**Core Concept**
The infant's condition is characterized by non-bilious vomiting, a palpable epigastric mass, and jaundice, suggesting an obstruction of the gastrointestinal tract. This condition is most likely due to a congenital anomaly causing an intestinal obstruction.

**Why the Correct Answer is Right**
The presence of a palpable epigastric mass and non-bilious vomiting in a 4-week-old infant is highly suggestive of an intestinal obstruction caused by a pyloric stenosis. Pyloric stenosis is a condition where the pylorus, the region of the stomach that connects to the small intestine, becomes narrowed, blocking the passage of food. This condition is often caused by hypertrophy of the pyloric muscle, leading to an increase in the thickness of the pyloric muscle wall, which in turn causes the pylorus to become narrowed. The resulting obstruction leads to non-bilious vomiting, which is a key clinical feature of this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the specific clinical presentation of the infant, which includes a palpable epigastric mass and non-bilious vomiting.
**Option B:** This option is incorrect because it does not take into account the age of the infant, which is 4 weeks, making it less likely to be a case of intussusception.
**Option C:** This option is incorrect because it does not provide a specific cause for the infant's symptoms, and is too broad.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that pyloric stenosis typically presents in infants between 3-6 weeks of age, and is more common in males. A palpable "olive" mass in the epigastrium is a classic physical examination finding in this condition.

**Correct Answer:** C. Pyloric stenosis.