The thoracic part of the sympathetic trunk consists of approximately 11 ganglia joined by longitudi-nal bundles of preganglionic and post-ganglionic fibres. In the superior part of the thorax, the trunk lies on the neck or head of the ribs. Inferiorly, it passes on to the bodies of the vertebrae as the bod-ies increase in width. The first thoracic gan-glion is frequently fused with the inferior cervical ganglion to form the cervicothoracic (stellate) ganglion on the neck of the first rib. This gangli-on may also include the secgangli-ond thoracic gangligangli-on.
Branches of the sympathetic trunk in the thorax
1. Grey and white rami communicantes are nerves which join each ganglion to one (or two)
CLINICAL APPLICATION 4.1 Pneumothorax Pneumothorax refers to a pathological accumulation of air
in the pleural cavity. Symptoms: a small pneumothorax is mostly asymptomatic with minimal physical signs. A large pneumothorax presents with sudden onset of chest pain and breathlessness. Signs: percussion in intercostal spaces yields a typical hyperresonant note due to the underlying air in the pleural cavity. Auscultation reveals absent breath sounds over the affected hemithorax. Causes: sponta-neous or primary pneumothorax occurs due to rupture of congenital subpleural blebs at the apices of the lung.
Secondary pneumothorax occurs as a complication of an underlying lung disease such as asthma, tuberculosis, or lung abscess. Traumatic pneumothorax occurs from blunt or penetrating injuries of the thorax. Iatrogenic pneumo-thorax may occur following procedures such as pleural biopsy, positive pressure ventilation, and faulty placement
of internal jugular or subclavian vein catheters. Tension pneumothorax results from an abnormal communication between the pleural cavity and the underlying lung act-ing as a one-way valve, allowact-ing air to enter the pleural space during inspiration but not allowing it to escape during expiration. The accumulation of large amount of air in one pleural cavity causes compression of the lung and a gross shift of the mediastinum to the opposite side, resulting in significant compression of the opposite lung.
Treatment: a small pneumothorax may resolve sponta-neously as air in the pleural cavity is absorbed. A large pneumothorax or tension pneumothorax will require the placement of a chest tube. The chest tube is placed within the pleural cavity, connected to an underwater seal drain-age, and suction is applied till the air in the pleural cavity is removed, the lung expands, and the air leak subsides.
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The posterior mediastinum
CLINICAL APPLICATION 4.3 Bronchogenic carcinoma A 65-year-old chronic smoker presents with a history of
cough, haemoptysis (coughing up of blood), dyspnoea (difficulty in breathing), and significant loss of weight and appetite. On examination, his respiratory rate is slightly in-creased and he has a palpable supraclavicular lymph node.
Auscultation reveals decreased breath sounds over the right lung. Chest X-ray and computerized tomography (CT) of the thorax reveal a large mass in the right lung. Biopsy of the mass confirms a diagnosis of bronchogenic carcinoma.
Study question 1: what is the most common risk factor for bronchogenic carcinoma? (Answer: the most com-mon risk factor worldwide is cigarette smoking.)
Study question 2: what is the possible cause for haemoptysis in this patient? (Answer: in lung cancer, haemoptysis indicates a malignant infiltration of bronchial vessels.)
Study question 3: what is the significance of an en-larged supraclavicular lymph node? (Answer: lymph from the lung drains to the lower cervical lymph nodes, which lie in the supraclavicular fossa. The clinical finding of an enlarged supraclavicular lymph node is known as the ‘Troisier’s sign’. It usually indicates an advanced stage of malignancy.) The supraclavicular node itself is called the ‘Virchow’s node’.
CLINICAL APPLICATION 4.2 Collapsed lung When a bronchus is blocked, the air in the lung
tis-sue distal to the block is absorbed into the pulmonary blood vessels, and that part of the lung collapses. Con-tinuing respiratory movements will cause the remainder of the lung to expand and fill the space vacated by the
shrinking lobe. If a large segment of the lung is collapsed, the mediastinum will shift towards the affected side as the opposite lung expands. Movement of the chest wall overlying a collapsed segment of the lung may be visibly or palpably reduced.
CLINICAL APPLICATION 4.4 Metastatic lung tumours
Metastatic lung tumours are malignancies that have spread to the lung from a primary tumour at another site—commonly the breast, colon, or urinary bladder.
Fig. 4.56 is a radiograph of a 55-year-old woman with metastatic lung cancer.
Fig. 4.56 Chest X-ray of a 55-year-old woman with metastatic lung tumours (arrows).
CLINICAL APPLICATION 4.5 Pericarditis A 40-year-old man presents with a history of low-grade
fever and sharp, stabbing chest pain behind the ster-num. The pain typically increases with cough and deep breathing and is partially relieved on sitting up and leaning forwards. Auscultation of the chest reveals an
audible friction rub heard over the region of the heart.
An echocardiogram reveals a mild pericardial effusion.
Study question 1: what is pericarditis? (Answer: peri-carditis is inflammation of the pericardium. It com-monly occurs as a complication of viral infections or
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The cavity of the thorax
CLINICAL APPLICATION 4.7 Myocardial infarction A 65-year-old man was admitted with sudden onset of
se-vere chest pain, nausea, vomiting, and breathlessness. His pulse was weak and rapid, blood pressure low, and breath sounds were harsh. An electrocardiogram (ECG) confirmed that he had had a myocardial infarction—a heart attack. A CT coronary angiogram revealed marked narrowing of the
coronary arteries and many of their branches due to ather-osclerosis. (Atherosclerosis is a pathological condition re-sulting in narrowing and hardening of arteries. Myocardial infarction is the death of cardiac muscle, which has been deprived of blood due to sudden blockage of one or both of the coronary arteries or their branches.)
CLINICAL APPLICATION 4.6 Valvular heart disease A 33-year-old man presents in the clinic with a history of
fatigue, palpitations, and gradually increasing breathless-ness over the past year. His blood pressure was 120/70 mmHg and pulse rate 80/minute. Examination of the cardiovascular system revealed a forceful apex beat in the seventh left intercostal space, 3 cm lateral to the mid-clavicular line. On auscultation, a pansystolic murmur was heard loudest at the mitral area and radiated to the left axilla. A diagnosis of mitral regurgitation was made.
Study question 1: what is the function of heart valves?
(Answer: heart valves permit unidirectional blood flow and prevent retrograde flow of blood.)
Study question 2: what would be the result of an in-competent mitral valve? (Answer: an inin-competent mitral valve causes regurgitation of left ventricular blood into the left atrium during ventricular systole.)
Study question 3: what is the normal position of the apex beat? (Answer: fifth left intercostal space, 1 cm me-dial to the mid-clavicular line.)
Study question 4: what is the probable cause for the apex beat being grossly displaced in this patient? (An-swer: the apex beat is shifted downwards and outwards, indicating a grossly enlarged left ventricle.)
Study question 5: list the components of the mitral valve complex. (Answer: the mitral valve complex in-cludes the mitral valve, chordae tendinae, papillary mus-cles of the left ventricle, and surrounding myocardium.
Dysfunction of any of these components can cause re-gurgitation of blood.)
Study question 5: can damaged heart valves be re-paired or replaced? (Answer: damaged heart valves can-not be repaired, but they can be replaced by prosthetic valves. Prosthetic valves are of two types: (1) mechanical valves are made of pyrolytic carbon and titanium; and (2) bioprosthetic valves are made of animal tissue. Tis-sue valves are again of two types: (1) xenografts—made from porcine valves or bovine pericardium; and (2) ho-mografts—from human cadavers.)
tuberculosis. Other common causes include connective tissue disorders, post-myocardial infarction, malignancy, and uraemia. A friction rub over the pericardium is a typical extra heart sound heard in pericarditis.)
Study question 2: what is pericardial effusion? (Answer:
pericardial effusion is a pathological collection of fluid in the pericardial cavity. Large effusions (>1000 ml) that de-velop gradually over a long period of time may not cause significant haemodynamic changes as the pericardium stretches to accommodate the fluid. However, rapidly de-veloping effusions (even 300 ml) can cause severe haemo-dynamic changes requiring urgent medical treatment.)
Study question 3: what is cardiac tamponade? (Answer:
a rapidly developing pericardial effusion that compresses the heart is called cardiac tamponade. Diastolic filling of ventricles is significantly compromised due to external pressure on the heart. Jugular venous pressure is elevated and systolic blood pressure often low. Heart sounds seem distant and muffled on auscultation. Pericardial tamponade is a medical emergency requiring urgent surgical drainage.)
Study question 4: how is pericardiocentesis done?
(Answer: an aspiration needle is introduced into the fifth left intercostal space near the sternum. This approach to the pericardial sac avoids going through the pleura or lung—both of which deviate to the left in this location, leaving the pericardium bare [Fig. 4.23].)
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The posterior mediastinum
Study question 1: what is the arterial supply of the heart? From where do these arteries arise? (Answer: the heart is supplied by the left and right coronary arteries.
They are branches of the ascending aorta and arise from the right and left posterior aortic sinuses, respectively.)
Study question 2: what arteries supply the interven-tricular septum? (Answer: the anterior interveninterven-tricular
branch of the left coronary artery and the posterior in-terventricular branch of the right coronary artery supply the interventricular septum. The anterior interventricular artery supplies a larger area of the septum.)
Study question 3: what is the arterial supply to the sino-atrial node? (Answer: the sino-atrial node is sup-plied by a branch of the right coronary artery.)
CLINICAL APPLICATION 4.8 Pacemaker The normal heartbeat is controlled by the sinus node. The electrical signal generated by the si-nus node spreads throughout the heart, causing it to beat. The most common reason for pacemaker implantation is because the sinus node function becomes too slow. The artificial pacemaker is im-planted subcutaneously below the left clavicle. Fig.
4.57 is an X-ray of a patient with a cardiac pace-maker. The pacemaker is in the subcutaneous tissue of the anterior chest wall.
Study exercise 1: follow the wire from the pace-maker through the large veins and chambers of the heart, naming the structures it lies in sequentially.
(Answer: the wire from the pacemaker runs through the left subclavian vein, left brachiocephalic vein, superior vena cava, and right atrium, through the right atrioventricular valve to the right ventricle.)
Fig. 4.57 X-ray of a patient with a cardiac pacemaker. The pacemaker is in the subcutaneous tissue of the anterior chest wall (A). Arrows = pacemaker wire.
A