- DISCUSSION
Amyloid is defined as a substance which: (1) stains positively with Congo red, (2) exhibits apple green birefringence by polarization microscopy, (3) shows aggregations of approximately 10 nm wide fibrils on electron microscopy, (4) exhibits a β-pleated sheet configuration, and (5) shows resistance to proteases other than pronase.
5 Progressive deposition of amyloid compresses and replaces normal tissue, and this leads to organ dysfunction and a wide variety of clinical syndromes, some of which have severe pathophysiological consequences.
Amyloidosis is usually seen in a systemic form, but 10-20% of cases can be localized.
4 Men are affected more than women, and the mean age of presentation is 55-60 years. Some causes of secondary amyloidosis are multiple myeloma (10-15%), rheumatoid arthritis (20-25%), tuberculosis (50%), or familial Mediterranean fever (26-40%).
4 Approximately one-third of patients with primary amyloidosis develop congestive heart failure. It is the leading cause of death in patients with primary and myeloma-related amyloidosis.
In case of hepatic amyloidosis, amyloid is deposited in the parenchyma, along the sinusoids within the space of Disse, or in blood vessel walls. Hepatocytes are severely compressed by extensive accumulation of amyloid and they may atrophy or nearly disappear. In advanced cases with massive infiltration, the liver is enlarged with rubbery elastic consistency, and it may show 'lardaceous liver' appearance on cut surface.
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Although hepatic involvement is very common in patients with amyloidosis, the clinical manifestations of hepatic involvement are usually mild. Symptomatic involvement, including rupture, portal hypertension or hepatic failure, is rare. Hepatomegaly and a borderline abnormal liver function test are the most frequent findings in patients with hepatic amyloidosis.
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5 However, serious symptoms such as hepatic failure and portal hypertension may develop. Spontaneous rupture and massive hemorrhage may occur; therefore, needle biopsy should be performed carefully. In one report 77% of the patient had an associated nephrotic syndrome, congestive heart failure, peripheral neuropathy, or orthostatic hypotension. Other signs of hepatic amyloidosis included proteinuria (88%), elevated serum alkaline phospatase (86%), abnormal serum protein electrophoresis (monoclonal protein or hypogammaglobulinemia, 64%), hyposplenism on the peripheral blood smear (62%), defined by the presence of Howell-Jolly bodies; and hepatomegaly (81%) disproportional to the liver enzyme abnormalities. Liver function tests were not sensitive or specific. Normal levels of aspartate aminotransferase, and bilirubin were seen in 32%. The median survival of the entire group was nine months.
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Radiological findings of hepatic involvement are nonspecific, Amorphous or irregular calcifications were occasionally identified within the amyloid deposit. Definitive diagnosis requires biopsy confirmation, as CT findings are nonspecific.
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6 The ultrasonographic findings of primary hepatic amyloidosis have not been well described. In one reported case, heterogeneous echogenicity was seen in the liver as in the present case.
The frequent findings of conventional precontrast and contrast-enhanced CT are an enlarged liver with heterogeneous decreased attenuation.
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6 Calcification may be seen rarely in the hepatic parenchyma. The hepatic parenchyma infiltrated more highly by amyloid may appear as focal hypoattenuating areas on contrast-enhanced CT scans. This finding probably resulted from impairment of blood flow due to vascular involvement and diffuse parenchymal infiltration of amyloid.
1 Delayed phase CT scans showed delayed enhancement with the presence of some focal hypoattenuating areas in the liver. The delayed enhancement was probably due to delayed passage of contrast medium in the involved parenchyma, and the hepatic parenchyma with prominent infiltration might appear as the focal hypoattenuating areas. Kim et al
5 suggested that hepatic amyloidosis have characteristic features of hepatic contour; and asymmetric and triangular hepatomegaly with the apex at the falciform ligament. This finding was believed to be the result of mild atrophic change of the lateral border of both hepatic lobes, in spite of hepatic enlargement reported in other infiltrative diseases.
MR imaging has been used for the evaluation of primary hepatic amyloidosis. One report showed that, although T2 value of the hepatic parenchyma was not changed, T1 value was increased and it could beused to monitoring of chemotherapy.
1 However, the reason for high signal intensity on T1 is not known.
One report showed that the deposition of amyloid in the spleen was identified in about 83% of patients at the time of autopsy.
1 Amyloid tends to infiltrate in the red pulp or blood vessel walls. The spleen may swell and harden by massive infiltration, and 'bacon spleen' appearance may be seen on cut surface in advanced cases. Splenic involvement is usually asymptomatic. Hyposplenism may occur and potentially increase the risk of serious infection. Spontaneous splenic rupture is a known consequence of splenic amyloidosis. CT findings of primary splenic amyloidosis include splenomegaly, calcification and poor contrast enhancement of the splenic parenchyma on conventional contrast-enhanced CT scans. Mild delayed enhancement was noted in the spleen on delayed phase CT scans.
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4 In the spleen, arterial phase CT showed the lack of parenchymal enhancement, and T2-weighted MR imaging showed decreased signal intensity.
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