Anatomy Exam 2: Thoracic Wall

Question 1

What structures enclose the thoracic cavity, and what are its divisions?

Answer 1

The ribs, sternum, and dorsal vertebrae enclose the thoracic cavity. The diaphragm provides the “floor” of the thoracic cavity, but has several hiatuses through which structures pass.

The thorax is divided into the central mediastinum, and two non-communicating pleural cavities.

Question 2

If the pectoralis major muscle is removed in a radical mastectomy, what motions are affected?

Answer 2

Flexion, adduction, medial rotation (think steering a car).

Question 3

From internal to external, describe the important layers/structures of the anterior thoracic wall

Answer 3

Ribs
Pectoralis minor
Pectoralis major
Pectoral fascia
Retromammary space
Breast tissue (containing lobules of mammary glands, lactiferous ducts, and suspensory ligaments)

Question 4

What is the parenchyma of the mammary glands?

Answer 4

The lobules of the mammary gland. These connect to the lactiferous ducts and are supported by suspensory ligaments.

Question 5

A physician asks a woman to place her hands on her hips and contract pectoralis major muscles. What is being observed?

Answer 5

The retromammary space allows for symmetrical and independent movement of pec major from the breast tissue (think Baywatch). If something (like a tumor) has invaded this space, it can fix the breast to the muscle, reducing this effect and causing asymmetrical movement dependent on pec major.

Question 6

A patient presents with dimpling of the breast. Provide a possible explanation for this presentation.

Answer 6

Suspensory ligaments in the breast support the lobules of the mammary glands and are present in great number in the breast tissue. If something (like a tumor) is infringing on the normal path of a suspensory ligament, the distortion will cause the skin to dimple as the ligament is shortened. This leads to a dimpled appearance of the skin (sometimes called peau d’orange – skin of the orange).

Sudden inversion of the nipples can be caused by the same process.

Question 7

Describe the blood supply to the breast.

Answer 7

Arterial:
Mammary branch of internal thoracic artery
Mammary branch of lateral thoracic artery
Mammary branch of thoracoacromial artery
Mammary branch of posterior intercostal arteries (which are branches of the thoracic aorta)

Venous:
Tributaries to axillary vein
Tributaries to internal thoracic vein

Question 8

What are two common ways breast cancer metastasizes?

Answer 8

Via the lymphatic system and venous drainage

Question 9

Describe lymphatic flow of the breast.

Answer 9

The central node receives drainage from the lateral/humeral, subscapular, and pectoral nodes.

This drains into the apical (infraclavicular/subclavian) node.

^ This system is collectively called the axillary lymph nodes and is responsible for 75% of lymph drainage from the breast.

The remainder drains to parasternal or subdiaphragmatic lymph nodes (moves medial or inferior).

Question 10

What is a sentinel node biopsy?

Answer 10

A sentinel node is the hypothetical first node that cancer would spread to. In the breast, the axillary nodes are collectively referred to as the sentinel nodes, as cancer would likely spread to them before anywhere else in the body.

When cancer is suspected, a biopsy is taken from sentinel nodes, and if no cx is present, it is unlikely that it has spread.

It is also important to remember that cx can travel medially to the parasternal nodes or inferiorally to the subdiaphragmatic nodes, so these may also be checked.

Question 11

How does rib 11 differ from rib 8? From rib 5?

Answer 11

Ribs 11 and 12 are floating ribs. They have no attachments to other ribs or to the sternum.

Ribs 8-10 are false ribs: they do not articulate with the sternum but do have cartilaginous attachments to their superior ribs.

Ribs 1-7 are true ribs, and attach to the sternum.

Question 12

Describe the important features of the head of the rib.

Answer 12

The head, located on the posterior aspect of the rib, has two facets which each articulate with thoracic vertebrae.

The superior facet articulates with the costal facet of the vertebrae above the rib, while the inferior facet articulates with the costal facet of the vertebrae below the rib.

Question 13

In order from medial to lateral, what are the important structure of the posterior portion of a rib?

Answer 13

The head (containing the super and inferior articular facets), the neck, and the tubercle (with an articular facet).

Question 14

Describe the tubercule of the a rib.

Answer 14

Lateral to the head and neck of the rib, the tubercle contains a facet which articulates with the transverse process of that rib’s vertebrae.

Question 15

Describe the articulations of a rib.

Answer 15

In the anterior, ribs articulate with cartilage. Where this cartilage articulates is dependent on whether the rib is a true, false, or floating rib.

In the posterior, the ribs articulate in 3 spots:
1.) the superior articular facet of the rib head articulates with the inferior costal facet of the vertebral body directly superior to the rib.

2. ) the inferior articular facet of the rib head articulates with the superior costal facet of the vertebral body directly below to the rib
3. ) the articular facet of the tubercle articulates with the vertebrae at the same level as the rib at the transverse process.

Ribs 1, 11, and 12 only articulate with their own vertebrae, not those above and below.

Question 16

What is the difference between a costovertebral joint and a costotransverse joint?

Answer 16

A costovertebral joint includes the articulations of the head of the rib: articulations with the vertebral bodies of the superior and inferior vertebrae. Ribs 1, 11, and 12 do not have costovertebral joiunts.

Costotransverse joints are the articulations made at the tubercle of each rib with the transverse process of its own vertebrae. All ribs have these.

Question 17

Describe innervation to the intercostal spaces of the thoracic wall.

Answer 17

Intercostal nerves at each level are the anterior rami of spinal nerves. These tuck into the costal groove inferior to the intercostal vein and artery (in that order). The nerve (as well as vessels) are between the inner and innermost layers of intercostal muscle.

Intercostal nerves give rise to cutaneous branches to innervate the skin.

Question 18

Describe arterial supply to the thoracic wall.

Answer 18

The INTERNAL THORACIC ARTERY originates at the subclavian artery and descends inferior (parallel to thoracic aorta). This feeds anterior intercostal arteries 1-6.

The internal thoracic artery branches around intercostal space 7:

• The MUSCULOPHRENIC artery branches laterally. This feeds anterior intercostal arteries 7-10.
• The SUPERIOR EPIGASTRIC artery continues to descend.

There are also POSTERIOR INTERCOSTAL ARTERIES. The first two are branches of the supreme intercostal artery. Posterior intercostal arteries 3-9 are fed by the thoracic aorta directly.

The anterior and posterior intercostal arteries anastamose, providing some redundancy. This is why a portion of the internal thoracic artery can be removed and used for a coronary bypass without significantly reducing blood flow to the thoracic wall.

Question 19

Describe venous drainage of the anterior thoracic wall.

Answer 19

Veins are named similarly to the arteries which they accompany.

The anterior internal thoracic veins, epigastric veins, and musculophrenic veins empty into the BRACHIOCEPHALIC vein.

Question 20

Describe venous drainage of the posterior thoracic wall.

Answer 20

The posterior veins empty into the AZYGOS SYSTEM.

• The azygos vein is on the right side, originates at the inferior vena cava, and drains into the superior vena cava. This drains the viscera of the mediastinum, plus the posterior and thoracoabdominal walls.

There is some variation between individuals on the left side.

• The accessory azygos is usually superior to the hemiazygos vein.
• Both drain into the azygos -> superior vena cava.

The accessory azygos usually drains around T7. Its tributaries are the 4-8th posterior intercostal veins and the left bronchial veins.

The hemiazygos usually drains around T8. Its has more tributaries than the accessory azygos, including the esophogeal and mediastinal veins, and posterior intercostal veins 9-11.

Question 21

Identify the contents and spatial relations within an intercostal space.

Answer 21

From external to internal, the intercostal space includes:
External intercostal muscle (“hands in pockets”)
Internal intercostal muscles (perpindicular to external)
Layer of vein (superior), artery (middle), and nerve (inferior) (*VAN), tucked within costal groove of superior rib
A 3rd muscular layer comprised of NONcontinuous: innermost intercostal muscle, subcostalis muscle, and transversus thoracis muscle.

Question 22

Describe the external intercostal muscles (blood supply, innervation) and their role in breathing.

Answer 22

These attach to the borders of ribs above and below, and fibers run inferoanteriorly (“hands in pockets”).

They are supplied by the anterior intercostal, posterior intercostal, and musculophrenic arteries.

They are innervated by the intercostal nerves.

When they contract during forced inspiration, they elevate ribs, increasing volume.

Question 23

Describe the internal intercostal muscles (blood supply, innervation), and their role in breathing.

Answer 23

These attach to the borders of the ribs above and below, and the fibers run inferoposteriorly (opposite of “hands in pockets”).

They are supplied by the anterior, posterior, and musclophrenic arteries.

They are innervated by the intercostal nerves.

During forced exhalation, they contract and depress the ribcage, reducing volume.

Question 24

Describe the 3 layers of innermost intercostal muscles (blood supply, innervation), and their role in breathing.

Answer 24

Three noncontinuous muscles: innermost intercostals, subcostalis, and transversus thoracis are deep to the intercostal neurovascular bundle. The fibers in all three run inferoposteriorly (opposite of “hands in pockets”).

All three are supplied by the anterior and musculophrenic arteries. The innermost and subcostalis muscles are also supplied by the posterior intercostal arteries, but the transverse thoracis is not.

All three are innervated by the intercostal nerves.

All three depress the ribcage during forced exhalation, reducing volume.

Attachments:
Innermost: attach to the borders of ribs above and below.

Subcostalis: are similar to innermost, but span 2-3 spaces.

Transversus thoracis: Attaches to the posterior aspect of the sternum and to costal cartilages.

Question 25

Where would a thoracentisis be positioned? A nerve block? Why?

Answer 25

Thoracentisis: trying to aspirate fluid that has accumulated in the pleural cavity. Want to avoid any vasculature or nerves. Using the intercostal space 8 helps access the pleural recess, avoiding organs. The needle should be placed above the rib, as VAN run in the costal groove on the inferior aspect of the rib.

Nerve block: trying to reach the nerve associated with a particular dematome to block pain or to diagnostically identify which nerve a symptom is associated with. Will want to position the needle on the inferior border of the rib, as the nerve is the most inferior structure in the costal groove along the inferior border of the rib.

Question 26

Compare anterior arterial blood supply between the different levels of intercostal spaces.

Answer 26

Anterior intercostal arteries that run through spaces 1-6 are supplied by the internal thoracic artery.

Anterior intercostal arteries that run through spaces 7-10 are supplied by the musculophrenic artery.

Question 27

Compare posterior arterial blood supply between the different levels of intercostal spaces

Answer 27

Posterior intercostal 1 and 2 are branches of the superior intercostal artery
The other posterior intercostals are branches of the descending thoracic aorta

Posterior intercostal arteries 1-9 stop short of the anterior end
Posterior intercostals 10 and 11 continue around the abdominal wall