Review Question - QID 109131

A 2-year-old male presents with his parents to his pediatrician for a well-child visit. The patient’s parents report that he is eating and sleeping well. He is meeting his developmental motor milestones, including beginning to run and navigating stairs. He has been slow to talk and can say about 20 words. He inconsistently points to objects or colors when prompted, and he does not follow one-step directions. On physical exam, the patient appears well-nourished and well-developed. He is in the 60th and 72nd percentile for height and weight, respectively. The patient has been known, since birth, to have the ocular finding seen in Figure A. On abdominal exam, his abdomen is soft and non-distended. A firm, left-sided mass can be felt on deep palpation. The mass is non-tender and does not cross the midline. His parents report that they have never noticed the mass before and cannot say when it developed. Urinalysis is performed and reveals the following:

Nitrites: negative
Leukocyte esterase: negative
Blood: positive
Bacteria: none
Protein: negative
Ketones: negative
Red blood cells: 44/hpf
White blood cells: 2/hpf

Which of the following is most likely to be found in this patient?