Elsevier

Digestive and Liver Disease

Volume 39, Issue 11, November 2007, Pages 1018-1023
Digestive and Liver Disease

Liver, Pancreas and Biliary Tract
Usefulness of chemical-shift MRI in discriminating increased liver echogenicity in glycogenosis

https://doi.org/10.1016/j.dld.2007.06.008Get rights and content

Abstract

Background

Glycogen storage diseases are inherited defects which cause accumulation of glycogen in the tissues. Hepatic steatosis is defined as accumulation of fat within hepatocytes. On sonography, liver shows increased echogenicity both in glycogen storage diseases and steatosis. Liver hyperechogenicity in glycogen storage diseases may depend on accumulation of glycogen and/or fat. Chemical-shift magnetic resonance imaging can discriminate tissues only containing water from those containing both fat and water.

Aim

The primary aim of the present study was to evaluate the usefulness of liver chemical-shift magnetic resonance imaging for detecting liver steatosis in patients with metabolic impairment due to glycogen storage diseases.

Subjects

Twelve patients with type I (n = 8) or type III (n = 4) glycogen storage diseases were studied and compared to 12 obese-overweight subjects with known liver steatosis. As control group 12 lean normal voluntary subjects were recruited.

Methods

Liver was evaluated by sonography and chemical-shift magnetic resonance imaging to calculate hepatic fat fraction.

Results

A significant difference in echogenicity between patients with glycogen storage diseases and normal subjects was observed (p < 0.05), while this difference was not present between overweight-obese and glycogen storage diseases patients. On the contrary, fat fraction was similar between glycogen storage diseases patients and normal subjects and different between glycogen storage diseases patients and overweight-obese (p < 0.05).

Conclusion

The present data suggest that chemical-shift magnetic resonance imaging may exclude fat deposition as a cause of liver hyperechogenicity in subjects with glycogen storage diseases.

Introduction

Glycogen storage diseases (GSDs) are inherited defects of glycogen metabolism, which cause accumulation of glycogen, of normal or abnormal quality, in the tissues.

Most of these diseases are inherited as autosomal recessive traits. The overall frequency of all forms of GSDs is approximately 1 in 20,000 live births. More than 12 types are recognized and were categorized in the order in which the enzymatic defects were identified. The most common childhood disorders are type I, II, III and IX. Type IA GSD is caused by a deficiency of glucose-6 phosphatase activity in the liver, kidneys and intestinal mucosa with excessive accumulation of glycogen in these organs. Clinical manifestations of type IA GSDs are growth retardation, hepatomegaly, hypoglycemia, lacticacidemia, hyperuricemia and hyperlipidemia. Type IB GSD is a variant of type IA caused by a defect in the system for transporting glucose-6-phosphate across the microsomal membrane. Type III glycogen storage disease is caused by deficiency of glycogen debranching enzyme activity. Deficiency of glycogen debranching enzyme produces hepatomegaly, hypoglycemia, short stature, variable skeletal myopathy and cardiomyopathy. Histology of the liver is characterized by distention of hepatocytes by glycogen [1].

On sonography (US), most patients with type I and type III GSDs show increased liver echogenicity [2], [3], [4]. On computed tomography (CT), glycogen deposition results in increased density [5].

Fatty liver or steatosis is defined as accumulation of fat within hepatocytes [6]. Hepatic fat can result from a variety of diseases including increased production or mobilization of fatty acids or decreased hepatic clearance of fatty acids due to hepatocellular injury [7]. On US, fatty liver produces a diffuse increased echogenicity with posterior beam attenuation [8], [9]. On CT, fatty change determines a low-density hepatic parenchyma [7]. Chemical-shift magnetic resonance imaging (MRI) (opposed-phase imaging) provides a method to differentiate tissues containing water “only” from those containing both fat and water [6]. Chemical-shift results when nuclei in different chemical environments experience slightly different magnetic fields strengths. Chemical-shift MRI is best suited to suppressing the signal from tissues that contain similar amounts of lipid and water, for example fatty liver; it is not a fat-suppressed sequence, as subcutaneous fat remains hyperintense on opposed-phase images [6], [10], [11].

On US, liver shows increased echogenicity both in GSD and in steatosis. Liver hyperechogenicity in GSDs may depend on the accumulation of either glycogen or fat [2], [4].

The primary aim of the present study was to evaluate the usefulness of liver chemical-shift MRI for detecting liver steatosis in patients with metabolic impairment due to glycogen storage diseases.

Section snippets

Patients and methods

A sample of 36 subjects admitted to the San Paolo Hospital, Milan, Northern Italy, between January 2004 and April 2006 was studied. The local Ethical Committee approved the protocol. A written informed consent was obtained from patients (pts), or their parents, after the details of the protocol had been fully explained.

Twelve pts (8 males, 4 females, aged 10–24 years) consecutively referred to the Department of Paediatrics for type I (n = 8) or type III (n = 4) GSDs were studied. Because no

Results

Table 1 shows some clinical characteristics of the studied subjects.

No focal liver lesions were observed in any patient.

Fat fraction calculated with MRI was significantly associated with liver echogenicity in overweight-obese subjects (Spearman's correlation coefficient, r = 0.881, p < 0.0001) but not in subjects with GSDs (r = 0.510, p = 0.102).

Liver echogenicity among patients with GSDs was classified as follows: grade 0 in five cases, grade 1 in two cases, grade 2 in two cases and grade 3 in the

Discussion

Diagnostic imaging is useful in the detection and quantification of fatty infiltration of the liver. In a study comparing US with histological examinations, US showed a sensitivity of 90%, and a specificity of 82%, with a positive predictive value of 87%, and a negative predictive value of 87% for steatosis [15]. Moreover, when compared with biopsies, US was 100% and 93% sensitive in detecting moderate or severe (>30%) fatty infiltration with positive predictive values of 62% and 76%,

Conflict of interest statement

None declared.

Acknowledgement

The Authors wish to thank Mr Guido Pasini, medical radiation technologist, for his skilled assistance.

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