What characterizes subcutaneous emphysema?

Subcutaneous emphysema is primarily characterized by swelling in the neck area accompanied by a crackling sensation, often referred to as "crepitus." This condition occurs when air leaks from the respiratory system or other areas into the subcutaneous tissues, leading to visible swelling and a distinctive crackling sound when the affected area is palpated. This phenomenon arises because the air trapped under the skin creates pockets of gas that can easily be felt and heard.

The other options do not accurately describe subcutaneous emphysema. While swelling in the extremities, intense headache, and sudden deafness can be associated with various medical conditions, they do not relate specifically to the presence of air under the skin, which is the hallmark of subcutaneous emphysema. The correct recognition of the symptoms helps in diagnosing the condition properly and addressing the underlying cause.