the breast at the level of the fourth intercostal space 10 cm from the midline. The nipple is pierced by 15 to 20 lactiferous ducts.
[2]. It contains circular and longitudinal smooth muscle fibres which can make the nipple stiff or flatten it, respectively. It has a few modified sweat and sebaceous glands. It is rich in nerve supply and has many sensory end organs at the termination of nerve fibres.
[3]. The skin surrounding the base of the nipple is pigmented and forms a circular area called the areola. This region is rich in modified sebaceous glands particularly at its outer margin.
[4]. These become enlarged during pregnancy and lactation to form raised tubercles of Montgomery.
[5]. Oily secretions of these glands lubricate the nipple and areola and prevent them from cracking during lactation. Apart from sebaceous glands, the areola also contains some sweat glands and accessory mammary glands.
[6]. The skin of the areola and nipple is devoid of hair, and there is no fat subjacent to it. Below the areola lie lactiferous sinus where stored milk is seen.
Parenchyma (Mammary Gland) .
[1]. Mammary gland is a compound tubuloalveolar gland which secretes milk. As it lies in superficial fascia, there is no capsule.
[2]. Mammary gland is a modified sweat gland. The gland consists of 15 to 20 lobes.
[3]. Each lobe is a cluster of alveoli and is drained by a lactiferous duct.
[4]. The lactiferous ducts converge towards the nipple and open on it. Near its termination, each duct has a dilatation called a lactiferous sinus .
Stroma .
[1]. It forms the supporting framework of the gland. It is partly fibrous and partly fatty.
[2]. The fibrous stroma forms septa known as the suspensory ligaments of Cooper, which anchor the skin and gland to the pectoral fascia .
[3].The fatty stroma forms the main bulk of the gland. It is distributed all over the breast, except beneath the areola and nipple.
Blood Supply .
The mammary gland is extremely vascular. It is supplied by branches of the following arteries .
[1]. Internal thoracic artery, a branch of the subclavian artery, through its perforating branches.
[2]. The lateral thoracic, superior thoracic and acromio-thoracic (thoraco-acromial) branches of the axillary artery.
[3]. Lateral branches of the posterior intercostal arteries. The arteries converge on the breast and are distributed from the anterior surface. The posterior surface is relatively avascular.
[4]. The veins follow the arteries. They first converge towards the base of the nipple where they form an anastomotic venous circle, from where veins run in superficial and deep sets.
[5]. The superficial veins drain into the internal thoracic vein and into the superficial veins of the lower part of the neck.
[6]. The deep veins drain into the axillary and posterior intercostal veins.
Nerve Supply .
[1]. The breast is supplied by the anterior and lateral cutaneous branches of the 4th to 6th intercostal nerves. The nerves convey sensory fibres to the skin, and autonomic fibres to smooth muscle and to blood vessels.
[2]. The nerves do not control the secretion of milk. Secretion is controlled by the hormone prolactin, secreted by the pars anterior of the hypophysis cerebri. The diagnosis and management of breast disease should be done carefully.
Lymphatic Drainage .
[1]. Lymphatic drainage of the breast assumes great importance to the surgeon because carcinoma of the breast spreads mostly along lymphatics to the regional lymph nodes.
[2]. The subject can be described under two heads—the lymph nodes and the lymphatic vessels.
Lymph Nodes .
Lymph from the breast drains into the following lymph nodes .
[1]. The axillary lymph nodes, chiefly the anterior (or pectoral) group. The posterior, lateral, central and apical groups of nodes also receive lymph from the breast either directly or indirectly.
[2]. The anterior thoracic (parasternal) nodes which lie along the internal mammary (thoracic) vessels .
[3]. Some lymph from the breast also reaches the supraclavicular nodes, the cephalic (deltopectoral) node, the posterior intercostal nodes (lying in front of the heads of the ribs), the subdiaphragmatic and subperitoneal lymph plexuses.
Lymphatic Vessels .
[1]. The superficial lymphatics drain the skin over the breast except for the nipple and areola. The lymphatics pass radially to the surrounding lymph nodes (axillary, anterior thoracic, supraclavicular and cephalic).
[2]. The deep lymphatics drain the parenchyma of the breast. They also drain the nipple and areola .
[3]. About 75% of the lymph from the breast drains into the axillary nodes; 20% into the anterior thoracic nodes; and 5% into the posterior intercostal nodes.
[4] . Among the axillary nodes, the lymphatics end mostly in the anterior group (closely related to the axillary tail) and partly in the posterior and apical groups.
[5] . Lymph from the anterior and posterior groups passes to the central and lateral groups, and through them to the apical group. Finally, it reaches the supraclavicular nodes.
[6]. The anterior thoracic nodes drain the lymph not only from the inner half of the breast, but from the outer half as well.
[7]. A plexus of lymph vessels is present deep to the areola. This is the subareolar plexus of Sappey. Subareolar plexus and most of lymph from the gland drain into the anterior or pectoral group of lymph nodes.
[8]. The lymphatics from the deep surface of the gland pass through the pectoralis major muscle and the clavipectoral fascia to reach the apical nodes, and also to the anterior thoracic nodes .
[9]. Lymphatics from the lower and inner quadrants of the breast may communicate with the subdiaphragmatic and subperitoneal lymph plexuses after crossing the costal margin and then piercing the anterior abdominal wall through the upper part of the linea alba.
[10]. Anterior and central groups of nodes are commonly involved in carcinoma breast.
Development of the Breast .
[1]. The breast develops from an ectodermal thickening, called the mammary ridge, milk line, or line of Schultz . This ridge extends from the axilla to the groin.
[2]. It appears during the fourth week of intrauterine life, but in human beings, it disappears over most of its extent persisting only in the pectoral region. The gland is ectodermal, and the stroma mesodermal in origin.
[3]. The persisting part of the mammary ridge is converted into a mammary pit. Secondary buds (15–20) grow down from the floor of the pit. These buds divide and subdivide to form the lobes of the gland.
[4]. The entire system is first solid, but is later canalised. At birth or later, the nipple is everted at the site of the original pit.
[5]. Growth of the mammary glands, at puberty is caused by oestrogens. Apart from oestrogens, development of secretory alveoli is stimulated by progesterone and by the prolactin hormone of the hypophysis cerebri.
[6]. Developmental anomalies of the breast are:
a. Amastia (absence of the breast),
b. Athelia (absence of nipple),
c. Polymastia (supernumerary breasts),
d. Polythelia (supernumerary nipples),
e. Gynaecomastia (development of breasts in a male) which occurs in Klinefelter’s syndrome.
Histology of Breast .
[1]. The mammary glands are specialised accessory glands of the skin, which have evolved in mammals to provide nourishment to the young ones.
[2]. Mammary gland consists of 15–20 lobes with the same number of ducts.
[3]. Each lobe is made up of many lobules containing acini. Histologically, only lobules are discernible in the gland.
Resting Phase in Non-Pregnant Adult Female
[1]. The mammary gland in this phase consists mainly of ducts and their branches . The stroma has connective tissue and fat cells.
[2]. The intralobular ducts are usually lined by low columnar epithelium resting on a basement membrane.
[3]. The intralobular connective tissue which is derived from the papillary layer of the dermis is more cellular containing fibroblasts.
[4]. The interlobular connective tissue, which lies between the ducts of adjacent lobules, is derived from the reticular layer of the dermis, and is more fibroreticular in nature. It contains fat lobules.
Lactating Phase .
[1]. The gland is full of acini with minimum amount of connective tissue. Some acini are lined by tall columnar cells, others by normal columnar cells.
[2]. The nucleus may be round or oval and is seen in the middle of the cell . Droplets of fat accumulate near the free surface of the cell.
[3]. Myoepithelial cells may be seen between the basement membrane and secretory cells.
[4]. Ducts are also seen, but they are fewer in number as compared to the acini. The bigger ducts are lined by stratified columnar or columnar epithelium.
Deep Fascia .
[1]. The deep fascia covering the pectoralis major muscle is called the pectoral fascia. It is thin and closely attached to the muscle by numerous septa passing between the fasciculi of the muscle.
[2]. It is attached superiorly to the clavicle and anteriorly to the sternum.
[3]. Superolaterally, it passes over the infraclavicular fossa and deltopectoral groove to become continuous with the fascia covering the deltoid.
[4]. Inferolaterally, the fascia curves round the inferolateral border of the pectoralis major to become continuous with the axillary fascia.
[5]. Inferiorly, it is continuous with the fascia over the thorax and the rectus sheath.
Muscles of Pectoral Region .
[1]. Pectoralis Muscle .
[1]. The pectoralis major is a large fan-shaped muscle that covers the superior part of the thorax . It has clavicular and sternocostal heads.
[2]. The sternocostal head is much larger and its lateral border forms the muscular mass that makes up most of the anterior wall of the axilla. Its inferior border forms the anterior axillary fold .
[3]. The pectoralis major and adjacent deltoid muscles form the narrow deltopectoral groove, in which the cephalic vein runs ; however, the muscles diverge slightly from each other superiorly and along with the clavicle, form the clavipectoral (deltopectoral) triangle.
[4]. Producing powerful adduction and medial rotation of the arm when acting together, the two parts of the pectoralis major can also act independently: the clavicular head flexing the humerus and the sternocostal head extending it back from the flexed position.
Origin of Pectoralis Muscle .
1. Anterior Surface of Medial two-thirds of Clavicle .
2. Half the breadth of anterior Surface of Manubrium and Sternum up to 6th Costal Cartilages .
3. Second to sixth Costal Cartilages , Sternal end of 6th Rib .
4. Aponeurosis of the external oblique muscle of abdomen .
Insertion of Pectoralis Muscle .
1. It is inserted by a bilaminar Tendon on the lateral lip of the bicipital groove in the form of U.
2.The Two Laminae are Continuous with each other inferiorly .
3. The anterior Lamina is Shorter and Thicker than longer and Thinner Posterior Laminae .
Nerve Supply of Pectoralis Muscle .
Medial and Lateral Pectoral Nerve .
Testing of clavicular head of pectoralis major .
To test the clavicular head of pectoralis major, the arm is abducted 90°; the individual then moves the arm anteriorly against resistance. If acting normally, the clavicular head can be seen and palpated.
Testing of sternocostal head of pectoralis major .
To test the sternocostal head of pectoralis major, the arm is abducted 60° and then adducted against resistance. If acting normally, the sternocostal head can be seen and palpated.
[2]. Pectoralis Minor .
[1]. The pectoralis minor lies in the anterior wall of the axilla where it is almost completely covered by the much larger pectoralis major .
[2]. The pectoralis minor is triangular in shape. Its base (proximal attachment) is formed by fleshy slips attached to the anterior ends of the 3rd–5th ribs near their costal cartilages. Its apex (distal attachment) is on the coracoid process of the scapula .
[3]. The pectoralis minor stabilizes the scapula and is used when stretching the upper limb forward to touch an object that is just out of reach. It also assists in elevating the ribs for deep inspiration when the pectoral girdle is fixed or elevated.
[4]. The pectoralis minor is a useful anatomical and surgical landmark for structures in the axilla (e.g., the axillary artery). With the coracoid process, the pectoralis minor forms a “bridge” under which vessels and nerves must pass to the arm.
[3]. Subclavius Muscle .
[1]. The subclavius lies almost horizontally when the arm is in the anatomical position . This small, round muscle is located inferior to the clavicle and affords some protection to the subclavian vessels and the superior trunk of the brachial plexus if the clavicle fractures.
[2]. The subclavius anchors and depresses the clavicle, stabilizing it during movements of the upper limb.
[3]. It also helps resist the tendency for the clavicle to dislocate at the sternoclavicular (SC) joint (e.g., when pulling very hard during a tug-of-war game).
[4]. Serratus anterior Muscle .
[1]. The serratus anterior overlies the lateral part of the thorax and forms the medial wall of the axilla . This broad sheet of thick muscle was named because of the saw-toothed appearance of its fleshy slips or digitations (L. serratus, a saw).
[2]. The muscular slips pass posteriorly and then medially to attach to the whole length of the anterior surface of the medial border of the scapula, including its inferior angle.
[3]. The serratus anterior is one of the most powerful muscles of the pectoral girdle. It is a strong protractor of the scapula and is used when punching or reaching anteriorly (some call it the “boxer’s muscle”).
[4]. The strong inferior part of the serratus anterior rotates the scapula, elevating its glenoid cavity so the arm can be raised above the shoulder. It also anchors the scapula, keeping it closely applied to the thoracic wall, enabling other muscles to use it as a fixed bone for movements of the humerus.
[5]. The serratus anterior holds the scapula against the thoracic wall when doing push-ups or when pushing against resistance (e.g., pushing a car).
[6]. To test the serratus anterior (or the function of the long thoracic nerve that supplies it), the hand of the outstretched limb is pushed against a wall. If the muscle is acting normally, several digitations of the muscle can be seen and palpated.
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