Click on Images for Enlarged View
The second picture is a T2 weighted axial image of the abdomen acquired 1 cm below the first. This demonstrates decreased signal in the liver, bone marrow and the pancreas. The signal of the spleen is again normal.
Diagnosis: Hemochromatosis / Hemosiderosis
Discussion: These two terms define iron overload. Hemosiderosis describes those conditions that are not associated with end organ damage. Hemochromatosis may be primary or secondary. Primary hemochromatosis affects 1/220 Caucasians of northern European ancestry causes increased intestinal absorption of dietary iron. Secondary hemochromatosis can be caused by multiple factors, eg., parenteral administration of Fe (from transfusions), increased absorption of normal dietary FE, increased dietary Fe load. Fe is stored in the body as hemosiderin or ferritin in the reticuloendothelial cells of liver, spleen and bone marrow (2-6gm). Deposition of excess amounts of Fe (10-20 gm) depends upon the underlying etiology. This is deposited in either parenchymal or reticuloendothelial cells. Conditions that lead to parenchymal cell deposition are hereditary hemochromatosis, cirrhosis, intravascular hemolysis. The excess Fe stores are seen in the parenchymal cell of the liver, pancreas, myocardium, endocrine glands, joints. Reticuloendothelial cell deposition is seen with multiple transfusions, rhabdomyolysis, extravascular hemolysis; and associated changes are seen only in the organs with RE cells - including the liver, spleen, and the bone marrow, but not pancreas.
The differentiation between the parenchymal vs RE cell deposition is important since parenchymal cell deposition is associated with end organ damage and increased risk of developing hepatocellular carcinoma. Up to 30% of people with this type of hemochromatosis will develop HCC if left untreated. Treatment in the pre-cirrhotic state can lead to a normal life expectancy. CT scan images will demonstrate increased attenuation of liver in up to 60% of patients only. MR imaging, with conventional spin- echo T2 weighted images, has sensitivity approaching 90%.
With the parenchymal cell deposition, decreased signal can be seen within the liver, spleen, pancreas and myocardium. With the RE deposition, pancreas will appear normal, since RE cells are not present in the pancreas. Of note, however, following saturation of RE cells (estimated capacity = 10 gm, which corresponds with 40 units of blood), subsequent redistribution occurs to parenchymal cells. Several studies have been conducted to quantitate FE concentration within the liver from its MR signal.
References:
Taveras J, Ferrucci, J. Radiology. J.B. Lippincott, 1995, Vol 5, Ch 62, pp. 4-7.
Gore RM, Levine MS, Laufer I. Textbook of Gastrointestinal Radiology. W. B.
Saunders & Co., 1194, pp. 1978-1980.
Siegelman ES, et al. Parenchymal versus Reticuloendothelial Iron Overload in the
liver: Distinction with MRI. Radiology, Vol 179, No. 2, p361-366.
Gomori JM, et al. Hepatic Iron Overload: Quantitative MRI. Radiology, Vol 179,
No.2, p367-369.
Submitted by: