A 57-day-old male infant was admitted with a 1-day history of fever. He had no previous history of infections, including urinary tract or other systemic infections, as confirmed by review of his medical records. During this episode, there was no hematuria, edema, night sweats, or weight loss. 

Laboratory investigations showed a white blood cell count of 12.84 × 10⁹/L (57.2% neutrophils), C-reactive protein (CRP) of 94.73 mg/L, and procalcitonin (PCT) of 1.72 ng/mL. Urinalysis revealed leukocytes 3+ and blood 3+, and microscopic examination of centrifuged urine sediment demonstrated >100 WBCs/HPF. Alpha-fetoprotein (AFP) was elevated at 791.86 ng/mL. Immunological evaluation, including serum immunoglobulin levels and T- and B-cell subsets, was normal. Standard urine culture with antibiogram showed no bacterial growth.

Renal ultrasound demonstrated a space-occupying lesion in the mid-pole of the left kidney measuring 1.6 × 1.0 × 1.2 cm, with a hyperechoic rim (0.3 cm thick) with a central hypoechoic area. Pelvic and lower abdominal MRI revealed a rounded left renal mass (isointense on T1- and T2-weighted images, slightly hyperintense on diffusion-weighted imaging) measuring 1.7 × 1.8 × 2.1 cm (Figure 1).

An ultrasound-guided biopsy was performed, and three 18-gauge core needle samples were obtained from the left renal lesion for histopathological evaluation.