(3) Pectoral Region, Thoracic Wall, Intro Radiology

thoracic cage

ribs and sternum

sternum

breastbone; composed of the manubrium, body, & xiphoid process

manubrium

the superior portion of the sternum. thickest & widest part.

body of sternum

middle portion of the sternum. longest part.

xiphoid process

inferior "sword like" portion of the sternum

true ribs

ribs 1-7. attach directly to sternum via costal cartilage.

false ribs

ribs 8-12. attach indirectly to sternum by cartilage.

floating ribs

ribs 11 & 12. do not attach to sternum (end in abdominal wall)

How ribs develop

1. Begin as a cartilaginous precursor that is laded invaded by bone-producing cells

2. Ossification starts proximally & moves around the body distally, but stops short of sternum.

3. Part that doesn't ossify becomes costal cartilages.

Synchondrosis

a joint in which 2 bones are united by cartilage

manubriosternal joint (superior sternal

synchondrosis)

synchondrosis between manubrium and body of the sternum

xiphisternal joint (inferior sternal

synchondrosis)

synchrondosis between xiphoid process and body of sternum

costochonral junctions

meeting of bone & cartilage (such as between ribs & costal cartilage)

Sternal Angle (Angle of Louis)

Ridge between manubrium and body at second rib. 2nd costal cartilage can be palpated laterally.

1st rib is hard to feel because

it is covered by the clavicle

Major parts of a rib

head, neck, tubercle, body

articular facets of rib

2 on rib head (articulate with vertebral bodies at superior or inferior costal facets) & 1 on rib tubercle (articulates with transverse process of thoracic vertebra at transverse costal facets)

ligaments of the ribs

Radiate ligament on front of head of rib connecting to body of vertebra. Superior costotransverse ligaments connect rib to transverse costal processes.

-Make ribs hard to dislodge

The heads of the 1st, 11th, and 12th ribs articulate with

only their own corresponding vertebral bodies

All ribs except 1, 11, 12 articulate with

two adjacent vertebrae

thoracoacromial artery

supplies blood to superior shoulder and pectoral regions (both pectoralis major & minor)

lateral pectoral nerve

provides motor innervation to clavicular head of pec major

cephalic vein

a large vein of the arm between deltoid & pec major that empties into the axillary vein

medial pectoral nerve

provides motor innveration to both pectoralis minor and the sternocostal head of pectoralis major

Clavipectoral fascia

dense layer between pectoralis major and minor. has a hole that enables passage of thoracoacromial artery, lateral pectoral nerve, and cephalic vein

pectoralis major

most superficial muscle on anterior chest that consists of 2 heads (1 originates in the medial head of the clavicle & the other the lateral end of the sternum). Inserts on proximal end of humerus.

pectoralis minor

anterior chest muscle deep to pectoralis major that is smaller. Originates in the 3rd, 4th, and 5th ribs. Inserts on the coracoid process of scapula.

long thoracic nerve

provides motor innervation to serratus anterior

lateral thoracic artery

supplies blood to the lateral chest wall

serratus anterior

the 3rd and last serratus muscle. Originates on the anterior medial border of scapula. Inserts on ribs 1-8/9.

external intercostal membrane

the non-muscular tendinous portion of the external intercostal muscle, located just lateral to the sternum in the intercostal space

external intercostals

most superficial intercostals. fibers run proximal to distal. Fibers begin at tubercules of ribs & disappear at costochondral junction.

internal intercostals

Deep to external intercostals. Fibers fun distal to proximal. Fibers begin at posterior axillary line and disappear at sternum.

innermost intercostals

Deepest layer of intercostal muscles. Fibers run distal to proximal. Present only laterally, running from angles of ribs to anterior axillary line.

transversus thoracis

derived from same muscle layer as innermost intercostals but appears medially instead of laterally. Originates at xiphisternal joint. Inserts at 2-6 costochondral junctions.

anterior intercostal arteries

branches of the internal thoracic arteries that supply blood to anterior thoracic wall. immediately deep to internal intercostals. disappear laterally at innermost intercostals.

2 main sources of blood supply to thoracic wall

thoracic aorta and internal thoracic artery (from subclavian artery)

posterior intercostal artery

branch of thoracic aorta that supplies blood to the thoracic wall. longer and wider than anterior intercostal artery (so supplies more blood). has a dorsal branch and a lateral branch.

Dorsal branch of posterior intercostal artery

supplies blood to the thoracic areas innervated by dorsal rami (so intrinsic back muscle)

lateral cutaneous branch of posterior intercostal artery

supplies blood to the side of the thoracic wall (midaxillary region)

anterior intercostal artery

branches from the internal thoracic artery and supplies blood to the intercostal muscles and mammary glands. thinner than posterior intercostal artery (so supplies less blood).

Innveration source for thoracic wall

intercostal nerve

intercostal nerve

systemic nerve in the thoracic cavity that is found between two ribs. branch of ventral rami of T1-T11. Has a lateral cutaneous branch and an anterior cutaneous branch.

lateral cutaneous branch of intercostal nerve

Exits through external intercostal muscle

anterior cutaneous branch of intercostal nerve

exits right before sternum

T7 dermatome

xiphoid process

breast location

-between 2nd and 6th ribs

-extends close to midaxillary line

-sits superficial to pectoralis minor and serratus interior

areola

pigmented area around the breast nipple

Areolar Glands (Glands of Montgomery)

modified sebaceous glands that help lubricate the nipple when nursing & secrete pheromones that promote suckling of an infant

lactiferous ducts

tubes that carry milk within the breast. converge toward nipple and widen into a lactiferous sinus.

lactiferous sinus

Reservoir for milk before it exits the nipple.

mammary glands

modified sweat glands that produce milk

suspensory ligaments (Cooper ligaments)

collagen fibers in the breast that function in support and shape maintenance

subcutaneous fat in the breast

makes up a large amount of breast volume, playing a large role in shape

Breast blood supply & lymphatic drainage

lateral and medial mammary branches

lateral mammary branches

supply blood to lateral side of breast. come from lateral thoracic artery and lateral cutaneous branches of posterior intercostal arteries

medial mammary branches

supply blood to medial side of breast. come from internal thoracic artery and its perforating branches

the lymphatic system functions in both

circulation (by helping collect blood plasma that has leaked through capillary bloods & returning that 15% to the circulatory system after filtering solids), and immunity (T & B lymphocytes)

Lymphatic drainage of the breast

axillary and parasternal nodes

axillary nodes

lateral route of lymphatic breast drainage. 75%.

parasternal nodes

medial route of lymphatic breast drainage. 25%

most (60% of) malignant breast tumors originate in the

upper right quadrant of the breast (nearest to axillary nodes)

level 1 nodes

breast lymph nodes lateral to pec minor. 65% 5 year survival rate for cancer found here.

level 2 nodes

breast lymph nodes central to pec minor. 31% 5 year survival rate for cancer found here.

level 3 nodes

breast lymph nodes medial to pec minor. very low (approx 0)% 5 year survival rate for cancer found here.

x-rays

electromagnetic waves with very short wavelengths and very high energies

how x-rays work

X-rays are fired at the patient through a cathode tube

X-rays are absorbed by materials which are very dense

X-rays are transmitted through materials which are not very dense

The X-rays that pass through are detected by a detector plate to form an X-ray image

Most Radiolucent/Least radiodense to Least

radiolucent/Most radiodense body componets (darkest black to brightest white)

Air, Fat, Water/most tissues, spongy bone, compact bone

PA vs lateral xrays

PA gives front view, lateral gives side view. Use both to get a 3D view.

PA vs AP xrays

PA gives a more accurate sizing of organs, but requires a patient to be able to stand upright. AP gives an artificial enlargement of organs due beams spreading more before hitting, but can be done on an unconscious pt lying down.

Contrast Enhanced (CE) X-rays

a contrast is injected to make arteries appear bone-dense (bright white). used for coronary angiograms.

How CT imagining works

uses xray waves but both pt and xray source are moving. A series of 1mm slices are segmented together to create 3D images.

CT image orientation

images are oriented as if patient were lying supine and observer is viewing from foot of bed (so things on a pt's right would be on the left of the image)

how MRI imaging works

-a magnet creates a magnetic field that puts body's protons in alignment

-a radio frequency coil produces a pulse that knocks protons out of alignment

-protons release energy during realignment, which produces images

MRIs are best for visualizing

soft tissue (muscle, fluid, fat, etc)

T1 MRI

MRI where fat appears the brightest white

T2 MRI

MRI where freestanding fluid appears the brightest white