Post-ablation and diagnostic I-131 or I-123 scans show thyroid remnant, nodal and distant (lung, bone) iodine-avid disease — and a list of physiological and contamination foci that must not be called metastases.
Orient first
- Physiological: salivary glands, stomach, bowel, bladder, breast (lactation), thymus.
- Contamination: hair, clothing, skin — re-image after washing.
- Radioiodine-refractory disease is FDG-avid; thyroglobulin rising with a negative iodine scan prompts FDG PET.
Acquire the study
- I-131 post-therapy scan at 3–7 days or diagnostic I-123/I-131 after TSH stimulation; whole-body planar with SPECT-CT of foci.
The manoeuvre
- Planar anterior and posterior acquisition: neck remnant uptake in the thyroid bed.
- Cervical nodes outside the bed — SPECT-CT to localise.
- Lungs: diffuse miliary or nodular uptake; bones: focal uptake with CT correlate.
- Physiological or contamination foci identified and named.
What confirms it
- Iodine-avid foci with anatomical correlate on SPECT-CT.
What licenses you to exclude it
- A negative diagnostic scan with undetectable stimulated thyroglobulin makes residual disease unlikely.
The classic misread
- Calling a thymic or breast uptake a metastasis.