A chest drain is inserted in the fifth intercostal space in the midaxillary line.
After the skin and subcutaneous tissue, which muscle is the first to be encountered by the dissecting forceps?
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Thorax for MRCS Part A
Thoracic anatomy covers the chest wall and intercostal spaces, the pleura and the diaphragm with its openings, the heart, pericardium and coronary circulation, the trachea, bronchi and lungs, and the mediastinum with the great vessels, the oesophagus and the nerves that cross it. Applied surgical anatomy is 75 of the 180 Paper 1 questions; the thorax contributes 6 of them. The useful knowledge is procedural: where to place a chest drain and why the neurovascular bundle sits under the rib, which lobe an inhaled foreign body reaches, what each diaphragmatic opening transmits and at which vertebral level, which coronary artery supplies the inferior wall, and how the phrenic, vagus and recurrent laryngeal nerves relate to the great vessels. Questions in this domain tend to describe a procedure, an injury or a radiograph and ask for the structure involved.
60 questions in the bank · 1 topics Updated 6 October 2026
Topics in this domain
- Thoracic anatomy60
What the paper tends to test
- Questions typically test chest drain and thoracocentesis anatomy — the safe triangle, the position of the neurovascular bundle and the layers the drain passes through.
- Expect the diaphragmatic openings and their vertebral levels: the caval opening at T8, the oesophageal hiatus at T10 and the aortic hiatus at T12, with what accompanies each.
- Bronchial questions ask why an inhaled foreign body goes to the right lung and which bronchopulmonary segment is dependent in a supine patient.
- Coronary questions usually match an infarct territory on the ECG to the artery involved, or ask which artery supplies the sinoatrial and atrioventricular nodes.
- Mediastinal questions test the relations of the arch of the aorta — the left recurrent laryngeal nerve, the ligamentum arteriosum and the thoracic duct — and the structures at risk in a sternotomy or a thoracotomy.
- Expect the surface markings of the pleura and the lungs, and why the pleura is at risk in surgery on the kidney and adrenal.
- The oesophagus is tested through its constrictions, its blood supply by thirds and its venous drainage to both the portal and the systemic systems.
Classic traps and discriminators
- The intercostal vein, artery and nerve run in the costal groove along the lower border of each rib, so a chest drain or needle is passed just above the upper border of the rib below the chosen space.
- The caval opening at T8 transmits the inferior vena cava and the right phrenic nerve; the oesophageal hiatus at T10 transmits the oesophagus and both vagal trunks; the aortic hiatus at T12 transmits the aorta, the thoracic duct and the azygos vein.
- The right main bronchus is wider, shorter and more vertical than the left, so inhaled material usually lodges on the right — in the apical segment of the right lower lobe if the patient was supine, the posterior basal segment if upright.
- The left recurrent laryngeal nerve hooks under the arch of the aorta behind the ligamentum arteriosum, so a left hilar tumour or an aortic arch aneurysm can present with a hoarse voice; the right recurrent laryngeal nerve loops under the right subclavian artery.
- The sinoatrial node is supplied by the right coronary artery in about 60% of people and the atrioventricular node by the right coronary artery in about 85–90%, which is why inferior infarction is the one that classically brings bradycardia and heart block.
- The phrenic nerve (C3, C4, C5) passes in front of the root of the lung and the vagus passes behind it — the distinction that places each nerve in a hilar dissection and explains which is at risk in a pericardial or an oesophageal operation.
Free thorax practice question
From the free sample — original, referenced, with the full explanation. Rate your confidence first.
Thorax questions, answered
Where is a chest drain inserted?
In the ‘safe triangle’ bounded by the lateral border of pectoralis major, the anterior border of latissimus dorsi and a horizontal line at the level of the nipple (about the fifth intercostal space), with its apex below the axilla. The drain is placed just above the rib to avoid the neurovascular bundle in the costal groove.
What are the surface markings of the pleura and the lungs?
The parietal pleura reaches the 8th rib in the mid-clavicular line, the 10th in the mid-axillary line and the 12th at the back; the lung reaches the 6th, 8th and 10th ribs at the same lines. Because the pleura extends below the 12th rib posteriorly it can be opened during a nephrectomy or adrenalectomy.
Which coronary artery supplies which part of the heart?
The left anterior descending artery supplies the anterior wall, the anterior two-thirds of the septum and the apex (leads V1–V4); the circumflex supplies the lateral wall (I, aVL, V5–V6); the right coronary artery supplies the inferior wall (II, III, aVF), the right ventricle and, in most people, the sinoatrial and atrioventricular nodes.
How many thorax anatomy questions are in MRCS Part A?
The ICBSE blueprint lists 6 of the 180 Paper 1 questions under the thorax, within the 75 for applied surgical anatomy. Chest trauma and cardiorespiratory physiology are separate blueprint lines and are covered under trauma and physiology.
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