**Core Concept**
Laryngomalacia is a congenital condition characterized by the softening of the tissues of the larynx (voice box), leading to partial airway obstruction. This condition is most commonly seen in premature infants and is often associated with inspiratory stridor, a high-pitched sound heard during inhalation.

**Why the Correct Answer is Right**
Laryngomalacia results from the collapse of the supraglottic structures, including the epiglottis, aryepiglottic folds, and arytenoids, during inspiration. The softening of these tissues is due to the immaturity of the cartilaginous framework and the lack of muscle tone in the affected area. As a result, the airway is partially obstructed, leading to the characteristic stridor.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because laryngomalacia is indeed more common in premature infants, who have not yet developed the cartilaginous framework of the larynx.
**Option B:** Incorrect because supraglottic collapse is the primary mechanism of airway obstruction in laryngomalacia.
**Option C:** Incorrect because laryngomalacia is not typically associated with a mass lesion or tumor.
**Option D:** Incorrect because while laryngomalacia can be associated with other conditions such as pulmonary hypertension, this is not a defining characteristic of the condition.

**Clinical Pearl / High-Yield Fact**
Laryngomalacia is often diagnosed clinically, based on the presence of inspiratory stridor and a soft, high-pitched sound heard during inhalation. A lateral neck X-ray or a flexible laryngoscopy may be used to confirm the diagnosis.

**Correct Answer:** D. Laryngomalacia is not typically associated with a mass lesion or tumor.