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Hepatic metastases

Hepatic metastases are 18-40 times more common than primary liver tumours 6. The most common sites of primary malignancy that seeds to liver are 2:

Epidemiology

The demographics of patients with liver metastases will mirror that of the underlying primaries, although in general it is safe to say that typically patients are elderly.

Clinical presentation

Liver metastases will usually be asymptomatic and found during work up of a malignancy which has presented in other ways. If metastatic burden is large then presentation, or symptoms related to the liver disease may include:

  • localised pain and tenderness due to capsular stretching
  • disordered liver metabolic function
  • ascites
  • low grade fever 2

Radiographic features

The difficulty in imaging the liver for metastatic disease is the high prevalence of benign liver lesions that can be misinterpreted as evidence of metastatic disease, thus dramatically changing a patients stage, and thus treatment options.

Liver haemangiomas, and to a lesser degree FNH are the main sources of confusion 3. Additionally pseudolesions (e.g. transient hepatic attenuation differences (THAD), focal fatty sparing / focal fatty change ) may further murky the waters. Therefore, an understanding of the various appearances of metastatic disease is crucial.

Ultrasound

Routine gray scale ultrasound, contrast enhanced ultrasound and intra-operative ultrasound all have roles to play.

Unfortunately not only do metastases have a wide range of appearances, but echogenicity changes of the liver due to fatty change make absolute statements difficult to make. In general however, metastases may appear as 3:

  • rounded and well defined
  • positive mass effect with distortion of adjacent vessels
  • hypoechoic - most common ~ 65% and is a concerning feature 8
  • hypoechoic halo due to compressed and fat spared liver
  • cystic, calcified, infiltrative and echogenic appearances are all possible - see liver metastases ultrasound appearances

Contrast enhanced ultrasound has similar characteristics as CT, able to distinguish between hypovascular liver lesions, and hypervascular liver lesions.

CT

The most common appearance of liver metastases is that of hypodense lesions on non-contrast scanning, and demonstrate less enhancement than surrounding liver 1. If there is concomitant hepatic steatosis, then the lesions may be iso or even slightly hyperdense. Enhancement is typically peripheral, and although there may be central filling in on portal venous phase, delayed phase will show washout; helpful in distinguishing metastases from liver haemangiomas 1.

Some primaries have a tendency to produce hyper-enhancing metastases, including RCC, thyroid, neuroendocrine etc.. see hypervascular liver lesions.

MRI

The appearance of liver metastases on MRI is of course also variable, but is more sensitive than CT for the detection of liver metastases 5. MRI examination of the liver may involve numerous sequences; see liver MRI protocol.

Most frequent appearances is 5:

  • T1 - moderately hypo intense
  • T2 - moderately hyper intense
  • C+ (Gd) - enhancement may be lesional or perilesional 7 (enhancement outside the confines of the T1 delineated lesion)
    • small lesions < 1.5cm tend to uniformly enhance.
    • larger lesions, > 1.5cm : the most common pattern of enhancement is of transient rim enhancement (i.e. with wash-out); helpful feature in distinguishing a metastasis from a liver haemangioma.
    • peri-lesional enhancement is most commonly seen in colorectal and pancreatic adenocarcinoma metastases 5.

Differential diagnosis

General imaging differential considerations include

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