Thorax Practice Questions

Q: In coronary bypass graft surgery, the internal thoracic artery is used as the coronary artery bypass graft. The anterior intercostal arteries in intercostal spaces three to six are ligated. Which of the following arteries will be expected to supply these intercostal spaces?

Posterior intercostal. The blood supply to the intercostal spaces is characterized by an extensive **anastomosis** between the anterior and posterior intercostal arteries. 1. **Why the Correct Answer is Right:** The **Internal Thoracic Artery (ITA)** normally gives off two anterior intercostal arteries for each of the upper six intercostal spaces. When the ITA is harvested for a coronary artery bypass graft (CABG) [1] and the anterior intercostal arteries are ligated, the blood supply to these spaces is maintained via **retrograde flow** from the **Posterior Intercostal Arteries**. These posterior arteries (branches of the Superior Intercostal artery for spaces 1-2 and the Thoracic Aorta for spaces 3-11) anastomose directly with the anterior arteries. This collateral circulation ensures that the intercostal muscles and overlying skin do not undergo ischemia. 2. **Analysis of Incorrect Options:** * **A & B (Musculophrenic & Superior Epigastric):** These are the terminal branches of the ITA [2]. While the musculophrenic artery supplies the lower (7th–9th) anterior intercostal spaces, it does not supply the 3rd–6th spaces mentioned in the question. * **D (Lateral Thoracic):** This is a branch of the second part of the Axillary artery. It primarily supplies the pectoral muscles and the lateral aspect of the breast, not the intercostal spaces directly. **Clinical Pearls for NEET-PG:** * **Gold Standard:** The Left Internal Mammary Artery (LIMA/ITA) is the preferred graft for the Left Anterior Descending (LAD) artery due to its superior long-term patency rates compared to venous grafts [1]. * **Origin:** The ITA arises from the first part of the **Subclavian Artery**. * **Coarctation of Aorta:** In post-ductal coarctation, the anastomosis between the anterior and posterior intercostal arteries becomes dilated to bypass the obstruction, leading to the classic radiological sign of **"Rib Notching."**

Q: All of the following are contents of the posterior mediastinum except?

Ascending aorta. **Explanation:** The mediastinum is divided into superior and inferior parts by the transverse thoracic plane (angle of Louis). The inferior mediastinum is further subdivided into anterior, middle, and posterior compartments [1]. **1. Why the Ascending Aorta is the correct answer:** The **Ascending Aorta** is a content of the **Middle Mediastinum** [2]. It arises from the left ventricle and is enclosed within the fibrous pericardium along with the pulmonary trunk and the heart. Since it does not pass into the posterior compartment, it is the "except" in this list. **2. Analysis of Incorrect Options (Contents of Posterior Mediastinum):** * **Esophagus:** This is a primary structure of the posterior mediastinum, descending behind the trachea and heart. * **Thoracic Duct:** It ascends in the posterior mediastinum between the azygos vein and the esophagus. * **Hemiazygous Vein:** Along with the Azygos and Accessory Hemiazygos veins, these form the venous drainage system located in the posterior mediastinum. * *Note: Other contents include the Descending Thoracic Aorta, Vagus nerves, and Splanchnic nerves.* **3. NEET-PG High-Yield Pearls:** * **The "DATES" Mnemonic:** To remember posterior mediastinal contents: **D**escending aorta, **A**zygos/Hemiazygos veins, **T**horacic duct, **E**sophagus, **S**ympathetic trunk/Splanchnic nerves. * **The Aorta's Journey:** The **Ascending Aorta** is in the Middle Mediastinum; the **Arch of Aorta** is in the Superior Mediastinum; the **Descending Thoracic Aorta** is in the Posterior Mediastinum [2]. * **Clinical Correlation:** Neurogenic tumors are the most common primary tumors found in the posterior mediastinum.

Q: Which is the most dependent bronchopulmonary segment in the supine position?

Right superior segment. The correct answer is **B. Right superior segment**. ### **Explanation** The "dependency" of a bronchopulmonary segment refers to its position relative to gravity. In the **supine (lying on back) position**, the **superior segment of the lower lobe** (specifically the right side) is the most posterior and gravity-dependent part of the lung [1]. This occurs because the superior segmental bronchus arises from the posterior aspect of the principal bronchus. When a patient is supine, gravity causes aspirated material (vomitus, blood, or foreign bodies) to flow directly into this posteriorly directed opening. The **right side** is more commonly affected than the left because the right main bronchus is wider, shorter, and more vertical. ### **Analysis of Incorrect Options** * **C & D (Posterior Basal Segments):** These segments are the most dependent when the patient is in the **upright (standing or sitting)** position. Aspirated material in a conscious, upright individual typically settles in the lung bases [1]. * **A (Left Superior Segment):** While also posterior, the left main bronchus is more horizontal and narrower due to the presence of the heart, making aspiration less likely compared to the right side. ### **Clinical Pearls for NEET-PG** * **Aspiration Pneumonia Sites:** * **Supine:** Superior segment of the Right Lower Lobe. * **Upright:** Posterior basal segment of the Right Lower Lobe. * **Right Lateral Decubitus:** Posterior segment of the Right Upper Lobe [1]. * **Foreign Body Localization:** Most common site is the **Right Main Bronchus** due to its vertical orientation (25° angle vs. 45° on the left). * **Postural Drainage:** Knowledge of these segments is vital for positioning patients to drain lung abscesses or secretions.

Q: After the pericardial sac has been opened anteriorly during surgery, by passing a surgical clamp through the transverse sinus, which structures can surgeons use to stop or divert circulation of blood?

Aorta and pulmonary trunk. The **transverse pericardial sinus** is a horizontal passage within the pericardial cavity located behind the two great outflow vessels of the heart. It is formed during embryonic development by the breakdown of the central part of the dorsal mesocardium. **Why Option C is Correct:** The transverse sinus acts as a natural "tunnel" that separates the **arterial outflow vessels** (Aorta and Pulmonary Trunk) from the **venous inflow vessels** (SVC, IVC, and Pulmonary Veins). * **Anterior boundary:** Ascending aorta and pulmonary trunk. * **Posterior boundary:** Superior vena cava (SVC) and the upper limit of the left atrium. By passing a clamp or ligature through this sinus, a surgeon can encircle the aorta and pulmonary trunk together [1]. This allows for the temporary clamping of these vessels to divert blood into a cardiopulmonary bypass machine during open-heart surgery [2]. **Why Other Options are Incorrect:** * **Options A, B, and D:** These include venous structures (SVC, IVC, or Pulmonary veins). These vessels lie posterior to the transverse sinus or are separated by the **oblique pericardial sinus** (a blind-ending recess behind the left atrium). They cannot be collectively encircled by a single clamp passed through the transverse sinus. **High-Yield Clinical Pearls for NEET-PG:** * **Boundaries:** Superiorly – Right pulmonary artery; Inferiorly – Left atrium. * **Oblique Sinus:** A "J-shaped" cul-de-sac behind the left atrium, bounded by the pulmonary veins and IVC. It allows for the expansion of the left atrium. * **Surgical Significance:** The transverse sinus is the key landmark for performing the **Pringle-like maneuver** of the heart (clamping the outflow tract).

Q: A patient sustains a knife wound through the right fourth intercostal space, 2 cm to the right of the sternum. Which structure is most likely penetrated?

Right middle lobe of the lung. The correct answer is **B. Right middle lobe of the lung.** To answer this question, one must understand the surface anatomy of the lungs and the heart. The right lung is divided into three lobes by the oblique and horizontal fissures. [1] 1. **Why Option B is Correct:** The **horizontal fissure** of the right lung typically follows the **4th rib and costal cartilage** anteriorly. [1] Therefore, any penetrating injury at or below the level of the 4th intercostal space (but above the 6th rib) on the right side will most likely involve the **Right Middle Lobe**. 2. **Why Option A is Incorrect:** The **Right Upper Lobe** lies superior to the horizontal fissure (above the 4th rib). A wound in the 1st or 2nd intercostal space would be more likely to involve this lobe. 3. **Why Option C is Incorrect:** The **Right Lower Lobe** is situated posteriorly and inferiorly. [1] Anteriorly, it lies below the oblique fissure, which reaches the midclavicular line at the 6th rib. It is not accessible at the 4th intercostal space anteriorly. 4. **Why Option D is Incorrect:** While the Right Atrium forms the right border of the heart, it is generally protected by the sternum and the medial edges of the lung/pleura. [2] At the 4th intercostal space, 2 cm lateral to the sternum, the knife would first penetrate the pleura and the lung parenchyma before reaching the pericardium. **High-Yield Clinical Pearls for NEET-PG:** * **Horizontal Fissure:** Extends from the oblique fissure at the midaxillary line to the **4th costal cartilage** anteriorly. [1] * **Oblique Fissure:** Begins at the T3 spine posteriorly and ends at the **6th costal cartilage** anteriorly. * **Auscultation Tip:** To listen to the Right Middle Lobe, place the stethoscope on the anterior chest wall below the 4th rib. * **Cardiac Border:** The right border of the heart is formed by the Right Atrium, extending from the 3rd to the 6th costal cartilages. [2]

Q: The subcostal nerve originates from which of the following?

Ventral rami of T12. The **subcostal nerve** is the name given to the **ventral ramus of the 12th thoracic nerve (T12)**. Unlike the first eleven thoracic spinal nerves, which run between the ribs as intercostal nerves, the T12 nerve travels below the 12th rib, hence the name "subcostal." [1] 1. **Why Option C is Correct:** Spinal nerves divide into ventral and dorsal rami after exiting the intervertebral foramen. The **ventral rami** of T1–T11 form the intercostal nerves, while the ventral ramus of **T12** becomes the subcostal nerve. It enters the abdomen behind the lateral arcuate ligament and supplies the muscles of the abdominal wall and the skin over the hip (gluteal region). [1] 2. **Why Other Options are Incorrect:** * **Options A & B (T6):** The ventral ramus of T6 is the 6th intercostal nerve, supplying the 6th intercostal space and the skin over the upper epigastrium. [1] * **Option D (Dorsal rami of T12):** Dorsal rami of all spinal nerves supply the deep muscles of the back and the overlying skin. They do not form named peripheral nerves like the subcostal or intercostal nerves. **High-Yield Clinical Pearls for NEET-PG:** * **Dermatome:** The subcostal nerve provides sensory innervation to the skin of the abdominal wall between the umbilicus and the pubic symphysis (specifically the T12 dermatome). * **Surgical Landmark:** During a **lumbar (nephrectomy) incision**, the subcostal nerve must be identified and protected as it runs along the lower border of the 12th rib. * **Nerve Plexus Contribution:** A branch of the T12 ventral ramus often joins the L1 ventral ramus to contribute to the formation of the **lumbar plexus**.

Q: Which anatomical structure does not form a part of the thoracic outlet?

Second rib. The **thoracic outlet** (clinically referred to as the superior thoracic aperture) is the narrow opening at the root of the neck. Anatomically, it is bounded by the **first thoracic vertebra (T1)** posteriorly, the **first rib** laterally, and the **superior border of the manubrium** anteriorly [2]. **Explanation of the Correct Answer:** * **D. Second rib:** The second rib does not form any part of the boundary of the thoracic outlet. The outlet is strictly defined by the inner margin of the **first rib**. Therefore, the second rib is anatomically inferior to this aperture and does not contribute to its formation or the clinical syndromes associated with it. **Explanation of Incorrect Options:** * **A & B. Brachial plexus and Subclavian vein:** These are vital structures that pass through the thoracic outlet to reach the upper limb [1]. The brachial plexus (roots and trunks) and the subclavian artery pass through the **interscalene triangle**, while the subclavian vein passes anterior to the scalenus anterior muscle [1]. * **C. Apex of lung:** The apex of the lung, covered by the cervical pleura (Sibson’s fascia), projects approximately 2–3 cm above the level of the first rib into the root of the neck, making it a key occupant of the thoracic outlet region. **Clinical Pearls for NEET-PG:** * **Thoracic Outlet Syndrome (TOS):** Compression of the neurovascular bundle (brachial plexus or subclavian vessels) within this space [1]. The most common cause is a **cervical rib** or an elongated transverse process of C7. * **Sibson’s Fascia:** Also known as the suprapleural membrane, it attaches to the inner border of the first rib and the transverse process of C7, protecting the underlying apex of the lung. * **Anatomical vs. Clinical:** Note that anatomists call this the "superior thoracic aperture," while clinicians call it the "thoracic outlet" [2].

Q: What structure passes through the diaphragm at the T12 vertebral level?

Thoracic duct. The diaphragm features three major openings (hiatuses) that allow structures to pass between the thorax and abdomen [1]. These are high-yield topics for NEET-PG, often remembered by the mnemonic **"I Voice 8, Ten Eggs At 12."** ### **Correct Answer: C. Thoracic duct** The **Aortic Hiatus** is located at the **T12** vertebral level. It is not a true hole in the muscular diaphragm but an osseo-aponeurotic opening behind the median arcuate ligament. Three structures pass through it (Mnemonic: **A**-**R**-**T**): 1. **A**orta 2. **R**azygos vein (Azygos vein) 3. **T**horacic duct ### **Why the other options are incorrect:** * **A. Esophagus:** Passes through the **Esophageal Hiatus** at the **T10** level. Other structures here include the Vagus nerves (anterior and posterior trunks) and esophageal branches of the left gastric vessels. * **B. Inferior Vena Cava (IVC):** Passes through the **Vena Caval Foramen** at the **T8** level, located within the central tendon. The right phrenic nerve also passes through this opening. * **D. Phrenic nerve:** The **left** phrenic nerve pierces the muscular part of the left dome of the diaphragm independently, while the **right** phrenic nerve passes through the T8 opening with the IVC. ### **High-Yield Clinical Pearls for NEET-PG:** * **Level Changes:** During inspiration, the IVC opening (T8) dilates to facilitate venous return, while the Esophageal opening (T10) constricts to prevent reflux. The Aortic opening (T12) is unaffected by contraction because it is fibrous. * **I-10-E-8-A-12 Rule:** * **I**VC = T**8** * **E**sophagus = T**10** * **A**orta = T**12**

Question 1

In coronary bypass graft surgery, the internal thoracic artery is used as the coronary artery bypass graft. The anterior intercostal arteries in intercostal spaces three to six are ligated. Which of the following arteries will be expected to supply these intercostal spaces?

Accepted Answer

Posterior intercostal

Answer

Musculophrenic

Answer

Superior epigastric

Answer

Lateral thoracic

Question 2

All of the following are contents of the posterior mediastinum except?

Accepted Answer

Ascending aorta

Answer

Hemiazygous vein

Answer

Thoracic duct

Answer

Esophagus

Question 3

A 3-year-old child is admitted to the emergency department with a particularly severe attack of asthma. Which of the following is the most important factor in increasing the intrathoracic capacity in inspiration?

Accepted Answer

Descent of the diaphragm, with protrusion of the abdominal wall, thereby increasing vertical dimensions of the thoracic cavity

Answer

"Pump handle movement" of the ribs, thereby increasing anterior-posterior dimensions of the thorax

Answer

"Bucket handle movement" of the ribs, increasing the transverse diameter of the thorax

Answer

Straightening of the forward curvature of the thoracic spine, thereby increasing the vertical dimensions of the thoracic cavity

Question 4

Which is the most dependent bronchopulmonary segment in the supine position?

Accepted Answer

Right superior segment

Answer

Left superior segment

Answer

Right posterior basal segment

Answer

Left posterior basal segment

Question 5

While performing thoracocentesis, along which border of the rib is it advisable to introduce the needle?

Accepted Answer

Upper border of the rib

Answer

Lower border of the rib

Answer

In the center of the intercostal space

Answer

In the anterior part of the intercostal space

Question 6

After the pericardial sac has been opened anteriorly during surgery, by passing a surgical clamp through the transverse sinus, which structures can surgeons use to stop or divert circulation of blood?

Accepted Answer

Aorta and pulmonary trunk

Answer

Superior and inferior vena cava

Answer

Aorta and pulmonary veins

Answer

Superior vena cava and pulmonary veins

Question 7

A patient sustains a knife wound through the right fourth intercostal space, 2 cm to the right of the sternum. Which structure is most likely penetrated?

Accepted Answer

Right middle lobe of the lung

Answer

Right upper lobe of the lung

Answer

Right lower lobe of the lung

Answer

Right atrium of the heart

Question 8

The subcostal nerve originates from which of the following?

Accepted Answer

Ventral rami of T12

Answer

Ventral rami of T6

Answer

Dorsal rami of T6

Answer

Dorsal rami of T12

Question 9

Which anatomical structure does not form a part of the thoracic outlet?

Accepted Answer

Second rib

Answer

Brachial plexus

Answer

Subclavian vein

Answer

Apex of lung

Question 10

What structure passes through the diaphragm at the T12 vertebral level?

Accepted Answer

Thoracic duct

Answer

Esophagus

Answer

Inferior Vena Cava

Answer

Phrenic nerve

Thorax — MCQs

Thorax — MCQs

On this page

Practice by Chapter

Want unlimited practice?