Okay, let's tackle this question about the age of presentation of pyloric stenosis. First, I need to recall the core concept here. Pyloric stenosis is a condition where the pylorus, the muscular valve connecting the stomach to the small intestine, becomes abnormally thickened and narrowed, leading to vomiting. The key here is the age when this typically presents.

The core concept is the typical age range for presentation. I remember that it's usually in infants, so the question is probably looking for a timeframe in the first few months of life. Now, the correct answer is likely around 2 to 8 weeks, maybe up to 12 weeks. I need to be precise here.

Why is that the case? The pathophysiology involves hypertrophy and hyperplasia of the pyloric muscle, which develops over the first few weeks. The obstruction leads to projectile vomiting after feeding, and the condition is more common in males. So the correct answer would be 2-12 weeks, but more commonly 2-8 weeks.

Now, the options: Let's say the options are A. 1-2 weeks, B. 2-8 weeks, C. 6-12 months, D. 1-2 years. The correct answer here is B. The other options are incorrect because A is too early for the hypertrophy to develop, C is too late as the condition typically presents in infancy, and D is way beyond the usual presentation period.

Clinical pearls: Remember that pyloric stenosis is a classic cause of non-bilious projectile vomiting in infants. The peak age is around 4-6 weeks. Also, it's important to differentiate from other causes of vomiting in infants, like GERD. The diagnosis is often made via ultrasound showing the thickened pyloric muscle. Treatment is usually surgical with pyloromyotomy.

So putting it all together, the correct answer is B. 2-8 weeks. The other options are either too early or too late. The key is the timeframe when the hypertrophy leads to obstruction symptoms.

**Core Concept**
Pyloric stenosis is a congenital condition characterized by hypertrophy and hyperplasia of the pyloric muscular wall, leading to gastric outlet obstruction. It typically presents in infants due to progressive narrowing of the pyloric canal, causing projectile, non-bilious vomiting.

**Why the Correct Answer is Right**
The classic age of presentation is **2–8 weeks**, with a peak at 4–6 weeks. This timing correlates with the development of hypertrophy of the pyloric muscle, which occurs postnatally. The obstruction worsens as the infant's gastric emptying increases with feeding, leading to symptoms. Ultrasound confirms the diagnosis by showing a pyloric muscle thickness >3 mm and length >14 mm.

**Why Each Wrong Option is Incorrect**
**Option A:** 1–2 weeks – Incorrect. Symptoms rarely present this early; hypertrophy develops gradually.
**Option C:** 6–12 months – Incorrect. Pyloric stenosis almost always presents within the first 3 months; later presentation is atypical.
**Option D:** 1–2 years – Incorrect. This age range excludes pyloric stenosis, which is a neonatal/infantile condition.

**Clinical Pearl / High-Yield

✓ Correct Answer: C. At 3 weeks of age