Thyroid Scan

General

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.

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.

The thyroid scan is usually preceded by a radioactive iodine uptake (RAIU) test. For additional information on the RAIU, refer to the study titled “Radioactive Iodine Uptake.”

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
Pregnancy is a general contraindication to procedures involving radiation.

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, Nursing Process, Clinical Judgement

Before the Study: Planning and Implementation


Teaching the Patient What to Expect

  • Discuss how this procedure can assist in evaluating the thyroid glands’ structure and function.
  • Explain that the procedure takes about 30 to 60 min and is performed in a nuclear medicine department.
  • Review the procedure with the patient.
  • Explain that pregnancy testing may be required.
  • Discuss how there may be moments of discomfort or pain when the IV line is inserted, allowing for infusion of fluids such as saline, anesthetics, sedatives, medications used in the procedure, or emergency medications.
  • Reassure the patient that the radionuclide poses no radioactive hazard and rarely produces adverse effects.

Procedural Information

  • Policies regarding breastfeeding before and after an imaging procedure may vary among facilities. For additional information, see Appendix A: Patient Preparation and Specimen Collection, subsection: Potential Contraindications and Complications Associated With Diagnostic Procedures.
  • Tc-99m pertechnetate is injected IV 30 min before scanning.
  • If oral radioactive nuclide is used instead (e.g., in conjunction with the RAIU), I-123 will be administered 24 hr before scanning.
  • Baseline vital signs are recorded and monitored throughout the procedure.
  • Positioning for this procedure is in a supine position on a flat table to obtain images of the neck area.
  • Once the study is completed, the needle 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: Implementation & Evaluation Potential Nursing Actions


Avoiding Complications

  • Monitor the patient for complications related to the procedure.
  • Explain the importance of immediately reporting symptoms such as fast heart rate, difficulty breathing, skin rash, itching, or chest pain to the appropriate health-care provider (HCP).
  • Establishing an IV site and injection of radionuclides are invasive procedures that can cause rare complications. For additional information, see Appendix A: Patient Preparation and Specimen Collection, subsection: Potential Contraindications and Complications Associated With Diagnostic Procedures.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.

Treatment Considerations

  • Follow postprocedure vital sign and assessment protocol.
  • Explain that the radionuclide is eliminated from the body within 6 to 24 hr.
  • Facilitate drinking increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body, unless containdicated.
  • 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

  • Refer to organizational policy for additional precautions that may include instructions on temporary or complete suspension of breastfeeding, hand washing, toilet flushing, limited contact with others, and other aspects of nuclear medicine safety.

Clinical Judgement

  • Consider who is best qualified to discuss treatment options and probable outcomes in a culturally competent manner.

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.