Heather Borders, MD
over 4 years ago
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Thymic Uptake of I-131
Joseph Junewick, MD FACR
|Diagnostic Category: Normal variant
|Created: over 4 years ago
|Updated: over 4 years ago
Teenager with papillary thyroid carcinoma. Thyroglobulin increased from 2.2 to 85 ng/mL.
Normal Thymic Uptake of I-131
NM – 7 day postablationI-131 whole body imaging shows intense thymic avidity; otherwise normal biodistribution.
CT – Normal thymic volume, contour and attenuation.
There is physiologic accumulation of iodine in the thymus gland. The thymus is visualized in 3.4 to 26.3% of radio-iodide scanning.
The basolateral surface of thyroid follicle cells express the sodium-iodine symporter gene which allows active transport of iodine into the cells with eventual organification. The sodium-iodine symporter gene is also expressed in extrathyroidal tissues, namely the thymus.
The radiobiological effects of I-131 therapy include gastrointestinal distress, dry eyes, dry mouth, transient immune suppression and temporary infertility. Long-term side effects include chronic dry eyes and mouth with resultant maladies, increased incidence of stomach, colon, bladder and salivary cancers and increased incidence of leukemia.
Wong WW and Avram AM. Posttherapy Thymus uptake demonstrated with SPECT/CT in a young girl with papillary thyroid cancer. Thyroid (2008); 18(8):919-920.
Intenzo C, et al. The thymus gland: The great mimicker of anterior mediastinal adenopathy on I-131 whole body scans. JNM (2006); 47(supp 1):317.