thyroid scan

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thyroid scan

A image obtained from the thyroid gland after oral administration of radioiodine. See Radioactive iodine uptake.

Thyroid Scan

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

Common use

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

Area of application

Thyroid.

Contrast

Oral radioactive iodine or IV technetium-99m pertechnetate.

Description

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 neoplasm, however, a biopsy must be performed.

This procedure is contraindicated for

  • high alert 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.

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’s)
  • Detect thyroid dysfunction
  • Differentiate between Graves’ disease and Plummer’s 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)

Potential diagnosis

Normal findings

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

Abnormal findings related to

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

Critical findings

    N/A

Interfering factors

  • Factors that may impair clear imaging

    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • Other nuclear scans or iodinated contrast medium radiographic studies done within the previous 24 to 48 hr.
    • Ingestion of foods containing iodine (iodized salt) or medications containing iodine (cough syrup, potassium iodide, vitamins, Lugol’s solution, thyroid replacement medications), which can decrease the uptake of the radionuclide.
    • Antithyroid medications (propylthiouracil), corticosteroids, antihistamines, warfarin, sulfonamides, nitrates, corticosteroids, thyroid hormones, and isoniazid, 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, which may inhibit organ visualization and cause unclear images.
  • Other considerations

    • Improper injection of the radionuclide that allows the tracer to seep deep into the muscle tissue can produce erroneous hot spots.
    • Consultation with a health-care provider (HCP) should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating. Pediatric & Geriatric Imaging Children and geriatric patients are at risk for receiving a higher radiation dose than necessary if settings are not adjusted for their small size. Pediatric Imaging Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (www.pedrad.org/associations/5364/ig/).
    • Risks associated with radiation overexposure can result from frequent x-ray or radionuclide procedures. Personnel working in the examination area should wear badges to record their level of radiation exposure.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in evaluating the thyroid glands structure and function.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, sedatives, or radionuclides.
  • Obtain a history of the patient’s endocrine system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Ensure thyroid blood tests are completed prior to this procedure.
  • Note any recent procedures that can interfere with test results, including examinations using iodinated contrast medium or radioactive nuclides.
  • Ensure that this procedure is performed before all radiographic procedures using iodinated contrast medium.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Address concerns about pain related to the procedure and explain that some pain may be experienced during the test. Inform the patient that the procedure is performed in a nuclear medicine department, usually by an HCP specializing in this procedure, with support staff, and takes approximately 30 to 60 min.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Explain that an IV line may be inserted to allow infusion of IV fluids such as normal saline, anesthetics, sedatives, radionuclides, medications used in the procedure, or emergency medications.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined.
  • Instruct the patient to fast for 8 to 12 hr prior to the procedure. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.

Intratest

  • Potential complications:
  • Although it is rare, there is the possibility of allergic reaction to the radionuclide. Have emergency equipment and medications readily available. If the patient has a history of allergic reactions to any substance or drug, administer ordered prophylactic steroids or antihistamines before the procedure.

  • Establishing an IV site and injecting radionuclides are invasive procedures. Complications are rare but do include bleeding from the puncture site related to a bleeding disorder, or the effects of natural products and medications known to act as blood thinners; hematoma related to blood leakage into the tissue following needle insertion; infection that might occur if bacteria from the skin surface is introduced at the puncture site; or nerve injury that might occur if the needle strikes a nerve.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure that the patient has complied with dietary restrictions for 8 to 12 hr prior to the procedure.
  • Ensure that the patient has removed all external metallic objects from the area to be examined prior to the procedure.
  • Instruct the patient to void prior to the procedure and to change into the gown, robe, and foot coverings provided.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Have emergency equipment readily available.
  • Instruct the patient to cooperate fully and to follow directions. Ask the patient to lie still during the procedure because movement produces unclear images.
  • Administer sedative to a child or to an uncooperative adult, as ordered.
  • Tc-99m pertechnetate is injected IV 20 min before scanning.
  • If oral radioactive nuclide is used instead, administer I-123 24 hr before scanning.
  • Place the patient in a supine position on a flat table to obtain images of the neck area.
  • Remove the needle or catheter and apply a pressure dressing over the puncture site.
  • Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.
  • Instruct the patient in the care and assessment of the injection site.
  • Advise the patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body, unless contraindicated. Tell the patient that radionuclide is eliminated from the body within 6 to 24 hr.
  • If a woman who is breastfeeding must have a nuclear scan, she should not breastfeed the infant until the radionuclide has been eliminated. This could take as long as 3 days. She should be instructed to express the milk and discard it during the 3-day period to prevent cessation of milk production.
  • Instruct the patient to flush the toilet immediately and to meticulously wash hands with soap and water after each voiding for 24 hr after the procedure.
  • Instruct all caregivers to wear gloves when discarding urine for 24 hr after the procedure. Wash gloved hands with soap and water before removing gloves. Then wash hands after the gloves are removed.
  • Recognize anxiety related to test results, and be supportive of perceived loss of independent function. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ACTH, angiography adrenal, biopsy thyroid, calcium, CT renal, cortisol, glucose, radioactive iodine uptake, sodium, thyroglobulin, thyroid antibodies, TBII, thyroid scan, TSH, TT3, T4, FT4, and US thyroid.
  • Refer to the Endocrine System table at the end of the book for related tests by body system.