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.