Notes on the Chest Wall
Rahul's Noteblog
Notes on Anatomy
Notes on Chest Wall
These are my notes on the thoracic cavity, which includes the lungs, heart, and great vessels. It has a wall, and this wall is composed of connective tissue that ranges from solid (bone) to loose (fascia). We want to understand how tissues are arranged to form a solid wall around the visceral cavities of the trunk. The surface of this wall shows landmarks that are useful in physical exam of a patient, and particularly for listening to the lungs and heart valves. The surface of the chest also contains the breast, a gland of prominent clinical significance, and muscles that have migrated onto the chest from the upper limb. I like to build the bony core of the wall, then work in from superficial to deep. Here goes:
Osteology of the pectoral region
Clavicle (primates are one of the few claviculate mammals)
• A strut for the upper limb positioning it laterally and connecting shoulder joint to midline.
• An S-shaped bone of late ossification and two joints.
Sternoclavicular joint - classified in different ways by different authorities.
• A plane synovial joint between clavicle and manubrium of sternum.
• This is the only bony connection between the upper limb and the trunk.
Acromioclavicular joint
A plane synovial joint between clavicle and acromion process of scapula
Sternum - a flat bone in anterior midline consisting of three developmental parts
Manubrium - the upper part of sternum that articulates with clavicle and first two ribs
Suprasternal notch (palpable) on superior surface at level of T2-T3 (thoracic vertebra 2 - thoracic vertebra 3)
Sternoclavicular joint at superolateral corner
• Articulation for first rib along lateral margin
• Articulation for second rib at manubriosternal junction (the sternal angle)
• Manubriosternal joint - an important, palpable landmark
A symphysis joint
• At level of lower border of T4
• Trachea bifurcates at this level just deep to sternum
Body [slides 8-10]
• Ossifies from four separate embryological segments
• Articulates directly with costal cartilages for ribs 2-7
Xiphoid process
• Joined to body via symphysis joint that ossifies in adulthood to become a synostosis
Xiphisternal joint at level of T9-T10
• Lower limit of anterior thoracic cavity
• Articulates with costal cartilage of rib 7
• Cartilaginous at birth; does not completely ossify until approximately age 40
• Superficial fascia of the pectoral region [slides 12-25]
• We expand our description of the region to include one of the most clinically important structures in the body, which happens to be located within the superficial fascia of the pectoral region - the breast, or mammary gland.
Mammary gland
• Mammary gland (breast) is an organ of lactation in females
• A modified sweat gland derived from ectoderm
• Extends from 2nd or 3rd rib to 6th or 7th costal cartilage and from sternum to beyond axillary fold
Surface structure
Nipple - pigmented projection at point of greatest prominence
• Holds 15-20 lactiferous duct openings
• In the undeveloped breast is located at approximately the 4th intercostal space
Areola - pigmented area surrounding nipple and containing areolar and sebaceous glands
Areolar glands - rudimentary milk glands
Glandular structure of the Mammary gland
Secretory unit - a lobe or lobule containing secretory cells
Lactiferous duct - tubular connection between secretory cell and opening on nipple
Lactiferous sinus - distal dilation of each duct prior to opening on nipple
Connective tissue - structural matrix for the gland
• Fibrous septae bind lobes together and tether breast to overlying skin
• Derived from tela subcutanea in which breast develops
• Suspensory ligaments of Cooper are well-developed fibrous septae of upper part of breast
• Inelastic and thus subject to dimpling and distortion when pathological
Fat - insulatory and protective padding around gland and connective tissue
Position on the body wall:
• Glandular elements lie within superficial fascia
• Separated from deep investing fascia of pectoralis major by loose connective tissue
• Potential space is the retromammary space; enables mobility of breast
• Shared lymphatic drainage often implicates muscle in spread of cancer
• Axillary tail of breast pierces deep fascia of pectoralis major to approximate axillary vessels
Development of breast
Prenatal
• Breasts begin as thickenings of epidermal columnar cells along the mammary line
• Mammary line (milk ridge) disappears by 6th-7th week, leaving paired mammary glands
• Nipple region inverted until 8th month; ducts patent at birth
• Pubertal - hormonal changes result in localized fat deposition and increased number of ducts
Pregnancy
• Hormonal changes further increase glandular potential, fat, and thus breast size
• Melanin production increases, darkening areolae and nipple
• Areolar glands secrete sebaceous lubricant for nipple prior to lactation
Postmenopausal
• Ducts and secretory units regress; fat slowly disappears
• Inelastic suspensory ligaments remain distended
Circulation of breast
• Take this opportunity to study a diagram of how blood leaves the heart through the aorta, then divides through large branches of it (carotid, subclavian) to reach the head, chest and upper limb. You should practice tracing blood from the aorta to a target structure such as the breast so that you know all of the possible routes. Anastomoses (look that up now if it is a strange word to you) are key to understanding how the body deals with occlusion or damage to blood vessels (and to what you might have to clamp in order to restrict flow to the structure in a surgical procedure). In general you need to be concerned about arteries more than veins since their anatomy is less variant and they have a layer of smooth muscle that keeps them open when they are cut. By comparison veins vary more in their routes and designs, and circulation through them is by passive pressure, which means that damage to them tends to be less life-threatening.
Arterial - richly supplied from four sources
• Internal thoracic artery sends perforating branches to supply medial breast
• Lateral thoracic artery supplies lateral breast via mammary branches
• Thoracoacromial trunk supplies lateral breast via pectoral branches
• Anterior and posterior intercostal arteries supply medial and lateral breast
Venous - mostly parallel arteries to axillary and subclavian veins
• Blood also returns to vertebral venous plexus via azygous system. Thus, spinal cord may be implicated in spread of infection or tumor
Lymphatic - very important clinically
• Lateral quadrants drain mostly to axillary nodes
• Medial quadrants also drain to axillary nodes
• Supplemental drainage to parasternal nodes and intercostal nodes
• Some drainage to opposite side nodes also possible
Innervation - by lateral and anterior cutaneous branches of 2nd-6th intercostal nerves
Congenital clinical manifestations
Polymastia - extra breasts (with or without nipples), usually in axilla or groin
Polythelia - persistence of multiple nipples
Amastia - mammary line (milk ridge) never develops
Gynecomastia - development of female breast in males
If you find yourself with time on your hands or with a particularly fast computer, you may find that internet searches of these clinical terms can be quite informative. Try using the Google search engine for images, then type in the bold terms above. This applies to all of the clinical lessons to come as well.
Muscles of the pectoral region [slides 26-40]
Pectoralis major - major fan-shaped muscle of ventral body wall [slides 26-27]
Lateral border forms anterior axillary fold
Superior border forms one boundary of deltopectoral triangle
Origin - clavicular head from medial half of clavicle; sternal head from manubrium to lower body
Insertion - lateral lip of intertubercular groove of humerus
Innervation - medial and lateral pectoral nerves (from medial and lateral cords of brachial plexus)
Actions - adducts and medially rotates humerus
• Draws shoulder anteriorly and medially
• Clavicular head fibers active in flexing humerus
• Sternal head fibers active in extending humerus from 30 degrees of flexion
Pectoralis minor - deep to pectoralis major; does not connect to humerus
Origin - outer surfaces of ribs 2-5 near costal cartilages and fascia of associated intercostal spaces
Insertion - coracoid process of scapula
Innervation - medial pectoral nerve
Actions - an accessory muscle of respiration when shoulder is in fixed position
• Stabilizes scapula by drawing it forward, medially and downward
• If scapula is fixed it elevates the ribs
• Subclavius - relatively insignificant muscle that protects neurovascular bundle underlying clavicle
Origin - upper border of first rib and costal cartilage
Insertion - inferior surface of clavicle
Innervation - nerve to subclavius (from upper trunk of brachial plexus)
Actions - draws clavicle downward and forward
Serratus anterior - overlies much of lateral thoracic wall [slides 28-29]
Origin - outer surfaces of ribs 1-8,9; lateral to pectoralis minor
Insertion - length of medial border of ventral surface of scapula
Innervation - long thoracic nerve (from upper trunk of brachial plexus)
Actions:
• Protracts and abducts scapula
• Holds scapula along posterior thoracic wall
• Laterally rotates scapula (counterclockwise, from posterior view)
• Elevates arm from horizontal to vertical
• Damage to the long thoracic nerve will paralyze this muscle, resulting in a condition known as "winged scapula" in which the vertebral border of the scapula is lifted off of the rib cage. The patient will be unable to abduct their arm above the horizontal. The long thoracic nerve is vulnerable during surgical procedures of the chest wall, particularly in radical mastectomies.
Intercostal connective tissue [slides 30-33]
Muscles
External intercostal muscle – outermost of three muscle layers between ribs
Origin and Insertion - superior and inferior margins of adjacent ribs
Innervation – ventral rami of segmental spinal nreves T1 – T11
Actions – largely hypothetical, but seem to assist in forced respiration
Internal intercostal muscle – the middle of three muscle layers between ribs
Innermost intercostal muscle – most internal layer, not continuous throughout rib cage
Neurovascular bundle [slides 34-39]
Ventral rami of thoracic spinal nerves track along underside of each rib, in the costal groove, between internal and innermost muscle layers
Intercostal arteries are a fusion of anterior and posterior intercostal vessels
Posterior intercostal arteries come directly from thoracic aorta
Anterior intercostal arteries commence at the sternum as branches of internal thoracic artery, itself ultimately a branch of the aorta
Internal thoracic artery splits at the costal margin into a branch that continues to track the ribcage margin inferiorly (musculophrenic artery) and a branch that follows more directly onto the abdominal wall (superficial epigastric artery)
Finally, the internal surface of the thoracic wall is lined by a specialization of the deep fascia called endothoracic fascia.
Additional Reading:
Histology and Cytology
1. Cell Components
2. Nervous Tissue
3. Muscle Tissue
4. Lymphoid Tissue
5. Integument
6. Respiratory System
7. Gastrointestinal System
8. Renal/Urinary System
9. Male Reproductive System
10. Female Reproductive System
Gross Anatomy
1. Back and Nervous System
2. Thorax
3. Abdomen, Pelvis, and Perineum
4. Upper Limb
5. Lower Limb
6. Head and Neck
7. Chest Wall
8. Shoulder
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