OUTLET OF THORAX By Dr Garima Sehgal Components

OUTLET OF THORAX By. Dr Garima Sehgal

Components of thoracic cage • Thoracic vertebrae • Ribs & costal cartilages • Sternum

Superior and inferior apertures of thorax �Inlet (superior aperture) �Closed by a diaphragm ? �Outlet (inferior aperture) �Closed by a diaphragm ?

Location

Attachments (Origin) –inferior view • Sternal • Costal • Lumbar

Apertures of the diaphragm � There are three large openings, 1) Aortic, 2) Oesophageal 3) Vena caval � and a number of smaller ones.

Aortic aperture 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

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.

Lesser apertures � 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

Thoracic aspect of diaphragm

Inferior view

Superior relations of diaphragm

Inferior relations of diaphragm

Vascular supply and lymphatic drainage � lower five intercostal & subcostal arteries � phrenic arteries 1. 2. 3. 4. 5. Superior phrenic inferior phrenic Musculophrenic Pericardiophrenic Superior epigastric

Phrenic veins � The right phrenic vein ends in the inferior vena cava. � The left phrenic vein is often double: one branch ends in the left renal or suprarenal vein, the other passes anterior to the oesophageal opening to join the inferior vena cava.

Phrenic nerve � two phrenic nerves � originate in the neck and pass down between the lung and heart to reach the diaphragm. � Root value (C 3 -C 5) predominantly C 4. � The phrenic nerves contain motor, sensory, and sympathetic nerve fibers.

Innervation � Motor supply the phrenic nerves � Sensory fibres � periphery lower six or seven intercostal nerves � central part Phrenic – • Right crus - both right and left phrenic nerves. • crural fibres contract slightly before the costal part, and this may be functionally significant.

Phrenic nerves contd…. . � Where do they pierce ? � phrenic nerve supplies the parietal pleura parietal peritoneum below, and the central diaphragm. The trunk divides into three branches - an anterior (sternal) branch - anterolateral branch - short posterior branch

Clinical importance � 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.

Functions of the diaphragm 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. � is � in lifting heavy weights. � muscular pump � Sphincter to orifice

Range of movement 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- 11 left cupola – T-12 After a forced expiration right 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

Development of diaphragm � Septum transversum � Pleuroperitoneal fold � Mesentry of oesophagus � Body wall

APPLIED ANATOMY

Posterolateral diaphragmatic hernia

Sliding, or type I, hiatus hernia � laxity of the phrenooesophageal membrane, allows the gastrooesophageal junction to slide into the thorax � usually acquired, � commonly occurs in the fifth decade of life. � found in more than 50% of patients with gastrooesophageal reflux. Hiatus hernia

Para-oesophageal, or type II, hiatus hernia � When the stomach herniates into the thorax alongside the oesophagus

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

� Referred pain – pain arising from structures served by the phrenic nerve is often to other somatic regions served by spinal nerves C 3 -C 5. (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 (C 3 -C 5)

Lesions of the phrenic nerve � 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 �