On deep palpation of the infant's abdomen, the NP palpates a 2-cm firm mass in the right upper quadrant (RUQ). This finding is consistent with:

Rationale: A. Hirschsprung’s disease typically presents with chronic constipation, abdominal distention, and failure to pass meconium, rather than a discrete RUQ mass. B. Wilm’s tumor is a renal malignancy in children that often presents as a firm, non-tender abdominal mass in the right or left upper quadrant, sometimes noticed by parents or during a routine exam. Care must be taken not to palpate aggressively, as the tumor is fragile and can rupture. C. Pyloric stenosis usually presents with projectile vomiting and a palpable “olive-like” mass in the right upper quadrant near the epigastrium, but the mass is smaller (~1–2 cm) and associated with gastric outlet obstruction symptoms. D. Intussusception may present with sausage-shaped abdominal mass and intermittent pain, often in the right lower quadrant, along with currant jelly stools, rather than a firm, fixed RUQ mass.