I-131 Uptake Post Therapy

Fig 1.  Radioactive iodine uptake midline to the body.  The scan was performed 10 days post iodine therapy.

A patient was presented to our department recently with papillary carcinoma.  The right lobe was removed in the early 1990's while the left lobe was removed in 2011. Follow up treatment was provided by administering 7500 MBq of I-131. Ten days after the therapy, a whole body iodine scan was presented with a focal uptake, midline to the body.  By the nature of the location, it's a bit tricky because we want to know if this is focal bowel activity (diverticulum ?) or is it a true lesion (met?).

There are a couple things that we can do to differentiate, or at least provide some clues,  in determining whether the "spot" is  bowel or something else.  They are the following:

1.  SPECT the area of concern to determine where it is within the body and try to correlate this information with any prior or current imaging "work ups".

2.   Acquire laterals, if the SPECT resolution is poor, and compare with correlative imaging.

3.  Have the patient return the department the next day and repeat the image over the midline to see if the "spot" would move.  This would help us to determine if this was bowel activity.

4.  Perform a SPECT/CT of the area to localize the "spot".

Lucky for us we do have a SPECT/CT in the department, and this is what we have acquired.

Fig. 2  Fused coronal image.

Fig. 3 Fused sagittal image.

Fig. 4  Fused transaxial image.

These are the fused images, since stand alone SPECT images of the site does not really provide as much information in comparison to SPECT/CT, because we can't locate where the "spot" is in relation to hard physical anatomy.

Regular biodistribution of iodine includes salivary, nasal-oral, hepatic, bowel and mammary uptake.  Having said that, the radioactive uptake seemed to be quite focal on both the anterior and posterior images, so it was suspicious from the beginning.  Furthermore, if you look closely at figure 1, a "star artifact" (expand the image) can be seen as well.  All in all, the "spot" was suspicious and it revealed a localized metastasis on the lumbar spine. A compression fracture which was also seen on the CT of the area may have contributed to the uptake as well (ie. inflammatory responses) but the patient did not complain of any discomfort.  

Furthermore a follow up biopsy of the spine (L3), confirmed bony involvement.