Gallium Scanning

The gallium scan is a total-body scan used to assess certain neoplasms and inflammatory lesions that attract gallium. It's usually performed 24 to 48 hours after the I.V. injection of radioactive gallium (67 Ga) citrate; occasionally, it's performed 72 hours after the injection or, in acute inflammatory disease, after 4 to 6 hours.

Because gallium has an affinity for both benign and malignant neoplasms and inflammatory lesions, exact diagnosis requires additional confirming tests, such as ultrasonography and computerized tomography scanning. Also be aware that many neoplasms and a few inflammatory lesions may fail to demonstrate abnormal gallium activity.

Purpose

• To detect primary or metastatic neoplasms and inflammatory lesions when the site of the disease hasn't been clearly defined and when the patient's condition won't be jeopardized by the time required for the procedure
• To evaluate malignant lymphoma and identify recurrent tumors following chemotherapy or radiation therapy.
• To clarify focal defects in the liver when liver-spleen scanning and ultra­sonography prove inconclusive
• To evaluate bronchogenic carcinoma when sputum culture proves positive for malignancy but other tests are normal or when hydrothorax is present and bronchoscopy is contraindicated

Patient preparation

• Explain to the patient that this test helps detect abnormal or inflammatory tissue.
• Tell him he needn't restrict food or fluids before the test.
• Explain that the test requires a total body scan (usually performed 24 to 48 hours after the I. V. injection of radioactive gallium).
• Tell him who will perform the test, where it will take place, and that it takes 30 to 60 minutes.
• Warn him that he may experience transient discomfort from the needle puncture during injection of the radioactive gallium. Reassure him, however, that the dosage is only slightly radioactive and isn't harmful.
• If a gamma scintillation camera is to be used, assure the patient that although the uptake probe and detector head may touch his skin, he'll experience no discomfort.
• If a rectilinear scanner is to be used, mention that it makes a soft, irregular clicking noise as it registers the radiation emissions.
• Make sure the patient or a responsible family member has signed a consent form.
• Administer a laxative, a cleansing enema, or both.

Procedure and posttest care

• The patient may be positioned erect or recumbent or in an appropriate combination of these positions, depending on his physical condition.
• Scans or scintigraphs of the patient are taken 24 to 48 hours after 67Ga citrate injection, from anterior and posterior views and, occasionally, lateral views.
• If the initial gallium scan suggests bowel disease and additional scans are necessary, give the patient a cleansing enema before continuing the test.

Precautions

• This test should precede barium studies because barium retention may hinder visualization of gallium activity in the bowel.
• Gallium scanning is usually contraindicated in children and during pregnancy or lactation; however, it may be performed if the potential diagnostic benefit outweighs the risks of exposure to radiation.

Normal Findings

Abnormal findings

Gallium scanning may reveal inflammatory lesions - discrete abscesses or diffuse infiltration. In pancreatic or perinephric abscess, gallium activity is relatively localized; in bacterial peritonitis, gallium activity is spread diffusely within the abdomen.

Abnormally high gallium accumulation is characteristic in inflammatory bowel diseases, such as ulcerative colitis and regional ileitis (Crohn's disease), and in carcinoma of the colon. However, because gallium normally accumulates in the colon, the detection of inflammatory and neoplastic diseases is sometimes difficult.

Abnormal gallium activity may be present in various sarcomas, Wilms' tumor, and neuroblastomas; carcinoma of the kidney, uterus, vagina, and stomach; and testicular tumors, such as seminoma, embryonal carcinoma, choriocarcinoma, and teratocarcinoma, which often metastasize via the lymphatic system. In Hodgkin's disease and malignant lymphoma, gallium scanning can demonstrate abnormal activity in one or more lymph nodes or in extranodal locations. However, gallium scanning supported by results of lymphangiography can gauge the extent of metastases more accurately than either test alone because neither test consistently identifies all neoplastic nodes.

After chemotherapy or radiation therapy, gallium scanning may be used to detect new or recurrent tumors. However, these forms of therapy tend to diminish tumor affinity for gallium without necessarily eliminating the tumor.

In the differential diagnosis of focal hepatic defects, abnormal gallium activity may help narrow the diagnostic possibilities. Gallium localizes in hepatomas, but not in pseudotumors; in abscesses, but not in pleural effusions; and in tumors, but not in cysts or hematomas.

In examining patients with suspected bronchogenic carcinoma, abnormal activity confirms the presence of tumor. However, because gallium also localizes in inflammatory pulmonary diseases, such as pneumonia and sarcoidosis, a chest X-ray should be performed to distinguish a tumor from an inflammatory lesion.

Interfering factors

• Hepatic and splenic intake (possible false-negative scans due to possible obscuring of abnormal para-aortic nodes in Hodgkin 's disease)
• Stool accumulation in bowel (poor imaging of retroperitoneal space)
• Residual barium from other tests done 1 week before the scan (possible poor imaging)