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Anatomy and embryology of the liver is presented in Chapter 15 . This chapter will continue with pathophysiology of cirrhosis.
Cirrhosis is the final stage of chronic liver disease, which is characterized by diffuse parenchymal necrosis, regeneration and scarring with abnormal tissue reconstruction ( Fig. 16.1 ).
Pathophysiology: Short-term or repetitive liver injury causes hepatocyte death. Collagen producing stellate cells are activated by cytokines, and fibrotic scarring occurs. Nodular regeneration accompanies fibrotic scarring.
Ultrasound (US) should be the first choice imaging tool, because of its low cost, speed, use of safe acoustic waves and patient comfort. US can be used to evaluate general appearance, blood flow changes, anatomic deviations and possible cirrhosis related complications. High frequency probes may be useful to detect micronodularity along the liver surface. In cirrhotic patients, US is critically important to detect the complications of portal hypertension, like ascites and splenomegaly.
Doppler imaging can be used to detect patency and direction of blood flow. Increased pulsatility of the portal vein tracing and loss of the normal triphasic hepatic vein tracing, may be signs of portal hypertension. Lesion vascularity can be assessed using Doppler imaging.
US based shear wave elastography measures the transverse acoustic propagation in a localized tissue. Higher signal propagation speed (shear wave speed, in m/s) may represent more severe fibrosis formation. Shear wave speed can be converted to Young’s modulus (in kPA), which represents tissue stiffness.
Contrast enhanced US (CEUS) uses microbubble based contrast. CEUS is useful to assess lesion vascularity in 3 phases: (1) arterial phase (15–30 seconds after administering contrast), (2) portal phase (30–60 seconds), (3) sinusoidal phase (60–240 seconds).
On unenhanced T1-weighted magnetic resonance imaging (MRI), the cirrhotic liver has low signal intensity. Dual-phase in-phase and out-of-phase gradient images are useful to characterize T1 relaxation features and parenchymal or lesional fat content.
On unenhanced T2-weighted MRI, the cirrhotic liver has high signal intensity. T2-weighted fast spin echo imaging is useful for bile duct, cyst and fluid collection assessment. T2-weighted imaging can also help differentiate regenerative nodules (RN) and dysplastic nodules (DN) types, but is not sensitive enough for hepatocellular carcinoma (HCC) characterization.
In MR elastography, shear waves are generated by a 40 to 120 Hz mechanical inducer ( Fig. 16.2 ). Higher velocity and wavelength represent higher stiffness values.
For cirrhosis evaluation, the important phases of image acquisition are: late arterial (35–40 seconds), portal venous (60–80 seconds) and equilibrium phases (3–5 minutes).
Early arterial phase images (20–25 seconds) can be useful to detect early enhancement of malignant lesions and to characterize lesion type.
Multiphasic computed tomography (CT) or MRI (≥1.5 T) based imaging can diagnose HCC. Biopsy of the lesion is not needed in most cases.
Arterial enhancement, washout, enhancing capsule and venous invasion are critical for HCC detection in cirrhotic cases.
Late arterial phase (35–40 s), portal venous phase (70–80 s) and delayed phase (3–5 min) should be part of a standard multiphase CT or MRI protocol.
Precontrast and dynamic gadolinium enhanced T1-weighted gradient recalled echo, T2-weighted (with and without fat suppression), in-phase and out-phase T1-weighted sequences, and diffusion-weighed imaging should be added to the MRI protocol.
Hepatobiliary and extracellular contrast agents are critical for cirrhosis and lesion characterization. Hepatobiliary contrast agents accumulate in hepatocytes and are excreted in bile. Extracellular contrast agents accumulate in the reticuloendothelial system, including Kupffer cells.
Using extracellular agents, HCC can be easily diagnosed by arterial phase hyperenhancement and portal venous/delayed phase washout. Hepatobiliary agents are highly sensitive to detect small HCC lesions and premalignant lesions.
PHASE | COMPUTED TOMOGRAPHY IMAGE QUALITY ASSESSMENT |
Late arterial phase |
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Portal venous phase |
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Delayed phase |
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