Accidental Mass in a Bath

A 4-year-old boy is brought to the clinic by his parents due to a painless, progressively enlarging left-sided abdominal mass noticed during bathing. He has occasional abdominal pain but no fever, weight loss, or night sweats. His past medical history is unremarkable. On examination, he is well-appearing, but his blood pressure is 130/85 mmHg. A firm, smooth, non-tender mass is palpated in the left abdomen, not crossing the midline. Urinalysis shows microscopic hematuria. Abdominal ultrasound reveals a well-defined renal mass, and MRI confirms a large, solid, unilateral left kidney tumor.