MRCS Part B Revision · Anatomy
Trachea — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Trachea is a surgical anatomy station. Three of the seventeen examined stations in the MRCS Part B OSCE are surgical anatomy. The anatomy stations put a prosected specimen, a model or an image in front of you and ask you to identify structures and say what they do, what they relate to and what happens when they are injured.
What you need to know for the Trachea station
The root of the neck and upper mediastinum dissected around the trachea, with the levels, the relations in the neck, the right main bronchus and the sternal angle as the questions.
Levels
The trachea begins at the lower border of the cricoid cartilage at C6 and ends at the carina, where it divides into the two main bronchi, at the level of the sternal angle, the disc between T4 and T5 in expiration, a vertebra lower in deep inspiration. It is 10 to 12 cm long and about 2 cm wide, held open by 15 to 20 incomplete rings of hyaline cartilage joined by fibro-elastic membrane, with the trachealis muscle closing the ring behind against the oesophagus, so the posterior wall is flat and can bulge into the lumen when the muscle contracts in a cough. It is lined by ciliated columnar epithelium with goblet cells, which sweep mucus up to the larynx.
Relations in the neck
In front, from the skin inwards: the investing fascia, the sternohyoid and sternothyroid muscles, the isthmus of the thyroid over the second to fourth rings with the pretracheal fascia, the inferior thyroid veins below the isthmus, the jugular venous arch in the suprasternal notch, and in a child or a short neck the left brachiocephalic vein and the thymus rising above the manubrium. At the sides, the lobes of the thyroid, the carotid sheaths with the common carotid arteries, and the recurrent laryngeal nerves running up in the grooves between trachea and oesophagus, with the inferior thyroid arteries crossing behind the sheaths. Behind, the oesophagus, which begins at the same level, and the prevertebral fascia over the cervical spine. A tracheostomy goes through the second and third rings, below the isthmus, which is divided or retracted, and it must avoid the brachiocephalic trunk crossing in front of the trachea at the thoracic inlet.
Relations in the thorax
The arch of the aorta lies on its left side and then in front of the left main bronchus; the brachiocephalic trunk and left common carotid artery lie in front of it as they leave the arch; the azygos vein arches over the right main bronchus to the superior vena cava; and the vagus nerves and the deep cardiac plexus lie around the bifurcation with the tracheobronchial lymph nodes, which are enlarged in sarcoidosis, lymphoma and lung cancer and splay the carina.
Why objects go right
The right main bronchus is wider, shorter, about 2.5 cm, and more vertical, leaving the trachea at about 25 degrees, because the carina lies to the left of the midline and the left bronchus has to pass under the aortic arch; so anything dropped down the trachea, an inhaled peanut or a tooth, or an endotracheal tube pushed too far, goes into the right lung. The right upper lobe bronchus leaves within 2 cm of the carina, which is why an over-advanced tube collapses that lobe.
The sternal angle
The ridge where the manubrium meets the body of the sternum, felt about 5 cm below the suprasternal notch, at the level of the second costal cartilage, from which the ribs are counted. It marks the plane of T4/5, and at that plane: the aortic arch begins and ends, the trachea bifurcates, the superior vena cava enters the pericardium, the azygos vein joins the cava, the thoracic duct crosses to the left, the pulmonary trunk divides, the ligamentum arteriosum and the left recurrent laryngeal nerve lie, and the superior mediastinum becomes the inferior.
Images from this station
What are you asked at the Trachea station?
The station runs to 14 questions over nine minutes. These are the questions as they are put to you; the model answers are in the question bank.
- Identify structures 1 and 2
- Identify structures 3-5
- Identify structures 6-7
- Identify vessels 8-9
- Identify vessels 10 and 11
- Identify vessels 12-13
- Identify vessels 14 and 15
- Identify nerves 16 and 17
- Identify structures 18-19
- At what level does the trachea originate and at what level does it divide?
- Describe the relationships of structures to the trachea in the neck
- Why are inhaled objects more likely to lodge themselves in the right main bronchus?
And 2 more at this station.
How is the anatomy station marked in MRCS Part B?
An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
FAQ
What does the Trachea station ask?
It opens with "Identify structures 1 and 2" and runs to 14 questions over nine minutes. An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
How many anatomy stations are there in MRCS Part B?
Three of the seventeen examined stations are surgical anatomy, and two more are surgical pathology. Together they make up the five Anatomy and surgical pathology stations of the Applied Knowledge component.
How are the anatomy stations marked?
Each station is marked out of 20 and all 20 marks are awarded for clinical knowledge and its application. You also receive a separate global rating of pass, borderline or fail for the station.
Are the specimens real?
Yes. Anatomy bays use prosected cadaveric specimens, models and images. Candidates report being shown photographs of specimens as well as the specimens themselves, so practise on real dissection photography rather than diagrams alone.
What happens if I get an early question wrong?
The intercollegiate guidance says that if a wrong answer would affect your performance on later questions at the same station, the examiner gives you the correct answer before moving on. One mistake does not have to cost you the whole bay.
How many stations are in the MRCS Part B OSCE?
Seventeen examined stations of nine minutes each, with a minute to read the task before each one. Two preparation stations and at least one rest station bring the circuit to about twenty, and the exam takes about three and a half hours.
What is the pass mark for MRCS Part B?
There is no published pass mark. The cut score is set separately for Applied Knowledge and Applied Skills, for each circuit, by borderline regression. Published pass rates across the 2024/25 diets ranged from 51% to 66%.
Can I fail a station and still pass?
Yes. There is no rule about how many stations you may fail: the cut score applies to your total mark in each component, so a weak station costs the marks you lost on it and strong stations elsewhere can make them back. Applied Knowledge and Applied Skills are passed separately and must both be passed at the same sitting, so a strong anatomy performance cannot rescue a weak communication one.
Dr Richard Miller, MBChB FRCS
Station summaries are reviewed against the current intercollegiate MRCS syllabus and the published marking blueprint. Guidance changes between diets: check the royal colleges' own pages before relying on a date, a fee or a threshold.
Practise this station
The question bank carries the model answer to every question above, with the rest of the anatomy stations.
More anatomy stations