Thyroid Scan

Synonym/Acronym:
Iodine thyroid scan, technetium thyroid scan, thyroid scintiscan.

Rationale
To assess thyroid gland size, structure, function, and shape toward diagnosing disorders such as tumor, inflammation, cancer, and bleeding.

Patient Preparation
There are no activity or medication restrictions unless by medical direction. Instruct the patient to fast for 8 to 12 hr prior to the procedure. Protocols may vary among facilities. Ensure that this procedure is performed before other radiographic procedures using iodinated contrast medium.

Normal Findings

  • Normal size, contour, position, and function of the thyroid gland with homogeneous uptake of the radionuclide.

Critical Findings and Potential Interventions
N/A

Overview

(Study type: Nuclear scan; related body system: Endocrine system.) The thyroid scan is a nuclear medicine study performed to assess thyroid size, shape, position, and function. It is useful for evaluating thyroid nodules, multinodular goiter, and thyroiditis; assisting in the differential diagnosis of masses in the neck, base of the tongue, and mediastinum; and ruling out possible ectopic thyroid tissue in these areas. Thyroid scanning is performed after oral administration of radioactive iodine-123 (I-123) or I-131 or IV injection of technetium-99m (Tc-99m). Increased or decreased uptake by the thyroid gland and surrounding area and tissue is noted: Areas of increased radionuclide uptake (“hot spots) are caused by hyperfunctioning thyroid nodules, which are usually nonmalignant; areas of decreased uptake (cold spots”) are caused by hypofunctioning nodules, which are more likely to be malignant. Ultrasound imaging may be used to determine if the cold spot is a solid, semicystic lesion or a pure cyst (cysts are rarely cancerous). To determine whether the cold spot depicts a malignant tumor, however, a biopsy must be performed.

Indications

  • Assess palpable nodules and differentiate between a benign tumor or cyst and a malignant tumor.
  • Assess the presence of a thyroid nodule or enlarged thyroid gland.
  • Detect benign or malignant thyroid tumors.
  • Detect causes of neck or substernal masses.
  • Detect forms of thyroiditis (e.g., acute, chronic, Hashimoto disease).
  • Detect thyroid dysfunction.
  • Differentiate between Graves disease and Plummer disease, both of which cause hyperthyroidism.
  • Evaluate thyroid function in hyperthyroidism and hypothyroidism (analysis combined with interpretation of laboratory tests, thyroid function panel including thyroxine and triiodothyronine, and thyroid uptake tests).

Interfering Factors

Contraindications

Patients who are pregnant or suspected of being pregnant, unless the potential benefits of a procedure using radiation far outweigh the risk of radiation exposure to the fetus and mother. Use of I-131 is contraindicated during pregnancy; it may cause permanent hypothyroidism in the developing fetus.

Factors that may alter the results of the study

  • Ingestion of foods containing iodine (iodized salt) or medications containing iodine (cough syrup, potassium iodide, vitamins, Lugol solution, thyroid replacement medications), which can decrease the uptake of the radionuclide.
  • Antihistamines, antithyroid medications (propylthiouracil), corticosteroids, isoniazid, nitrates, sulfonamides, thyroid hormones, and warfarin, which can decrease the uptake of the radionuclide.
  • Increased uptake of iodine in persons with an iodine-deficient diet or who are on phenothiazine therapy.
  • Vomiting and severe diarrhea, which can affect absorption of orally administered radionuclide.
  • Gastroenteritis, which can interfere with absorption of orally administered radionuclide.
  • Metallic objects (e.g., jewelry, body rings) within the examination field, other nuclear scans done within the previous 24 to 48 hr, or iodinated contrast from a previous radiological procedure, which may inhibit organ visualization and cause unclear images.
  • Improper injection of the radionuclide that allows the tracer to seep deep into the muscle tissue can produce erroneous hot spots.
  • Inability of the patient to cooperate or remain still during the procedure because movement can produce blurred or otherwise unclear images.

Potential Medical Diagnosis: Clinical Significance of Results

Abnormal Findings In:

  • Adenoma
  • Cysts
  • Fibrosis
  • Goiter
  • Graves disease (diffusely enlarged, hyperfunctioning gland)
  • Hematoma
  • Metastasis
  • Plummer disease (nodular hyperfunctioning gland)
  • Thyroiditis (Hashimoto disease)
  • Thyrotoxicosis
  • Tumors, benign or malignant

Nursing Implications

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Inform the patient this procedure can assist in evaluating the thyroid glands’ structure and function.
  • Explain to the female patient that she may be asked the date of her last menstrual period. Generally, pregnancy screening is not indicated for Tc-99m scans; however, depending on the radionuclide to be used, testing may be performed in accordance with the facility’s imaging and radionuclide administration policies. In all cases, the benefits and risks should be discussed with the HCP before proceeding with the study.
  • Explain to the patient who is breastfeeding that depending on the type of radionuclide and dose used, temporary or complete cessation of breastfeeding may be recommended. Policies may vary among facilities. Benefits and risks should be discussed with the HCP before the patient makes an informed decision to continue or temporarily suspend breastfeeding. If the patient remains concerned about potential fetal harm, facility guidelines may recommend suspending breastfeeding for a dose/tracer dependent period of time during which the infant may be bottle fed with formula or milk expressed prior to the procedure.
  • Review the procedure with the patient.
  • Explain that there may be moments of discomfort or pain experienced when the IV line is inserted to allow infusion of fluids such as saline, anesthetics, sedatives, radionuclides, medications used in the procedure, or emergency medications.
  • Explain that the procedure takes about 30 to 60 min and is performed in a nuclear medicine department.
  • Explain that Tc-99m pertechnetate is injected IV 20 min before scanning.
  • If oral radioactive nuclide is used instead, I-123 will be administered 24 hr before scanning.
  • Reassure the patient that the radionuclide poses no radioactive hazard and rarely produces adverse effects.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined prior to the procedure.
  • Baseline vital signs and neurological status are recorded. Protocols may vary among facilities.
  • Positioning for this procedure is in a supine position on a flat table to obtain images of the neck area.
  • Explain that once the study is completed, the needle or catheter is removed and a pressure dressing applied over the puncture site.

Potential Nursing Actions

Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

  • Ensure thyroid blood tests are completed prior to this procedure.

After the Study: Potential Nursing Actions

Avoiding Complications

  • Establishing an IV site and injection of radionuclides are invasive procedures. Complications are rare but include risk for allergic reaction (related to contrast reaction), hematoma (related to blood leakage into the tissue following needle insertion), bleeding from the puncture site (related to a bleeding disorder or the effects of natural products and medications with known anticoagulant, antiplatelet, or thrombolytic properties), or infection (which might occur if bacteria from the skin surface is introduced at the puncture site).
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, bronchospasm).
  • Explain the importance of immediately reporting symptoms such as fast heart rate, difficulty breathing, skin rash, itching, or chest pain to the appropriate HCP.
  • Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.

Treatment Considerations

  • Explain that the radionuclide is eliminated from the body within 6 to 24 hr.
  • Unless contraindicated, instruct the patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body.
  • Instruct the patient to resume usual diet, fluids, medications, and activity as directed by the HCP.
  • Administer ordered antiemetics as needed.
  • Discuss the care and assessment of the injection site.
  • Explain that application of cold compresses to the puncture site may reduce discomfort or edema.

Safety Considerations

    Followup Evaluation and Desired Outcomes

    • Understands that depending on the results of this study, additional testing may be performed to monitor disease progression and determine the need for a change in therapy.

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