Pheochromocytoma scanning is a nuclear study performed to identify the presence of this tumor in the body. The tumor arises from the chromaffin cells of the sympathetic adrenal system, with 90 percent occurring within the adrenal medulla and 10 percent in extra-adrenal sites. A higher percentage of the extramedullary tumor sites occur in children. The defining characteristic of pheochromocytomas is the production of excessive catecholamines (epinephrine, norepinephrine) with epinephrine-secreting tumors found in the intra-adrenal site and norepinephrine-secreting tumors found in the intra-adrenal or extra-adrenal sites. About 10 percent are malignant, with an increased incidence in the extra-adrenal sites.²⁶

The study involves a total body scanning after the IV injection of iodine 131 (131I) administered as metaiodobenzylguanidine (MIBG) I 131, composed of bretylium and guanethidine, which localizes sympathetic tissue. Imaging is performed primarily to localize the tumor site rather than to formulate a diagnosis; the site is revealed by an abnormal uptake of the radionuclide at the intra-adrenal or extra-adrenal sites. Laboratory measurements of catecholamines in the urine and blood are performed to determine an increased secretion of these substances and, combined with CT and ultrasonography, provide definitive diagnostic information. Once diagnosed, surgical removal of the tumor is the most effective treatment.²⁷

• Normal uptake of radionuclide in all areas of the body: liver, spleen, urinary bladder, salivary gla-nds, heart, and adrenal glands; no adrenergic tumor

• Inability of client to remain still during the procedure
• Barium in the gastrointestinal tract from previous diagnostic procedures

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Indications

• Confirming a diagnosis and localizing an adren-ergic tumor when CT has not provided a definitive diagnosis
• Identifying extra-adrenal sites of a tumor such as the organ of Zuckerkandl revealed by increased uptake
• Confirming a suspected tumor in the area of the adrenal glands revealed by an abnormal uptake of the radionuclide
• Identifying and localizing related tumors such as neuroblastomas, carcinoid tumors, and paraganglionomas (tumors found outside of the adrenal medulla)
• Diagnosing medullary cancer of the thyroid gland

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").

• Assess for iodine allergy, and note the results of catecholamine measurement in blood and urine laboratory tests.

The client is placed on the examining table in a supine or sitting position. The radiopharmaceutical is injected IV and the client is returned to the hospital room or requested to return to the department in 24 hours. The client is requested to remain very still during the procedure, and imaging of the whole body is performed at that time and then again in 48 and 72 hours as the radionuclide localizes in the sympathetic tissues of the body. Renal scanning is also performed to outline the kidneys. In some instances, an additional scan takes place 4 days after the injection. The daily scanning is necessary because the tumor can be visualized on a specific day or on all days.

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").

• Administer supersaturated potassium iodide 10 days after the injection of the radiopharmaceutical.