Okay, let's tackle this question about pyloric stenosis in infants. The question is asking for the clinical features that are NOT associated with pyloric stenosis. First, I need to recall what the typical signs and symptoms of pyloric stenosis are.

Pyloric stenosis is a condition where the pylorus (the muscular valve that connects the stomach to the small intestine) becomes thickened and narrowed, leading to gastric outlet obstruction. This usually occurs in infants between 2 weeks and 6 months of age. The classic presentation includes projectile vomiting, which is non-bilious because the obstruction is proximal to the duodenum. The vomiting is typically postprandial and can be forceful. Infants may also have a palpable olive-shaped mass in the epigastrium, which is the hypertrophied pyloric muscle. Other signs might include dehydration, weight loss, and metabolic alkalosis due to loss of gastric acid from vomiting.

Now, the question is structured as an EXCEPT question, meaning one of the options listed is not a clinical feature. Let's consider common features and possible distractors. The options aren't provided, but common incorrect options might include bilious vomiting (which would suggest a lower obstruction like duodenal atresia), or features like jaundice which aren't part of pyloric stenosis. Another possible incorrect option could be constipation, but in pyloric stenosis, the infant might actually have fewer stools due to decreased oral intake, but it's not a defining feature. Alternatively, a non-palpable mass could be a wrong option, but the mass is a key finding.

Wait, the correct answer is the one that's NOT a feature. So if an option lists bilious vomiting, that's incorrect. Bilious vomiting would indicate that the obstruction is beyond the ampulla of Vater, which is not the case in pyloric stenosis. Therefore, if one of the options is "Bilious vomiting," that would be the correct answer to the EXCEPT question.

Let me structure the explanation. The core concept is the pathophysiology of pyloric stenosis leading to gastric outlet obstruction. The correct answer would be the option that contradicts known features. The incorrect options would include actual features like projectile vomiting, olive-shaped mass, metabolic alkalosis, etc. The wrong options might include bilious vomiting, constipation, or jaundice. So, if the correct answer is an option stating bilious vomiting, that's the exception.

**Core Concept**
Pyloric stenosis in infants is characterized by gastric outlet obstruction due to pyloric muscle hypertrophy. Key clinical features include non-bilious projectile vomiting, a palpable "olive-shaped" mass in the epigastrium, and metabolic alkalosis from gastric acid loss.

**Why the Correct Answer is Right**
Bilious vomiting indicates obstruction at or beyond the ampulla of Vater (e.g., duodenal atresia), not pyloric stenosis. In pyloric stenosis, vomiting is non-bilious because bile is produced in the liver and secreted into the duodenum *after* the pylorus. The absence of bilious vomiting differentiates pyloric stenosis from lower gastrointestinal obstructions.

**Why Each Wrong Option is Incorrect**
**Option A:** Projectile vomiting is a hallmark of

✓ Correct Answer: D. Metabolic acidosis