Surface Landmarks of the Thorax — MCQs
Liver biopsy is performed through the 8th intercostal space at the midaxillary line to avoid injury to which structure?
When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?
Which of the following is NOT a surface marking of the oblique fissure of the lung?
A patient presents with winging of the scapula. Which nerve is most likely involved?
Winging of scapula is due to paralysis of
Apex of the lung is best assessed by
The thoracic duct crosses from the right to the left at the level of
What is the SI unit of illuminance (brightness of light on a surface)?
Which bone connects the sternum to the scapula?
The lower two thirds of the following hematoxylin and eosin stained specimen is similar in appearance to which of the following structures?
Surface Landmarks of the Thorax Indian Medical PG Practice Questions and MCQs
Question 1: Liver biopsy is performed through the 8th intercostal space at the midaxillary line to avoid injury to which structure?
- A. Lung
- B. Pleural cavity (Correct Answer)
- C. Subdiaphragmatic space
- D. Gall bladder
Explanation: Liver biopsy is performed through the 8th intercostal space at the midaxillary line to avoid injury to which structure? ***Pleural cavity*** - Liver biopsy is performed at the **8th intercostal space at the midaxillary line** during **arrested expiration** to avoid injury to the **pleural cavity containing lung tissue**. - At this level, the **inferior margin of the lung** is typically at or above the 8th rib, retracting further upward during expiration. - The **costodiaphragmatic recess** (the potential space where parietal pleura of the chest wall meets the diaphragmatic pleura) extends down to approximately the **10th intercostal space** at the midaxillary line. [1] - By choosing the 8th intercostal space during expiration, the needle passes through the **apposed pleural membranes** (where no lung parenchyma is present), then through the **diaphragm** directly into the **liver**. - This technique minimizes the risk of **pneumothorax** by avoiding lung tissue while still accessing the liver through the thoracic route. [1] *Lung* - The lung's inferior border at the midaxillary line typically reaches the **8th rib** (or 8th intercostal space), but during **expiration**, it retracts upward. - While avoiding lung injury is important, the specific anatomical landmark used is the **pleural recess** below the lung margin, not the lung itself. [1] - The correct choice of intercostal space ensures the needle trajectory is **below the lung parenchyma**. *Subdiaphragmatic space* - The needle **must pass through** the subdiaphragmatic space to reach the liver; this space is not avoided but rather is part of the intended pathway. - The subdiaphragmatic space contains the liver and is the target region for the biopsy. *Gall bladder* - The gall bladder is located on the **inferior surface of the right lobe of the liver**, typically in a more **anterior and medial position**. - The **midaxillary line** approach at the 8th intercostal space targets the **posterior-lateral aspect** of the liver, well away from the gall bladder. - While avoiding the gall bladder is important to prevent **bile peritonitis**, this is achieved by the **lateral positioning**, not specifically by the choice of the 8th intercostal space.
Question 2: When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?
- A. The iliac crests (Correct Answer)
- B. The lowest pair of ribs bilaterally
- C. The inferior angles of the scapulae
- D. The posterior superior iliac spines
Explanation: ***The iliac crests*** - A line drawn between the **highest points of the iliac crests** on both sides typically intersects the L4 vertebral body or the L4-L5 intervertebral space. - This anatomical landmark provides a **safe entry point** for lumbar puncture, avoiding the spinal cord which usually ends at L1-L2. *The lowest pair of ribs bilaterally* - The lowest pair of ribs (12th ribs) corresponds to the **twelfth thoracic vertebra (T12)**, which is much higher than the desired lumbar puncture site. - Using this landmark would place the needle at a level where the **spinal cord is still present**, posing a significant risk of injury. *The inferior angles of the scapulae* - The inferior angle of the scapula typically corresponds to the **seventh thoracic vertebra (T7)**. - This landmark is also too superior for a safe lumbar puncture and does not accurately localize the lumbar spine. *The posterior superior iliac spines* - The posterior superior iliac spines (PSIS) are located at the level of the **S2 vertebra**, which is too far inferior for a standard lumbar puncture at L4-L5. - While they are important pelvic landmarks, they are not used for determining the L4 vertebral spine in this context.
Question 3: Which of the following is NOT a surface marking of the oblique fissure of the lung?
- A. 6th costal cartilage
- B. T3
- C. 5th rib
- D. 7th rib (Correct Answer)
Explanation: ***7th rib*** - The **oblique fissure** typically extends from the spine at approximately the **T3 vertebral level** anteriorly to the **6th costal cartilage**. [1] - The **7th rib** is generally inferior to the typical anterior termination point of the oblique fissure. [1] *T3* - The **oblique fissure** begins posteriorly at the level of the **spinous process of T3**. [1] - This marks the superior-posterior extent of the fissure on the surface. *5th rib* - The **oblique fissure** crosses the **5th intercostal space** on the lateral chest wall. [1] - This point helps map the fissure's path between its posterior and anterior endpoints. *6th costal cartilage* - The **oblique fissure** terminates anteriorly near the **6th costal cartilage** in the midclavicular line. [1] - This represents the inferior-anterior most point of the fissure on the chest wall.
Question 4: A patient presents with winging of the scapula. Which nerve is most likely involved?
- A. Thoracodorsal nerve
- B. Lateral pectoral nerve
- C. Long thoracic nerve (Correct Answer)
- D. Musculocutaneous nerve
Explanation: ### Long thoracic nerve - The long thoracic nerve innervates the **serratus anterior muscle**, which is responsible for scapular protraction and upward rotation. - Damage to this nerve paralyzes the serratus anterior, leading to **winging of the scapula** as the medial border and inferior angle of the scapula become prominent. ### Thoracodorsal nerve - This nerve supplies the **latissimus dorsi muscle**, which is involved in adduction, extension, and internal rotation of the humerus [1]. - Injury to the thoracodorsal nerve would weaken movements of the shoulder, but not directly cause **scapular winging**. ### Lateral pectoral nerve - The lateral pectoral nerve innervates the **pectoralis major muscle** (upper and middle parts) [1]. - Damage to this nerve primarily affects shoulder adduction and internal rotation, but does not result in **scapular winging**. ### Musculocutaneous nerve - This nerve innervates the **coracobrachialis**, **biceps brachii**, and **brachialis muscles** in the anterior compartment of the arm. - Injury to the musculocutaneous nerve would impair elbow flexion and forearm supination, and is unrelated to **scapular movement**.
Question 5: Winging of scapula is due to paralysis of
- A. Serratus anterior (Correct Answer)
- B. Rhomboid major
- C. Trapezius
- D. Levator scapulae
Explanation: ***Serratus anterior*** - The **serratus anterior muscle** is responsible for **protraction and rotation of the scapula**, holding it close to the thoracic wall. - Paralysis of this muscle, often due to injury to the **long thoracic nerve**, causes the **medial border of the scapula** to protrude posteriorly, a condition known as **medial scapular winging**. - This is the **classic and most common cause** of scapular winging. *Rhomboid major* - The rhomboid major muscle primarily performs **retraction and downward rotation of the scapula**. - Paralysis of this muscle would lead to the scapula being displaced laterally and superiorly, not winging. *Trapezius* - The trapezius muscle has multiple actions, including **elevating, depressing, retracting, and rotating the scapula**. - Paralysis of the trapezius (e.g., due to **accessory nerve damage**) can cause **lateral scapular winging** where the inferior angle protrudes, along with shoulder drooping and difficulty shrugging. - However, **serratus anterior paralysis** is the classic answer for scapular winging in exam contexts. *Levator scapulae* - The levator scapulae muscle is primarily involved in **elevating and downwardly rotating the scapula**. - Dysfunction of this muscle would impair shoulder elevation but would not be the direct cause of scapular winging.
Question 6: Apex of the lung is best assessed by
- A. AP view
- B. PA view
- C. Lordotic view (Correct Answer)
- D. Oblique view
Explanation: ***Lordotic view*** - The **lordotic view** is a specialized chest X-ray projection specifically designed to visualize the **lung apices** clearly by projecting the clavicles superiorly. - This view is achieved by leaning the patient backward (lordotic position) while the X-ray beam is angled, or by angling the X-ray tube itself superiorly. *AP view* - The **AP (Anteroposterior) view** often projects the **clavicles over the lung apices**, obscuring them and making thorough assessment difficult. - This general chest X-ray view is primarily used when the patient cannot stand or sits upright for a PA view. *PA view* - Similar to the AP view, the standard **PA (Posteroanterior) view** can also have the **clavicles superimpose the lung apices**, making subtle apical pathology hard to detect. - While a routine chest X-ray, it's not optimal for detailed evaluation of the uppermost lung regions. *Oblique view* - **Oblique views** are primarily used to separate superimposed structures or to better visualize specific areas that are obscured in standard AP or PA views, but they are not the best for the apices. - They are often employed to assess the pleura, hilum, or specific lung segments by rotating the patient.
Question 7: The thoracic duct crosses from the right to the left at the level of
- A. T12 vertebra
- B. T2 vertebra
- C. T4-T5 vertebra (Correct Answer)
- D. T6 vertebra
Explanation: ***T4-T5 vertebra*** - The **thoracic duct** crosses from the right to the left side of the vertebral column at the level of the **T4-T5 vertebrae**, specifically just above the root of the left lung. - This crossover is an important anatomical landmark as it signifies the duct's ascent towards the neck to drain into the left subclavian vein. *T12 vertebra* - The **thoracic duct** originates from the **cisterna chyli** at the level of the L1 or L2 vertebra and ascends into the thorax at or below the T12 vertebra, it does not cross over at this level. - This level primarily marks its entry into the thoracic cavity, not its main crossover point. *T6 vertebra* - While the **thoracic duct** is present in the thorax at this level, it does not undergo its characteristic crossover from right to left at the T6 vertebra. - The duct continues its ascent along the right side of the vertebral column before moving across. *T2 vertebra* - By the level of the T2 vertebra, the **thoracic duct** has already crossed to the left side of the vertebral column and is ascending towards its termination in the neck. - The crossover event occurs more inferiorly, at the T4-T5 level.
Question 8: What is the SI unit of illuminance (brightness of light on a surface)?
- A. Luminance
- B. Lux (Correct Answer)
- C. Candela
- D. Lumen
Explanation: ***Lux*** - **Lux** is the SI unit specifically designated for **illuminance**, which measures the **luminous flux** incident on a surface per unit area. - It quantifies the perceived **brightness** of light on a surface, taking into account the human eye's sensitivity to different wavelengths. *Luminance* - **Luminance** is a measure of the **intensity of light emitted or reflected from a surface** in a given direction, expressed in candelas per square meter (cd/m²). - It describes the brightness of a surface as perceived by the eye, but unlike illuminance, it is **independent of the incident light**. *Candela* - The **candela** is the SI base unit of **luminous intensity**, measuring the **power emitted by a light source in a particular direction**. - It doesn't describe the **brightness on a surface** but rather the output of the light source itself. *Lumen* - The **lumen** is the SI unit of **luminous flux**, representing the total amount of **visible light emitted by a source per unit time**. - While related to brightness, it describes the **total light output** of a source, not the illuminance on a specific surface.
Question 9: Which bone connects the sternum to the scapula?
- A. Clavicle (Correct Answer)
- B. First rib
- C. Manubrium
- D. Second rib
Explanation: ***Clavicle*** - The **clavicle**, or collarbone, is the only bone that directly connects the **axial skeleton** (via the sternum) to the **appendicular skeleton** (via the scapula). - It articulates medially with the **manubrium** of the sternum at the sternoclavicular joint and laterally with the **acromion** of the scapula at the acromioclavicular joint. *First rib* - The **first rib** articulates with the **manubrium** of the sternum but does not connect directly to the scapula. - Its primary role is to form part of the **thoracic cage**, protecting internal organs. *Manubrium* - The **manubrium** is the superior part of the **sternum** and articulates with the clavicles and the first two ribs. - It does not directly connect to the **scapula**; rather, the clavicle mediates this connection. *Second rib* - The **second rib** articulates with both the **manubrium** and the body of the sternum at the **sternal angle**. - Like the first rib, it is part of the **thoracic cage** and does not directly connect to the scapula.
Question 10: The lower two thirds of the following hematoxylin and eosin stained specimen is similar in appearance to which of the following structures?
- A. Articular disk
- B. Pinna
- C. Epiphyseal growth plate
- D. Intervertebral disk (Correct Answer)
Explanation: ***Intervertebral disk*** - The lower two-thirds of the specimen shows **hyaline-like cartilage** that histologically resembles the **transition zone** of the intervertebral disk, where the inner annulus fibrosus transitions from the nucleus pulposus. - While the nucleus pulposus itself is gelatinous and notochordal in origin, the **inner annulus fibrosus** contains fibrocartilage with regions that can appear similar to hyaline cartilage, particularly in the transitional zones. - The specimen's appearance, with **chondrocytes in lacunae** within a relatively homogeneous matrix, matches the cartilaginous components found in intervertebral disk structure. *Articular disk* - Articular disks are composed predominantly of **fibrocartilage**, characterized by **dense parallel collagen fiber bundles** clearly visible in the matrix and chondrocytes arranged in linear rows between collagen bundles. - The homogeneous matrix appearance in the specimen lacks the prominent fibrous architecture typical of articular disks. *Pinna* - The pinna (external ear) is supported by **elastic cartilage**, which contains abundant **elastic fibers** in its extracellular matrix providing flexibility and resilience. - With H&E staining, elastic cartilage would show a more textured matrix, and special stains would demonstrate extensive elastic fiber networks not present in this specimen. *Epiphyseal growth plate* - While the epiphyseal growth plate consists of **hyaline cartilage**, it exhibits highly characteristic **zonal organization**: resting zone, proliferative zone (with columnar arrangement), hypertrophic zone, and zone of calcification. - The specimen lacks the distinct columnar arrangement and zonal stratification that defines an active epiphyseal growth plate.
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