Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : In a lateral thoracic radiograph, solid lesions in the dependent lung may not be visualized.
Reason (R) : The non-dependent lung suffers atelectasis, and hides the lesion beneath it.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
• C. (A) is correct but (R) is not correct.
• D. (A) is not correct but (R) is correct.

Hint:

To ensure complete evaluation of both lung fields:
Always take three radiographic views (Right Lateral, Left Lateral, and Ventrodorsal/Dorsoventral).
A lesion in the left lung is best seen in a right lateral view because the left lung is non-dependent (well-aerated) in that position.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
When performing thoracic radiography on animals in lateral recumbency, gravity and body weight affect lung inflation.
The "down-side" lung is referred to as the dependent lung, while the "up-side" lung is the non-dependent lung.

Step 2: Detailed Explanation:
Let us evaluate the physiological and radiographic changes in lateral recumbency:
- Assertion (A): In lateral recumbency, the weight of the heart, mediastinum, and abdominal organs presses down on the lower lung, causing compression atelectasis (partial collapse) of the dependent lung.
Because the dependent lung loses its air inflation, it becomes soft-tissue dense.
Any solid soft-tissue lesions (such as nodules or masses) in this dependent lung will blend in with the collapsed lung tissue (silhouetting), making them invisible on the radiograph. Thus, Assertion (A) is correct.
- Reason (R): This statement is incorrect because it identifies the wrong lung.
It is the dependent (down-side) lung that suffers atelectasis.
The non-dependent (up-side) lung remains well-aerated, providing excellent contrast that makes any solid lesions within it easy to see. Thus, Reason (R) is false.

Step 3: Final Answer:
Assertion (A) is correct but Reason (R) is not correct.