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:
- gastrointestinal tract (via portal circulation)
- breast cancer
- lung cancer
- genitourinary system
- essentially all metastatic solid malignancies
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.
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
- low grade fever 2
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.
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
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.
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 Gd): 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.
- 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.
General differential imaging considerations include:
- usually hyperechoic
- no mass effect
- characteristic discontinuous peripheral nodular enhancement with gradual 'filling in' 1
hepatocellular carcinoma (HCC)
- more often solitary when compared with metastases
- may also have hypoechoic halo on ultrasound
focal nodular hyperplasia (FNH)
- often younger patients
- central scar, with persistent delayed enhancement
- hepatic adenoma
- pseudolesions (often found in cirrhotic liver)
- multiple biliary hamartomas
- hepatic peliosis
- 1. Vogl TJ, Lencioni R, Hammerstingl RM et-al. Magnetic Resonance Imaging in Liver Disease, Technical Approach, Diagnostic Imaging of Liver Neoplasms, Focus on a New Superparamagnetic Contrast Agent. Thieme. (2003) ISBN:1588902366. Read it at Google Books - Find it at Amazon
- 2. Doherty GM, Way LW. Current surgical diagnosis & treatment. McGraw-Hill Medical. (2006) ISBN:007142315X. Read it at Google Books - Find it at Amazon
- 3. Lencioni R, Cioni D, Bartolozzi C. Focal liver lesions, detection, characterization, ablation. Springer Verlag. (2005) ISBN:3540644644. Read it at Google Books - Find it at Amazon
- 4. Lin E, Garg K, Escott E et-al. Practical differential diagnosis for CT and MRI. Thieme Medical Pub. (2008) ISBN:1588906558. Read it at Google Books - Find it at Amazon
- 5. Semelka RC. Abdominal-pelvic MRI. Wiley. (2006) ISBN:0471692735. Read it at Google Books - Find it at Amazon
- 6. Namasivayam S, Martin DR, Saini S. Imaging of liver metastases: MRI. Cancer Imaging. 2007;7 : 2-9. doi:10.1102/1470-7330.2007.0002 - Free text at pubmed - Pubmed citation
- 7. Danet IM, Semelka RC, Leonardou P et-al. Spectrum of MRI appearances of untreated metastases of the liver. AJR Am J Roentgenol. 2003;181 (3): 809-17. AJR Am J Roentgenol (full text) - Pubmed citation
- 8. Wernecke K, Vassallo P, Bick U et-al. The distinction between benign and malignant liver tumors on sonography: value of a hypoechoic halo. AJR Am J Roentgenol. 1992;159 (5): 1005-9. AJR Am J Roentgenol (abstract) - Pubmed citation
- 9. Sommer WH, Zech CJ, Bamberg F et-al. Fluid-fluid level in hepatic metastases: a characteristic sign of metastases of neuroendocrine origin. Eur J Radiol. 2012;81 (9): 2127-32. doi:10.1016/j.ejrad.2011.09.012 - Pubmed citation
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