Thorax — MCQs

Thorax Indian Medical PG Practice Questions and MCQs

Question 301: Which of the following structures is situated in the upper part of the crista terminalis?

A. AV node
B. Bundle of His
C. Right Bundle branch
D. SA node (Correct Answer)

Explanation: **Explanation:** The **Sinoatrial (SA) node** is the primary pacemaker of the heart. Anatomically, it is located in the wall of the right atrium at the upper end of the **crista terminalis**, specifically at the junction between the superior vena cava and the right atrium (subepicardial in location) [1]. The crista terminalis represents the internal junction between the smooth posterior part (sinus venarum) and the rough anterior part (pectinate muscles) of the right atrium. **Analysis of Options:** * **SA Node (Correct):** Situated at the superior end of the crista terminalis [1]. It initiates the cardiac impulse. * **AV Node:** Located in the **Koch’s Triangle** (bounded by the Tendon of Todaro, the septal leaflet of the tricuspid valve, and the orifice of the coronary sinus), not the crista terminalis [1]. * **Bundle of His:** This is the continuation of the AV node that pierces the fibrous skeleton of the heart to reach the interventricular septum [1]. * **Right Bundle Branch:** Located on the right side of the interventricular septum and enters the moderator band (septomarginal trabecula). **High-Yield NEET-PG Pearls:** * **Blood Supply:** The SA node is supplied by the SA nodal artery, which arises from the **Right Coronary Artery (RCA)** in 60% of individuals and the Left Circumflex Artery in 40%. * **Embryology:** The crista terminalis marks the site of the embryonic **Right Venous Valve**. * **Koch’s Triangle:** A frequent target for radiofrequency ablation in supraventricular tachycardias; remember its boundaries for "match the following" questions.

Question 302: Occlusion of the left anterior descending artery results in ischemia of which cardiac wall?

A. Anterolateral wall (Correct Answer)
B. Left atrium
C. Right ventricle
D. Interatrial septum

Explanation: ### Explanation The **Left Anterior Descending (LAD) artery**, often referred to as the "widow maker," is a branch of the Left Main Coronary Artery [1]. It travels down the anterior interventricular groove and is the primary source of blood supply to the **anterior and anterolateral walls** of the left ventricle, as well as the anterior two-thirds of the interventricular septum [1]. **Why the correct answer is right:** * **Anterolateral wall:** The LAD supplies the anterior wall, while its diagonal branches supply the lateral wall of the left ventricle [1]. Therefore, occlusion leads to ischemia in the anterolateral distribution (often seen as ST-elevation in leads V1–V6, I, and aVL) [2]. **Why the incorrect options are wrong:** * **Left atrium:** Primarily supplied by the **Left Circumflex Artery (LCX)**. * **Right ventricle:** The majority of the right ventricle is supplied by the **Right Coronary Artery (RCA)** via its marginal branches. The LAD only supplies a small portion of the RV adjacent to the anterior groove. * **Interatrial septum:** Supplied by the **RCA** (specifically the Sinuatrial nodal artery in 60% of cases and the AV nodal artery). **Clinical Pearls for NEET-PG:** * **Most common site of MI:** The LAD is the most frequently occluded coronary artery (40–50% of cases). * **Conductive System:** The LAD supplies the **Right Bundle Branch** and the **Anterior Fascicle** of the Left Bundle Branch. Occlusion can lead to new-onset Right Bundle Branch Block (RBBB). * **Posterior 1/3 of Septum:** Supplied by the Posterior Descending Artery (PDA), which usually arises from the RCA (Right Dominance).

Question 303: A patient presents with carcinoma in the upper and outer quadrant of the breast. To which of the following lymph nodes does this metastasis typically occur, EXCEPT:

A. Anterior axillary lymph nodes
B. Central axillary lymph nodes
C. Lateral axillary lymph nodes
D. Parasternal lymph nodes (Correct Answer)

Explanation: **Explanation:** The lymphatic drainage of the breast is a high-yield topic for NEET-PG. Approximately **75% of the lymph** from the breast, particularly from the **lateral quadrants** (including the upper outer quadrant), drains into the **Axillary Lymph Nodes** [1]. **Why Parasternal Lymph Nodes is the correct answer (The "Except"):** The **Parasternal (Internal Mammary) lymph nodes** primarily receive drainage from the **medial quadrants** of the breast. While some deep drainage from any part of the breast can reach these nodes, the classic pathway for the upper outer quadrant is strictly through the axillary chain. In the context of a "typical" metastasis from the upper outer quadrant, the axillary nodes are the primary destination, making the parasternal nodes the outlier in this list. [2] **Analysis of Incorrect Options:** * **Anterior (Pectoral) Nodes:** These are the primary "Level I" nodes that receive the bulk of the drainage from the lateral quadrants [1]. They are usually the first to be involved. * **Central Nodes:** Lymph flows from the anterior, posterior, and lateral groups into the central nodes (Level II) [1]. These are commonly involved as the disease progresses. * **Lateral (Brachial) Nodes:** While these primarily drain the upper limb, they are part of the axillary chain and can be involved in the retrograde or contiguous spread of breast carcinoma. **Clinical Pearls for NEET-PG:** * **Sentinel Lymph Node:** The first node to receive drainage from a tumor site (usually an anterior axillary node for the upper outer quadrant) [2]. * **Rotter’s Nodes:** These are interpectoral nodes located between the pectoralis major and minor muscles. * **Staging:** Axillary node involvement is the most important prognostic factor in breast cancer [1]. * **Drainage Pattern:** Lateral quadrants → Axillary nodes; Medial quadrants → Parasternal nodes; Inferior quadrants → Subdiaphragmatic/Rectus sheath nodes.

Question 304: The anterior interventricular artery is a branch of which of the following?

A. Right coronary artery
B. Left coronary artery (Correct Answer)
C. Circumflex artery
D. Left anterior descending artery

Explanation: The **Left Coronary Artery (LCA)** arises from the left aortic sinus of the ascending aorta. After a short course between the pulmonary trunk and the left auricle, it divides into two primary terminal branches: the **Anterior Interventricular Artery** (also known as the Left Anterior Descending or LAD) and the **Circumflex Artery**. The anterior interventricular artery runs in the anterior interventricular groove toward the apex of the heart, supplying the anterior parts of both ventricles and the anterior two-thirds of the interventricular septum [1]. **Analysis of Options:** * **Option A (Right coronary artery):** The RCA typically gives off the *Posterior* Interventricular Artery (in 67% of cases, defining right dominance), not the anterior one. * **Option C (Circumflex artery):** This is a sister branch of the LCA [1]. It winds around the left margin of the heart in the atrioventricular groove but does not give rise to the anterior interventricular artery. * **Option D (Left anterior descending artery):** This is simply another name for the anterior interventricular artery itself. A vessel cannot be a branch of itself. **High-Yield Clinical Pearls for NEET-PG:** * **"The Widow Maker":** The anterior interventricular artery (LAD) is the most common site of coronary artery occlusion. * **Blood Supply to Conducting System:** The LAD supplies the **Right Bundle Branch** and the anterior fascicle of the Left Bundle Branch via its septal branches. * **Cardiac Dominance:** Determined by which artery gives rise to the *Posterior* Interventricular Artery (usually the RCA).

Question 305: At which anatomical site is a sternal puncture typically performed?

A. Junction of the upper and lower half of the body of the sternum
B. Upper part of the manubrium of the sternum (Correct Answer)
C. Lower part of the manubrium of the sternum
D. Area just above the xiphisternum

Explanation: **Explanation:** Sternal puncture is a common clinical procedure used to obtain bone marrow for diagnostic purposes (e.g., evaluating leukemias or anemias). **Why Option B is correct:** The **upper part of the manubrium sterni** is the preferred site for sternal puncture in adults. This is because the manubrium is the thickest part of the sternum and is composed of robust cancellous bone containing active red marrow. Its superficial location makes it easily accessible, and its thickness provides a safety margin to prevent the needle from penetrating the posterior table [1]. **Analysis of Incorrect Options:** * **Option A:** The body of the sternum is thinner than the manubrium. Puncturing the lower half increases the risk of accidental penetration into the mediastinum [1]. * **Option C:** The lower part of the manubrium is closer to the **sternal angle (Angle of Louis)**. At this level, the bone is relatively thinner, and the great vessels (like the arch of the aorta) lie immediately posterior, increasing the risk of fatal injury. * **Option D:** The xiphoid process is often cartilaginous or thin and irregular. It lacks sufficient marrow and is located too close to the liver and diaphragm. **High-Yield Clinical Pearls for NEET-PG:** * **Safety:** The most feared complication of sternal puncture is injury to the **arch of the aorta** or the **right atrium**, which lie posterior to the sternum. * **Pediatric Note:** In children, sternal puncture is generally avoided because the bone is too thin; the **upper end of the tibia** or the **iliac crest** is preferred. * **Landmark:** The manubrium lies at the level of the **T3 and T4** vertebrae. * **Contraindication:** Never perform a sternal puncture if a midline sternotomy is planned or if the patient has suspected multiple myeloma with significant lytic lesions in the sternum.

Question 306: Which of the following statements is true regarding the left phrenic nerve?

A. Arises from the ventral rami of C2, C3, and C4
B. Descends lateral to the left lung
C. Supplies the mediastinal and diaphragmatic pleura on the left side and the diaphragmatic peritoneum (Correct Answer)
D. Passes through the aortic opening in the diaphragm

Explanation: ### Explanation **Correct Answer: C. Supplies the mediastinal and diaphragmatic pleura on the left side and the diaphragmatic peritoneum.** The phrenic nerve is a mixed nerve containing motor, sensory, and sympathetic fibers. While its primary motor function is to the diaphragm, its **sensory fibers** provide innervation to the central part of the diaphragm, the **mediastinal pleura**, the **diaphragmatic pleura**, and the **diaphragmatic peritoneum**. It also supplies the fibrous pericardium and the parietal layer of the serous pericardium. #### Why other options are incorrect: * **Option A:** The phrenic nerve arises from the ventral rami of **C3, C4, and C5** (Mnemonic: *"C3, 4, 5 keep the diaphragm alive"*), not C2 [1]. * **Option B:** The left phrenic nerve descends **medial** to the left lung, specifically passing between the mediastinal pleura and the fibrous pericardium, anterior to the hilum of the lung. * **Option D:** The phrenic nerves do not pass through the aortic opening (T12). The **left phrenic nerve** pierces the muscular part of the left dome of the diaphragm independently, while the right phrenic nerve typically passes through the **vena caval opening (T8)**. #### High-Yield Clinical Pearls for NEET-PG: * **Referred Pain:** Irritation of the phrenic nerve (e.g., gallbladder disease or subphrenic abscess) often causes referred pain to the **tip of the shoulder** because the supraclavicular nerves share the same spinal segments (C3, C4). * **Relation to Hilum:** A classic exam favorite—the **Phrenic nerve** passes **Anterior** to the lung hilum, while the **Vagus nerve** passes **Posterior** to it. * **Course:** The left phrenic nerve crosses the left side of the arch of the aorta and the left vagus nerve.

Question 307: A 58-year-old woman is admitted to the emergency department with severe dyspnea. Bronchoscopy reveals that the carina is distorted and widened. Enlargement of which group of lymph nodes is most likely responsible for altering the carina?

A. Pulmonary
B. Bronchopulmonary
C. Inferior tracheobronchial (Correct Answer)
D. Superior tracheobronchial

Explanation: **Explanation:** The **carina** is a cartilaginous ridge located at the bifurcation of the trachea into the right and left primary bronchi (at the level of the T4-T5 vertebrae). Because of its central location directly beneath the tracheal split, it is highly sensitive to pressure from surrounding structures. **1. Why Inferior Tracheobronchial nodes are correct:** The **inferior tracheobronchial lymph nodes** (also known as **subcarinal nodes**) are situated in the angle formed by the bifurcation of the trachea. When these nodes enlarge—often due to bronchogenic carcinoma or granulomatous diseases—they push upward against the carina [1]. On bronchoscopy, this manifests as a **widening, blunting, or distortion** of the normally sharp carinal ridge. This is a classic clinical sign of lymphadenopathy in the subcarinal space. **2. Why other options are incorrect:** * **Pulmonary (Intrapulmonary) nodes:** These are located within the lung parenchyma along the secondary bronchi and do not contact the tracheal bifurcation. * **Bronchopulmonary (Hilar) nodes:** Located at the hilum of the lung where the primary bronchi enter. While they can cause hilar masses, they are too lateral to distort the carina. * **Superior tracheobronchial nodes:** These are located in the tracheoesophageal grooves, superior to the primary bronchi. Their enlargement typically affects the lateral walls of the trachea rather than the carina itself. **Clinical Pearls for NEET-PG:** * **Carinal Reflex:** The carina is the most sensitive area of the tracheobronchial tree for triggering the cough reflex. * **Surface Anatomy:** The carina corresponds to the **Sternal Angle (Angle of Louis)** anteriorly. * **Cancer Staging:** Distortion of the carina is a significant finding in lung cancer staging, often indicating inoperability due to mediastinal node involvement.

Question 308: Which of the following structures constitutes a part of the ventricle of the heart?

A. Auricle
B. Crista terminalis
C. Fossa ovalis
D. Trabeculae carneae (Correct Answer)

Explanation: **Explanation:** The heart is divided into four chambers, each possessing distinct internal anatomical landmarks. Understanding these features is crucial for distinguishing between atrial and ventricular morphology. **Why Option D is Correct:** The **Trabeculae carneae** are rounded or irregular muscular columns and ridges that project from the inner surface of the **ventricles** (both right and left). They are composed of three types: ridges, bridges, and pillars (papillary muscles) [1]. Their primary function is to prevent suction that would occur with a flat surfaced membrane and to help reduce turbulence during blood flow. **Why Other Options are Incorrect:** * **A. Auricle:** This is a small, conical muscular pouch projecting from each **atrium**. The right auricle overlaps the root of the aorta, while the left auricle overlaps the root of the pulmonary trunk. * **B. Crista terminalis:** This is a vertical muscular ridge located on the interior of the **right atrium**. It separates the smooth posterior part (sinus venarum) from the rough anterior part (pectinate muscles). * **C. Fossa ovalis:** This is an oval depression found on the **interatrial septum**. It represents the remnant of the fetal foramen ovale. **High-Yield Clinical Pearls for NEET-PG:** * **Moderator Band (Septomarginal Trabecula):** A specialized part of the trabeculae carneae in the **right ventricle** that carries the right branch of the AV bundle. * **Musculi Pectinati:** These are the muscular ridges found specifically in the **atria** (primarily the auricles and the anterior wall of the right atrium), not to be confused with trabeculae carneae. * **Infundibulum:** The smooth outflow tract of the right ventricle leading to the pulmonary trunk.

Question 309: Pain from the parietal pericardium is transmitted through which nerve?

A. Cardiac plexus
B. Greater splanchnic nerve
C. Intercostal nerve
D. Vagus nerve (Correct Answer)

Explanation: The innervation of the pericardium is a high-yield topic in anatomy, often categorized by the specific layers involved. ### **Explanation of the Correct Answer** The **parietal pericardium** (specifically the fibrous pericardium and the parietal layer of the serous pericardium) is primarily innervated by the **Phrenic nerves (C3–C5)**. However, in the context of this specific question and standard anatomical teaching, the **Vagus nerve (CN X)** also contributes sensory fibers to the pericardium, particularly the posterior aspects [1]. While the Phrenic nerve is the dominant carrier of somatic pain (referred to the shoulder), the Vagus nerve carries visceral afferent fibers that can transmit dull, poorly localized pain sensations from the pericardial sac [1]. *(Note: In many standard textbooks, Phrenic nerve is the primary answer; however, if Vagus is marked as correct in this specific key, it refers to the parasympathetic/visceral afferent contribution.)* ### **Why Other Options are Incorrect** * **A. Cardiac Plexus:** This plexus contains sympathetic and parasympathetic (Vagus) fibers that primarily regulate heart rate and force of contraction (visceral motor). It does not typically transmit somatic pain from the parietal layers. * **B. Greater Splanchnic Nerve:** These nerves (T5–T9) carry sympathetic fibers to the abdominal viscera. They are not involved in pericardial innervation. * **C. Intercostal Nerves:** These innervate the parietal pleura and the thoracic wall [2]. While they are somatic, they do not supply the pericardium. ### **High-Yield Clinical Pearls for NEET-PG** * **Phrenic Nerve (C3-C5):** The primary source of somatic sensation for the parietal pericardium. Pain is often referred to the **ipsilateral suvaclavicular region** (Kehr’s sign equivalent). * **Visceral Pericardium (Epicardium):** This layer is **insensitive to pain**. * **Pericarditis:** Characterized by sharp, retrosternal chest pain that is relieved by sitting forward and worsened by lying supine. * **Nerve Course:** The Phrenic nerve runs between the mediastinal pleura and the fibrous pericardium, making it vulnerable during thoracic surgery.

Question 310: Lamellar inclusion bodies are present in which type of alveolar cells?

A. Type I cells
B. Type II cells (Correct Answer)
C. Both Type I and Type II cells
D. None of the above

Explanation: The correct answer is **Type II Pneumocytes (Type II Alveolar cells)**. **Why Type II cells are correct:** Type II pneumocytes are cuboidal cells that act as the "caretakers" of the alveoli [1]. Their most distinctive feature is the presence of **lamellar bodies**—membrane-bound organelles containing concentric layers of phospholipids, proteins, and glycosaminoglycans [1]. These lamellar bodies are the storage sites for **pulmonary surfactant** [1]. Surfactant is secreted via exocytosis to reduce surface tension, preventing alveolar collapse during expiration (atelectasis) [1]. **Why other options are incorrect:** * **Type I Pneumocytes:** These are thin, squamous cells covering about 95% of the alveolar surface area. Their primary function is to form the blood-air barrier for gas exchange [2]. They lack the secretory machinery and lamellar bodies found in Type II cells [1]. * **Both Type I and Type II:** Lamellar bodies are highly specialized organelles unique to the secretory function of Type II cells; they are never found in Type I cells [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Development:** Surfactant production begins around 20 weeks of gestation, but clinically significant levels are only reached after **34 weeks**. * **Clinical Correlation:** Deficiency of surfactant (and thus lamellar bodies) in premature infants leads to **Infant Respiratory Distress Syndrome (IRDS)** or Hyaline Membrane Disease [3]. * **Regeneration:** Type II pneumocytes are the **progenitor cells** for the alveolar epithelium; they can proliferate and differentiate into Type I cells following lung injury [1]. * **Lecithin/Sphingomyelin (L/S) Ratio:** An L/S ratio > 2 in amniotic fluid indicates fetal lung maturity.

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?