Renal Fusion Presenting as Pancake Kidney

We present the case of a male patient who, at 3 months of age, underwent abdominal and pelvic ultrasound due to acute gastroenteritis. Incidentally, the ultrasound revealed bilateral absence of the kidneys in the renal fossae. The pelvic ultrasound [Figure 1a] showed a single discoid renal mass in the midline of the pelvic cavity, consistent with complete renal fusion (pancake kidney). Magnetic resonance imaging [Figure 1b] corroborated the diagnosis.

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Figure 1:

(a) Pelvic ultrasound shows fusion of the kidneys at the medial parenchymal margins (white arrow), resulting in a single, centrally located discoid renal mass in the midline of the pelvic cavity, measuring 5.5 cm in bipolar diameter. The renal parenchyma is normal in thickness and echogenicity, with preserved corticomedullary differentiation. Hydronephrosis or calyceal dilation is absent. (b) Coronal T2-weighted magnetic resonance imaging shows a single discoid-shaped renal mass (PK) located superiorly to the bladder (B), in the midline of the pelvic cavity, corroborating the diagnosis of pancake kidney.

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At 10 years, the patient demonstrated a decline in renal function. The estimated glomerular filtration rate was 78 mL/min/1.73m². The urine protein-to-creatinine ratio was elevated (66 mg/g), while the albumin-to-creatinine ratio was within normal limits (<30 mg/g). These findings are consistent with CKD stage G2A1 according to KDIGO. Serum creatinine, urea, albumin, and electrolytes remained within the reference ranges. There was no history of urinary tract infections. Follow-up renal ultrasounds after the development of CKD demonstrated no changes, with imaging findings consistent with those of the initial examinations.

Pancake kidney is a rare form of complete renal fusion in which both kidneys form a single discoid organ. It is typically an incidental finding but may be associated with other genitourinary anomalies.^1,2 Differential diagnoses include horseshoe kidney and crossed fused renal ectopia. Although many patients maintain normal renal function, there is a risk of developing CKD.³