Introduction
The liver is the primary organ of deposition, and hepatomegaly (an enlarged liver) occurs as the first sign of disease. The overload of iron and its accumulation in hepatic cells and Kupffer cells is seen in hemochromatosis (a disorder characterized by excessive iron deposition leading to multiple organ failure) and hemosiderosis (excessive deposition of hemosiderin (iron) in the tissues, respectively. With the advent of new imaging techniques for liver diseases, there has been an increase in early and accurate diagnosis.
Ultrasound is an easy and simple imaging technique for diagnosing liver diseases. It is used as a complementary method along with more advanced techniques. In recent times, elastography has been adopted for measuring the stiffness and elasticity of the liver. Ultrasonography elastography makes it one of the most valuable techniques for diagnosing liver diseases because of its non-invasiveness, non-inferior diagnostic capability, and relative cost-effectiveness.
What Are the Imaging Modalities for Diagnosing and Managing Liver Disease?
The primary imaging techniques for diagnosing liver disease include:
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Liver ultrasonography.
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Computed tomography (CT).
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Magnetic resonance imaging (MRI).
Postcontrast imaging helps to distinguish diseases depending on the degree of composition and vascularity. Postcontrast hepatic imaging can be divided into three distinct phases:
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Arterial phase.
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Portal venous phase.
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Delayed venous phase.
Ultrasound is a method of choice as a screening technique. In most hepatic imaging, contrast-enhanced multidetector CT (MDCT) is a modality of choice. MRI shows a better characterization of the lesions with equivocal features on ultrasound and computed tomography.
How Is Ultrasound Used for Diagnosing and Managing Liver Disease?
Ultrasonography is generally the first imaging technique for evaluating and screening for focal and diffuse liver diseases. The advantages of ultrasound include:
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It is readily available.
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It has a low cost.
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It is non-invasive.
On ultrasound, the liver pathologies are seen with different patterns, such as generalized hypoechogenicity in the case of acute hepatitis and diffuse malignant lesions. Generalized hyperechogenicity is seen in diffuse hepatic steatosis and anechoic or hyperechoic lesions, as many benign (non-cancerous) and malignant (cancerous) lesions. The following are some of the benign hyperechoic (increase in density of sound waves compared to surrounding structures in an ultrasound) lesions:
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Hemangioma (noncancerous growths of blood vessels).
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Hepatic adenoma (benign liver lesions associated with anabolic steroids and the oral contraceptive pill).
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Focal nodular hyperplasia (a benign lesion or tumor formed in the liver).
Malignant hyperechoic lesions include:
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Renal cell carcinoma (cancer involving the kidney cells).
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Melanoma (cancer of the melanocytes or cells that are responsible for the color of the skin).
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Cholangiocarcinoma (cancer of the bile ducts).
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HCC or hepatocellular carcinoma (liver cancer).
Ultrasonography is used in combination with other techniques and tools and plays an essential role in diagnosing and treating different liver diseases like:
Ultrasound with color Doppler can provide information about the liver vasculature, such as the flow and direction of the portal vein. The portal vein blood normally flows away from the liver hepatomegaly flow. Therefore, retrograde flow from the periphery to the central area is suggestive of liver cirrhosis with portal hypertension. Doppler ultrasound can evaluate the patency of the portal vein prior to transplant as well as hepatic artery thrombosis after the transplant.
A percutaneous liver biopsy can be performed under the guidance of ultrasound or CT. Ultrasound is the technique of choice for both focal, targeted biopsy and non-focal liver biopsy in cases with a good target window. A CT-guided biopsy is majorly reserved for lesions not clearly visible on ultrasound.
The indications for focal liver biopsies include:
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Unknown focal liver lesions.
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Presence of metastasis in the liver without a specific source.
The indications for non-focal liver biopsy include:
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Primary biliary cirrhosis.
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Staging of parenchymal diseases like cirrhosis.
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Non-alcoholic fatty liver disease.
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Assessment of hepatic storage disease.
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Determining the presence of rejection after liver transplant.
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Presence of abnormal liver function tests without any specific etiology.
How Is Computed Tomography Used for Diagnosing and Managing Liver Disease?
Computed tomography imaging of the liver is performed with the following different protocols:
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Unenhanced, single-phase.
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Dual-phase.
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Triphasic contrast-enhanced protocols.
All the above liver CT protocols are essential in evaluating various liver pathologies. The single-phase contrast-enhanced CT is generally the modality of choice; the liver has the maximum enhancement in the portal venous phase in CT, typically 70 seconds after intravenous contrast injection.
It primarily provides information about diffuse liver diseases, like hypovascular metastatic liver disease and liver cirrhosis. The primary imaging technique in the portal venous and late arterial phases is the dual-phase contrast-enhanced CT. It is obtained 35 seconds (approximately) after intravenous injection and provides better information about hypervascular lesions.
How Is Magnetic Resonance Imaging Used for Diagnosing and Managing Liver Disease?
Magnetic resonance imaging (MRI) has advantages and disadvantages compared to ultrasound and computed tomography. MRI is considered the best imaging technique for liver diseases because of the following reasons:
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Higher cross-sectional resolution.
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Lack of ionizing radiation.
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Characterization of focal liver lesions.
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Presence of extracellular and hepatocyte-specific contrast agents.
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It provides better and more accurate information about the diffuse liver lesion.
The disadvantages include:
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More expensive.
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It takes longer to acquire images.
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It requires patient cooperation, like breath-holding.
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It has better and fewer motion artifacts.
What Are the Other Imaging Techniques for Diagnosing and Managing Liver Disease?
Another imaging technique for assessing liver diseases, like the presence and degree of hepatic steatosis, is gradient recalled echo (GRE) MRI. However, the gold standard method for evaluating the presence of early fibrotic and inflammatory changes is liver biopsy. Further, a newer technique called magnetic resonance elastography was introduced, which was originally known as ultrasound elastography. It helps to measure liver stiffness and the degree of fibrosis. Its sensitivity and specificity are better compared to ultrasound elastography, which has limited use in obese patients and patients with ascites.
Conclusion
Liver Imaging Reporting and Data System (LI-RADS) is a standardized system for reporting and classifying liver lesions at an increased risk of developing into hepatocellular carcinoma (HCC). LIRAD helps in the categorization of lesions into probably benign, definitely benign, probably, or definitely malignant. It guides clinicians, radiologists, and surgeons for surveillance guidelines and recommendations if a biopsy is necessary.
Before initiating any treatment, the first step to evaluate liver pathology is dependent on the patient's clinical situation, availability of different imaging techniques, and technician and physician familiarity with the test. Ultrasound and computed tomography scans are the first choices of imaging modality to assess diffuse and focal liver lesions. Further treatment and imaging are performed based on the finding of ultrasound and CT scans.
