Thyroid scanning is a nuclear study performed to assist in diagnosing thyroid dysfunction and benign or malignant thyroid tumor. Normally, the thyroid reveals a homogeneous uptake of the radionuclide; an absent or diminished uptake is an indication of pathology. The most frequent indication for thyroid scanning is the presence of a nodule or enlarged thyroid gland.

The procedure is performed after an IV injection of 99mTc administered as technetium Tc 99m pertechnetate, with imaging taking place in 20 minutes, or an oral ingestion of 123I as iodide I 123, with imaging in 4 or 24 hours. Iodide I 123 is the most commonly used radiopharmaceutical because of its short half-life and lower radiation exposure. Iodine 131 administered as metaiodobenzylguanidine (MIBG) I 131 is used in scanning for thyroid cancer and therapy.

The classification of "cold" nodules results from a decrease or absence of radioactivity in the gland and suggests a malignant tumor. "Hot" nodules result from an increase or normal activity in the gland, and this finding suggests a benign tumor or thyrotoxicosis.^38,39 Thyroid scanning with iodide I 123 is usually performed in combination with a radioactive iodine uptake study on the same day. Thyroxine (T4) level is also obtained to diagnose thyroiditis and thyroid function tests to diagnose Graves' disease. Thyroid ultrasound and nodal biopsy can be performed to confirm a diagnosis.

• Normal size, shape, weight, position, and function of the thyroid gland with a homogeneous uptake of the radiopharmaceutical; no thyroiditis, Graves' disease, or benign or malignant tumor

• Inability of client to remain still during the procedure
• Other recent nuclear scans or radiologic studies using iodinated media that can affect uptake of the radionuclide
• Dietary intake deficient in iodine content, because this increases uptake, or intake of foods containing iodine, because this decreases uptake
• Vomiting or diarrhea, or both, that can decrease uptake of the radionuclide
• Medications such as thyroid drugs, multivitamins, steroids, cough medications, thyroid hormone antagonists, or phenothiazines

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Indications

• Assessing palpable nodules and differentiating these from benign tumor cyst (uptake of radionuclide) and malignant tumor (absence of uptake)
• Determining the cause of neck or substernal masses
• Differentiating between Graves' disease with a diffuse and enlarged thyroid and Plummer's disease with a nodular thyroid, both resulting in hyperthyroidism
• Evaluating thyroid function in hyperthyroidism and hypothyroidism when analyzed with laboratory thyroid function tests, thyroxine (T4), triiodothyronine (T3), and thyroid uptake tests
• Diagnosing thyroiditis conditions such as acute or chronic Hashimoto's thyroiditis revealed by uptake below or above normal, depending on disease stage
• Determining the thyroid gland as a primary site in clients with metastatic tumors

Contraindications

• Pregnancy, unless the benefits of performing the procedure greatly outweigh the risks to the fetus

[Section Outline]

• Indications
• Contraindications

Nursing Care Before the Procedure

Client teaching and physical preparation are the same as for any nuclear scan study (see section under "Brain Scanning").

• Instruct the client to restrict iodine-containing foods for 2 to 3 weeks before the procedure.
• Inform the client of the scanning schedule and explain that the procedure takes 30 minutes.
• Restrict food and fluids for 2 to 4 hours before the study, according to policy and physician preference.
• History should include medications taken or withheld before the procedure, previous scans or radiologic studies, results of laboratory tests, and foods or medications containing iodine ingested before the study.

The client is given iodide I 123 by mouth in a capsule or technetium Tc 99m pertechnetate by IV injection, depending on which has been ordered. The client is placed on the examining table in a supine position, and imaging is performed 20 minutes after an IV injection or 2 to 4 hours after an oral dose. The client is requested to remain still and the scanning camera is moved over the neck. Additional scanning after the oral dose can be performed in 24 hours. Counts per minute are obtained and the percentage of uptake is calculated, using the dose administered and the decay factor.⁴⁰

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any nuclear scan study (see section under "Brain Scanning").

• Resume withheld food, fluid, and medications after the study.