Cross-sectional Anatomy: Thorax — MCQs
The thymus is located in which part of the body?
Which of the following structures pass through the aortic hiatus of the diaphragm?
Esophagus is present in which mediastinum?
PA view of chest X-ray is given here. What is the diagnosis?
Which airway structure enters the lung at the hilum?
Which chamber enlargement shows a double right heart border with a wide subcarinal angle?
Caldwell’s view is used for:
Identify the structure shown in CT abdomen section. (Recent NEET Pattern 2018-19)
Shenton's Line is present in which joint?
Which of the following radiographic projections is used to demonstrate the base of the skull, sphenoid sinus, position and orientation of the condyles, and fractures of the zygomatic arch?
Cross-sectional Anatomy: Thorax Indian Medical PG Practice Questions and MCQs
Question 1: The thymus is located in which part of the body?
- A. Superior mediastinum
- B. Middle mediastinum
- C. Posterior mediastinum
- D. Anterior mediastinum (Correct Answer)
Explanation: ***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
Question 2: Which of the following structures pass through the aortic hiatus of the diaphragm?
- A. Inferior vena cava
- B. Oesophagus
- C. Vagus nerve
- D. Azygos vein (Correct Answer)
Explanation: ***Azygos vein*** - The **aortic hiatus** is located at the level of the **T12 vertebra** and transmits the aorta, **thoracic duct**, and often the azygos vein. - The azygos vein ascends through the posterior mediastinum and typically enters the thorax via the aortic hiatus or an opening in the right crus of the diaphragm. *Inferior vena cava* - The inferior vena cava (IVC) passes through the **caval opening** of the diaphragm, located more anteriorly at the level of **T8 or T9**. - The caval opening is within the central tendinous part of the diaphragm. *Oesophagus* - The oesophagus passes through the **oesophageal hiatus** of the diaphragm, which is typically found at the level of **T10**. - This hiatus is formed by muscular fibres of the right crus of the diaphragm. *Vagus nerve* - The **vagus nerves** (left and right) accompany the oesophagus through the **oesophageal hiatus** at the T10 level. - They participate in the formation of the oesophageal plexus.
Question 3: Esophagus is present in which mediastinum?
- A. Anterior
- B. Posterior (Correct Answer)
- C. Middle
- D. Superior
Explanation: ***Posterior*** - The **esophagus** is primarily located in the **posterior mediastinum**, where the bulk of its length (from T4/T5 to T10) traverses [2]. - It lies **posterior** to the **trachea** and **heart**, anterior to the vertebral column [2]. - For examination purposes, the esophagus is considered a **key structure of the posterior mediastinum** [2]. - Note: The uppermost part (cervical and upper thoracic) does pass through the superior mediastinum, but the majority lies in the posterior compartment. *Anterior* - The **anterior mediastinum** is a small space located between the **sternum** and the pericardium. - It primarily contains **connective tissue**, remnants of the thymus, lymph nodes, and the internal thoracic vessels [1]. - The esophagus does not traverse this compartment. *Middle* - The **middle mediastinum** is centrally located and prominently contains the **heart** and the roots of the great vessels [1]. - It also houses the **pericardium**, the main bronchi, and the phrenic nerves [1]. - The esophagus passes **posterior** to this compartment, not through it. *Superior* - The **superior mediastinum** extends from the thoracic inlet to the level of the sternal angle (T4/T5). - It contains large vessels like the **aortic arch** and its branches, the SVC, trachea, and thymus [1]. - While the **uppermost part of the thoracic esophagus** does pass through the superior mediastinum, this represents only a small portion of its total length.
Question 4: PA view of chest X-ray is given here. What is the diagnosis?
- A. Right Pneumothorax with left tracheal shift (Correct Answer)
- B. Left Pneumothorax with right tracheal shift
- C. Left Pneumothorax with left tracheal shift
- D. Right Pneumothorax with right tracheal shift
Explanation: ***Right Pneumothorax with left tracheal shift*** - The image shows a large **radiolucency (black area) on the right side** of the chest, indicative of **air in the pleural space**, consistent with a **right-sided pneumothorax**. - The **trachea is shifted towards the left** (away from the pneumothorax), which is the **expected finding** in pneumothorax due to increased pressure in the right pleural space pushing mediastinal structures to the contralateral side. - In pneumothorax, the trachea and mediastinum shift **away from** the affected side due to the pressure effect of air accumulation in the pleural cavity. - This **contralateral tracheal deviation** is a classic radiological sign of pneumothorax and helps confirm the diagnosis. *Right Pneumothorax with right tracheal shift* - While the **right pneumothorax** is correctly identified, the tracheal shift direction is incorrect. - In pneumothorax, the trachea shifts **away from** the affected side (contralateral), not toward it (ipsilateral). - **Ipsilateral tracheal shift** would suggest volume loss (atelectasis) or lung collapse, not pneumothorax alone. *Left Pneumothorax with right tracheal shift* - The pneumothorax is clearly on the **right side**, not the left. - The radiolucency and absent lung markings are visible on the right hemithorax. - A left pneumothorax would show these findings on the left side. *Left Pneumothorax with left tracheal shift* - There is **no pneumothorax on the left side** of the chest. - The left lung shows normal vascular markings and no evidence of pleural air. - This combination would be medically implausible as it suggests pneumothorax with ipsilateral shift.
Question 5: Which airway structure enters the lung at the hilum?
- A. Primary/Principal bronchus (Correct Answer)
- B. Secondary bronchus
- C. Bronchiole
- D. Tertiary bronchus
Explanation: ***Primary/Principal bronchus*** - The **primary/principal bronchus** (main bronchus) is the largest airway structure that enters each lung at the **hilum** [2]. - It then divides into secondary bronchi within the lung lobes. *Secondary bronchus* - **Secondary bronchi** (lobar bronchi) branch off from the primary bronchi *after* the primary bronchus has already entered the lung. - They supply the individual **lobes** of the lung. *Tertiary bronchus* - **Tertiary bronchi** (segmental bronchi) are further divisions of the secondary bronchi. - They supply the **bronchopulmonary segments**, which are smaller functional units within the lung lobes. *Bronchiole* - **Bronchioles** are smaller airway passages that branch from the tertiary bronchi and lack cartilage [1]. - They are located deeper within the lung tissue, well past the hilum.
Question 6: Which chamber enlargement shows a double right heart border with a wide subcarinal angle?
- A. Left atrium (Correct Answer)
- B. Left ventricle
- C. Right atrium
- D. Right ventricle
Explanation: ***Left atrium*** - A **double right heart border** on a chest X-ray is a classic sign of **left atrial enlargement**, as the enlarged left atrium bulges into the right atrial silhouette. - The **wide subcarinal angle** (angle between the mainstem bronchi) also indicates left atrial enlargement, as the expanding left atrium pushes the bronchi apart. *Left ventricle* - **Left ventricular enlargement** primarily manifests as a **downward and leftward displacement of the apex** and increased cardiac silhouette on the left. - It does not typically cause a double right heart border or widening of the subcarinal angle. *Right atrium* - **Right atrial enlargement** usually presents as a **prominent right heart border** that extends further to the right than normal. - It does not result in a double right heart border or affect the subcarinal angle. *Right ventricle* - **Right ventricular enlargement** leads to an **anterior bowing of the sternum** (in severe cases) and an upward and leftward displacement of the cardiac apex. - It pushes the left ventricle posteriorly and does not produce a double right heart border or a wide subcarinal angle.
Question 7: Caldwell’s view is used for:
- A. Maxillary sinus
- B. Frontal sinus (Correct Answer)
- C. Ethmoidal sinus
- D. Sphenoid sinus
Explanation: ***Frontal sinus*** - The Caldwell view is a **posteroanterior (PA) radiographic projection** of the skull, specifically designed to visualize the **frontal sinuses** and anterior ethmoid air cells. - In this view, the X-ray beam is angled at 15-20 degrees caudally to the orbitomeatal line, allowing for good visualization of the frontal sinuses above the orbital structures. *Maxillary sinus* - The **Waters view (occipitomental view)** is primarily used for optimal visualization of the **maxillary sinuses**, providing a clear view free from superimposition of the petrous ridges. - While portions of the maxillary sinuses may be visible on a Caldwell view, it is not the primary or best projection for them. *Ethmoidal sinus* - The Caldwell view offers some visualization of the **anterior ethmoidal air cells**, but the **posterior ethmoidal air cells** are better seen on other views like the **lateral view** or specialized CT scans. - The **lateral view** provides a good overall view of all paranasal sinuses, including the ethmoid, but not with the specific clarity for the anterior ethmoids that Caldwell provides. *Sphenoid sinus* - The **sphenoid sinus** is best visualized on **lateral skull radiographs** or **submentovertex (base) view**, where it can be seen centrally located posterior to the nasal cavity. - The Caldwell view does not provide adequate visualization of the sphenoid sinus due to superimposition of other structures and the anatomical position of the sphenoid sinus deep in the skull base.
Question 8: Identify the structure shown in CT abdomen section. (Recent NEET Pattern 2018-19)
- A. Inferior vena cava
- B. Portal vein (Correct Answer)
- C. Splenic vein
- D. Superior mesenteric vein
Explanation: ***Portal vein*** - The arrow points to a vessel receiving blood from the splenic and superior mesenteric veins, which is characteristic of the **portal vein** entering the **liver parenchyma**. - The portal vein is typically seen anterior to the **inferior vena cava** and posterior to the **common hepatic artery** at this level. *Inferior vena cava* - The **inferior vena cava (IVC)** is a large, retroperitoneal vessel located posterior to the liver and to the right of the aorta. - The structure indicated by the arrow is clearly within the liver substance, not in the typical position of the IVC. *Splenic vein* - The **splenic vein** runs horizontally behind the body of the pancreas and joins with the superior mesenteric vein to form the portal vein. - The vessel shown is within the liver, distal to the formation of the portal vein. *Superior mesenteric vein* - The **superior mesenteric vein (SMV)** typically runs vertically in the mesentery and joins the splenic vein to form the portal vein. - The indicated structure is within the liver hilum, not in the anatomical location of the SMV.
Question 9: Shenton's Line is present in which joint?
- A. Knee
- B. Shoulder
- C. Elbow
- D. Hip (Correct Answer)
Explanation: **Explanation:** **Shenton’s Line** is a fundamental radiological landmark used to assess the integrity of the **Hip joint** on an Anteroposterior (AP) X-ray. It is an imaginary curved line formed by the continuous arc of the **inferior border of the superior pubic ramus** and the **medial border of the femoral neck**. 1. **Why Hip is Correct:** In a normal, healthy hip, this arc is smooth and unbroken. A disruption or "step-off" in Shenton’s Line is a critical diagnostic sign indicating pathology, most commonly a **femoral neck fracture**, **developmental dysplasia of the hip (DDH)**, or a **slipped capital femoral epiphysis (SCFE)**. 2. **Why Other Options are Incorrect:** * **Knee:** Radiological assessment of the knee focuses on lines like the *Blumensaat’s line* (intercondylar notch) or the *Insall-Salvati ratio* (patellar height). * **Shoulder:** Key lines include the *Moloney’s line* (scapular arc), used to detect dislocations. * **Elbow:** The primary landmarks here are the *Anterior Humeral Line* and the *Radiocapitellar Line*, used to diagnose supracondylar fractures and radial head dislocations. **High-Yield Clinical Pearls for NEET-PG:** * **DDH:** Shenton’s line is broken (superiorly displaced femur) and is often used alongside *Hilgenreiner* and *Perkin* lines. * **Positioning:** A broken Shenton’s line can occasionally be a false positive if the hip is significantly externally rotated; however, in the context of trauma, it is highly suggestive of a fracture. * **Ward’s Triangle:** Another high-yield hip landmark referring to an area of low bone density in the femoral neck, susceptible to osteoporosis.
Question 10: Which of the following radiographic projections is used to demonstrate the base of the skull, sphenoid sinus, position and orientation of the condyles, and fractures of the zygomatic arch?
- A. Temporomandibular joint (TMJ) surgery
- B. Submentovertex projection (Correct Answer)
- C. Reverse-Towne projection
- D. Facial profile survey
Explanation: ### Explanation **Correct Answer: B. Submentovertex projection** The **Submentovertex (SMV) projection**, also known as the **Jugular view** or **Base view**, is obtained by directing the X-ray beam perpendicular to the infraorbitomeatal line, entering through the midline of the floor of the mouth. * **Why it is correct:** This projection provides a clear view of the **skull base** (including the foramen ovale and spinosum), the **sphenoid and ethmoid sinuses**, and the **mandibular condyles**. It is specifically the gold standard among plain films for demonstrating the **zygomatic arches** in a "bucket-handle" appearance, making it essential for diagnosing isolated zygomatic arch fractures. **Analysis of Incorrect Options:** * **A. TMJ Surgery:** This is a clinical procedure, not a radiographic projection. While imaging (like MRI or Transcranial views) is used for TMJ assessment, "surgery" does not describe a diagnostic view. * **C. Reverse-Towne projection:** This view is primarily used to visualize the **mandibular condyles and neck**, especially to detect medial displacement of a fractured condyle. It does not provide an adequate view of the skull base or zygomatic arches. * **D. Facial profile survey:** This usually refers to a lateral cephalometric or lateral facial view, used primarily for soft tissue profiles and gross bony discrepancies in the sagittal plane, but it lacks the orientation to visualize the skull base or the axial symmetry of the zygomatic arches. **NEET-PG High-Yield Pearls:** * **Water’s View (Occipitomental):** Best for Maxillary sinuses and orbital floor (blow-out fractures). * **Caldwell View (Occipitofrontal):** Best for Frontal and Ethmoid sinuses. * **Towne’s View:** Best for the Occipital bone and posterior fossa. * **Zygomatic Arch:** If SMV is not an option, the "Jug-handle view" is a modified SMV with reduced exposure specifically for the arches.
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