Bone scan using 99mTc-MDP is performed for a patient with prostate cancer. The scan shows diffuse skeletal uptake with no renal excretion visible — so-called 'superscan.' This finding indicates:
- A Widespread skeletal metastases with very high bone-to-soft tissue ratio ✓
- B Normal scan with high renal uptake artifact
- C Renal failure causing poor tracer excretion
- D Injection outside a vein (extravasation)
Correct answer: A. Widespread skeletal metastases with very high bone-to-soft tissue ratio
Explanation
The 'superscan' on 99mTc-MDP bone scintigraphy shows diffusely increased skeletal uptake with absent or markedly reduced renal and soft-tissue background activity. The mechanism is overwhelming uptake by numerous metastatic deposits throughout the skeleton leaving minimal free tracer for renal excretion. In prostate (osteoblastic) and breast cancer, superscan indicates extensive skeletal metastases and is a poor prognostic marker. It must not be misreported as normal. Renal failure alone does not cause the uniformly increased skeletal activity pattern.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.