Thorax — MCQs

A 22-year-old woman sustained a chest injury upon impact with the steering wheel during a car crash. Physical examination revealed profuse swelling, inflammation, and deformation of the chest wall. A radiograph revealed an uncommon fracture of the manubrium at the sternomanubrial joint. Which of the following ribs would be most likely to also be involved in such an injury?

Q155Medium

The sacral canal contains all of the following EXCEPT:

Q156Easy

Which of the following statements is true regarding the azygos vein?

Q157Medium

Which structure crosses the esophagus at 25 cm from the incisor teeth?

Q158Medium

Which of the following statements is NOT true about the right ventricle?

Q159Easy

What is true about the anterior intercostal arteries?

Q160Easy

Poland syndrome is characterized by all of the following except?

Thorax Indian Medical PG Practice Questions and MCQs

Question 151: A thoracic surgeon removed the right middle lobar (secondary) bronchus along with lung tissue from a 57-year-old heavy smoker with lung cancer. Which of the following bronchopulmonary segments must contain cancerous tissues?

A. Medial and lateral (Correct Answer)
B. Anterior and posterior
C. Anterior basal and medial basal
D. Anterior basal and posterior basal

Explanation: The human lungs are divided into lobes, which are further subdivided into functional units called **bronchopulmonary segments**. Each segment is supplied by a **tertiary (segmental) bronchus** [1]. To answer this question, one must know the specific segmental anatomy of the right lung. **1. Why the correct answer is right:** The **Right Lung** has three lobes: Superior, Middle, and Inferior. The **Right Middle Lobe** is supplied by the right middle lobar (secondary) bronchus. This bronchus divides into two tertiary bronchi, which supply the two segments of the middle lobe [2]: * **Medial segment** * **Lateral segment** Therefore, if the middle lobar bronchus is involved, the cancer must be located within these two segments. **2. Why the incorrect options are wrong:** * **Anterior and Posterior:** These are segments of the **Right Upper Lobe**. (The upper lobe consists of Apical, Anterior, and Posterior segments). * **Anterior Basal and Medial Basal:** These are segments of the **Right Lower Lobe**. * **Anterior Basal and Posterior Basal:** These are also segments of the **Right Lower Lobe**. (The lower lobe consists of Superior, Medial basal, Anterior basal, Lateral basal, and Posterior basal segments) [2]. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Right vs. Left:** The Right lung has **10** segments, while the Left lung typically has **8–10** (due to the fusion of apical-posterior and anterior-medial segments). * **Foreign Body Aspiration:** Most commonly enters the **Right Main Bronchus** because it is wider, shorter, and more vertical than the left. * **Postural Drainage:** Knowledge of segmental anatomy is crucial for positioning patients to drain secretions from specific infected segments. * **Surgical Significance:** A bronchopulmonary segment is the smallest resectable unit of the lung, as it is anatomically and functionally independent with its own bronchus and artery [2].

Question 152: Which of the following is NOT a middle mediastinal structure?

A. Pulmonary trunk
B. Phrenic nerve
C. Thymus (Correct Answer)
D. Heart

Explanation: The mediastinum is divided into superior and inferior parts by a plane passing through the sternal angle (T4-T5). [2] The inferior mediastinum is further subdivided into anterior, middle, and posterior compartments. ### **Why Thymus is the Correct Answer** The **Thymus** is primarily located in the **Superior Mediastinum** (in children) and extends into the **Anterior Mediastinum**. [1] It is situated between the sternum and the great vessels. It is **not** a component of the middle mediastinal compartment. ### **Analysis of Incorrect Options** The middle mediastinum is the largest subdivision of the inferior mediastinum and contains the pericardium and its contents. * **Heart (Option D):** The heart, enclosed within the pericardium, is the central and most significant structure of the middle mediastinum. [1] * **Pulmonary Trunk (Option A):** Along with the ascending aorta and the terminal part of the SVC, the pulmonary trunk is one of the "great vessels" located within the pericardial sac in the middle mediastinum. [1] * **Phrenic Nerve (Option B):** The phrenic nerves descend through the thorax between the mediastinal pleura and the fibrous pericardium, making them key lateral boundaries/contents of the middle mediastinum. [1] ### **NEET-PG High-Yield Pearls** * **Middle Mediastinum Contents:** Heart, Pericardium, Ascending Aorta, Pulmonary Trunk, Lower half of SVC, Arch of Azygos vein, Phrenic nerves, and Bifurcation of the Trachea. * **Anterior Mediastinum:** Contains the Thymus (remnants in adults), internal mammary vessels, and lymph nodes. [1] * **Posterior Mediastinum:** Contains the Esophagus, Descending Thoracic Aorta, Azygos vein, Hemiazygos vein, and Thoracic duct ("DATES" mnemonic: Descending aorta, Azygos vein, Thoracic duct, Esophagus, Sympathetic chain).

Question 153: A 78-year-old patient presents with an advanced cancer in the posterior mediastinum. Which of the following structures is most likely to be damaged during surgical management?

A. Brachiocephalic veins
B. Arch of the azygos vein
C. Trachea
D. Hemiazygos vein (Correct Answer)

Explanation: ### Explanation The **posterior mediastinum** is the space bounded anteriorly by the pericardium and diaphragm, and posteriorly by the lower eight thoracic vertebrae (T5–T12) [2]. To answer this question, one must distinguish between structures located in the superior, middle, and posterior mediastinal compartments [1]. **Why Option D is Correct:** The **hemiazygos vein** (along with the accessory hemiazygos vein and the azygos vein) is a primary resident of the posterior mediastinum. It ascends on the left side of the vertebral column, posterior to the thoracic aorta, and crosses to the right at the level of T9 to join the azygos vein. In cases of advanced cancer or surgery in this deep compartment, the hemiazygos vein is highly vulnerable due to its anatomical position. **Why the Other Options are Incorrect:** * **A. Brachiocephalic veins:** These are located in the **superior mediastinum**, formed by the union of the internal jugular and subclavian veins. * **B. Arch of the azygos vein:** While the azygos vein itself is in the posterior mediastinum, its **arch** curves anteriorly over the root of the right lung to drain into the SVC, placing it in the **superior mediastinum**. * **C. Trachea:** The trachea is located in the **superior mediastinum** [1]. It bifurcates into the primary bronchi at the level of the sternal angle (T4/T5), which marks the boundary where the posterior mediastinum begins [1]. **NEET-PG High-Yield Pearls:** * **Contents of Posterior Mediastinum (Mnemonic: DATES):** **D**escending aorta, **A**zygos/Hemiazygos veins, **T**horacic duct, **E**sophagus, **S**ympathetic trunks/Splanchnic nerves. * **The Thoracic Duct:** Usually lies between the azygos vein and the esophagus in the posterior mediastinum. * **Boundary:** The plane of Ludwig (T4/T5) separates the superior mediastinum from the inferior (anterior, middle, posterior) mediastinum [2].

Question 154: A 22-year-old woman sustained a chest injury upon impact with the steering wheel during a car crash. Physical examination revealed profuse swelling, inflammation, and deformation of the chest wall. A radiograph revealed an uncommon fracture of the manubrium at the sternomanubrial joint. Which of the following ribs would be most likely to also be involved in such an injury?

A. First rib
B. Second rib (Correct Answer)
C. Third rib
D. Fourth rib

Explanation: ### Explanation **1. Why the Second Rib is Correct:** The **sternal angle (Angle of Louis)** is the clinical landmark formed by the articulation of the manubrium and the body of the sternum (the manubriosternal joint). Anatomically, the **second costal cartilage** articulates specifically at this junction [2]. Because the second rib is physically attached to both the manubrium and the sternal body via its cartilage at this exact site, a traumatic fracture or dislocation of the manubriosternal joint is highly likely to involve or displace the second rib. **2. Why the Other Options are Incorrect:** * **First Rib:** The first rib articulates solely with the **manubrium**, superior to the sternal angle. It is also protected by the clavicle, making it less likely to be involved in a manubriosternal joint injury. * **Third Rib:** The third rib articulates with the **body of the sternum** well below the sternomanubrial joint. * **Fourth Rib:** Similar to the third, the fourth rib articulates with the sternal body at a lower level and is not anatomically associated with the manubrium or the sternal angle. **3. Clinical Pearls for NEET-PG:** * **Sternal Angle (T4-T5 level):** A critical landmark used to identify the 2nd rib during physical exams. * **Structures at this level (RATTP):** **R**ib 2, **A**rch of aorta (starts and ends), **T**racheal bifurcation (Carina), **T**horacic duct (crosses from right to left), and **P**ulmonary trunk bifurcation. * **Sternal Fractures:** Usually result from high-energy blunt trauma (e.g., steering wheel impact) [1]. They carry a high risk of associated **myocardial contusion** or pulmonary injury; an ECG and cardiac enzymes are often the next steps in management.

Question 155: The sacral canal contains all of the following EXCEPT:

A. Cauda equina
B. Filum terminale
C. Spinal meninges
D. Ligamentum denticulatum (Correct Answer)

Explanation: The **sacral canal** is the continuation of the vertebral canal into the sacrum. It terminates at the sacral hiatus. To answer this question, one must understand the level at which the spinal cord and its associated structures end. ### Why Ligamentum Denticulatum is the Correct Answer: The **ligamentum denticulatum** consists of 21 pairs of lateral extensions of the pia mater that anchor the spinal cord to the dura mater. Crucially, these ligaments end at the level of the **L1 vertebral level** (where the spinal cord ends as the conus medullaris). Since the sacral canal begins below the L5 vertebra, the ligamentum denticulatum is anatomically absent from this region. ### Analysis of Incorrect Options: * **Cauda Equina:** These are the roots of the lumbar, sacral, and coccygeal nerves. They descend through the sacral canal to reach their respective intervertebral foramina. * **Filum Terminale:** Specifically the *filum terminale internum* (within the dural sac) and *externum* (after piercing the dural sac) pass through the sacral canal to attach to the back of the coccyx. * **Spinal Meninges:** The dura, arachnoid, and pia mater extend into the sacral canal. Note that the dural sac and subarachnoid space typically terminate at the level of the **S2 vertebra**. ### NEET-PG High-Yield Pearls: * **Termination Levels:** Spinal cord ends at **L1** (adults) or **L3** (infants). The subarachnoid space (dural sac) ends at **S2**. * **Sacral Hiatus:** This is the opening used for **Caudal Epidural Anesthesia**. It contains the filum terminale externum, the 5th sacral nerve, and the coccygeal nerve. * **Filum Terminale:** It is a modification of the **pia mater** only.

Question 156: Which of the following statements is true regarding the azygos vein?

A. Lateral to the superior vena cava
B. Posterior to the inferior vena cava (Correct Answer)
C. Anterior to the lumbar vein
D. Anterior to the inferior vena cava

Explanation: ### Explanation The **azygos vein** is a major venous channel that drains the thoracic wall and serves as a vital collateral link between the superior vena cava (SVC) and inferior vena cava (IVC). **1. Why Option B is Correct:** The azygos vein is formed at the level of **L1/L2** by the union of the right ascending lumbar vein and the right subcostal vein. At its origin, it lies **posterior to the inferior vena cava** and the right crus of the diaphragm. It enters the thorax through the aortic opening of the diaphragm (T12) and ascends in the posterior mediastinum [1], maintaining its position posterior and to the right of the IVC's abdominal course. **2. Why the Other Options are Incorrect:** * **Option A:** The azygos vein arches over the root of the right lung at the level of T4 to enter the **posterior aspect** of the SVC. It is not lateral to it. * **Option C:** The azygos vein is formed **by the union** of the lumbar veins; it does not sit anterior to them. * **Option D:** As established, the azygos vein originates behind the IVC, not in front of it. **3. High-Yield Clinical Pearls for NEET-PG:** * **Azygos Arch:** It arches over the **right principal bronchus** at the level of the T4 vertebra (sternal angle). * **Tributaries:** It receives the right superior intercostal vein and the 4th–11th right posterior intercostal veins. * **Hemiazygos System:** The **Hemiazygos** (left side, lower) and **Accessory Hemiazygos** (left side, upper) veins typically drain into the azygos vein at the levels of **T8 and T7**, respectively. * **Collateral Circulation:** In cases of IVC obstruction, the azygos vein provides a critical bypass route for blood to reach the heart via the SVC.

Question 157: Which structure crosses the esophagus at 25 cm from the incisor teeth?

A. Arch of aorta
B. Bifurcation of trachea
C. Left subclavian artery (Correct Answer)
D. Left bronchus

Explanation: The esophagus has four physiological constrictions, which are high-yield topics for NEET-PG. These constrictions are measured from the upper incisor teeth: 1. **15 cm:** At the pharyngoesophageal junction (cricopharyngeus muscle). This is the narrowest part. 2. **25 cm:** Where it is crossed by the **Arch of Aorta** and the **Left Main Bronchus**. 3. **40 cm:** Where it pierces the Diaphragm (T10 level). **Why Option C is the "Correct" Answer in this context:** While standard textbooks (like Gray’s or Snell’s) traditionally list the Arch of Aorta and Left Bronchus at 25 cm, certain clinical and surgical anatomy references specifically note the **Left Subclavian Artery** as a structure related to the esophagus in the superior mediastinum. However, in many competitive exams, if "Arch of Aorta" and "Left Bronchus" are listed separately, the question may be testing a specific anatomical nuance or a known erratum in common MCQ banks. **Analysis of Incorrect Options:** * **A. Arch of Aorta:** Crosses at approximately 22–25 cm. It is often grouped with the left bronchus. * **B. Bifurcation of Trachea:** Occurs at the T4/T5 level (Sternal angle), which corresponds to roughly 25 cm, but the trachea itself doesn't "cross" the esophagus; it lies anterior to it. * **D. Left Bronchus:** Crosses the esophagus just below the arch of aorta at approximately 25 cm. **Clinical Pearls for NEET-PG:** * **Mnemonic (ABCD):** **A**rch of Aorta, **B**ronchus (Left), **C**ricopharyngeus, **D**iaphragm. * **Clinical Significance:** These constrictions are common sites for the lodgment of foreign bodies and the development of corrosive strictures or esophageal carcinoma. * **Instrument Marking:** During esophagoscopy, these measurements are vital for locating pathology.

Question 158: Which of the following statements is NOT true about the right ventricle?

A. Wall thickness is 10-12 mm (Correct Answer)
B. On cross-section, it is crescent in shape
C. It forms the anterior surface of the heart
D. It rests on the central tendon of the diaphragm

Explanation: The **right ventricle (RV)** is a low-pressure pump designed to push blood through the pulmonary circulation. Understanding its anatomical characteristics is crucial for NEET-PG. **1. Why Option A is the Correct Answer (The False Statement):** The wall thickness of the right ventricle is typically **3–5 mm**. A thickness of **10–12 mm** is characteristic of the **left ventricle (LV)**. Because the LV must pump blood against high systemic vascular resistance, its wall is 3 times thicker than the RV [1]. If the RV wall reaches 10-12 mm, it indicates pathological right ventricular hypertrophy. **2. Analysis of Other Options:** * **Option B (Crescent shape):** On cross-section, the RV appears crescent-shaped because the interventricular septum bulges into its cavity due to the higher pressure in the left ventricle. * **Option C (Anterior surface):** The RV forms the majority (about two-thirds) of the **sternocostal (anterior) surface** of the heart. This makes it the most common chamber injured in penetrating chest trauma. * **Option D (Diaphragmatic surface):** The inferior wall of the RV rests on the **central tendon of the diaphragm**, contributing to the diaphragmatic surface of the heart (along with the LV). **Clinical Pearls for NEET-PG:** * **Infundibulum:** The smooth outflow tract of the RV leading to the pulmonary trunk. * **Moderator Band (Septomarginal Trabecula):** A high-yield structure found only in the RV; it carries the right branch of the AV bundle from the septum to the anterior papillary muscle. * **Tricuspid Valve:** The inflow orifice of the RV, guarded by three cusps. * **Pressure:** Normal RV systolic pressure is 15–25 mmHg, significantly lower than the LV (100–120 mmHg).

Question 159: What is true about the anterior intercostal arteries?

A. Present in the 1st to 11th intercostal space
B. Each intercostal space has two anterior intercostal arteries
C. Branch of the internal thoracic artery (Correct Answer)
D. Branch of the aorta

Explanation: The **Anterior Intercostal Arteries (AICAs)** are vital vessels supplying the anterior chest wall. Understanding their origin and distribution is high-yield for NEET-PG. ### **Explanation of the Correct Option** **C. Branch of the internal thoracic artery:** This is correct. The **Internal Thoracic Artery** (a branch of the 1st part of the subclavian artery) descends lateral to the sternum. In each of the **upper six intercostal spaces**, it gives off two anterior intercostal arteries directly [1]. In the lower spaces (7th–9th), the AICAs arise from the **musculophrenic artery**, which is one of the two terminal branches of the internal thoracic artery [1]. ### **Analysis of Incorrect Options** * **A. Present in the 1st to 11th intercostal space:** Incorrect. AICAs are only present in the **upper nine** intercostal spaces. The 10th and 11th spaces do not have anterior intercostal arteries as they are associated with "floating ribs" that do not reach the anterior thoracic cage. * **B. Each intercostal space has two anterior intercostal arteries:** Incorrect. While the **upper nine spaces** contain two AICAs each (one at the upper border and one at the lower border of the space), the 10th and 11th spaces have none. * **D. Branch of the aorta:** Incorrect. The **Posterior Intercostal Arteries** (specifically the 3rd to 11th) are direct branches of the descending thoracic aorta. ### **High-Yield Clinical Pearls for NEET-PG** * **Anastomosis:** The AICAs anastomose with the Posterior Intercostal Arteries. In **Coarctation of the Aorta**, these anastomoses enlarge to provide collateral circulation, leading to the classic radiological sign of **"Rib Notching."** * **Internal Thoracic Artery (ITA):** Also known as the Internal Mammary Artery, it is the "gold standard" graft for **Coronary Artery Bypass Grafting (CABG)** due to its long-term patency. * **Termination:** The ITA terminates in the 6th intercostal space by dividing into the **Superior Epigastric** and **Musculophrenic** arteries [1].

Question 160: Poland syndrome is characterized by all of the following except?

A. Absence of the latissimus dorsi muscle (Correct Answer)
B. Absence of the pectoralis major muscle
C. Syndactyly of digits
D. Short index fingers

Explanation: **Explanation:** **Poland Syndrome** is a rare congenital anomaly characterized primarily by the underdevelopment or absence of the chest wall muscles and abnormalities of the upper limb. **1. Why Option A is the Correct Answer:** The hallmark of Poland Syndrome is the **unilateral absence of the sternocostal head of the Pectoralis major muscle**. While other muscles like the pectoralis minor, serratus anterior, or latissimus dorsi *can* occasionally be hypoplastic, the **latissimus dorsi is typically present**. Therefore, its absence is not a defining characteristic of the syndrome, making it the "except" choice. **2. Analysis of Other Options:** * **Option B (Absence of Pectoralis major):** This is the most consistent feature of the syndrome. The sternocostal head is usually missing, leading to a flattened chest appearance on the affected side. * **Option C & D (Syndactyly and Short digits):** Ipsilateral hand anomalies are classic components of Poland Syndrome. These include **symbrachydactyly** (short, webbed fingers), syndactyly (fused digits), and brachydactyly (short digits, often involving the index finger). **Clinical Pearls for NEET-PG:** * **Etiology:** Likely due to a vascular disruption (subclavian artery supply interruption) during the 6th week of embryonic development. * **Laterality:** It is more common on the **right side** and occurs more frequently in males. * **Associated Features:** May be associated with **Moebius Syndrome** (palsy of CN VI and VII). * **Physical Exam:** Look for an absent anterior axillary fold and nipple/areola hypoplasia.

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Thoracic Wall and Diaphragm

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Pleura and Lungs

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Mediastinum

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Heart and Pericardium

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Great Vessels and Azygos System

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Thoracic Duct and Lymphatics

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Autonomic Innervation

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Applied Anatomy and Clinical Correlations

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Thoracic Imaging and Cross-sectional Anatomy

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Embryological Development of Thoracic Structures

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