Liver Spleen Scanning
In liver-spleen scanning, a gamma camera records the distribution of radioactivity within the liver and spleen after I.V. injection of a radioactive colloid. The colloid most commonly used, technetium sulfide-99m (99mTc), concentrates in the reticuloendothelial cells through phagocytosis. About 80% to 90% of the injected colloid is taken up by Kupffer's cells in the liver, 5% to 10% by the spleen, and 3% to 5% by bone marrow. The gamma camera images either organ instantaneously without moving.
Although the indications for this test include the detection of focal disease, such as tumors, cysts, and abscesses, liver-spleen scanning demonstrates focal disease nonspecifically as a cold spot (a defect that fails to take up the colloid) and may fail to detect focal lesions smaller than 3/4" (2 cm) in diameter. Although clinical signs and symptoms may aid diagnosis, liver-spleen scanning frequently requires confirmation by ultrasonography, computed tomography, gallium scanning, or biopsy.
Procedure and posttest care
Because the liver and spleen contain equal numbers of reticuloendothelial cells, both organs normally appear equally bright on the image. However, distribution of radioactive colloid is generally more uniform and homogeneous in the spleen than in the liver. The liver has various normal indentations and impressions, such as the gallbladder fossa and falciform ligament, that may mimic focal disease.
Although liver-spleen scanning may fail to detect early hepatocellular disease, it shows characteristic, distinct patterns as such disease progresses. The most prominent sign of hepatocellular disease is a shift of the radioactive colloid that's caused by reduced hepatic blood flow and impaired function of Kupffer's cells. This inhibits distribution of the colloid in the liver, causing the liver to appear uniformly decreased or patchy. The spleen and bone marrow then take up the abnormally large amounts of the colloid unabsorbed by the liver, thus concentrating more radioactivity than the liver, and appear brighter on the scan. This same distribution pattern (colloid shift) also accompanies portal hypertension due to extrahepatic causes.
Hepatitis and cirrhosis are both associated with hepatomegaly and a colloid shift, but certain characteristics help distinguish them. In hepatitis, distribution of the colloid is usually uniformly decreased; in cirrhosis, it's patchy. Splenomegaly is typical in cirrhosis but not in hepatitis.
Metastasis to the liver or spleen may appear on the scan as a focal defect and requires biopsy to confirm the diagnosis. Liver metastasis usually originates in the GI or genitourinary tract, the breasts, or the lungs and is more common than metastasis to the spleen. After metastasis is confirmed, serial liver-spleen studies are useful in evaluating effectiveness of therapy.
Because cysts, abscesses, and tumors fail to take up the radioactive colloid, they appear on the scan as solitary or multiple focal defects. Hepatic cysts may appear as solitary defects; polycystic hepatic disease, as multiple defects. Splenic cysts are rarer than hepatic cysts and may have a parasitic or nonparasitic origin. Ultrasonography can confirm hepatic or splenic cysts.
Intrahepatic abscesses are usually pyogenic or amebic. Subphrenic abscesses, located beneath the diaphragm, may distort the dome of the right lobe. Splenic abscesses are characteristic in bacterial endocarditis. All abscesses require gallium scanning or ultrasonography to confirm diagnosis.
Benign hepatic tumors - such as hemangiomas, adenomas, and hamartomas - require confirming biopsy or flow studies. Primary malignant tumors, such as hepatomas, also require biopsy. Benign splenic tumors are rare and include hemangiomas, fibromas, myomas, and hamartomas. Primary malignant splenic tumors are also rare, except in lymphoreticular malignancies such as Hodgkin's disease. Splenic tumors also require biopsy to confirm diagnosis. Although focal disease usually inhibits uptake of radioactive colloid, both obstruction of the superior vena cava and Budd-Chiari syndrome cause markedly increased uptake.
A left upper quadrant mass may result from splenomegaly or, if the liver is grossly extended across the abdomen, from hepatomegaly. A right upper quadrant mass may result from hepatomegaly; a right lower quadrant mass may be a Riedel's lobe or a large dependent gallbladder. Splenic infarcts, often associated with bacterial endocarditis and massive splenomegaly, appear as peripheral defects, with decreased and irregular colloid distribution.
Scanning can assess hepatic injury after abdominal trauma. Intrahepatic hematoma appears as a focal defect; subcapsular hematoma, as a lentiform defect on the periphery of the liver; patic laceration, as a linear defect.
Scanning can also detect splenic injury after abdominal trauma. Splenic hematoma appears as a focal defect in or next to the spleen and may transect it. Subcapsular hematoma appears as a lentiform defect on the periphery of the spleen; splenic laceration appears as a linear defect.
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