Evaluation of computed tomography in the assessment of liver iron overload. A study of 46 cases of idiopathic hemochromatosis

Whole-body R2∗ mapping to quantify tissue iron in iron storage organs: reference values and a genotype

AIM

To define reference values for the transverse relaxation rate (R2∗) in iron storage organs and to investigate the role of human haemochromatosis protein (HFE) genotype on iron storage.

MATERIALS AND METHODS

Whole-body magnetic resonance imaging (MRI) including a five-echo gradient-echo sequence was performed in 483 volunteers (269 men, mean age 59.3 ± 12.2 years) without clinical evidence of an iron storage disease at 1.5 T. R2∗ values were assessed for liver, spleen, pancreas, heart, bones, and brain parenchyma. The HFE genotype was determined regarding the single nucleotide polymorphisms (SNPs) rs74315324, rs1799945, rs41303501, rs1800562, rs1800730. R2∗ values were compared among participants without and with at least one mutation. R2∗ reference values were defined using volunteers without any mutation.

RESULTS

Three hundred and one participants had no mutations in any HFE SNP, 182 had at least one mutation. HFE gene mutations were distributed as (heterozygous/homozygous) rs1799945:132/9, rs1800562:33/1, and rs1800730:11/0. Mean R2∗ values ± SD (per second) in the group without mutation were: liver: 33.4 ± 12.7, spleen: 24.1 ± 13.8, pancreas: 27.2 ± 6.6, heart: 32.7 ± 11.8, bone: 69.3 ± 21.0, brain parenchyma: 13.9 ± 1.2. No significant difference in R2∗ values were found between participants with and without the HFE gene mutation for any examined iron storage organ (p_liver=0.09, p_spleen=0.36, p_pancreas = 0.08, p_heart = 0.36, p_bone = 0.98, p_brain=0.74).

CONCLUSION

Reference values of R2∗ in iron storage organs are feasible to support the diagnosis of iron storage diseases. Non-specific mutations in HFE SNPs appear not to affect the phenotype of tissue iron accumulation.

Confounding factors of non-invasive tests for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) affects at least 25% of the general adult population worldwide. Because only a fraction of the patients would develop liver-related complications, it is preferable to perform non-invasive tests as the initial assessment. This review summarizes the known and potential confounding factors that affect the performance of non-invasive tests of hepatic steatosis and fibrosis in patients with NAFLD. Clinicians may apply the knowledge and exercise caution in selecting investigations and interpreting test results when confounding factors are present.

CT and MR imaging findings of the livers in adults with Fontan palliation: an observational study

PURPOSE

To describe liver imaging findings and complications on computed tomography (CT) or magnetic resonance imaging (MRI) in adults with Fontan palliation and investigate whether imaging features show correlations with clinical and physiological parameters.

METHODS

Our Institutional Review Board approved this retrospective study. Two blinded abdominal radiologists reviewed abdominal CT (n = 21) and MRI (n = 16) images between September 2011 and October 2017 in 37 adults (median age 27 years, interquartile range 21-36 years, 14 males [38%]) with a Fontan palliation (median post-Fontan duration 22 years, interquartile range 19-28 years). Correlation between CT/MRI findings and clinical parameters including laboratory results within 6 months of CT/MRI examinations was assessed by Spearman's rank correlation coefficient.

RESULTS

Lobulated hepatic surface and blunt hepatic edge were seen in 92% (34/37) and 95% (35/37) of patients, respectively. Surface nodularity was noted in 32% (12/37). In 7 patients, there were 11 hepatic nodules which showed arterial-phase hyperenhancement and washout. Among them, 2 were biopsy-proven hepatocellular carcinomas (HCCs), and the remaining 9 were focal nodular hyperplasia (FNH)-like nodules. Suprahepatic inferior vena cava (IVC) diameter showed positive correlations with post-Fontan duration (p < 0.01), serum gamma-glutamyl transferase (p < 0.01), and total bilirubin (p < 0.01).

CONCLUSION

The livers in post-Fontan adults show a unique morphology of blunt edge and lobulating surface with occasional nodularity. There is a diagnostic challenge in distinguishing HCCs from FNH-like nodules in post-Fontan population due to overlapping imaging findings. Suprahepatic IVC diameter is a potentially useful imaging marker that reflects hepatic dysfunction in Fontan palliation.

Diagnosis and Treatment of Genetic HFE-Hemochromatosis: The Danish Aspect

This paper outlines the Danish aspects of HFE-hemochromatosis, which is the most frequent genetic predisposition to iron overload in the five million ethnic Danes; more than 20,000 people are homozygous for the C282Y mutation and more than 500,000 people are compound heterozygous or heterozygous for the HFE-mutations. The disorder has a long preclinical stage with gradually increasing body iron overload and eventually 30% of men will develop clinically overt disease, presenting with symptoms of fatigue, arthralgias, reduced libido, erectile dysfunction, cardiac disease and diabetes. Subsequently the disease may progress into irreversible arthritis, liver cirrhosis, cardiomyopathy, pancreatic fibrosis and osteoporosis. The effective standard treatment is repeated phlebotomies, which in the preclinical and early clinical stages ensures a normal survival rate. Early detection of the genetic predisposition to the disorder is therefore important to reduce the overall burden of clinical disease. Population screening seems to be cost-effective and should be considered.

Opportunistic Screening for Hereditary Hemochromatosis With Unenhanced CT: Determination of an Optimal Liver Attenuation Threshold

OBJECTIVE

The purpose of this study was to assess whether a specific liver attenuation threshold for unenhanced CT allows both sensitive opportunistic detection of unsuspected hereditary hemochromatosis and low overall screening test-positive rates.

MATERIALS AND METHODS

We used a standard ROI placement method on unenhanced CT studies of 3357 consecutive adults (mean age, 57.0 years) with no symptoms of liver disease who underwent colorectal screening. Hepatic attenuation (in HU) was measured to assess test-positive rates at various liver attenuation thresholds. To assess sensitivity, unenhanced hepatic CT attenuation was also measured in 12 patients with hereditary hemochromatosis (mean age, 48.3 years), who were homozygous for the HFE C282Y mutation. All scans were obtained at 120 kV. Serum ferritin levels were recorded for the hereditary hemochromatosis cohort.

RESULTS

Mean liver attenuation ± SD among screened adults was 59.4 ± 12.7 HU, compared with 78.7 ± 13.1 HU (range, 59-105 HU) in the hereditary hemochromatosis cohort (p < 0.001). Screening test-positive rates were 30.6% (n = 1028) at 65 HU, 8.2% (n = 275) at 70 HU, 1.2% (n = 39) at 75 HU, and 0.2% (n = 7) at 80 HU. Corresponding sensitivities for hereditary hemochromatosis at these thresholds were 83.3% (10/12) at 65, 70, and 75 HU; and 50.0% (6/12) at 80 HU. Serum ferritin levels were elevated in all patients with hereditary hemochromatosis (mean, 1678 ng/mL; range, 477-3991 ng/mL).

CONCLUSION

An unenhanced CT liver attenuation threshold of 75 HU was sensitive (83.3%) for hereditary hemochromatosis while maintaining an acceptably low screening test-positive rate (1.2%). An unexplained liver attenuation of 75 HU or more on unenhanced CT should trigger appropriate laboratory investigation for iron overload; early intervention with phlebotomy can limit or prevent organ damage in patients with hemochromatosis.

Assessing the Non-tumorous Liver: Implications for Patient Management and Surgical Therapy

INTRODUCTION

Hepatic resection is performed for various benign and malignant liver tumors. Over the last several decades, there have been improvements in the surgical technique and postoperative care of patients undergoing liver surgery. Despite this, liver failure following an extended hepatic resection remains a critical potential postoperative complication. Patients with underlying parenchymal liver diseases are at particular risk of liver failure due to impaired liver regeneration with an associated mortality risk as high as 60 to 90%. In addition, live donor liver transplantation requires a thorough presurgical assessment of the donor liver to minimize the risk of postoperative complications.

RESULTS AND CONCLUSION

Recently, cross-sectional imaging assessment of diffuse liver diseases has gained momentum due to its ability to provide both anatomical and functional assessments of normal and abnormal tissues. Various imaging techniques are being employed to assess diffuse liver diseases including magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound (US). MRI has the ability to detect abnormal intracellular and molecular processes and tissue architecture. CT has a high spatial resolution, while US provides real-time imaging, is inexpensive, and readily available. We herein review current state-of-the-art techniques to assess the underlying non-tumorous liver. Specifically, we summarize current approaches to evaluating diffuse liver diseases including fatty liver alcoholic or non-alcoholic (NAFLD, AFLD), hepatic fibrosis (HF), and iron deposition (ID) with a focus on advanced imaging techniques for non-invasive assessment along with their implications for patient management. In addition, the role of and techniques to assess hepatic volume in hepatic surgery are discussed.

Different forms of iron accumulation in the liver on MRI

Magnetic resonance imaging (MRI) is a well-established imaging modality to evaluate increased iron deposition in the liver. Both standard liver imaging series with in-phase and out-of-phase T1-weighted sequences for visual detection, as well as advanced T2- and T2*-weighted measurements may be used for mapping the iron concentration. In this article, we describe different forms of liver iron accumulation (diffuse, heterogeneous, multinodular, focal, segmental, intralesional, periportal, and lobar) and hepatic iron sparing (focal, geographic and nodular). Focal iron sparing is characterized by hypointense areas on R2* map and hyperintense areas on T2* map. We also illustrate MRI findings of simultaneous hepatic iron and fat accumulation. Coexistence of iron (siderosis) and fat (steatosis) can make interpretation of in- and out-of-phase T1-weighted images difficult; calculation of proton density fat fraction and R2* maps can characterize abnormal signal changes observed on in- and out-of-phase images. Knowledge of different forms of hepatic iron overload and iron sparing and evaluation of T2* and R2* maps would allow correct diagnosis of iron-associated liver disorders.

Hypoparathyroidism and subclinical hypothyroidism with secondary hemochromatosis

Hemochromatosis is an inherited genetic disorder of iron metabolism which can also occur as a secondary result of iron-overload. It leads to organ damage such as cardiomyopathy, liver cirrhosis, hypogonadism, and diabetes. This paper discusses a case of secondary hemochromatosis associated with repeated transfusions, presenting as asymptomatic hypoparathyroidism and subclinical hypothyroidism with multiple organ involvement. The 29-year-old female, who had severe aplastic anemia, received multiple transfusions totaling approximately 1,400 units of red blood cells over 15 years. During her routine laboratory examination, hypocalcemia was detected with decreased intact parathyroid hormone and increased thyroid stimulating hormone. Serum ferritin, iron, and total iron binding capacity had increased to 27,583.03 ng/mL, 291 µg/dL, and 389 µg/dL, respectively. She had unusually bronze skin and computed tomography revealed iron deposition in the thyroid, liver, and heart. Multiorgan involvement as seen in this case is rare in hemochromatosis associated with secondary transfusions. To the best of the author's knowledge, this is the first case report in Korea of hypoparathyroidism and subclinical hypothyroidism due to iron deposition in the parathyroid and thyroid gland.

An autopsy case of secondary iron-overload cardiomyopathy

A woman over 70 years of age presented with anemia and appetite loss. She had no history of blood transfusions, although she had been receiving iron infusions for anemia for seven years. She had an elevated serum ferritin level (7,951 ng/mL) one month before admission. Abdominal computed tomography showed increased hepatic density and echocardiography showed normal heart valves and heart-wall motion. The patient eventually experienced atrial tachycardia and atrial fibrillation and died of heart failure. An autopsy revealed iron deposits in the liver, pancreas, adrenal glands, thyroid gland, gastric mucosa and myocardium. Iron-overload cardiomyopathy was diagnosed based on the iron deposits, myocardial disarray and interstitial fibrosis.

Magnetic resonance imaging quantification of liver iron

Iron overload is the histologic hallmark of hereditary hemochromatosis and transfusional hemosiderosis but also may occur in chronic hepatopathies. This article provides an overview of iron deposition and diseases where liver iron overload is clinically relevant. Next, this article reviews why quantitative noninvasive biomarkers of liver iron would be beneficial. Finally, we describe current state-of-the-art methods for quantifying iron with MR imaging and review remaining challenges and unsolved problems.

Iron overload cardiomyopathy: better understanding of an increasing disorder

The prevalence of iron overload cardiomyopathy (IOC) is increasing. The spectrum of symptoms of IOC is varied. Early in the disease process, patients may be asymptomatic, whereas severely overloaded patients can have terminal heart failure complaints that are refractory to treatment. It has been shown that early recognition and intervention may alter outcomes. Biochemical markers and tissue biopsy, which have traditionally been used to diagnose and guide therapy, are not sensitive enough to detect early cardiac iron deposition. Newer diagnostic modalities such as magnetic resonance imaging are noninvasive and can assess quantitative cardiac iron load. Phlebotomy and chelating drugs are suboptimal means of treating IOC; hence, the roles of gene therapy, hepcidin, and calcium channel blockers are being actively investigated. There is a need for the development of clinical guidelines in order to improve the management of this emerging complex disease.

Influence of iron chelation on R1 and R2 calibration curves in gerbil liver and heart

MRI is gaining increasing importance for the noninvasive quantification of organ iron burden. Since transverse relaxation rates depend on iron distribution as well as iron concentration, physiologic and pharmacologic processes that alter iron distribution could change MRI calibration curves. This article compares the effect of three iron chelators, deferoxamine, deferiprone, and deferasirox, on R1 and R2 calibration curves according to two iron loading and chelation strategies. Thirty-three Mongolian gerbils underwent iron loading (iron dextran 500 mg/kg/wk) for 3 weeks followed by 4 weeks of chelation. An additional 56 animals received less aggressive loading (200 mg/kg/week) for 10 weeks, followed by 12 weeks of chelation. R1 and R2 calibration curves were compared to results from 23 iron-loaded animals that had not received chelation. Acute iron loading and chelation-biased R1 and R2 from the unchelated reference calibration curves but chelator-specific changes were not observed, suggesting physiologic rather than pharmacologic differences in iron distribution. Long-term chelation deferiprone treatment increased liver R1 50% (P < 0.01), while long-term deferasirox lowered liver R2 30.9% (P < 0.0001). The relationship between R1 and R2 and organ iron concentration may depend on the acuity of iron loading and unloading as well as the iron chelator administered.

Myocardial and liver iron status using a fast T*2 quantitative MRI (T*2qMRI) technique

This work demonstrates the use of a fast and precise methodology for evaluating myocardial and liver iron status in multitransfused thalassemic patients by means of a fast T(2) (*) quantitative MRI (T(2) (*)qMRI) technique. Myocardial and liver T(2) (*) values were calculated in 48 thalassemic patients and 21 normal subjects on a 1.5T MRI system using a breath-hold 2D single-slice multiecho gradient-echo (MEGRE) sequence (16 echoes, TR/TE1/TE16/FA = 160/2.7/37.65 ms/25 degrees ). No ECG gating was used. Myocardial T(2) (*), liver T(2) (*), and myocardial to muscle (CR/MS) and liver to muscle (LV/MS) T(2) (*) ratios were correlated with serum ferritin concentration (SFC) levels for all patients. Significant differences in myocardial and liver mean T(2) (*), CR/MS, and LV/MS T(2) (*) values between patients and normal subjects were found (P < 0.0005). Differences in paraspinous muscle mean T(2) (*) values between patients and normal subjects were not significant. Myocardial T(2) (*) and CR/MS T(2) (*) values were not correlated with SFC levels. Liver T(2) (*) and LV/MS T(2) (*) values were significantly correlated with SFC (r = 0.540, P < 0.0005). Myocardial T(2) (*) and CR/MS T(2) (*) values were not correlated with either liver T(2) (*) or LV/MS T(2) (*) values, respectively. We conclude that myocardial and liver iron deposition can be evaluated using the fast non-ECG-gated T(2) (*)qMRI technique.

Bone marrow changes in beta-thalassemia major: quantitative MR imaging findings and correlation with iron stores

The purpose of this study is to describe the MR imaging features of bone marrow in beta-thalassemia major and investigate their relation to ferritin, liver and spleen siderosis. Spinal bone marrow was prospectively assessed on abdominal MR studies of 40 transfused beta-thalassemic patients and 15 controls using T1-w, Pd, T2*-w Gradient Echo (GRE) and T1-w turbo Spin Echo (TSE) sequences. Signal intensity (SI) ratios of liver, spleen and bone marrow to paraspinous muscles (L/M, S/M, B/M respectively) and the respective T2 relaxation rates (1/T2) were calculated. Serum ferritin levels were recorded. Bone marrow hypointensity in at least T2*-w GRE sequence was noted in 29/40 (72.5%) patients. Eleven/40 patients exhibited normal B/M on all MR sequences. Five/40 patients had normal B/M and low L/M. B/M correlated with L/M in T1-w TSE sequence only (r = 0.471, p = 0.05). B/M correlated with S/M and mean ferritin values in all sequences (r > 0.489, p < 0.01 and r > - 0.496, p < 0.03 respectively). Marrow 1/T2 did not correlate with ferritin values or liver and spleen 1/T2. B/M in transfused beta-thalassemic patients is related to splenic siderosis and ferritin levels. Although marrow is usually hypointense, it may occasionally display normal SI coexisting with liver hypointensity, a pattern typical of primary hemochromatosis.

Computed tomography in nonalcoholic fatty liver disease: a useful tool for hepatosteatosis assessment?

The value and/or limitations of computed tomography (CT) in assessment of hepatosteatosis are not well studied in nonalcoholic fatty liver disease (NAFLD). We prospectively evaluated the accuracy of CT in assessing the amount of hepatosteatosis in NAFLD patients and the impact of demographic and histopathologic variables on CT images. Forty patients with biopsy-proven NAFLD were eligible. Of these, 10 exhibited hepatic iron overload. Liver and spleen attenuation measurements were obtained and spleen-minus-liver attenuation difference (DeltaS-LA) was calculated. A good correlation between DeltaS-LA and pathological hepatosteatosis was observed (r = 0.837, P < 0.0001). Liver iron overload did not affect this correlation, although the mean DeltaS-LA was significantly lower in patients with iron overload. No correlation was detected between DeltaS-LA and hepatic inflammation, fibrosis, or body mass index. We conclude that DeltaS-LA derived from CT may be a useful tool for predicting the amount of hepatosteatosis in NAFLD patients as it is not affected by various individual factors.

Non-invasive assessment of hepatic iron stores by MRI

BACKGROUND

MRI has been proposed for non-invasive detection and quantification of liver iron content, but has not been validated as a reproducible and sensitive method, especially in patients with mild iron overload. We aimed to assess the accuracy of a simple, rapid, and easy to implement MRI procedure to detect and quantify hepatic iron stores.

METHODS

Of 191 patients recruited, 17 were excluded and 174 studied, 139 in a study group and 35 in a validation group. All patients underwent both percutaneous liver biopsy with biochemical assessment of hepatic iron concentration (B-HIC) and MRI of the liver with various gradient-recalled-echo (GRE) sequences obtained with a 1.5 T magnet. Correlation between liver to muscle (L/M) signal intensity ratio and liver iron concentration was calculated. An algorithm to calculate magnetic resonance hepatic iron concentration (MR-HIC) was developed with data from the study group and then applied to the validation group.

FINDINGS

A highly T2-weighted GRE sequence was most sensitive, with 89% sensitivity and 80% specificity in the validation group, with an L/M ratio below 0.88. This threshold allowed us to detect all clinically relevant liver iron overload greater than 60 micromol/g (normal value <36 micromol/g). With other sequences, an L/M ratio less than 1 was highly specific (>87%) for raised hepatic iron concentration. With respect to B-HIC range analysed (3-375 micromol/g), mean difference and 95% CI between B-HIC and MR-HIC were quite similar for study and validation groups (0.8 micromol/g [-6.3 to 7.9] and -2.1 micromol/g [-12.9 to 8.9], respectively).

INTERPRETATION

MRI is a rapid, non-invasive, and cost effective technique that could limit use of liver biopsy to assess liver iron content. Our MR-HIC algorithm is designed to be used on various magnetic resonance machines.

Review article: haemochromatosis

Hereditary haemochromatosis is the prototype disease for primary iron overload. The disorder is very common, especially amongst subjects of Northern European extraction. It is characterized by an autosomal recessive mode of inheritance, and most cases are homozygous for the C282Y mutation in the HFE gene. Haemochromatosis is now recognized to be a complex genetic disease with probable significant environmental and genetic modifying factors. The early diagnosis of individuals at risk for the development of haemochromatosis is important, because survival and morbidity are improved if phlebotomy therapy is instituted before the development of cirrhosis. The cost-effectiveness and utility of large-scale screening for haemochromatosis have been questioned given that many individuals with the homozygous C282Y mutation do not have iron overload or end-organ damage. However, the use of phenotypic tests, such as serum transferrin-iron saturation, for initial screening avoids the problem of the identification of non-expressing homozygotes. Liver biopsy remains important in management to determine the presence or absence of cirrhosis, particularly amongst patients with serum ferritin levels greater than 1000 ng/mL or elevated liver enzymes. Those with non-HFE haemochromatosis who cannot be identified on genotypic testing should have a liver biopsy to establish diagnosis. Patients with end-stage liver disease may develop liver failure or primary liver cancer, and liver transplantation may be required. Liver transplantation for haemochromatosis is associated with a poorer outcome compared with other indications because of infections and cardiac complications.

Diffuse liver disease

During the last decade, the role of the radiologist in evaluating patients with diffuse liver disease has increasingly expanded. In many cases, the management choices for the hepatologist in the imaging work-up of a patient with suspicion of a diffuse liver disease have significantly widened. In some instances, imaging may point directly to the diagnosis; in many instances, imaging helps narrow the differential diagnosis or is crucial in the follow-up of patients. Although some rare entities still have nonspecific radiologic features, the imaging pattern, in combination with appropriate clinical information, may provide the most likely diagnosis.

The effect of haemosiderosis and blood transfusions on the T2 relaxation time and 1/T2 relaxation rate of liver tissue

Patients with chronic anaemia need repeated blood transfusions, which eventually lead to iron overload. The excess iron from blood transfusions is deposited in the reticuloendothelial system and in the parenchymal cells of the liver, spleen and other organs. Cellular damage is likely to occur when iron overload in the liver is pronounced. Liver biopsy is still necessary to evaluate the degree of haemosiderosis or haemochromatosis. To avoid this invasive procedure, methods have been sought to determine the concentration of iron in liver tissue and to estimate the effect of the treatment of haemosiderosis or haemochromatosis. In this MRI study, the T2 relaxation time and the 1/T2 relaxation rate of liver were determined in 23 patients who had undergone repeated blood transfusions for chronic anaemia. The first 60 transfusions had the greatest influence on the measured T2 relaxation time, with T2 relaxation time decreasing as haemosiderosis progresses. The 1/T2 relaxation rate increases significantly in a linear fashion when the number of blood transfusions increases up to 60. After 60 transfusions the influence of additional blood transfusions on the T2 value was minimal; the same response, although in reverse, was seen in the 1/T2 relaxation rate curve. One possible explanation for this may be that the MR system could detect the effect of only a limited amount of iron excess and any concentration over this limit gives a very short T2 relaxation time and a very weak signal from the liver, which is overwhelmed by background noise. However, in mild and moderate haemosiderosis caused by blood transfusions, T2 relaxation time and 1/T2 relaxation rate reflect iron accumulation in liver tissue.

Noninvasive methods for quantitative assessment of transfusional iron overload in sickle cell disease

Because optimal management of iron chelation therapy in patients with sickle cell disease and transfusional iron overload requires accurate determination of the magnitude of iron excess, a variety of techniques for evaluating iron overload are under development, including measurement of serum ferritin iron levels, x-ray fluorescence of iron, magnetic resonance imaging, computed tomography, and measurement of magnetic susceptibility. The most promising methods for noninvasive assessment of body iron stores in patients with sickle cell anemia and transfusional iron overload are based on measurement of hepatic magnetic susceptibility, either using superconducting quantum interference device (SQUID) susceptometry or, potentially, magnetic resonance susceptometry.

Transfusional hemochromatosis: quantitative relation of MR imaging pituitary signal intensity reduction to hypogonadotropic hypogonadism

PURPOSE

To assess the relationship between magnetic resonance (MR) imaging pituitary signal intensity reduction in patients with transfusional hemochromatosis and the clinical manifestation of hypogonadotropic hypogonadism.

MATERIALS AND METHODS

Pituitary MR imaging at 0.5 T was performed in 38 consecutive patients affected by secondary hemochromatosis and in 20 healthy volunteers. Serum ferritin levels were estimated in the affected population. Twenty (53%) of the 38 patients had hypogonadotropic hypogonadism diagnosed. Pituitary-to-fat signal intensity ratios were calculated from coronal gradient-echo (GRE) T2*-weighted MR images. The relationship between the quantitative reduction of the pituitary-to-fat signal intensity ratio and the clinical manifestation of pituitary dysfunction was assessed in the affected population. Signal intensity reduction in the anterior lobe of the pituitary gland was also correlated with the serum ferritin level.

RESULTS

The degree of reduction of the pituitary-to-fat signal intensity ratio correlated with the presence of hypogonadotropic hypogonadism, with a sensitivity of 90%, a specificity of 89%, and an overall accuracy of 89%. In addition, the reduction of pituitary signal intensity was greater in patients with higher ferritin levels (r = -0.55, r(2) = -0.30, P <.001).

CONCLUSION

The degree of signal intensity reduction, measured as the pituitary-to-fat signal intensity ratio for GRE T2*-weighted images, in patients with secondary hemochromatosis correlates with the severity of pituitary dysfunction.

Magnetic resonance iron-free nodules in genetic hemochromatosis

OBJECTIVE

In hemochromatosis, areas of normal hepatic magnetic resonance (MR) signal intensity indicate the presence of iron-free-nodules, which are strongly suspected of being neoplastic. The goal of the study was to define the prevalence and the nature of these iron-free MR nodules at the time of diagnosis in 116 patients included in a prospective study assessing the accuracy of MR imaging (MRI) in the quantification of liver iron overload.

METHODS

Seventy-nine of the 116 patients had homozygous hemochromatosis on a phenotypic basis. Fifteen-millimeter-thick contiguous slices were performed using T1- and T2-weighted gradient echo sequences with a 0.5 Tesla magnet.

RESULTS

Six of 79 homozygous hemochromatotic patients had one or more MR iron-free nodules. Five of the six patients proved to have malignant tumors. Four of six iron-free nodules were hepatocellular carcinoma (5% in the hemochromatosis group and 17.5% in hemochromatotic patients with severe fibrosis).

CONCLUSIONS

The present data confirm the high prevalence of liver cancer at the time of diagnosis, mainly in cirrhotic patients greater than 45 years of age, and indicate that, when performing MRI for liver iron quantification, a complete hepatic MRI examination is preferable to a simple signal measurement in patients at risk for hepatocellular carcinoma.

Dual-energy CT in the diagnosis and quantification of fatty liver: limited clinical value in comparison to ultrasound scan and single-energy CT, with special reference to iron overload

BACKGROUND/AIMS

It has been suggested that dual-energy CT could differentiate irregular fatty liver from other hypodense lesions. We compared dual-energy CT to ultrasound scan and single-energy CT in the diagnosis and quantification of fatty liver, with special reference to iron overload.

METHODS

Twenty-seven patients were included according to ultrasound: fatty liver (n=16) and normal liver (n=11). Single and dual-energy CT were performed. Attenuation measurements of hepatic lobes and control tissues were taken at 140 kV and 80 kV CT-guided liver biopsy was done in fatty liver patients, the degree of infiltration was estimated, and the histologic iron overload determined (iron overload, n=11; iron-free, n=5).

RESULTS

The mean changes in attenuation for the right hepatic lobe were: normal liver: -0.8 (ns); iron overloaded fatty liver: 1.5 (ns); and iron-free fatty liver: 7.7 (p<0.0053). A spleen-liver attenuation differential threshold of 12H (140 kV, single-energy CT) and a right hepatic lobe 140 kV to 80 kV attenuation differential threshold of 9 H (dual-energy CT) were specific for fatty liver. Histology confirmed all cases of fatty liver diagnosed by ultrasound, independently of iron overload. Ultrasound did not differentiate cases of irregular from diffuse fatty liver detected on CT. Iron overload produced a masking effect in CT, decreasing its sensitivity: fatty liver was diagnosed in 67% of cases by single-energy CT and in 20% by dual-energy CT. Degree of fatty infiltration correlated with single-energy CT.

CONCLUSIONS

Ultrasound diagnosed fatty liver best. Single-energy CT quantifies fatty infiltration, and best differentiates the irregular from the diffuse forms. Dual-energy CT is limited by poor sensitivity, especially in iron overload.

Review article: the screening, diagnosis and optimal management of haemochromatosis

Haemochromatosis was first recognized as a disease entity over a century ago and its hereditary nature recognized over 60 years ago. However it was only in late 1996 that the haemochromatosis gene was cloned and a single C282Y mutation confirmed as being the cause of all HLA-linked iron overload in Caucasian populations. Haemochromatosis is common, occurring in approximately 1 in 300 people in Caucasian populations, and untreated can cause serious morbidity and early death. However, the disease remains much underdiagnosed for reasons such as lack of awareness of the disease, the presence of normal liver function tests and the lack or non-specific nature of symptoms. A commercially available DNA-based test for the haemochromatosis gene is likely to be available in the near future but its place in the diagnosis and management of the disorder is not yet clear. Assessment of body iron stores by measurement of serum ferritin and transferrin saturation, hepatic iron stores and hepatic architecture by liver biopsy will remain important in the future. The haemochromatosis mutation itself has as yet no known influence on morbidity other than via iron loading and organ failure, in particular, hepatic cirrhosis. Thus, diagnosing patients before the development of hepatic cirrhosis is crucial because iron depletion by venesection treatment before the development of cirrhosis results in a normal life expectancy.

In situ measurement of iron overload in liver tissue by dual-energy methods

The errors for determining liver iron content by dual-energy computed tomography (dual-energy CT) are calculated for the ideal case where only monochromatic x-ray beams are used. Because of the strong influence of spatial resolution on the radiation dose needed to reduce the error to a given level, we have also calculated the error in dual-energy transmission measurements alone, where the spatial information along the beam path is lost. The prediction of error was tested by simulations and measurements using x-rays emitted by radioactive isotopes and synchrotron radiation. Good agreement between calculation, simulation and measurement was found. It is shown that concentrations of liver iron content (disregarding variation of tissue composition) can be studied with a skin dose of about 30 mGy using dual-energy CT and even with much lower dose using dual-energy transmission measurements. However, there are sources of error besides photon noise, especially errors caused by variation of tissue composition. For example dual-energy CT, although suggested to avoid artifacts caused by fat in the case of a fatty liver, still is affected by fat. The magnitude of these errors is discussed qualitatively, and possibilities for their reduction are suggested. For a definitive estimate of errors of iron content measurements with optimized apparatus more experimental data for well defined variations of body tissue, especially in the case of haemochromatosis, are needed.

Practice guideline development task force of the College of American Pathologists. Hereditary hemochromatosis

Hereditary hemochromatosis is an autosomal recessive disorder, the gene for which occurs in approximately 10% of Americans, most of whom are unaffected heterozygotes. Approximately 5/1000 white Americans are homozygous and at risk of developing severe and potentially lethal hemochromatosis. The disorder affects numerous organ systems, but the most common symptoms are fatigue, palpitations, joint pains, and impotence; the most common signs are those that relate to hypothalamic, cardiac, hepatic or pancreatic dysfunction, including poor cold tolerance, impotence in males, amenorrhea in females, cardiac arrhythmias, dyspnea, edema, hepatosplenomegaly, spider telangiectases, ascites, deformity, swelling or limitation of motion of joints, weight loss, hyperpigmentation. Characteristic abnormalities of laboratory tests include elevated serum iron concentration, high transferrin saturation, elevated serum ferritin concentration, elevated serum transaminases, hyperglycemia and low values for thyroid-stimulating hormone (TSH) and gonadotropins. Death may be the result of cardiac arrhythmia, congestive heart failure, liver failure or liver cancer. Since many of these complications cannot be reversed once they have developed, early diagnosis and treatment are essential. In view of the high prevalence in the American population (prevalence varies with ethnic background), the low cost of diagnosis and treatment, the efficacy of treatment if begun early, and, on the other hand, high costs and low success rate of late diagnosis and treatment, systematic screening for hemochromatosis is warranted for all persons over the age of 20 years. The initial screening should be by measurement of serum iron concentration and transferrin saturation. The practice guideline provides a diagnostic algorithm for cases in which the serum transferrin saturation is 60% or greater. It also provides guidelines for clinical management.

Liver iron stores in patients with secondary haemosiderosis under iron chelation therapy with deferoxamine or deferiprone

Total body iron stores including liver and spleen iron were assessed by non-invasive SQUID biomagnetometry. The liver iron concentration was measured in groups of patients with beta-thalassaemia major or other posttransfusional siderosis under treatment with the oral iron chelator deferiprone (n = 19) and/or with parenteral deferoxamine (n = 33). An interquartile range for liver iron concentrations of 1680-4470 micrograms/g liver was found in these patients. In both groups a poor correlation between liver iron and serum ferritin values was observed. Repeated measurements of liver and spleen iron concentrations as well as determination of liver and spleen volume by sonography were performed in six patients under continuous deferiprone treatment for 3-15 months. In this group detailed information was obtained on the whole body iron store (5-36g) and the iron excretion rates (14-34 mg/d) for each patient. As indicated by decreasing liver iron concentrations, five out of six subjects showed a negative iron balance (2-13 mg/d). Conventional measurements of both serum ferritin and urine iron excretion gave fluctuating results, thus being only of limited use in the control of iron depletion therapy. The non-invasive biomagnetic liver iron quantification is a precise and clinically verified technique which offers more direct information on the long-term efficacy of an iron depletion therapy than the hitherto used methods. This technique may be of use in the clinical evaluation of new oral iron chelators.

CT and MRI of diffuse liver disease

CT and MRI contribute important information to the clinical evaluation of diffuse liver disease. In some cases, these modalities can establish a diagnosis that was not ascertained histologically, which is often the case when sampling errors prevent a definitive tissue diagnosis. Characteristic alterations of liver attenuation on CT, signal changes on MRI, and morphological changes appreciated with both modalities can be used to diagnose fatty infiltration, some parenchymal deposition diseases, and cirrhosis. Furthermore, hepatocellular disease can be confirmed in the setting of indeterminate clinical and laboratory findings. Significant overlap in the imaging findings of this wide range of disorders continues to limit specificity; however, at a minimum, these techniques provide a rapid means to a noninvasive evaluation that often guides clinical decisions. Faster scanning techniques available with CT and MRI may provide additional information by assessing contrast dynamics. This review of CT and MRI in diffuse liver disease considers the diagnostic utility and clinical implications of these modalities. Pathological findings relevant to imaging considerations are discussed.

Assessment of liver iron overload by T2-quantitative magnetic resonance imaging: correlation of T2-QMRI measurements with serum ferritin concentration and histologic grading of siderosis

PURPOSE

To correlate hepatic 1/T2 values obtained by means of a T2-Quantitative MRI (T2-QMRI) technique with three widely applied methods for the evaluation of hemosiderosis, i.e., (a) liver iron concentrations (LFeC) (b) serum ferritin (SF), and (c) histologic grading of siderosis. The impact of coexisting hepatitis was also considered. T2-QMRI measurements were compared with signal intensity (SI) ratio measurements on conventional SE images.

MATERIALS AND METHODS

Liver T2 relaxation times were calculated in 40 thalassemic patients, on a 0.5 T magnetic resonance imaging system using a multiple spin-echo sequence with parameters: TR = 2500 ms, TE = 12 ms in 20 symmetrically repeatable echoes.

RESULTS

(a) 1/T2 values were well correlated (r = 0.97) with liver iron concentrations, which ranged from 2.32 to 18.0 mg/g dry weight (normal < 1.6 mg/g). (b) 1/T2 values were also correlated with serum ferritin levels (r = 0.84). At various 1/T2 values, serum ferritin levels were higher for the anti-HCV(+) patients than the anti-HCV(-) ones. (c) T2 values corresponding to successive grades of siderosis presented statistically significant differences. (d) SI ratio measurement assigned less statistically significant results, as compared to T2 values.

CONCLUSION

T2-QMRI measurement of T2 relaxation time is more accurate than SI ratios in evaluating liver iron overload. It is particularly useful for hemosiderotic patients with coexisting hepatitis since, in this case, serum ferritin is not considered a reliable index of hemosiderosis.

Clinical manifestations and therapy of transfusional haemosiderosis

Long-term blood transfusions lead to the accumulation of iron that in the absence of chelation therapy causes complications such as liver cirrhosis, growth failure, hypogonadism, hypothyroidism, hypoparathyroidism, diabetes and myocardiopathy. The last still represents the most frequent cause of death in haemosiderotic transfusion-dependent patients. At the moment the only chelator widely used is desferrioxamine (DFX). The drug works best when administered as a continuous infusion, mainly by the subcutaneous route. To patients with severe iron overload, impending organ failure, or poor compliance to chelation, DFX can be administered intravenously, through an externalized central catheter or, preferably, a subcutaneous port. Several studies have shown the effectiveness of DFX in reducing the iron burden, thus preventing the complications, once considered inevitable, of iron overload, and even in reverting some, but not all, of the iron-induced dysfunctions. Practical and psychological support are necessary to ensure satisfactory compliance with a therapy that is cumbersome and difficult. Toxic effects of DFX such as growth failure, hearing impairment and bone abnormalities seem to occur mainly in patients who have received high doses of DFX despite a low iron burden. Visual loss and renal and pulmonary toxicities, on the contrary, seem to be more directly related to high DFX peak doses administered irrespective of the patient's amount of iron overload. After bone marrow transplantation, phlebotomy or erythrocytoapheresis might be necessary to reduce further the iron accumulated during years of transfusions.

Iron overload cardiomyopathies: new insights into an old disease

Iron overload cardiomyopathy is an old disease that has evolved from a rare undiagnosable and untreatable condition to a now much more common, diagnosable, and potentially treatable condition. Pathologically it is due to a direct free iron effect on the myocytes, and not due to interstitial infiltration. This also implies that the disease process is reversible if the tissue iron concentration can be controlled. The advent of magnetic resonance imaging and future genetic identification can identify the population at risk. Chelation therapy, including newer forms of oral chelators, likely will be more commonly available to benefit an ever increasing number and spectrum of the population. Further active research will be needed to improve our pathophysiological understanding and clinical treatment of this increasingly common condition.

Liver iron quantification: studies in aqueous iron solutions, iron overloaded rats, and patients with hereditary hemochromatosis

For the noninvasive liver iron quantification by MRI in human iron overload diseases, fundamental proton relaxation mechanisms were studied in aqueous solutions with ferritin and other iron compounds, in experimentally iron overloaded rats, and in patients with iron overload diseases. MR-relaxation rates as a function of iron concentrations in the range of 0-7.5 mg Fe/g aqueous iron solutions, 0-5.4 mg Fe/g rat liver in vivo, and 0.16-4.9 mg Fe/g human liver in vivo were determined from multi- and sets of single-spin echo sequences (1.5 T imager). As predicted by theory, transverse relaxation rates (1/T2) in aqueous iron solutions, in liver tissue of rats, and in human liver tissue increased linearly with the iron concentration. A preliminary calibration for the liver iron quantification by MRI was performed from in vivo measurements of liver 1/T2-relaxation rates and liver iron quantification by atomic absorption spectroscopy in biopsies from 13 patients. With the single spin-echo method, precise in vivo liver iron quantification in humans also above 2.0 mg Fe/g liver tissue (T2 < 15 ms) should be accomplished on any imager with shortest spin-echo time available, at least TE < 20 ms.

Etiologies, consequences, and treatment of iron overload

From a global perspective, severe systemic iron overload occurs predominantly in individuals affected by geographically specific genetic mutations that permit the daily absorption from the diet of more iron than is physiologically needed. Two main types of hereditary iron overload are well recognized: (1) HLA-linked hemochromatosis in populations derived from Europe and (2) iron overload complicating thalassaemia major and intermedia syndromes in Southeast Asia, the Middle East, and the Mediterranean. Another very common form of iron overload occurs in Africa and is clearly related to high dietary iron content; recent evidence suggests that a genetic predisposition may also contribute to the pathogenesis. Patients with iron overload may develop multiorgan system toxicity; aggressive therapy with phlebotomy or iron chelation to remove excess iron from the body prevents organ damage and prolongs life.

Differentiation between heterozygotes and homozygotes in genetic hemochromatosis by means of a histological hepatic iron index: a study of 192 cases

The biochemical hepatic iron index, defined as the ratio of hepatic iron concentration (expressed as micromoles per gram dry weight) to age permits accurate prediction of genetic status in patients with genetic hemochromatosis. However, the hepatic iron concentration is not always available. Therefore a histological hepatic iron index, defined as the ratio of total histological iron score (range = 0 to 60) to age, was evaluated in a total of 192 Australian and French patients with genetic hemochromatosis. These subjects had been classified previously as heterozygotes (n = 18) or homozygotes (n = 174) according to clinical and familial data only. Biochemical hepatic iron index and histological hepatic iron index were well correlated (Spearman's test: rho = 0.75, p < 0.0001). Both were significantly (p < 0.0001) increased in homozygotes (respectively, 6.7 +/- 3.8 [range = 1.2 to 22.6] and 0.62 +/- 0.28 [range = 0.14 to 1.5]) compared with heterozygotes (respectively, 1 +/- 0.4 [range = 0.45 to 1.6] and 0.08 +/- 0.05 [range = 0 to 0.14]). The histological hepatic iron index was less than 0.15 in all heterozygotes and greater than 0.15 in all but two homozygotes. These data show that the age-dependent nature of iron accumulation can also be accommodated by calculating the histological hepatic iron index and that histological study is an accurate means of predicting the genetic status of hemochromatosis patients when hepatic iron concentration is not available.

MR imaging of hepatic iron overload in rat

To investigate the relationship of hepatic signal intensity and T2 with histologic grading in an animal model of oral iron overload and to determine the duration of feeding necessary to produce abnormalities detectable on magnetic resonance (MR) images, hepatic iron overload was induced in 12 rats by feeding them a diet supplemented with 4% carbonyl iron for 2-11 weeks. Iron overload seen on MR images was graded independently and blindly by two radiologists as normal, mild, moderate, or severe. The rats were killed, and histologic findings were graded blindly by four pathologists using a similar subjective scale. Hepatic T2 values were estimated from spin-echo images. In the rats with iron overload, intracellular iron deposition was noted on histologic studies. On MR images, hepatic signal intensity and T2 decreased after only 2 weeks of dietary iron overload, and both continued to decrease with longer duration of feeding. There was significant correlation between iron overload duration and changes on MR images and between MR images and histologic grading (r = .92, P = .0001 for both). The mean T2 of hepatic iron overload decreased with longer duration of feeding.

Magnetic resonance imaging and assessment of liver iron content in genetic hemochromatosis

Computed tomography (CT) scanning is not highly sensitive in the assessment of liver iron content and magnetic resonance imaging (MRI) appears to be more efficient. The aim of this study was to determine the effectiveness of MRI in the evaluation of liver iron content using a standard spin-echo technique. The study included 23 patients with genetic hemochromatosis and 24 non-iron-overloaded patients as controls. A comparison was made of: (a) MRI signal intensity of liver, spleen, paravertebral muscles and subcutaneous adipose tissue using two different spin-echo sequences (SE 500/28; SE 2000/28,56); (b) liver attenuation determined by a single energy CT scan; and (c) a biochemical determination of hepatic iron. There was a significant decrease in liver signal intensity in the genetic hemochromatosis group (256 +/- 201, mean +/- S.D.) compared with the control group (801 +/- 413, p less than 0.001), but there was no correlation with liver iron concentration. However, such a correlation was found and was even more highly significant than in CT when the ratio between the liver and another organ was taken into account. For a lower limit of liver/spleen ratio calculated at 0.46 (mean 2 S.D. in the control group), the specificity (0.96) of MRI was satisfactory, but the sensitivity (0.78) remained insufficient (MRI being unable to detect an iron overload of up to 125 mumol/g). Hopefully, these results might be improved in the near future by using more sensitive sequences such as gradient echo sequences.

Usefulness and limitations of laboratory and hepatic imaging studies in iron-storage disease

Liver biopsy with measurement of hepatic iron concentration is the most certain procedure for evaluation of iron-storage disease, although use of computed tomography and magnetic resonance imaging procedures recently have been proposed as alternative, noninvasive methods for estimating the degree of iron overload. The results of these imaging procedures were compared with those of other noninvasive techniques and liver biopsies in 48 patients. Final diagnoses, based on synthesis of clinical and laboratory data, included (a) primary hemochromatosis (n = 25; 19 homozygous, 6 heterozygous); (b) secondary hemochromatosis (n = 7); (c) alcoholic liver disease (n = 11); (d) chronic active hepatitis (n = 3); and (e) other (n = 2). Serum ferritin and computed tomography or magnetic resonance scanning had 100% sensitivity in detecting hepatic iron overload more than fivefold above the upper limit of normal (greater than 10.7 mumol Fe/100 mg dry liver) but did not detect lesser degrees of iron overload reliably, including those found in 6 of 13 patients with untreated homozygous primary hemochromatosis and 3 of 7 with secondary hemochromatosis. Computed tomography and magnetic resonance imaging were more specific than ferritin (64% and 92% vs. 21%) in the detection of iron excess, more than five times the upper limit of normal. Among magnetic resonance imaging measures, the ratio of the second echo signal intensities of liver to paraspinous muscle was the most sensitive and most specific for detection of this degree of iron overload. The degree of correlation between hepatic iron concentration and results of noninvasive laboratory or imaging studies were insufficient to permit prediction of hepatic iron content by noninvasive studies alone. It is concluded that computed tomography or magnetic resonance scanning as currently usually used is not cost-effective in routine evaluation of iron overload, although these imaging procedures may play a role in patients in whom liver biopsy is contraindicated. Because of their low cost and ready availability, serum ferritin and transferrin saturation tests remain the preferred screening studies for iron overload. Liver biopsy with quantitative iron measurement remains the study of choice for the definitive diagnosis of hemochromatosis.