Chapter 6
Liver metastases

Ersan Altun¹, Mohamed El-Azzazi^1,2,3,4, Richard C. Semelka¹, and Miguel Ramalho^1,5

¹The University of North Carolina at Chapel Hill, Department of Radiology, Chapel Hill, NC, USA

²University of Dammam, Department of Radiology, Dammam, Saudi Arabia

³King Fahd Hospital of the University, Department of Radiology, Khobar, Saudi Arabia

⁴University of Al Azhar, Department of Radiology, Cairo, Egypt

⁵Hospital Garcia de Orta, Department of Radiology, Almada, Portugal

• Metastases are the most common malignant tumors of the liver.
  
• The liver, lungs, and bones are the most common sites of metastases in the body.
  
• Liver metastases usually appear as multiple nodules, but may also appear as a solitary nodule (colon cancer is the primary that has the greatest tendency to result in a solitary metastasis). Multiple nodules may form confluent masses. The presence of diffuse nodular metastases may mimic cirrhotic liver. Isolated infiltrative parenchymal metastatic lesions are also occasionally seen. Isolated infiltrative metastatic lesions may also be seen along the portal tracts and in the porta hepatis.
  
• Metastasis may be complicated by hemorrhage, central necrosis, or cystic change. Metastases may also contain calcifications, which are most frequently associated with mucinous adenocarcinomas of the colon and ovary, and medullary thyroid carcinoma.
  
• The presence of diffuse nodular metastases may mimic cirrhotic liver, especially following response to chemotherapy (an appearance most often seen with breast cancer).
  
• CT features of liver metastases on precontrast images
  
  
  
  • Usually seen as hypoattenuating lesions (Figure 6.1)
    
  • May be seen as hyperattenuating lesions if they contain hemorrhage or high protein such as mucin as in hemorrhagic metastases, or mucinous tumors such as ovarian mucinous tumors or mucinous colon carcinoma.
    
  • Calcifications may be seen in the metastases of mucinous adenocarcinoma of the colon and ovary, and medullary thyroid cancer.
  
  
• MR features of liver metastases on precontrast sequences
  
  
  
  • Mild to moderately high in signal intensity on T2-WIs (Figure 6.2).
    
  • Moderately low in signal intensity on T1-WIs (Figure 6.2).
    
  • High signal intensity on T1-WIs may be seen in various metastatic lesions due to the presence of paramagnetic substances, including extracellular methemoglobin (hemorrhagic metastases), melanin (malignant melanoma) (Figure 6.3), protein (ovarian adenocarcinoma, multiple myeloma, and pancreatic mucinous cystic tumors) (Figure 6.4), and coagulative necrosis (colon adenocarcinoma).
  
  
• Target sign
  
  
  
  • A central area of high signal intensity on T2-WIs and low signal intensity on T1-WIs corresponds to central liquefactive necrosis (Figures 6.2 and 6.5).
    
  • Peripheral rim of tissue with relatively lower signal on T2-WI and relatively higher signal on T1-WI corresponds to viable tumor (Figure 6.5).
  
  
• Halo sign
  
  
  
  • A central area of lower signal intensity relative to the higher intensity tumor periphery on T2-WI (Figure 6.6) and a central higher signal intensity relative to lower signal intensity on T1-WI.
    
  • The central area corresponds to coagulative necrosis, fibrin, and mucin, while the tumor periphery corresponds to viable tumor cells.
    
  • Seen not uncommonly (approximately 25%), metastases from colorectal carcinoma.

• Enhancement of metastases on CT and MRI
  
  
  
  • Enhancement characteristics of metastases are better defined on MRI than CT, reflecting that MRI is more sensitive to gadolinium contrast than CT to iodine contrast, and MRI is generally performed multiphase, whereas CT with only 1 postcontrast phase, or with fewer phases than MRI, because of radiation concerns.
    
  • The enhancement of metastatic lesions is frequently peripheral (ring type of enhancement) and limited to the outer margins of the lesion (Figure 6.7).
    
  • Perilesional Enhancement
    
  • However, perilesional enhancement may also be seen not uncommonly. The enhancement occurs beyond the margins of the lesion delineated on precontrast images. This is observed most frequently in colon cancer and pancreatic ductal adneocarcinoma.
    
  • Perilesional enhancement may develop due to hepatic parenchyma compression, associated peripheral desmoplastic reaction, inflammatory infiltrates, and neovascularization.
    
  • More common in hypovascular metastases and uncommon in hypervascular metastases.
    
  • Perilesional enhancement may be
    
    
    
    1. Circumferential:
       
       
       
       • May be observed in colon adenocarcinoma metastases (Figures 6.8 and 6.9).
       
       
    2. Wedge-shaped:
       
       
       
       • May be seen in metastases from pancreatic ductal adenocarcinoma (Figures 6.9 and 6.10).

• The pattern of lesional enhancement of liver metastases has a strong association with the size of the lesion.
  
  
  
  1. Ring enhancement:
     
     
     
     • Is the most characteristic appearance of liver metastases.
       
     • Usually seen when the lesion is > 1.5 cm.
       
     • On hepatic arterial dominant phase images, the outer margin of the metastasis (the most vascularized portion) enhances prominently and the inner portion has negligible enhancement (Figures 6.1, 6.2, 6.4–6.8).
       
     • On interstitial phase images, there is an equilibration of enhancement as the contrast gradually reaches the less vascularized central tumor and its interstitial compartment (Figures 6.2 and 6.6).
       
     • The outer margin demonstrates a decrease in the degree of enhancement that may appear as heterogeneous fading to near isointensity (isodensity on CT) or wash-out, and the inner area shows an increase in the degree of enhancement in later phases (Figure 6.11).
       
     • The centripetal enhancement with the wash-out of the outer margin observed in the interstitial phase is highly suggestive of malignancy, and most typical of hypervascular metastases such as carcinoid and neuroendocrine tumors such as gastrinoma (Figure 6.12).
     
     
  2. Homogeneous enhancement:
     
     
     
     • Usually when the lesion is <1.5-cm (Figures 6.13–6.15).
     
     
  3. Heterogeneous:
     
     
     
     • Uncommon.
       
     • Usually when the lesion is >1.5 cm (Figure 6.16).
       
     • Usually reflects necrosis or hemorrhage within the metastases.