Nonvisualized Kidney on [99mTc]Tc-DTPA Renography: Incidental Detection of Unilateral Renal Agenesis Confirmed by SPECT-CT

Unilateral renal agenesis may remain clinically silent until adulthood because the contralateral kidney can maintain overall renal function through compensatory adaptation. A 22-year-old asymptomatic man was incidentally found to have a solitary functioning kidney (SFK) during renal scintigraphy performed as part of a research protocol. He had no clinical complaints, unremarkable physical findings, and preserved renal function, with normal serum creatinine levels (1.01 mg/dL) and estimated glomerular filtration rate (105 mL/min/1.73 m2). Dynamic renal scintigraphy using technetium-99m diethylenetriaminepentaacetic acid demonstrated tracer uptake exclusively in the left kidney, with complete absence of function on the right side. Subsequent single photon emission computed tomography-computed tomography (SPECT-CT) confirmed the absence of right renal tissue both anatomically and functionally, consistent with right unilateral renal agenesis. The left kidney showed preserved perfusion, filtration, and excretion, reflecting effective compensatory adaptation. This case emphasizes that nonvisualization of a kidney on planar renography requires systematic evaluation and that hybrid SPECT-CT can provide decisive anatomical–functional correlation. Long-term surveillance remains important because congenital SFK carries risks of hypertension, proteinuria, and progressive renal impairment.