57 Graves Disease and Cold Nodule

Clinical Presentation

A 46-year-old woman presents with a very large palpable mass in the left thyroid lobe and markedly abnormal thyroid function test values:

• Thyrotropin (thyroid-stimulating hormone [TSH]), < 0.01 μU/mL (normal range, 0.5–6.0 μU/mL)

• Serum thyroxine (T₄), 25.4 μg/dL (normal range, 4.6–12.0 μg/dL)

• Serum triiodothyronine (T₃), 1087 ng/dL (normal range, 80–180 ng/dL)

• Thyroid peroxidase (TPO) antibodies, negative

Fig. 57.1 Right anterior oblique pinhole collimator view, ¹²³I.

Fig. 57.2 Anterior pinhole collimator view, ¹²³I.

Fig. 57.3 Left anterior oblique pinhole collimator view, ¹²³I.

Technique

• 0.500 mCi of ¹²³I administered orally 24 hours before uptake and scan

• Five-minute pinhole collimator images in right anterior oblique, anterior, and left anterior oblique projections

• Appropriately shielded sodium iodide thyroid probe positioned with the crystal surface 25 cm from the surface being measured. Obtain counts of the following for 2 minutes:

Thyroid bed

Thigh (body background)

Room background

Pill standard (in a neck phantom)

• Calculate the iodine uptake with the following formula:

Image Interpretation

The 24-hour uptake measures 85% by thyroid probe. The uptake of 85% at 24 hours is markedly increased (expected range, 15–30%). Three views (Figs. 57.1, 57.2, and 57.3) demonstrate a large, well-defined “cold” nodule in the left lobe of the thyroid gland, corresponding to the palpated nodule, within an otherwise diffusely enlarged but homogeneous gland.

Differential Diagnosis

(Two coexisting thyroid conditions)

• For the right lobe and left upper lobe, Graves disease

• In the left lower lobe, primary malignant neoplasm or metastasis versus a benign condition (eg, abscess, adenoma, adenomatous hyperplasia, colloid cyst, hematoma, lymphocytic thyroiditis, parathyroid adenoma)