OUTLET OF THORAX

OUTLET OF

THORAX

By-Dr Garima

Sehgal

Components of thoracic

cage•Thoracic

vertebrae•Ribs & costal

cartilages•Sternum

Inlet (superior aperture)

Closed by a diaphragm ?

Outlet (inferior aperture)

Closed by a diaphragm ?

Superior and inferior apertures of thorax

Location

Attachments (Origin) –inferior view

• Sternal

• Costal

• Lumbar

There are three large openings,

1) Aortic, 2) Oesophageal3) Vena caval

and a number of smaller ones.

Apertures of the diaphragm

osseo-aponeurotic opening

Lowest & most posterior

to the left of the midline

level -lower border of T-12

lies behind the diaphragm

Transmits aorta, thoracic duct, lymphatic trunks from the lower posterior thoracic wall and, sometimes, the azygos and hemiazygos veins

Aortic aperture

Oesophageal aperture Level T-10 in front and left of, the

aortic opening is bounded by muscle

fibres of the right crus. It transmits oesophagus, gastric nerves, oesophageal branches

of the left gastric vessels

lymphatics

Vena caval aperture Highest Level disc between

T-8 & T-9 quadrilateral, and

located in the central area of the tendon –so aponeurotic.

traversed by – inferior vena cava

and by some branches of the right phrenic nerve.

Two in each crus: one transmits the greater,other the lesser, splanchnic nerve.

Intercostal nerves and vessels pass in between the muscular slips of origin

Sympathetic trunks usually enter the abdominal cavity behind the medial arcuate ligament.

Subcostal nerves and vessels pass behind the Openings for minute veins frequently occur in

the central tendon

Lesser apertures

Thoracic aspect of diaphragm

Inferior view

Superior relations of diaphragm

Inferior relations of diaphragm

lower five intercostal & subcostal arteries

phrenic arteries 1. Superior phrenic2. inferior phrenic3. Musculophrenic4. Pericardiophrenic5. Superior

epigastric

Vascular supply and lymphatic drainage

The right phrenic vein ends in the inferior vena cava.

The left phrenic vein is often double:

Phrenic veins

one branch ends in the left renal or suprarenal vein, the other passes anterior to the oesophageal opening to join the inferior vena cava.

two phrenic nerves originate in the neck and

pass down between the lung and heart to reach the diaphragm.

Root value (C3-C5) predominantly C4.

The phrenic nerves contain motor, sensory, and sympathetic nerve fibers.

Phrenic nerve

Motor supply - the phrenic nerves

Sensory fibres –

periphery - lower six or seven intercostal nerves

central part - Phrenic

Innervation

•Right crus - both right and left phrenic nerves. •crural fibres contract slightly before the costal part, and this may be functionally significant.

Where do they pierce ?

phrenic nerve supplies the parietal pleura parietal peritoneum below, and the central diaphragm.

Phrenic nerves contd…..

The trunk divides into three branches - an anterior (sternal) branch

- anterolateral branch- - short posterior branch

in avoiding surgical damage.

Thoracoabdominal incisions in a circumferential manner do not involve any significant branches of the phrenic nerves and preserve diaphragmatic function.

incisions of the central tendon are safe.

Clinical importance

is the major muscle of inspiration (67% of the vital capacity)

diaphragm lends additional power to all expulsive efforts like sneezing, coughing, laughing, crying, urinating, defaecating etc.

in lifting heavy weights.

muscular pump

Sphincter to orifice

Functions of the diaphragm

Diaphragmatic excursion - 1.5 cm in quiet breathing. During deep ventilation - from 6 to 10 cm.

After a forced inspiration right cupola - level of T- 11left cupola – T-12

After a forced expirationright cupola -level anteriorly with the fourth costal cartilage, laterally with the fifth, sixth and seventh ribs, and posteriorly with the eighth and the left cupola is a little lower

Range of movement

Septum transversum

Pleuroperitoneal fold

Mesentry of oesophagus

Body wall

Development of diaphragm

APPLIED ANATOMY

Posterolateral diaphragmatic hernia

Sliding, or type I, hiatus hernia

laxity of the phreno-oesophageal membrane, allows the gastro-oesophageal junction to slide into the thorax

usually acquired, commonly occurs in the

fifth decade of life. found in more than 50% of

patients with gastro-oesophageal reflux.

Hiatus hernia

Para-oesophageal, or type II, hiatus hernia

When the stomach herniates into the thorax alongside the oesophagus

Reflux of gastric contents into the oesophagus,

risk of inhalation into the lungs prevented by a physiological antireflux

barrier located at the gastro-oesophageal junction

components of this barrier 1. specialized smooth muscle of the wall 2. fibres of the crura

Oesophageal reflux

Repeated stress may eventually compromise the integrity of the hiatus, so that the muscular hiatal tunnel widens.

Referred pain – pain arising from structures served by the phrenic nerve is often to other somatic regions served by spinal nerves C3-C5. (Kehr's sign ?).

A hiccough is a spasmodic contraction of the diaphragm, which pulls air against the closed folds of the larynx. Irritation of the phrenic nerve (or the tissues supplied by it) leads to the hiccough reflex.

Patients suffering spinal cord injuries below the neck are still able to breathe effectively, despite any paralysis of the lower limbs as the phrenic nerve arises from the neck (C3-C5)

The phrenic nerve may be involved in traumatic lesions of the upper brachial plexus. Cardiac surgery thoracic surgery, tumours of the lung or mediastinum infections such as typhoid and polio. Division in the neck completely paralyses the

corresponding half of the diaphragm, which atrophies.

leads to paradoxical movement of the diaphragm

best observed fluoroscopically

Lesions of the phrenic nerve