Thorax — MCQs

Thorax Indian Medical PG Practice Questions and MCQs

Question 361: Which of the following ribs does not articulate directly with the sternum?

A. 2nd rib
B. 5th rib
C. 4th rib
D. 8th rib (Correct Answer)

Explanation: ### Explanation The human thoracic cage consists of 12 pairs of ribs, which are classified based on their anterior attachments into three categories: 1. **True Ribs (1st–7th):** These articulate directly with the sternum via their own individual costal cartilages. 2. **False Ribs (8th–10th):** These do **not** articulate directly with the sternum. Instead, their costal cartilages join the cartilage of the rib immediately above them (forming the costal margin), which eventually attaches to the 7th costal cartilage. 3. **Floating Ribs (11th–12th):** These have no anterior attachment and end in the abdominal musculature. **Why Option D is Correct:** The **8th rib** is a "false rib." Its cartilage attaches to the 7th costal cartilage rather than the sternum itself. Therefore, it lacks a direct sternal articulation. **Why Other Options are Incorrect:** * **Options A, B, and C (2nd, 5th, and 4th ribs):** These are all "true ribs." They possess dedicated costal cartilages that articulate directly with the sternum (the 2nd rib at the sternal angle; the 4th and 5th at the body of the sternum). --- ### High-Yield Clinical Pearls for NEET-PG: * **Sternal Angle (Angle of Louis):** A critical landmark at the T4-T5 vertebral level where the **2nd rib** articulates. It is used for counting ribs during clinical examinations. * **Atypical Ribs:** Remember the mnemonic **"1, 2, 10, 11, 12"**. * **First Rib:** It is the shortest, broadest, and most curved. It has a scalene tubercle and grooves for the subclavian artery and vein. It rarely fractures due to its protected position. * **Costochondritis:** Inflammation of the costal cartilages (usually 2nd–5th) that can mimic myocardial infarction pain.

Question 362: What is true about the right principal bronchus?

A. Narrower
B. Horizontal
C. Shorter (Correct Answer)
D. All are true

Explanation: The right principal bronchus is anatomically distinct from the left due to the asymmetrical arrangement of thoracic organs, particularly the heart and the aorta. ### **Why "Shorter" is Correct** The right principal bronchus is approximately **2.5 cm long**, whereas the left is about 5 cm long. It is shorter because it divides into the superior lobar bronchus sooner after entering the hilum of the right lung. ### **Analysis of Incorrect Options** * **A. Narrower:** This is incorrect. The right bronchus is **wider** than the left because the right lung has a larger volume and greater capacity, requiring a larger airway. * **B. Horizontal:** This is incorrect. The right bronchus is more **vertical** (inclined at about 25° to the median plane), while the left bronchus is more horizontal (inclined at 45°). This is because the heart pushes the left bronchus more laterally. ### **High-Yield NEET-PG Clinical Pearls** * **Foreign Body Aspiration:** Because the right bronchus is **wider, shorter, and more vertical** (forming a more direct line with the trachea), inhaled foreign bodies are significantly more likely to lodge in the right lung than the left. * **Eparterial Bronchus:** The right superior lobar bronchus is also called the "eparterial" bronchus because it passes *above* the right pulmonary artery. * **Length Comparison:** Remember the "Rule of 1, 2, 3": The right bronchus is ~1 inch (2.5 cm), the left is ~2 inches (5 cm), and the trachea is ~4-5 inches (10-12 cm).

Question 363: By which week of gestation does the cardiac septum develop?

A. 5-8 weeks (Correct Answer)
B. 9-12 weeks
C. 12-16 weeks
D. 16-18 weeks

Explanation: The development of the heart is a critical milestone in embryology, beginning as a simple tube and transforming into a four-chambered organ. Septation of the heart occurs primarily between the 5th and 8th weeks of gestation. During this period, several key septa form simultaneously: * **Atrial Septum:** The *septum primum* and *septum secundum* develop to divide the common atrium. * **Ventricular Septum:** The muscular interventricular septum grows upward, while the membranous part is formed by the fusion of the endocardial cushions and the aorticopulmonary septum. * **Aorticopulmonary Septum:** Neural crest cells contribute to the spiral septum that divides the truncus arteriosus into the aorta and pulmonary trunk. By the end of the **8th week**, the basic structural framework of the heart, including the valves and chambers, is complete. **Why other options are incorrect:** * **9-12 weeks:** By this stage, the heart is already fully formed and functional; this period focuses on the maturation of other organ systems (e.g., the kidneys and external genitalia). * **12-18 weeks:** These stages represent the late first and second trimesters, where fetal growth and physiological refinement occur, far beyond the window of primary organogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Critical Period:** The heart is most sensitive to teratogens (like Rubella or Alcohol) between weeks 3 and 8. * **Endocardial Cushions:** These are the "master builders" of the heart, contributing to both atrial and ventricular septa and the AV valves. Defects here are common in **Down Syndrome**. * **First Functional Organ:** The heart is the first functional organ to develop; it starts beating by day 21-22 (4th week).

Question 364: What is the most common site of a Morgagni hernia?

A. Left anterior
B. Right posterior
C. Right anterior (Correct Answer)
D. Left posterior

Explanation: ### Explanation **Morgagni hernia** is a type of congenital diaphragmatic hernia (CDH) that occurs through the **Foramen of Morgagni**. This is an anatomical defect in the anterior diaphragm between the sternal and costal attachments (sternocostal triangle). **1. Why "Right Anterior" is correct:** The Foramen of Morgagni is located **anteriorly**, immediately retrosternal. While the potential space exists on both sides, **90% of Morgagni hernias occur on the right side**. This is because the heart and the pericardial attachments provide structural support and a physical barrier on the left side, preventing herniation. **2. Analysis of Incorrect Options:** * **Left anterior (Option A):** Rare (approx. 2-5%) due to the protective presence of the heart and pericardium. * **Right/Left posterior (Options B & D):** Posterior diaphragmatic defects are associated with **Bochdalek hernias** [1]. These occur through the pleuroperitoneal canal and are much more common than Morgagni hernias [1]. **3. Clinical Pearls for NEET-PG:** * **Mnemonic:** "Morgagni is **M**ore **A**nterior" (M-A), whereas "Bochdalek is **B**ack and **L**ateral" (B-L). * **Frequency:** Bochdalek is the most common CDH overall (approx. 85-90%) [1], while Morgagni is rare (approx. 2-3%). * **Presentation:** Unlike Bochdalek hernias, which often cause acute respiratory distress in neonates [1], Morgagni hernias are frequently **asymptomatic** and discovered incidentally on chest X-rays in adults as a mass in the right cardiophrenic angle. * **Contents:** The most common organ to herniate through the Foramen of Morgagni is the **transverse colon**, followed by the omentum and liver.

Question 365: What is the sensory supply to the diaphragm?

A. Phrenic nerve
B. Intercostal nerves
C. Both phrenic and intercostal nerves (Correct Answer)
D. None of the above

Explanation: The diaphragm is a unique musculotendinous structure with a dual sensory nerve supply based on its embryological development and anatomical regions. ### **Explanation of the Correct Answer** The diaphragm receives sensory innervation from two distinct sources: 1. **Phrenic Nerve (C3, C4, C5):** It provides sensory fibers to the **central part** of the diaphragm, including the mediastinal pleura and the diaphragmatic peritoneum covering the central tendon. 2. **Intercostal Nerves (Lower 6 or 7):** These supply the **peripheral part** of the diaphragm, including the costal pleura and the peritoneum covering the peripheral muscular portion [1]. Because the diaphragm spans from the central tendon to the peripheral ribs, both nerve sets are required for complete sensory coverage. ### **Analysis of Incorrect Options** * **Option A (Phrenic nerve):** While the phrenic nerve is the *sole motor* supply to the entire diaphragm and the *primary* sensory supply to the center, it does not cover the periphery. * **Option B (Intercostal nerves):** These only supply the peripheral rim [1]. Relying solely on intercostal nerves would leave the central portion of the diaphragm without sensation. ### **NEET-PG High-Yield Clinical Pearls** * **Referred Pain:** Irritation of the central diaphragm (phrenic nerve) causes referred pain to the **tip of the shoulder** (C4 dermatome). Irritation of the peripheral diaphragm (intercostal nerves) causes referred pain to the **lower thoracic and abdominal walls** [1]. * **Motor Supply:** Remember the mnemonic *"C3, 4, 5 keeps the diaphragm alive."* The phrenic nerve is the only motor supply. * **Embryology:** The central tendon develops from the **Septum Transversum**, while the periphery develops from the **Pleuroperitoneal membranes** and body wall mesoderm, explaining the dual nerve supply.

Question 366: Which of the following statements regarding the trachea is incorrect?

A. It is characterized by C-shaped cartilages.
B. Its outer diameter is approximately 2 cm.
C. It contains more than 20 hyaline cartilages. (Correct Answer)
D. The isthmus of the thyroid gland is typically located at the level of the 2nd, 3rd, and 4th tracheal rings.

Explanation: The trachea is a fibrocartilaginous tube that serves as the primary airway. Understanding its anatomical dimensions and relations is crucial for NEET-PG. **Why Option C is the correct (incorrect statement):** The trachea typically contains **16 to 20** C-shaped hyaline cartilages. Stating that it contains "more than 20" is anatomically incorrect. These rings are incomplete posteriorly to allow for the expansion of the esophagus during swallowing. **Analysis of other options:** * **Option A:** The trachea is indeed characterized by **C-shaped cartilages**. The posterior gap is closed by the **trachealis muscle** (smooth muscle), which helps regulate the diameter of the lumen. * **Option B:** The outer diameter of the trachea in an adult is approximately **2 cm** (20 mm) in males and slightly less in females. The internal diameter is roughly 1.2 cm. * **Option D:** This is a high-yield anatomical relation. The **isthmus of the thyroid gland** crosses the trachea at the level of the **2nd, 3rd, and 4th tracheal rings**. This is a critical landmark during surgical procedures like tracheostomy. **High-Yield Clinical Pearls for NEET-PG:** * **Length:** The trachea is approximately **10–11 cm** long. * **Extent:** It begins at the lower border of the cricoid cartilage (**C6**) and bifurcates at the level of the sternal angle (**T4/T5**). * **Carina:** The lowermost cartilage at the bifurcation is the carina, which is the most sensitive area of the tracheobronchial tree for the cough reflex. * **Blood Supply:** The upper part is supplied by the **inferior thyroid arteries**, while the lower part receives supply from the bronchial arteries.

Question 367: Which structure is located at the Angle of Louis?

A. Arch of aorta (Correct Answer)
B. Azygos vein
C. Common carotid artery
D. Clavicle

Explanation: The **Angle of Louis** (Sternal Angle) is a vital clinical landmark located at the junction of the manubrium and the body of the sternum, corresponding to the level of the **T4-T5 intervertebral disc**. ### Why Option A is Correct The Sternal Angle marks the **beginning and the end of the Arch of Aorta**. The ascending aorta terminates here to become the arch, and the arch terminates here to become the descending thoracic aorta [1]. ### Why Other Options are Incorrect * **B. Azygos vein:** While the Azygos vein arches over the root of the right lung to enter the Superior Vena Cava at this level, the vein itself is a posterior mediastinal structure; the Arch of Aorta is the more definitive landmark associated with this plane. * **C. Common carotid artery:** These arise from the arch of aorta (left) or brachiocephalic trunk (right) and ascend into the neck, well above the T4 level [1]. * **D. Clavicle:** The clavicles articulate with the manubrium at the sternoclavicular joints, which are located superior to the Angle of Louis. ### NEET-PG High-Yield Facts: The "RATTP" Mnemonic The Sternal Angle is the site of several critical anatomical events (Mnemonic: **RATTP**): 1. **R**ib 2: Articulation of the second costal cartilage. 2. **A**rch of Aorta: Starts and ends here [1]. 3. **T**racheal Bifurcation: The trachea divides into right and left principal bronchi (Carina). 4. **T**horacic Duct: Crosses from the right to the left side. 5. **P**ulmonary Trunk: Bifurcates into right and left pulmonary arteries. **Clinical Pearl:** The Angle of Louis is the primary landmark used for counting ribs during physical examinations and marks the boundary between the **Superior and Inferior Mediastinum**.

Question 368: In post-ductal coarctation of the aorta, which of the following may form collaterals?

A. Vertebral artery
B. Suprascapular artery
C. Subscapular artery
D. None of the above (Correct Answer)

Explanation: In **post-ductal coarctation of the aorta**, the narrowing occurs distal to the origin of the left subclavian artery. To bypass this obstruction and provide blood to the lower body, a collateral circulation develops between the branches of the **subclavian artery** (proximal to the block) and the **intercostal arteries** (distal to the block). [1] **Why "None of the above" is correct:** The primary collateral pathway involves the **Internal Thoracic (Mammary) Artery**. Blood flows from the Subclavian → Internal Thoracic [2] → Anterior Intercostal arteries → **Posterior Intercostal arteries** (via retrograde flow) → Descending Thoracic Aorta. While branches of the thyrocervical and costocervical trunks contribute, the specific arteries listed in the options do not typically form the functional bypass to the descending aorta. **Analysis of Incorrect Options:** * **Vertebral Artery:** While a branch of the subclavian, it supplies the brain and spinal cord; it does not participate in the intercostal bypass system. * **Suprascapular Artery:** This artery supplies the muscles of the posterior scapula. While it may participate in scapular anastomosis, it is not a primary collateral for bypassing aortic coarctation. * **Subscapular Artery:** This is a branch of the **axillary artery**. In coarctation, the pressure is elevated in the subclavian and its immediate branches; the subscapular artery is not part of the classic internal thoracic-intercostal circuit. **High-Yield Clinical Pearls for NEET-PG:** * **Rib Notching:** Dilated, tortuous posterior intercostal arteries erode the lower borders of the 3rd to 8th ribs (Roesler’s sign). * **Physical Exam:** Characterized by **radio-femoral delay** and upper limb hypertension with lower limb hypotension. * **Key Collateral:** The **Internal Thoracic Artery** is the most important vessel in this compensatory mechanism. [2]

Question 369: Which of the following is true about the right principal bronchus?

A. Short and thin
B. Short and broad (Correct Answer)
C. Long and broad
D. Long and thin

Explanation: The trachea bifurcates at the level of the sternal angle (T4-T5) into the right and left principal (primary) bronchi. The anatomical differences between these two are high-yield topics for NEET-PG. [1] **Why the correct answer is right:** The **right principal bronchus** is anatomically designed to be more in line with the trachea. It is approximately **2.5 cm long** (short) and has a **wider diameter** (broad) compared to the left. It descends at a more vertical angle (about 25 degrees from the median plane), making it a direct continuation of the tracheal path. **Analysis of incorrect options:** * **A, C, & D:** These are incorrect because they describe characteristics of the **left principal bronchus**. The left bronchus is **longer (5 cm)** and **thinner (narrower)** because it must pass inferolaterally to reach the hilum of the left lung, passing under the aortic arch and anterior to the esophagus. It is also more horizontal (45-degree angle). **Clinical Pearls for NEET-PG:** 1. **Foreign Body Aspiration:** Due to being shorter, broader, and more vertical, inhaled foreign bodies are significantly more likely to lodge in the **right principal bronchus** (specifically the right lower lobe). 2. **Azygos Vein:** The azygos vein arches over the right principal bronchus to enter the Superior Vena Cava (SVC). [1] 3. **Eparterial Bronchus:** The right bronchus gives off a superior lobar branch *before* entering the hilum, known as the eparterial bronchus (situated above the pulmonary artery). All branches of the left bronchus are hyparterial (below the artery).

Question 370: A 10-year-old boy is admitted to the hospital with retrosternal discomfort. A CT scan reveals a midline tumor of the thymus gland. Which of the following veins would most likely be compressed by the tumor?

A. Right brachiocephalic
B. Left brachiocephalic (Correct Answer)
C. Right internal jugular
D. Left internal jugular

Explanation: Explanation: The thymus gland is located in the **superior and anterior mediastinum**, situated immediately posterior to the manubrium sterni and anterior to the great vessels. [1] **Why the Left Brachiocephalic Vein is Correct:** The **left brachiocephalic vein** runs an oblique, horizontal course from left to right, passing directly **posterior to the thymus** and the manubrium. Because of its long, transverse path across the midline to join the right brachiocephalic vein (forming the Superior Vena Cava), it is the vessel most vulnerable to compression by midline thymic masses or tumors. **Why the Other Options are Incorrect:** * **Right Brachiocephalic Vein:** This vein has a more vertical and lateral course on the right side. While it is posterior to the thymus, it is less likely to be compressed by a midline mass compared to the long, horizontal segment of the left vein. * **Internal Jugular Veins (Right & Left):** These veins are located in the neck, lateral to the carotid arteries. They join the subclavian veins to form the brachiocephalic veins behind the sternoclavicular joints. Since they are superior to the mediastinum, they are not typically compressed by a thymic tumor. **NEET-PG High-Yield Pearls:** * **Anatomical Relations:** From anterior to posterior in the superior mediastinum: Thymus → Large Veins (Brachiocephalic) → Large Arteries (Arch of Aorta & branches) → Trachea → Esophagus → Thoracic Duct. * **Left vs. Right:** The left brachiocephalic vein is **twice as long** as the right and crosses the three major branches of the aortic arch. * **Clinical Correlation:** In children, the thymus is large and active; in adults, it undergoes fatty atrophy but can still be the site of a **Thymoma**, which is classically associated with **Myasthenia Gravis**. [2]

Practice by Chapter

Thoracic Wall and Diaphragm

Practice Questions

Pleura and Lungs

Practice Questions

Mediastinum

Practice Questions

Heart and Pericardium

Practice Questions

Great Vessels and Azygos System

Practice Questions

Thoracic Duct and Lymphatics

Practice Questions

Autonomic Innervation

Practice Questions

Applied Anatomy and Clinical Correlations

Practice Questions

Thoracic Imaging and Cross-sectional Anatomy

Practice Questions

Embryological Development of Thoracic Structures

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free

Thorax — MCQs

Thorax — MCQs

On this page

Practice by Chapter

Want unlimited practice?