Metastatic Bone Survey
Snapshot
For osteoblastic skeletal metastases (e.g. prostate, breast), the ⁹⁹ᵐTc bone scan remains a cheap, sensitive whole-body survey, with SPECT/CT for equivocal lesions. ¹⁸F-NaF PET/CT offers higher sensitivity and resolution. Purely lytic disease (myeloma, some renal/lung metastases) is better assessed with FDG PET or MRI.
Osteoblastic metastases provoke reactive bone formation that diphosphonates and fluoride target. Lytic lesions with little osteoblastic reaction are the classic blind spot of bone-seeking agents.
OsteoblasticBone scan/NaF
LyticPrefer FDG/MRI
SPECT/CTFor equivocal
When to image
- Staging/restaging skeletal metastases in breast and prostate cancer (for high-risk prostate cancer, PSMA PET/CT is more accurate than CT plus bone scan — proPSMA).
- New bone pain with known malignancy.
- Monitoring skeletal response (with caution for flare).
How to read it
- Multiple randomly distributed lesions favour metastases.
- Solitary or degenerative-pattern uptake often needs SPECT/CT.
- Beware the treatment “flare” — increased uptake in the first months after effective therapy; in prostate cancer (PCWG3) new lesions on the first follow-up scan need confirmation by ≥2 further new lesions on a scan ≥6 weeks later.
Protocol
- ⁹⁹ᵐTc-MDP whole-body + SPECT/CT of equivocal sites, or ¹⁸F-NaF PET/CT.
- Correlate with tumour markers and cross-sectional imaging.
Pitfalls
- Lytic metastases under-detected on bone-seeking agents.
- Flare phenomenon mimics progression.
- Degenerative uptake is the commonest false positive.
Evidence & guidelines
- Bone scan is an established, cost-effective skeletal survey for osteoblastic disease.
- ¹⁸F-NaF PET/CT is more sensitive than planar bone scintigraphy for osteoblastic metastases (SNM NaF guideline, Segall et al., J Nucl Med 2010;51:1813–1820); disease biology guides modality choice.
Practise with a case
- New bone foci after starting endocrine therapy · Intermediate