I-131 Uptake in Teratoma

Fig 1 WBI scan performed 10 days post 125mCi treatment of I-131 therapy for thyroid Ca.

A whole body iodine scan was performed 10 days post I-131 therapy for a patient who was diagnosed with thyroid cancer.  For the most part the scan seems relatively normal, with residual activity within the thyroid bed and salivary glands.  The liver is within normal limits.  However in the lower left hemipelvis, there appears to be an increased I-131 avidity.  Of course to investigate this further we performed a SPECT/CT.

Above is the MIP for the SPECT (doesn't look like much), but when fused with the CT, the following is presented.

Fig. 2  Sagittal section of the I-131 activity.  The fat containing mass measures approximately 

5.8 x 3.3 cm.

Fig. 3  Coronal section, noting the uptake in the lower left hemipelvis.

The I-131 fat containing lesion within the left pelvis is in keeping with a left ovarian teratoma.  These are also know as an ovarian dermoids.  Most dermoids/teratomas are benign, and they contain a mix bag of mature and immature tissue such as skin, hair, thyroid tissue, sweat glands, blood, cartilage and even teeth!  Generally the appearance of fat within the teratoma along with an irregular component of coarse calcifications help to distinguish these entities when imaging with CT and MRI.  The gross anatomy is quite interesting to look at, since they are varied in nature with respect to their appearance and construction.

Normal Uptake on WBI

Fig. 1  Whole body iodine, 10 days post administration of a therapeutic dose of I-131.

Whole body iodine (WBI) imaging was performed on a patient who was administered 3.7GBq of I-131 ten days prior for papillary carcinoma.  A total thyroidectomy was also performed as part of the treatment process earlier in the year.

For the most part the thyroid bed was unremarkable as well as the rest of the image, except for a focal uptake in the right upper quadrant.  Generally the technologists are fairly cautious at our facility, since a metastatic survey was being performed, a SPECT/CT of the area was also included in the study.

Fig. 2 Coronal section of the SPECT/CT, noting the uptake within the liver.  Most likely being gallbladder uptake of the I-131.

Fig. 3  Transaxial CT used in conjuction with the SPECT to localise the I-131 uptake.

Fig. 4  Fused transaxial SPECT/CT, confirming the uptake of the radioactive iodine is inside  the gallbladder.

Why is this interesting?  Well for one thing, this is something that we do not normally see on our WBI images.  Normally we see diffuse liver uptake in this area,  but it is not totally uncommon to visualise the gallbladder.  This is well documented in the literature and the article does discuss some possibilities of what can potentially cause this normal uptake.  Conditions such as cholecystitis, hypokinetic gallbladder function due to stones or an abnormal gallbladder morphology are just some of the potential reasons.  Most often an ultrasound is ordered to confirm or correlate if there are any underlying issues that may be involved with the gallbladder.

Bottomline, gallbladder uptake is normal.  It is not commonly seen, but from a technical perspective we would rather be "safe than sorry" by performing extra imaging such as a SPECT/CT.  Iodine is not the best isotopes to image with and with high energy collimators, it would have been tough to identify based on static images.

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.