Findings: Following the oral administration of 436 microcuries of I-123 sodium iodide, the patient returned to the department in 24 hours for imaging over the neck. A cold nodule is seen within the mid to lower aspect of the left thyroid gland. The right thyroid gland demonstrates homogeneous activity.

Diagnosis: Cold thyroid nodule.

Discussion: Cold thyroid nodules are nonspecific and have both benign and malignant causes. 75% of cold nodules are secondary to colloid cysts or adenomas. Other benign causes include lymph nodes or an abscess, however, these are less common. Although the incidence for carcinoma is more common in cold nodules than hot nodules, the incidence is still low and ranges from 15 to 25%.

Factors suggesting a benign etiology include older, female patients as well as multiple nodules. A nodule that decreases in size while on thyroid hormone is suggestive of a benign etiology.

It should be noted that ultrasound can differentiate a solid from cystic lesion. However, the distinction between a benign or malignant solid lesion cannot be made.

References:
Mettler FA, Jr., Guiberteau MJ. Essentials of Nuclear Medicine Imaging, 4th Edition.
W. B. Saunders, Philadelphia. 1998:112-116.

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