Will a renal calculus be visualized on a fluorodeoxyglucose positron emission tomography (FDG‑PET) scan?

Kidney Stones Are Generally NOT Visible on Standard FDG-PET Scans

Kidney stones themselves do not typically appear on FDG-PET scans because they are metabolically inert calcifications that do not take up the radiotracer fluorodeoxyglucose (FDG). However, they will be visible on the CT portion of a PET/CT scan, which is the standard imaging modality used today.

Understanding What PET Scans Detect

FDG-PET imaging detects metabolic activity by tracking glucose uptake in tissues. Kidney stones are:

• Crystalline deposits of minerals (calcium, uric acid, etc.)
• Metabolically inactive structures
• Unable to take up FDG radiotracer under normal circumstances

The CT component of PET/CT will show kidney stones with high sensitivity (97% for noncontrast CT), as virtually all renal calculi are radiopaque on CT imaging 1.

Important Exception: Rare FDG Uptake in Stones

In uncommon cases (approximately 11.5% of patients with urinary calculi), kidney stones can demonstrate high FDG uptake 2. This phenomenon includes:

• SUVmax values ranging from 11.7 to 143.0 in affected stones
• Occurs in both renal and bladder calculi
• Stone sizes varying from sandy particles to 19mm
• Mechanism remains unclear but likely related to surrounding inflammation or infection

This finding is critical to recognize because:

• It can mimic malignancy on PET imaging
• Misinterpretation could lead to unnecessary interventions
• Correlation with the CT portion of the scan is essential to identify the calcified nature of the lesion

Clinical Implications

When reviewing a PET/CT scan:

1. Always correlate PET findings with the CT images - The CT will definitively show whether a focus of uptake corresponds to a calcification/stone
2. Consider infection - High FDG uptake around renal structures in ADPKD patients may indicate cyst infection rather than stone disease 3
3. Avoid misdiagnosis - Recognition of this non-malignant FDG accumulation pattern prevents false-positive cancer diagnoses 2

Bottom Line for Clinical Practice

If you're ordering imaging specifically to detect kidney stones, noncontrast CT (not PET scan) is the appropriate test with 97% sensitivity 1. PET/CT is not indicated for stone disease evaluation. However, if a patient undergoes PET/CT for oncologic purposes and has kidney stones, the stones will be visible on the CT portion, and rarely may show unexpected FDG uptake that should not be mistaken for malignancy 2.