Mediastinum and Pleurae pdf - Thorax

Basic Anatomy

C H A P T E R O U T L I N E

(continued)

natomy

asic

Chest Cavity

vertebrae (see Fig. 3.2).

body of the sternum and behind by the lower eight thoracic

The inferior mediastinum is bounded in front by the

duct, (d) descending aorta, and (e) sympathetic trunks.

phrenic nerves on each side, (c) esophagus and thoracic

(a) Thymus, (b) heart within the pericardium with the

vertebrae (see Fig. 3.2).

manubrium sterni and behind by the first four thoracic

The superior mediastinum is bounded in front by the

(e) esophagus and thoracic duct, and (f) sympathetic trunks.

(a) Thymus, (b) large veins, (c) large arteries, (d) trachea,

the following order from anterior to posterior.

ber that the major mediastinal structures are arranged in

For purposes of orientation, it is convenient to remem

between the pericardium and the vertebral column.

which lies

posterior mediastinum,

and the sternum; and the

which is a space between the pericardium

mediastinum,

anterior

which consists of the pericardium and heart; the

middle mediastinum,

astinum is further subdivided into the

thoracic vertebra posteriorly (Fig. 3.2). The inferior medi

angle anteriorly to the lower border of the body of the 4th

by an imaginary plane passing from the sternal

mediastina

inferior

superior

The mediastinum is divided into

sympathetic trunks.

and lymph nodes, the vagus and phrenic nerves, and the

blood vessels, the trachea and esophagus, the thoracic duct

contains the remains of the thymus, the heart and large

to the sternum and posteriorly to the vertebral column. It

neck and inferiorly to the diaphragm. It extends anteriorly

extends superiorly to the thoracic outlet and the root of the

The mediastinum, though thick, is a movable partition that

lungs (Figs. 3.1, 3.2, and 3.3).

and the laterally placed pleurae and

mediastinum,

chest cavity can be divided into a median partition, called

that separates the chest from the abdominal viscera. The

only structure (apart from the pleura and the peritoneum)

Fig. 3.5). The diaphragm, which is a very thin muscle, is the

about one fingerbreadth above the clavicle on each side (see

the diaphragm. It extends upward into the root of the neck

The chest cavity is bounded by the chest wall and below by

the

Mediastinum

and

Superior Mediastinum

Inferior Mediastinum

C H A P T E R O B J E C T I V E S

To learn the structure of the heart, including its conducting

pericardial cavity,

thoracic cavity, pleural cavity

To be able to define what is meant by the term

To understand the general arrangement of the thoracic viscera

■

and their relationship to one another and to the chest wall.

■

mediastinum and

to learn the arrangement of the pleura relative to the lungs. This

information is fundamental to the comprehension of the function

and disease of the lungs.

■

Appreciating that the heart and the lungs are enveloped in

serous membranes that provide a lubricating mechanism for

these mobile viscera and being able to distinguish between

such terms as

(pleural space),

and costodiaphragmatic recess.

■

system and the arrangement of the different chambers and

valves, which is basic to understanding the physiologic and

pathologic features of the heart. The critical nature of the

blood supply to the heart and the end arteries and myocardial

infarction is emphasized.

Trauma to the chest wall can result in disruption of these

are located within the thoracic cavity, namely, the aorta, the

To understand that the largest blood vessels in the body

■

pulmonary arteries, the venae cavae, and the pulmonary veins.

vessels, with consequent rapid hemorrhage and death.

Because these vessels are hidden from view within the

thorax, the diagnosis of major blood vessel injury is often

delayed, with disastrous consequences to the

patient.

Esophagus 100

Blood Supply of the Esophagus 100

Lymph Drainage of the Esophagus 100

Nerve Supply of the Esophagus 100

Thymus 100

Blood Supply 100

Cross-Sectional Anatomy of the Thorax 102
Radiographic Anatomy 102

Posteroanterior Radiograph 102

Right Oblique Radiograph 105

Left Oblique Radiograph 105

Bronchography and Contrast

Visualization of the Esophagus 105

Coronary Angiography 107

CT Scanning of the Thorax 107

CHAPTER 3

The Thorax: Part II—The Thoracic Cavity

esophagus

aygos vein aorta

left atrium

right atrium

right ventricle

left ventricle

pleural space

parietal pleura

right lung,
lower lobe

left lung,
lower lobe

right lung,
upper lobe

right oblique

fissure

left oblique

fissure

visceral serous

pericardium

parietal serous

pericardium

fibrous pericardium

sternum

pericardial cavity

visceral pleura

FIGURE 3.1

Cross section of the thorax at the level of the eighth thoracic vertebra. Note the arrangement of the pleura and

pleural cavity (space) and the fibrous and the serous pericardia.

Deflection of Mediastinum

mine the diagnosis and degree of spread of carcinoma of the

bifurcation of the trachea. The procedure can be used to deter

superior mediastinum is explored down to the region of the

midline in the neck just above the suprasternal notch, and the

opening the pleural cavities. A small incision is made in the

mens of tracheobronchial lymph nodes are obtained without

phrenic nerves, and sometimes the trachea, main bronchi, and

Other pressure effects can be seen on the sympathetic trunks,

severe congestion of the veins of the upper part of the body.

tumor can partially occlude the superior vena cava, causing

producing paralysis of the left vocal fold. An expanding cyst or

enlargement may compress the left recurrent laryngeal nerve,

idly spread to involve the mediastinal lymph nodes, which on

enlarging tumor or organ. A tumor of the left lung can rap

the mediastinum, their functions can be interfered with by an

Because many vital structures are crowded together within

itself by the patient’s being breathless and in a state of shock; on

astinum is displaced to the opposite side. This condition reveals

in rhythmic pulsation, and the esophagus distends as each bolus

effect of the preserving fluids, is an inflexible, fixed structure. In

In the cadaver, the mediastinum, as the result of the hardening

the living, it is very mobile; the lungs, heart, and large arteries are

of food passes through it.

If air enters the pleural cavity (a condition called pneumotho-

rax), the lung on that side immediately collapses and the medi-

examination, the trachea and the heart are found to be displaced

to the opposite side.

Mediastinitis

The structures that make up the mediastinum are embedded in

loose connective tissue that is continuous with that of the root

of the neck. Thus, it is possible for a deep infection of the neck

to spread readily into the thorax, producing a mediastinitis.

Penetrating wounds of the chest involving the esophagus may

produce a mediastinitis. In esophageal perforations, air escapes

into the connective tissue spaces and ascends beneath the fas-

cia to the root of the neck, producing subcutaneous emphysema.

Mediastinal Tumors or Cysts

esophagus.

Mediastinoscopy

Mediastinoscopy is a diagnostic procedure whereby speci-

bronchus.

C L I N I C A L N O T E S

Basic Anatomy

of the suprapleural membrane at the thoracic outlet; and a

extends into the root of the neck to line the undersurface

phragm and the lateral aspect of the mediastinum and

the thoracic wall, covers the thoracic surface of the dia

which lines

parietal layer,

Each pleura has two parts: a

the development of the lungs in Figure 3.4.

pleurae, it might be helpful to look at the illustrations of

num within the chest cavity (Fig. 3.3). Before discussing the

The pleurae and lungs lie on either side of the mediasti

Pleurae

T12

manubrium

sternal

angle

body of

sternum

xiphoid

process

posterior
mediastinum

inferior
mediastinum

superior
mediastinum

diaphragm

mediastinum

middle

mediastinum

FIGURE 3.2

Subdivisions of the mediastinum.

vertebral column

mediastinum

mediastinal pleura
(parietal pleura)

visceral pleura

pleural cavity
(space)

costal pleura
(parietal pleura)

body of

sternum

hilum of lung

costal
cartilages

diaphragmatic pleura
(parietal pleura)

FIGURE 3.3

Pleurae from above and in front. Note the posi

tion of the mediastinum and the hilum of each lung.

laryngotracheal tube

coelomic cavity

lung bud

coelomic cavity

parietal pleura

visceral pleura

parietal pleura

pleural cavity

lung

thoracic

wall

diaphragm

costodiaphragmatic
recess

parietal pleura

pleural cavity

visceral pleura

root of lung

visceral pleura

FIGURE 3.4

Formation of the lungs. Note that each lung bud

the surface that it covers. The cervical pleura extends up

parietal pleura according to the region in which it lies or

For purposes of description, it is customary to divide the

each other with the minimum of friction.

pleura as a thin film and permits the two layers to move on

which covers the surfaces of the

pleural fluid,

sue fluid, the

The pleural cavity normally contains a small amount of tis

pleural cavity [slitlike] space and the larger chest cavity.)

This is probably to avoid the confusion between the

cavity.

pleural

instead of the anatomic term

pleural space

term

(Figs. 3.3 and 3.4). (Clinicians are increasingly using the

pleural cavity

from one another by a slitlike space, the

The parietal and visceral layers of pleura are separated

(Fig. 3.5).

nary ligament

pleural cuff hangs down as a loose fold called the

monary vessels and large bronchi during respiration, the

(Figs. 3.3, 3.4, and 3.5). To allow for movement of the pul

entering and leaving the lung at the hilum of each lung

by means of a cuff of pleura that surrounds the structures

The two layers become continuous with one another

fissures (Figs. 3.1, 3.3, 3.4, 3.5, and 3.6).

of the lungs and extends into the depths of the interlobar

which completely covers the outer surfaces

visceral layer,

growth of the lung.

to a slitlike space called the pleural cavity as a result of the

with parietal pleura. The original coelomic cavity is reduced

covered with visceral pleura and the thoracic wall is lined

to fill a greater part of the cavity. Note also that the lung is

invaginates the wall of the coelomic cavity and then grows

pulmo-

CHAPTER 3

left costodiaphragmatic recesses and the right and left

fully occupy the pleural cavities at four sites: the right and

ties. However, during quiet inspiration, the lungs do not

full inspiration, the lungs expand and fill the pleural cavi

During

lung root.

sels and bronchi that constitute the

except at its hilum, where it is attached to the blood ves

the visceral pleura. It is thus seen that each lung lies free

vessels and bronchi and here becomes continuous with

the hilum of the lung, it is reflected as a cuff around the

boundary of the mediastinum (see Figs. 3.3 and 3.5). At

covers and forms the lateral

mediastinal pleura

The

(Figs. 3.4 and 3.5).

costodiaphragmatic recess

inspiration is referred to as the

area of the pleural cavity into which the lung expands on

the costal and diaphragmatic pleurae separate. This lower

ration, the margins of the base of the lung descend, and

other below the lower border of the lung. In deep inspi

costal and diaphragmatic pleurae are in apposition to each

the diaphragm (Figs. 3.3 and 3.5). In quiet respiration, the

covers the thoracic surface of

diaphragmatic pleura

The

tebral bodies, and the back of the sternum (Fig. 3.3).

costal cartilages, the intercostal spaces, the sides of the ver

lines the inner surfaces of the ribs, the

costal pleura

The

to 4 cm) above the medial third of the clavicle.

membrane (see Fig. 2.13). It reaches a level 1 to 1.5 in. (2.5

into the neck, lining the undersurface of the suprapleural

The Thorax: Part II—The Thoracic Cavity

costomediastinal recesses.

six intercostal nerves.

the phrenic nerve and around the periphery by the lower

The diaphragmatic pleura is supplied over the domes by

nerve.

The mediastinal pleura is supplied by the phrenic

costal nerves.

The costal pleura is segmentally supplied by the inter

ture, touch, and pressure and is supplied as follows:

The parietal pleura (Fig. 3.7) is sensitive to pain, tempera

described on pages 54 and 55.

The surface markings of the lungs and pleurae were

lungs slide in and out of the recesses.

inspiration and expiration, the anterior borders of the

are separated by a capillary layer of pleural fluid. During

between the costal and mediastinal parietal pleurae, which

anterior margins of the pleura. They are slitlike spaces

are situated along the

costomediastinal recesses

The

come together again.

lungs ascend so that the costal and diaphragmatic pleurae

the recesses. During expiration, the lower margins of the

ing inspiration, the lower margins of the lungs descend into

are separated only by a capillary layer of pleural fluid. Dur

between the costal and diaphragmatic parietal pleurae that

are slitlike spaces

costodiaphragmatic recesses

The

Nerve Supply of the Pleura

■

cervical pleura

(parietal pleura)

mediastinal pleura

(parietal pleura)

cuff of pleura

diaphragmatic pleura

(parietal pleura)

pulmonary ligament

lower lobe

upper lobe

bronchi

costal pleura

(parietal pleura)

oblique fissure

left lung

visceral pleura

pulmonary veins

FIGURE 3.5

Different areas of the parietal pleura. Note the cuff of pleura (

Arrows

and leaving the hilum of the left lung. It is here that the parietal and the visceral layers of pleura become continuous.

) that surrounds structures entering

dotted lines

indicate the position of the costodiaphragmatic recess.

Basic Anatomy

by dividing into right and left principal (main)

carina

line of the neck. In the thorax, the trachea ends below at

level of the 6th cervical vertebra. It descends in the mid

the larynx at the lower border of the cricoid cartilage at the

tube (Fig. 3.9). It begins in the neck as a continuation of

The trachea is a mobile cartilaginous and membranous

Trachea

monary plexus (Fig. 3.7).

touch. It receives an autonomic nerve supply from the pul

but is insensitive to common sensations such as pain and

The visceral pleura covering the lungs is sensitive to stretch

the

nerve

first rib

trachea

cervical dome of

pleura

right vagus

right phrenic

nerve

brachiocephalic

artery

infrahyoid

muscles

thymus left common carotid artery

left internal jugular vein

internal thoracic artery

left phrenic nerve

left vagus nerve

left subclavian artery

left recurrent laryngeal

nerve

first thoracic nerve

thoracic duct

sympathetic trunk

esophagus

superior vena

cava

right phrenic

nerve

right lung

azygos vein

right vagus nerve

trachea

esophagus

sympathetic

trunk

thoracic duct

left recurrent laryngeal

nerve

left lung

left vagus nerve

left phrenic nerve

arch of aorta

manubrium sterni

thymus

FIGURE 3.6

Cross section of the thorax.

below.

At the 4th thoracic vertebra, as seen from

At the inlet, as seen from above.

Phrenic nerves
(C3, C4, and C5)

Intercostal

nerves

(T1-T11)

Parietal pleura

Visceral pleura

Nerves of
pulmonary plexus
(vagus and
sympathetic)

FIGURE 3.7

Diagram showing the innervation of the parietal

and visceral layers of pleura.