Thorax — MCQs
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All of the following are branches of the internal thoracic artery except?
What is the normal right tracheobronchial angle?
What is the surface marking of the mitral valve?
A patient presents with a penetrating chest wound associated with intrathoracic hemorrhage. A thoracotomy is performed via an incision in the 4th/5th intercostal space, starting 1 cm away from the lateral margin of the sternum. This approach is taken to avoid injury to which of the following structures?
Which among the following is a typical intercostal nerve?
The thoracic duct crosses the posterior mediastinum at the level of which vertebra?
A 3-day-old newborn has difficulties breathing. A CT scan of his chest and abdomen reveals the absence of the central tendon of the diaphragm. Which of the following structures failed to develop normally?
A 37-year-old woman undergoes a routine breast examination. The physician notes that the skin of the breast moves with the underlying breast tissue, indicating normal attachment. What anatomical structures are responsible for this normal attachment of the breast tissue to the overlying skin?
What is the primary blood supply to the thoracic part of the esophagus?
The great cardiac vein drains into which structure?
Thorax Indian Medical PG Practice Questions and MCQs
Question 511: All of the following are branches of the internal thoracic artery except?
- A. Pericardiophrenic artery
- B. Posterior intercostal arteries (Correct Answer)
- C. Superior epigastric artery
- D. Musculophrenic artery
Explanation: The **internal thoracic artery** (also known as the internal mammary artery) is a branch of the first part of the subclavian artery. It descends behind the costal cartilages and terminates at the level of the 6th intercostal space. ### **Explanation of Options:** * **Correct Answer: B. Posterior intercostal arteries** The **posterior** intercostal arteries (for spaces 3–11) are branches of the **descending thoracic aorta**. The first two posterior intercostal arteries arise from the superior intercostal artery (a branch of the costocervical trunk). In contrast, the internal thoracic artery gives off the **Anterior** intercostal arteries for the upper six intercostal spaces. * **A. Pericardiophrenic artery:** This is a long, thin branch of the internal thoracic artery that accompanies the phrenic nerve to the diaphragm, supplying the pericardium and pleura. * **C & D. Superior epigastric and Musculophrenic arteries:** These are the two **terminal branches** of the internal thoracic artery [1]. The superior epigastric enters the rectus sheath, while the musculophrenic runs along the costal margin to supply the lower intercostal spaces and the diaphragm [1]. ### **High-Yield NEET-PG Pearls:** 1. **Coronary Artery Bypass Graft (CABG):** The internal thoracic artery (especially the left) is the "gold standard" conduit for CABG due to its superior long-term patency rates. 2. **Anastomosis:** The superior epigastric artery (from internal thoracic) anastomoses with the inferior epigastric artery (from external iliac), providing a collateral pathway in cases of aortic coarctation [1]. 3. **Termination:** It ends at the **6th intercostal space** by dividing into its terminal branches.
Question 512: What is the normal right tracheobronchial angle?
- A. 10-15 degrees
- B. 25-30 degrees (Correct Answer)
- C. 40-50 degrees
- D. 80-90 degrees
Explanation: The trachea bifurcates into the right and left principal bronchi at the level of the sternal angle (T4-T5). The angles at which these bronchi deviate from the median plane are asymmetrical and clinically significant. **Explanation of the Correct Answer:** The **right principal bronchus** is wider, shorter, and more vertical than the left. It deviates from the tracheal axis at an angle of **25-30 degrees**. This vertical orientation is a key anatomical feature that dictates the path of least resistance for airflow and foreign bodies. **Analysis of Incorrect Options:** * **Option A (10-15 degrees):** This is too acute; no major bronchial bifurcation occurs at this narrow angle. * **Option C (40-50 degrees):** This represents the **left tracheobronchial angle**. The left bronchus is narrower, longer, and more horizontal (approx. 45 degrees) because it must pass under the aortic arch and over the heart to reach the hilum. * **Option D (80-90 degrees):** This is the **subcarinal angle** (the total angle between the two bronchi), which typically ranges from 50 to 90 degrees. **Clinical Pearls for NEET-PG:** 1. **Foreign Body Aspiration:** Due to the wider diameter and more vertical angle (25-30°), inhaled foreign bodies are significantly more likely to lodge in the **right principal bronchus** (specifically the posterior segment of the right lower lobe). 2. **Aspiration Pneumonia:** In a supine patient, infected material most commonly gravitates toward the **superior segment of the right lower lobe** due to this anatomical alignment. 3. **Carina:** The internal ridge at the bifurcation is the carina. Widening or distortion of the subcarinal angle (seen on CXR) often indicates **left atrial enlargement** (mitral stenosis) or lymphadenopathy.
Question 513: What is the surface marking of the mitral valve?
- A. Behind the sternal end of the left 4th costal cartilage (Correct Answer)
- B. Behind the sternal end of the right 4th costal cartilage
- C. Left 4th intercostal space in the midclavicular line
- D. Left 3rd intercostal space in the midclavicular line
Explanation: The surface marking of heart valves is a high-yield topic for NEET-PG, requiring a clear distinction between where a valve is **anatomically located** versus where it is **best auscultated**. ### **Explanation of the Correct Answer** The **Mitral (Bicuspid) valve** is anatomically situated behind the left half of the sternum, opposite the **left 4th costal cartilage**. It is the most posterior and left-sided of all the heart valves. [1] ### **Analysis of Incorrect Options** * **Option B:** The **Tricuspid valve** is located behind the right half of the sternum at the level of the 4th/5th intercostal spaces. [1] * **Option C:** This is the **Auscultatory Area** for the mitral valve (the apex beat). While the valve is anatomically behind the 4th cartilage, the sound is carried by the flow of blood to the 5th left intercostal space in the midclavicular line. * **Option D:** The **Pulmonary valve** is located at the level of the left 3rd costal cartilage (at its junction with the sternum). [1] ### **High-Yield NEET-PG Pearls** To remember the anatomical positions of the valves from superior to inferior, use the mnemonic **"PAMT"** (3, 3.5, 4, 4.5): 1. **P**ulmonary: Left 3rd costal cartilage. [1] 2. **A**ortic: Left 3rd intercostal space. [1] 3. **M**itral: Left 4th costal cartilage. [1] 4. **T**ricuspid: Right 4th/5th intercostal space. [1] **Clinical Note:** Always distinguish between **Anatomical Position** (where the valve is) and **Auscultatory Area** (where you place the stethoscope). For the Mitral valve, the anatomical position is the left 4th costal cartilage, but the auscultatory area is the 5th intercostal space.
Question 514: A patient presents with a penetrating chest wound associated with intrathoracic hemorrhage. A thoracotomy is performed via an incision in the 4th/5th intercostal space, starting 1 cm away from the lateral margin of the sternum. This approach is taken to avoid injury to which of the following structures?
- A. Pleura
- B. Intercostal artery
- C. Internal thoracic artery (Correct Answer)
- D. Intercostal nerve
Explanation: The correct answer is **Internal thoracic artery (ITA)**. The internal thoracic artery (also known as the internal mammary artery) arises from the first part of the subclavian artery. It descends vertically behind the costal cartilages, approximately **1 to 1.25 cm lateral to the margin of the sternum**. By placing a thoracotomy incision at least 1 cm away from the sternal edge, surgeons ensure they do not inadvertently transect this vessel, which could lead to significant secondary hemorrhage or compromise a potential graft source for coronary artery bypass [3]. **Analysis of Incorrect Options:** * **Pleura (A):** The parietal pleura lines the inner surface of the thoracic wall. Any penetrating wound or surgical incision into the intercostal space will inevitably encounter or pierce the pleura to reach the thoracic cavity; it cannot be avoided by lateral displacement [4]. * **Intercostal artery (B) & Nerve (D):** The neurovascular bundle (Vein, Artery, Nerve - VAN) runs in the **costal groove** along the inferior border of the rib. To avoid these structures, incisions are typically made along the **upper border of the lower rib** in the intercostal space, rather than by adjusting the distance from the sternum [1]. **NEET-PG High-Yield Pearls:** * **Termination:** The ITA terminates in the 6th intercostal space by dividing into the **musculophrenic** and **superior epigastric** arteries [3]. * **Clinical Use:** The ITA is the "gold standard" conduit for Coronary Artery Bypass Grafting (CABG), particularly the Left ITA (LIMA) to the LAD [2]. * **Pericardiocentesis:** To avoid the ITA during needle insertion into the pericardial sac (Larrey’s point), the needle is inserted in the left infrasternal angle (between the xiphoid and costal margin).
Question 515: Which among the following is a typical intercostal nerve?
- A. First
- B. Second
- C. Third (Correct Answer)
- D. Seventh
Explanation: ### Explanation In human anatomy, intercostal nerves are the anterior rami of the first eleven thoracic spinal nerves ($T1$–$T11$). They are classified into **typical** and **atypical** nerves based on their course and distribution. #### Why the Third Intercostal Nerve is Typical A **typical intercostal nerve** (3rd, 4th, 5th, and 6th) is one that remains strictly confined to its own intercostal space. It supplies only the structures of the thoracic wall (intercostal muscles, parietal pleura, and skin over the space) [3] and does not contribute to the brachial plexus or extend into the abdominal wall. The **3rd nerve** fits these criteria perfectly. #### Analysis of Incorrect Options * **A. First ($T1$):** Atypical. Its large upper branch joins the $C8$ nerve to form the lower trunk of the **brachial plexus**. It lacks a lateral cutaneous branch and sometimes a substituted anterior cutaneous branch. * **B. Second ($T2$):** Atypical. Its lateral cutaneous branch is known as the **intercostobrachial nerve** [2], which crosses the axilla to supply the skin of the medial side of the arm. * **D. Seventh ($T7$):** Atypical (Thoraco-abdominal). Nerves $T7$ through $T11$ leave their respective intercostal spaces to enter the abdominal wall [1]. Therefore, they supply both the thoracic and abdominal parietes. #### NEET-PG High-Yield Pearls * **Typical Nerves:** $T3, T4, T5, T6$. * **Atypical Nerves:** $T1, T2, T7, T8, T9, T10, T11$. * **Neurovascular Bundle:** Located in the costal groove between the Internal Intercostal and Innermost Intercostal muscles. The order from superior to inferior is **V-A-N** (Vein, Artery, Nerve). * **Clinical Correlation:** During a thoracocentesis (pleural tap), the needle is inserted at the **upper border of the rib below** to avoid damaging the main neurovascular bundle.
Question 516: The thoracic duct crosses the posterior mediastinum at the level of which vertebra?
- A. T5 (Correct Answer)
- B. T6
- C. T7
- D. T8
Explanation: **Explanation:** The thoracic duct is the largest lymphatic vessel in the body, responsible for draining lymph from most of the body (except the right upper quadrant). Understanding its course is high-yield for NEET-PG. **1. Why T5 is Correct:** The thoracic duct enters the thorax through the **aortic opening** of the diaphragm at the level of **T12**. It ascends in the posterior mediastinum to the right of the midline, situated between the azygos vein and the aorta [1]. At the level of the **T5 vertebra**, the duct crosses from the right side to the left side of the vertebral column. After crossing, it enters the superior mediastinum and eventually empties into the junction of the left internal jugular and left subclavian veins. **2. Analysis of Incorrect Options:** * **T6 & T7:** These levels are part of the duct's ascent within the posterior mediastinum while it is still positioned on the right side of the midline. * **T8:** This is the level of the caval opening in the diaphragm. The thoracic duct is already well into its ascent through the posterior mediastinum by this point. **3. Clinical Pearls & High-Yield Facts:** * **Origin:** It begins as a continuation of the **cisterna chyli** (at T12/L1). * **Relations at T5:** The crossing occurs posterior to the esophagus and the aortic arch. * **Chylothorax:** Injury to the thoracic duct during thoracic surgery leads to the accumulation of milky lymph in the pleural cavity [1]. * **Mnemonic:** Remember **"The duck (duct) lies between two gooses"**—the Azy**gos** vein and the Esopha**gus** (or the Haema-zy**gos** and Azy**gos**).
Question 517: A 3-day-old newborn has difficulties breathing. A CT scan of his chest and abdomen reveals the absence of the central tendon of the diaphragm. Which of the following structures failed to develop normally?
- A. Pleuroperitoneal folds
- B. Pleuropericardial folds
- C. Septum transversum (Correct Answer)
- D. Cervical myotomes
Explanation: ### Explanation The diaphragm is a composite structure derived from four embryonic sources. Understanding these sources is high-yield for NEET-PG. **1. Why Septum Transversum is Correct:** The **septum transversum** is a thick mass of cranial mesoderm that migrates between the heart and the liver. In the developing embryo, it forms the primitive mesenchymal partition that partially separates the thoracic and abdominal cavities. It eventually gives rise to the **central tendon of the diaphragm**. Failure of this structure to develop or fuse properly results in the absence of the central tendon. **2. Analysis of Incorrect Options:** * **Pleuroperitoneal folds (A):** These contribute to the **posterolateral** parts of the diaphragm. Failure of these folds to fuse with the septum transversum results in a **Bochdalek hernia**, the most common type of congenital diaphragmatic hernia [1]. [2] * **Pleuropericardial folds (B):** These are involved in the formation of the **fibrous pericardium** and the pleuropericardial membranes, not the diaphragm. * **Cervical myotomes (D):** Specifically myotomes from **C3-C5** migrate into the diaphragm to form the **muscular component**. While they provide the contractile tissue, they do not form the central tendon. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Diaphragm Development:** "**S**ome **M**uscles **P**ave **D**iaphragm" (**S**eptum transversum, **M**esentery of esophagus/Crura, **P**leuroperitoneal folds, **D**erivatives of body wall). * **Nerve Supply:** The phrenic nerve (C3, 4, 5) supplies the diaphragm, reflecting its origin from cervical somites. "C3, 4, 5 keep the diaphragm alive." * **Bochdalek vs. Morgagni:** Bochdalek is **Back** and **Left** (posterolateral) [1]; Morgagni is **Anterior** and **Right** (retrosternal).
Question 518: A 37-year-old woman undergoes a routine breast examination. The physician notes that the skin of the breast moves with the underlying breast tissue, indicating normal attachment. What anatomical structures are responsible for this normal attachment of the breast tissue to the overlying skin?
- A. Cooper's ligaments (Correct Answer)
- B. Cruciate ligaments
- C. Falciform ligament
- D. Poupa's ligaments
Explanation: **Explanation:** The correct answer is **Cooper’s ligaments** (also known as the Suspensory ligaments of Cooper). These are fibrous connective tissue bands that extend from the deep fascia (covering the pectoralis major muscle) through the mammary gland substance to the overlying dermis of the skin [1]. They provide structural support and maintain the framework of the breast. When a tumor (carcinoma) involves these ligaments, they contract, leading to "puckering" or **dimpling of the skin**, which is a classic clinical sign of breast malignancy [2]. **Analysis of Incorrect Options:** * **Cruciate ligaments:** These are found in the **knee joint** (Anterior and Posterior Cruciate Ligaments) and are responsible for stabilizing the joint against anterior and posterior displacement. * **Falciform ligament:** This is a peritoneal fold that attaches the **liver** to the anterior abdominal wall and diaphragm. * **Poupart’s ligament:** This is a synonym for the **Inguinal ligament**, which runs from the anterior superior iliac spine (ASIS) to the pubic tubercle. **High-Yield Clinical Pearls for NEET-PG:** * **Peau d'orange:** This is the "orange peel" appearance of the breast skin caused by **lymphatic obstruction**, not Cooper’s ligaments. * **Retraction of the Nipple:** This occurs when a tumor involves the **lactiferous ducts**, causing them to fibrose and shorten. * **Blood Supply:** The internal mammary (thoracic) artery and the lateral thoracic artery provide the primary blood supply to the breast. * **Lymphatic Drainage:** Approximately 75% of lymph drains into the **axillary nodes** (primarily the Pectoral/Anterior group).
Question 519: What is the primary blood supply to the thoracic part of the esophagus?
- A. Aorta (Correct Answer)
- B. Inferior thyroid artery
- C. Gastric artery
- D. Superior thyroid artery
Explanation: The esophagus is a muscular tube approximately 25 cm long, divided into cervical, thoracic, and abdominal segments. Its blood supply is segmental, reflecting its course through different body cavities. ### **Why Aorta is Correct** The **thoracic part** of the esophagus is the longest segment. Its primary arterial supply comes directly from the **Thoracic Aorta** via multiple **esophageal branches**. Additionally, it receives collateral supply from the bronchial arteries (which are also branches of the aorta). ### **Why Other Options are Incorrect** * **B & D (Inferior and Superior Thyroid Arteries):** The **Inferior Thyroid Artery** (a branch of the thyrocervical trunk) supplies the **cervical part** of the esophagus. The superior thyroid artery primarily supplies the larynx and thyroid gland, not the esophagus. * **C (Gastric Artery):** The **Left Gastric Artery** (a branch of the celiac trunk) and the left inferior phrenic artery supply the **abdominal part** of the esophagus. ### **High-Yield NEET-PG Pearls** * **Venous Drainage:** This is a classic site for **Portosystemic Anastomosis**. The lower end of the esophagus drains into both the azygos vein (systemic) and the left gastric vein (portal). In portal hypertension, these veins dilate to form **esophageal varices**. * **Lymphatic Drainage:** Follows a "rule of thirds"—Upper third to deep cervical nodes, middle third to mediastinal nodes, and lower third to celiac nodes. * **Constrictions:** The esophagus has four natural constrictions (at 6, 9, 11, and 15 inches from the incisor teeth). The most common site for a foreign body to lodge is the first constriction (cricopharyngeal junction).
Question 520: The great cardiac vein drains into which structure?
- A. Right atrium
- B. Inferior vena cava
- C. Coronary sinus (Correct Answer)
- D. Superior vena cava
Explanation: The **coronary sinus** is the primary venous channel of the heart, responsible for draining approximately 60-70% of the cardiac venous blood. The **great cardiac vein** begins at the apex of the heart, ascends in the anterior interventricular sulcus (alongside the anterior interventricular artery), and eventually enters the left end of the coronary sinus [1]. **Why the other options are incorrect:** * **Right Atrium:** While the coronary sinus itself empties into the right atrium (between the IVC opening and the tricuspid valve), the great cardiac vein does not drain into it directly [1]. Only the **anterior cardiac veins** and **thebesian veins** (venae cordis minimae) drain directly into the right atrium. * **Inferior Vena Cava (IVC):** The IVC returns deoxygenated blood from the lower half of the body to the right atrium; it does not receive direct tributaries from the intrinsic cardiac veins. * **Superior Vena Cava (SVC):** The SVC returns blood from the head, neck, and upper limbs; it has no direct involvement in cardiac venous drainage. **High-Yield NEET-PG Pearls:** 1. **Tributaries of Coronary Sinus:** Great cardiac vein, Middle cardiac vein (in the posterior interventricular sulcus), Small cardiac vein, and the Oblique vein of the left atrium (Vein of Marshall). 2. **The Valve of Thebesius:** This is the rudimentary valve guarding the opening of the coronary sinus into the right atrium. 3. **Anatomical Course:** The great cardiac vein is the venous companion of the **Left Anterior Descending (LAD) artery**. [1] 4. **Clinical Significance:** The coronary sinus is often used as a landmark for placing leads during cardiac resynchronization therapy (CRT) [1].
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
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