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Hepatic metastases

Hepatic metastases are 18-40 times more common than primary liver tumours 6. Ultrasound, CT, and MRI are all useful for detection of hepatic metastases and and evaluation across multiple postcontrast CT series or MRI pulse sequences is necessary. The most common sites of primary malignancy that metastasizes 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 patients are typically elderly.

Clinical presentation

Liver metastases are usually asymptomatic and found during work up of a malignancy which has presented in other ways. If hepatic metastatic burden is large then the 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

One of the main difficulties in liver imaging 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 Focal nodular hyperplasia (FNH), are the main sources of confusion 3. Additionally pseudolesions (e.g. transient hepatic attenuation differences (THADs), focal fatty sparing / focal fatty change) may further muddy 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 background 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 to CT, able to distinguish between hypovascular liver lesions, and hypervascular liver lesions.

CT

The most common appearance of liver metastases is that of hypoattenuating lesions on non-contrast exam, and they demonstrate less enhancement than surrounding liver on post-contrast studies 1. If there is concomitant hepatic steatosis, then the lesions may be iso or even slightly hyperattenuating. 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 renal cell carcinoma, thyroid carcinoma, neuroendocrine tumours etc. (see hypervascular liver lesions)

MRI

The appearance of liver metastases on MRI is also variable, but MRI 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), and choice of the gadolinium contrast agent (extracellular contrast agent or Eovist) is an important consideration.

Most frequent appearances are 5:

  • T1: moderately hypointense
  • T2: mildy to moderately hyperintense
  • C+ (extracellular gadolinium contrast): enhancement may be lesional or perilesional 7 (enhancement outside the confines of the T1 delineated lesion)
    • small lesions <1.5 cm tend to uniformly enhance.
    • larger lesions, >1.5 cm tend to show transient rim enhancement (i.e. with wash-out); helpful feature in distinguishing a metastasis from a liver haemangioma.
    • perilesional enhancement is most commonly seen in colorectal and pancreatic adenocarcinoma metastases 5.
  • C+ (Eovist):
    • ​Eovist is often useful for detection and confirmation of metastatic disease
    • on the delayed phase, metastatic lesion do not retain any Eovist and essentially appear as "holes" in the liver

Fluid-fluid levels are considered a specific finding for neuroendocrine tumour metastases 9.

Differential diagnosis

General differential imaging considerations include:

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