Thorax Practice Questions

Q: Which structures are located anterior to the transverse sinus?

Aorta. ***Aorta*** - The **transverse sinus of the pericardium** is a passage within the pericardial cavity that separates the great arteries (aorta and pulmonary trunk) anteriorly from the atria and great veins posteriorly. - The **ascending aorta** and **pulmonary trunk** are both located anterior to the transverse sinus. - This anatomical relationship is clinically important during cardiac surgery, as the transverse sinus can be used to pass ligatures around the great vessels. *Right atrium* - The **right atrium** is located posterior to the transverse sinus. - It forms part of the posterior wall of the pericardial cavity and receives the superior and inferior venae cavae. - The transverse sinus separates the atria from the anteriorly positioned great arteries. *Left atrium* - The **left atrium** is also positioned posterior to the transverse sinus. - It forms the base of the heart and receives the pulmonary veins. - Like the right atrium, it lies behind the plane of the transverse sinus. *Right pulmonary artery* - The **right pulmonary artery** is a branch of the pulmonary trunk that passes to the right lung. - While the **pulmonary trunk** itself is anterior to the transverse sinus, the **right pulmonary artery** branch courses laterally and posteriorly, passing behind the ascending aorta and superior vena cava. - Therefore, the right pulmonary artery is NOT considered anterior to the transverse sinus in the same way the main great vessels (aorta and pulmonary trunk) are.

Q: Which of the following muscles is considered the most powerful elevator of the ribs?

External intercostals. ***External intercostals*** - The **external intercostals** are the **most powerful and primary elevators of the ribs** during inspiration [1]. - Their fibers run **obliquely downward and forward** from the rib above to the rib below, providing optimal mechanical advantage for rib elevation [1]. - They are the **principal muscles of normal inspiration**, actively contracting to elevate the ribs and increase the anteroposterior and lateral dimensions of the thoracic cavity [1]. - Their action is continuous during normal breathing, making them the most significant contributors to rib elevation. *Levatores costarum* - The **levatores costarum** are small muscles originating from transverse processes of vertebrae and inserting into the rib below. - While they do elevate ribs, they are considered **accessory muscles of inspiration** with a minor role. - Their primary function may be more related to **spinal stabilization** than powerful rib elevation. - They are not as powerful or mechanically effective as the external intercostals. *Serratus posterior inferior* - The **serratus posterior inferior** muscles primarily function to **depress the lower ribs**, aiding in forced expiration. - Their action is antagonistic to rib elevation and thus they are not involved in raising the ribs. *Serratus posterior superior* - The **serratus posterior superior** muscles assist in **elevating the upper ribs** during inspiration. - They are **accessory muscles of inspiration** but play a minor role compared to the external intercostals. - Their action is limited to the upper ribs (ribs 2-5) and they are not continuously active during normal breathing.

Q: All of the following are true about Sibson's fascia except which of the following?

Arises from scalenus anterior. ***Arises from scalenus anterior*** - This statement is **FALSE** and is the correct answer to this "EXCEPT" question. - Sibson's fascia (suprapleural membrane) does **NOT** arise from the scalenus anterior muscle. - It is a fibrous extension of the **deep cervical fascia** that arises primarily from the **transverse process of the 7th cervical vertebra (C7)** and extends to attach to the **inner border of the first rib**. - While it may have fascial connections with scalene muscles (particularly scalenus medius and minimus), it does not directly arise from scalenus anterior. *Subclavian artery passes beneath it* - This statement is **TRUE**. - The subclavian artery passes through the thoracic inlet and courses beneath (inferior to) the dome-shaped Sibson's fascia. - Sibson's fascia forms a protective dome over the lung apex, and the subclavian vessels pass below this fascial layer in the root of the neck. *Attached to cervical pleura* - This statement is **TRUE**. - Sibson's fascia is firmly **attached to the cervical pleura** (the pleura covering the apex of the lung). - This attachment reinforces and supports the pleural dome, preventing herniation of the lung apex into the neck during respiratory movements. *It forms the suprapleural membrane* - This statement is **TRUE**. - Sibson's fascia is synonymous with the **suprapleural membrane**. - This membrane strengthens the parietal pleura at the thoracic inlet and maintains the integrity of the pleural cavity at its superior aspect [1].

Q: All of the following attach to the first rib, EXCEPT:

Scalenus posterior. ***Scalenus posterior*** - The **scalenus posterior** muscle typically inserts onto the **second rib**, not the first rib. - Its primary actions involve elevating the second rib and flexing the neck laterally. *Scalenus anterior* - The **scalenus anterior** muscle originates from the cervical vertebrae and inserts onto the **first rib**. - It helps elevate the first rib during inspiration and flex the neck. *Scalenus medius* - The **scalenus medius** muscle also originates from the cervical vertebrae and inserts onto the **first rib**, posterior to the scalenus anterior. - It also aids in elevating the first rib and flexing the neck. *Suprapleural membrane* - The **suprapleural membrane**, also known as **Sibson's fascia**, is a fibrous sheet that covers the apex of the lung and is attached to the inner border of the **first rib**. - It acts as a protective dome over the lung apex.

Q: Which of the following does not form the left border of the heart?

Pulmonary veins. **Pulmonary veins** - The pulmonary veins are positioned posteriorly and drain into the **left atrium**, thus they do not form part of the visible left cardiac border on a standard chest X-ray or during superficial anatomical viewing [1]. - The **left border of the heart** is primarily formed by the left ventricle, with contributions from the aortic arch and pulmonary trunk more superiorly [3]. *Left ventricle* - The **left ventricle** constitutes the major part of the left border of the heart, extending from the base to the apex [4]. - Its location and size make it a prominent feature on the left silhouette. *Aortic arch* - The **aortic arch** is located superior to the heart and gives rise to major systemic arteries [2]. - It forms a portion of the **upper left border** of the mediastinal silhouette, contributing to the cardiovascular outline. *Pulmonary trunk* - The **pulmonary trunk** arises from the right ventricle and branches into the pulmonary arteries [3]. - It contributes to the **upper left border** of the heart, medial to the aortic arch, as it courses superiorly before bifurcating.

Q: Majority of bronchogenic lung cysts occur in which?

Mediastinum. ***Mediastinum*** - **Bronchogenic cysts** most commonly occur in the **mediastinum** (approximately 60-70% of cases), particularly in the **subcarinal** or **paratracheal** regions [1]. - These cysts develop from abnormal budding of the primitive foregut during embryonic development [1]. - The mediastinum is the most comprehensive answer, as cysts can occur in various mediastinal locations. *Near the carina* - The **subcarinal region** (near the carina) is indeed one of the most common specific sites for mediastinal bronchogenic cysts [1]. - However, this represents only one specific location within the mediastinum, whereas cysts also commonly occur in paratracheal, hilar, and other mediastinal regions. - "Mediastinum" is the more complete answer as it encompasses all these locations. *Peribronchial tissue* - While bronchogenic cysts are derived from bronchial tree anomalies, the term **peribronchial tissue** is too vague and not the standard anatomical classification used. - The majority are found in well-defined mediastinal compartments, not simply described as "peribronchial." *Base of the lung* - **Intrapulmonary bronchogenic cysts** account for only 30-40% of cases, making them less common than mediastinal cysts. - Intrapulmonary cysts may be mistaken for other lung pathologies like **pulmonary sequestration** or congenital cystic adenomatoid malformation.

Q: Vasa vasorum of the ascending aorta arises from?

Right coronary artery. ***Right coronary artery*** - The **vasa vasorum** supplying the ascending aorta primarily originates from the **right coronary artery**. - The right coronary artery provides branches that penetrate the adventitia and outer media of the **ventral (anterior) aspect** of the ascending aorta. - Additional contributions come from branches of the **brachiocephalic trunk** and **subclavian arteries** that supply the dorsal aspect. - These small vessels are essential for providing nutrients and oxygen to the thick aortic wall, which cannot be adequately supplied by diffusion alone [2]. *Left coronary artery* - While the left coronary artery does contribute to the vasa vasorum network, it is **not the primary source** for the ascending aorta. - The left coronary artery primarily gives rise to the **left anterior descending (LAD)** and **circumflex arteries**, which mainly supply the heart muscle itself [1]. *Anterior interventricular artery* - This artery, also known as the **left anterior descending (LAD)**, is a branch of the left coronary artery. - It primarily supplies the **interventricular septum** and the **anterior wall of the left ventricle** [1]. - It does not significantly contribute to the vasa vasorum of the ascending aorta. *Posterior interventricular artery* - This artery, typically a branch of the **right coronary artery** (in right-dominant circulation), supplies the **posterior interventricular septum** and posterior walls of the ventricles [1]. - It has no direct involvement in supplying the vasa vasorum of the ascending aorta.

Q: The thymus is located in which part of the body?

Anterior mediastinum. ***Correct: Anterior mediastinum*** - The **thymus** is primarily located in the **anterior mediastinum** (also called the prevascular compartment) [1] - It lies behind the **sternum** and in front of the **pericardium** and great vessels [1] - In children, the thymus is large and may extend upward into the **superior mediastinum** and inferiorly to the level of the 4th costal cartilage [2] - In adults, the thymus undergoes **involution** but remains primarily an anterior mediastinal structure - This is the standard classification in modern anatomy texts including **Gray's Anatomy** *Incorrect: Superior mediastinum* - The **superior mediastinum** extends from the thoracic inlet to the **sternal angle** (level of T4/T5) - While the thymus may extend into the superior mediastinum, especially in children, it is **not primarily classified** as a superior mediastinal structure [2] - Superior mediastinum contains: thymus (upper portion), great vessels (aortic arch, brachiocephalic vessels, SVC), trachea, esophagus, thoracic duct, vagus and phrenic nerves [2] *Incorrect: Middle mediastinum* - The **middle mediastinum** contains the **heart within the pericardium** and the **phrenic nerves** [2] - It extends from the **sternal angle** superiorly to the **diaphragm** inferiorly - The thymus lies **anterior** to the pericardium, not within the middle mediastinum *Incorrect: Posterior mediastinum* - The **posterior mediastinum** lies behind the pericardium and contains the **descending thoracic aorta**, **esophagus**, **thoracic duct**, **azygos venous system**, and **sympathetic chains** - The thymus is located in the **most anterior** part of the mediastinum, far from the posterior compartment

Q: Intercostal veins drain into which structure?

Azygos vein. ***Azygos vein*** - The **posterior intercostal veins** drain into the **azygos system (azygos, hemiazygos, and accessory hemiazygos veins)**, which then empties into the superior vena cava [1]. - The azygos vein is centrally located in the posterior mediastinum and serves as a major venous drainage pathway for the thoracic wall [1]. *Left subclavian vein* - The left subclavian vein primarily drains the **left upper limb**. - It receives the **thoracic duct** and occasionally the left external jugular vein, but not the intercostal veins directly. *Internal jugular vein* - The internal jugular vein drains blood from the **brain, superficial face, and neck**. - It joins with the subclavian vein to form the brachiocephalic vein, but does not receive direct intercostal drainage. *Inferior vena cava* - The inferior vena cava drains deoxygenated blood from the **lower body, including the legs, kidneys, and liver**. - It does not directly receive intercostal veins, which primarily drain into the azygos system or brachiocephalic veins.

Q: While performing drainage of fluid from the pleural cavity, the needle is introduced through all of the following structures except which one?

Pulmonary pleura. ***Pulmonary pleura*** - The needle for pleural fluid drainage, or thoracentesis, passes through the **parietal pleura** [1] but not the **pulmonary (visceral) pleura**. - Puncturing the pulmonary pleura would indicate the needle has entered the lung parenchyma, which is an avoidable complication. *Skin* - The **skin** is the outermost layer and the first structure the needle penetrates during a thoracentesis. - It must be sterilized prior to the procedure. *Thoracic fascia* - The needle passes through the **superficial fascia** and then the **deep fascia** covering the intercostal muscles. - These fascial layers provide structural support and enclose the musculature of the thoracic wall. *Intercostal muscles* - The needle traverses the **external**, **internal**, and **innermost intercostal muscles** as it moves deeper into the thoracic cavity. - The neurovascular bundle runs between the internal and innermost intercostals, hence the needle is typically inserted over the superior border of the rib to avoid it [1].

Question 1

Which structures are located anterior to the transverse sinus?

Accepted Answer

Aorta

Answer

Right atrium

Answer

Left atrium

Answer

Right pulmonary artery

Question 2

Which of the following muscles is considered the most powerful elevator of the ribs?

Accepted Answer

External intercostals

Answer

Levatores costarum

Answer

Serratus posterior inferior

Answer

Serratus posterior superior

Question 3

All of the following are true about Sibson's fascia except which of the following?

Accepted Answer

Arises from scalenus anterior

Answer

Subclavian artery passes beneath it.

Answer

Attached to cervical pleura

Answer

It forms the suprapleural membrane

Question 4

All of the following attach to the first rib, EXCEPT:

Accepted Answer

Scalenus posterior

Answer

Scalenus medius

Answer

Suprapleural membrane

Answer

Scalenus anterior

Question 5

Which of the following does not form the left border of the heart?

Accepted Answer

Pulmonary veins

Answer

Left ventricle

Answer

Aortic arch

Answer

Pulmonary trunk

Question 6

Majority of bronchogenic lung cysts occur in which?

Accepted Answer

Mediastinum

Answer

Near the carina

Answer

Peribronchial tissue

Answer

Base of the lung

Question 7

Vasa vasorum of the ascending aorta arises from?

Accepted Answer

Right coronary artery

Answer

Left coronary artery

Answer

Anterior interventricular artery

Answer

Posterior interventricular artery

Question 8

The thymus is located in which part of the body?

Accepted Answer

Anterior mediastinum

Answer

Superior mediastinum

Answer

Middle mediastinum

Answer

Posterior mediastinum

Question 9

Intercostal veins drain into which structure?

Accepted Answer

Azygos vein

Answer

Left subclavian vein

Answer

Internal jugular vein

Answer

Inferior vena cava

Question 10

While performing drainage of fluid from the pleural cavity, the needle is introduced through all of the following structures except which one?

Accepted Answer

Pulmonary pleura

Answer

Thoracic fascia

Answer

Skin

Answer

Intercostal muscles

Thorax — MCQs

Thorax — MCQs

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