Primary (Idiopathic) Hemochromatosis
Genetic hemochromatosis (GH) results from excessive gastrointestinal absorption and deposition of iron in tissues such as liver, heart, pancreas, anterior pituitary, joints, and skin. Early in the disease process, iron accumulation is restricted to the liver. Over time, iron deposition progresses to involve other organs, primarily the pancreas and heart.
A diagnostic feature of idiopathic hemochromatosis is that signal intensity of the spleen is not substantially decreased on T2-weighted or T2*-weighted images, due to accumulation of iron within the parenchyma of the liver and pancreas and lack of selective uptake by the RES in the spleen. The presence of iron deposition in the pancreas correlates with irreversible changes of cirrhosis in the liver.
In patients with GH, cirrhosis and HCC develop over time. HCC reveals high signal intensity on a low-signalintensity background of liver parenchyma on T2-weighted images (Siegelman et al. 1996).
Transfusional iron overload can cause excess iron deposition. Fibrosis is usually mild despite even heavy iron stores, and cirrhosis is rare. Iron deposition in the RES results in low signal intensity of the spleen, liver, and bone marrow on MR images, best shown on T2- or T2*- weighted images.
Transfusional hemochromatosis can be differentiated from genetic hemochromatosis by the signal intensity of the spleen, which is usually normal in genetic hemochromatosis, whereas signal intensity of the pancreas is normal with most cases of transfusional overload. In massive iron overload (e.g., >100 units) direct tissue deposition may occur in other cells and tissues, notably the pancreas (Siegelman et al. 1996).
In moderate to severe forms of iron deposition the T2-shortening effect of iron results in low signal on T1- weighted images as well. If liver and spleen are gray on in-phase SGE iron deposition is considered moderate, and if liver and spleen are near to being signal voids iron deposition is severe.