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Thorax


Surface Anatomy

Fig. 5.1a and b, Regions of the thorax.

Fig. 5.2, Projection of the rib cage onto the thoracic wall.

Fig. 5.3a and b, Surface landmarks of the anterior thoracic wall; in the male (a) and female (b).

Fig. 5.4a and b, Projections of the borders of the lungs and pleura onto the anterior (a) and posterior thoracic (b) walls.

Fig. 5.5, Projections of the trachea and bronchial bifurcation onto the thoracic wall.

Fig. 5.6, Projections of the heart and the cardiac valves onto the thoracic wall.

Surface Landmarks and Projections to Vertebral Levels
Surface Landmark Ribs/Intercostal Space (ICS) Vertebral Projection Orientation
Suprasternal (jugular) notch Between upper sternoclavicular joints Level T2/T3 Trachea entering mediastinum;
inferior thyroid veins, thyroid ima artery
Manubrium of sternum Rib I Level T3/T4 Aortic arch; superior vena cava; thymus
Sternal angle (of LOUIS); manubriosternal joint Rib II Level T4/T5 Marks transition from superior to inferior mediastinum, and the articulation with the second costal cartilage
Nipple (male) ICS IV
Body of sternum Ribs II–VI
(false ribs VIII–X)		 Level T5–T9 Tricuspid valve (5 th costal cartilage);
right ventricle
Infrasternal angle Level T9/T10
Xiphisternal plane (T9)		 Central tendon of diaphragm with attachment of fibrous pericardium

Cutaneous Innervation

Fig. 5.7, Dermatomes of the anterior thoracoabdominal wall. The structure of the intercostal nerves is shown in chapter 12 (Neuroanatomy).

Fig. 5.8, Segmental innervation of the skin and corresponding cutaneous nerves of the posterior thoracic wall.

Fig. 5.9, Segmental innervation of the skin and corresponding cutaneous nerves of the anterior thoracic wall ( Fig. 12.75 ).

Clinical Remarks

Following a varicella-zoster virus infection (chicken pox), the virus may reside dormant in neurons of the dorsal root ganglion. Upon reactivation a painful cutaneous eruption occurs, known as shingles, that is confined to the respective dermatome.

[ E545 ]

Mammary Gland

Fig. 5.10a and b, Breast, right side; lateral (a) and anterior (b) views.

Fig. 5.11, Breast; sagittal section.

Fig. 5.12, Milk line.

Clinical Remarks

The absence of the nipples (athelia) or breasts (amastia, mammary aplasia) are rare congenital anomalies that can occur uni- or bilaterally. Supernumerary nipples or breasts are called polythelia or polymastia, respectively. This is usually hereditary and can also affect males. When breast growth occurs in males (possibly due to hormonal disorders), this condition is called gynecomastia.

Mammary Gland – Blood Supply

Fig. 5.13, Epifascial blood vessels of the thorax .

Fig. 5.14, Arteries and veins of the mammary gland. Arteries are labelled and corresponding veins are shown.

Mammary Gland – Lymphatic Drainage

Fig. 5.15, Superficial axillary lymph vessels and nodes in the axillary fossa; anterior view.

Fig. 5.16, Lymphatic drainage, regional lymph nodes and blood supply of the female breast.

Clinical Remarks

Surgery for breast cancer is performed either as removal of the whole breast ( mastectomy ) or as breast-conserving surgery only removing the tumor with some normal tissue around it ( lumpectomy ) followed by radiation therapy.

Structure/Function

Lymph nodes of the female breast are categorized into three hierarchical levels. The pectoralis minor muscle acts as a boundary:

  • Level I lies lateral to the pectoralis minor.

  • Level II lies inferior to the pectoralis minor.

  • Level III lies medial to the pectoralis minor.

The parasternal lymph nodes of both sides are interconnected. Level I lymph nodes are referred to as sentinel (= the one that keeps guard) nodes which are usually also the first lymph nodes of metastatic colonization. The number of affected lymph nodes in the three hierarchical levels is directly related to the survival rate. Breast carcinoma of the medial quadrants can metastasize via the interconnected parasternal lymph nodes to the contralateral side.

Frequency of mammary carcinoma in relation to the location in percentage.

Rib Cage and Sternum

Fig. 5.17a and b, Thoracic skeleton; anterior (a) and posterior (b) views.

Fig. 5.18, Thoracic skeleton. Chest X-ray in posterior-anterior beam projection. The ribs are numbered on their posterior aspects.

Fig. 5.19a and b, Sternum; anterior (a) and lateral (b) views.

Structure/Function

The first rib is not palpable as it is covered by the clavicle and the associated muscles.

The angle of LOUIS (sternal angle) is a palpable surface landmark for the:

  • transition from superior to inferior mediastinum;

  • articulation with the 2 nd costal cartilage;

  • horizontal thoracic level of vertebra T4/T5;

  • tracheal bifurcation.

The sternum (similar to the iliac bone) contains red bone marrow in adults and is accessible for bone marrow aspiration (biopsy).

Ribs and Costovertebral Joints

Fig. 5.20, Ribs; ribs I–III: superior view; rib VIII: inferior view.

Fig. 5.21, Costovertebral joints; shown for vertebrae T7 and T8.

Clinical Remarks

Supernumerary or accessory ribs are common in the cervical region (cervical ribs), mostly C7, and can occur uni- or bilaterally. Cervical ribs may connect to the first thoracic rib or to the sternum and may cause a compression of the brachial plexus and the subclavian artery (thoracic outlet syndrome: TOS).

Intercostal Muscles

Fig. 5.22, Muscles of the posterior thoracic wall; anterior view with anterior part of the thoracic cage removed.

Fig. 5.23, Muscles of the anterior thoracic wall; posterior view with posterior part of the thoracic cage removed.

Fig. 5.24, Superior thoracic aperture and intercostal muscles; anterior view.

Diaphragm

Fig. 5.25, Diaphragm.

Fig. 5.26, Chest X-ray in posterior-anterior (P/A) projection. The right dome of the diaphragm projects higher than its left dome.

Fig. 5.27, Innervation of the diaphragm: phrenic nerve.

Structure/Function

Due to the size of the liver the dome of the right hemidiaphragm reaches further cranially and projects to the level of thoracic vertebra T8 as seen in a chest X-ray or axial CT or MRI scans. The left dome of the diaphragm projects to the level of T9.

Clinical Remarks

Injury to the phrenic nerve may occur in the neck or the mediastinum where it courses in close proximity to the hilum of the lung. Phrenic nerve lesions cause unilateral diaphragmatic paralysis which usually remains asymptomatic during normal daily activity.

Fig. 5.28, Blood supply of the diaphragm; inferior view.

Fig. 5.29a und b, Diaphragm; lateral (a) and inferior (b) views. a

Blood Supply of the Diaphragm
Origin of Artery Arterial Branch Supply to
Internal thoracic artery (branch of subclavian artery) Pericardiacophrenic artery (courses with phrenic nerve) Domes of diaphragm
Musculophrenic artery Costal parts of diaphragm
Phrenicoabdominal branch Sternal parts of diaphragm
Thoracic aorta Superior phrenic arteries Lumbar part of diaphragm
Abdominal aorta Inferior phrenic arteries Major blood supply to diaphragm

Muscles of Respiration

Structure/Function

Excursions of the thorax during respiration; schematic drawing. [ L126 ]

The driving force for respiration at rest is the contraction of the diaphragm resulting in an increased vertical dimension of the thorax. In forced respiration, the inspiratory muscles of the thoracic wall contribute to increased transverse and anteroposterior dimensions of the thorax.

Pump handle and bucket handle movements of the rib cage during respiration; schematic drawings. [ L126 ]

The pump handle movement represents the elevation of the ribs resulting in an increased anteroposterior (A/P) dimension of the inferior thorax. The bucket handle movement reflects the lateral elevation of the middle part of the lower ribs which increases the transverse dimension of the thorax.

Muscles of Respiration
Muscle Innervation Action
Scalene muscles
(anterior, middle and posterior scalene) 		Muscular branches of cervical and brachial plexus (C3–C6) Inspiration (auxiliary)
Elevation of 1 st rib (anterior and middle scalene muscles) and of 2 nd rib (posterior scalene muscle)
External intercostal muscles Intercostal nerves Inspiration (elevation of ribs)
Internal intercostal muscles Intercostal nerves Expiration (depression of ribs)
Innermost intercostal muscles Intercostal nerves Expiration (depression of ribs)
Transversus thoracis muscle Intercostal nerves Expiration (depression of ribs)
Subcostal muscle (inconsistent) Intercostal nerves Expiration (depression of ribs)
Diaphragm Phrenic nerve (C3–C5) Inspiration
Latissimus dorsi muscle ( chapter 2 ) Thoracodorsal nerve (C6–C8) Forced expiration (coughing)
Compresses lower rib cage when arms are fixed

Thoracic Wall – Blood Supply

Fig. 5.30, Arteries of the superior two intercostal spaces.

Fig. 5.31, Arteries of the thoracic wall.

Fig. 5.32, Veins of the thoracic wall.

Thoracic Wall – Neurovascular Structures

Fig. 5.33, Intercostal arteries.

Fig. 5.34, Intercostal veins.

Fig. 5.35, Intercostal nerves.

Structure/Function

The intercostal neurovascular structures course between the internal and innermost intercostal muscles with a typical topography from superior to inferior: vein – artery – nerve (VAN). Thus, the intercostal nerve is the least protected by the costal groove.

Fig. 5.36a and b, Position of the intercostal neurovascular structures; longitudinal section (a) and schematic illustration (b). The collateral branches appear near the costal angle.

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