CT and MRI Imaging of LIVER metastases

Metastases are the most common malignant liver lesions and the most common indication for hepatic imaging.

They are up to 18 times more frequent than primary neoplasms

Liver is second to regional lymph nodes as a site of metastatic disease

Some primary tumors are prone to cause a liver-dominant disease: - Colorectal cancer - Neuroendocrine tumors - Gastrointestinal sarcomas

Detection,absolute quantification and localization of liver metastases are crucial as the findings alter the

clinical outcome of the disease and patient management-interventional treatments,Surgical resection Complications-Liver function,Biliary obstruction

All metastases start out small

Liver metastases from extrahepatic primary tumours arrive as cellular emboli in arterial or venous blood. Histopathological studies suggest that these clumps of tumour cells lodge in the pre-sinusoidal arterioles, in the terminal portal venules, in the sinusoids themselves, or in the adjacent spaces of Disse.

Factors favouring the liver as a fertile ground for seeding metastatic tumours include its

1. high volume of blood (about 25% of cardiac output), 2. its favourable microscopic anatomy (liver sinusoids are of

suitable size for trapping cells and there are gaps of similar size in the subendothelial basement membrane) and

3. its rich biochemical environment, which favours rapid growth.

The rate at which microscopic metastases enlarge varies and depends, inter alia on the site of the primary tumour, its histological cell type, its grade of malignancy, the presence of subpopulations of different cell types and probably also on local environmental factors within the liver

colorectal

BreastLungmelanoma

General imaging characteristics commonly manifest as multifocal, discrete lesions in both lobes

only 20 % of liver metastases present as solitary lesions

In 15-20% of cases only one lobe is effected

The pathology of metastatic deposits in the liver closely resembles the primary tumor, i.e. they are usually as vascular as their primary tumors

Metastases are classified as two types on imaging1. Hypovacular-common2. Hypervascular

Hypovascular lesions

CT

Most are low or isoattenuating on plain scan

CECT-They demonstrate less enhancement than surrounding liver  

Hypovascular lesions are best imaged on portal venous phase.

On contrast-enhanced scans liver metastases may display slight peripheral enhancement with a hypoattenuating center.

Hypovascular mets from Ca lung

Plain Art

PVP Delayed

Hypovascular mets from CA breast

Ring like enhacement on arterial phase

Plain Art

PVP

Delayed

Hypovascular mets from panc ca

Irregular/Infilterative

38 y/F AdenoCa Rectum

62 yr /M,Ca stomach

Hypervascular metastases Hypervascular metastases-are best seen on arterial phase-and they can show

diffuse homogenous enhancement, Peripheral rim or Hetrogenous enhacement

Peripheral washout specific but not sensitive On the portal venous phase of scanning, some highly vascular may appear as

isoattenuating to normal liver

Common sites of origin-

1. primary neuroendocrine tumors (eg, pancreatic islet cell tumor, carcinoid tumor, or pheochromocytoma),

2. renal cell carcinoma, 3. thyroid carcinoma, 4. choriocarcinoma, 5. melanoma, 6. and sarcomas- Leiomyosarcoma7. Occasionally pancreas, ovary, or breast

Hypervascular carcinoid mets

Arterial phase enhacementIso to hypo on pvp

Hypervascular mets from pancreatic adenocarcinoma

Metastatic deposit is as vascular as the primary tumor

Metastatic Gist 43yr /F•Nearly 50% of patients with GISTs present with metastasis

•similar to those of primary tumors: hyperattenuating, enhancing masses that can be heterogeneous because of necrosis, hemorrhage, or cystic degeneration. Often, tumor vessels are evident within the tumors

•Response to imatinib-transition from a heterogeneously hyperattenuating pattern to a homogeneously hypoattenuating pattern with resolution of the enhancing tumor nodules and a decrease in tumor vessels

Contd-T2

T1

Arterial

Delayed

DWI

Dual Phase versus multiphase scanning Much has been written concerning the indications for dual- and triple-

phase scanning.

The specific technique used will depend largely on the individual indication for the study.

For example, in the follow-up of a patient with known hypovascular

liver metastases, portal venous phase scanning is appropriate.

General screening for liver disease is well performed CT during the portal venous phase.

In patients with a clinical suspicion of hypervascular lesions, the addition of unenhanced and, particularly, arterial phase images is beneficial.

Although many lesions can be characterized with a uniphasic approach, multiphase scanning may also aid in lesion characterization

MRI MRI is usually used as a as problem-solving rather than a primary technique in the diagnosis

of liver metastases

Gadolinium-enhanced MRI improves both the detection of focal liver masses and the differentiation of benign from malignant lesions.Hepatobiliary agents increase the sensitivity.

DWI-Metastases show diffusion restriction. A combination of DWI and Gd enhaced MRI is optimum.

Most metastases are hypo- to isointense on T1 and iso- to hyperintense on T2-weighted image

Target sign on T2-hyperintense rim or halo (viable tumor) surrounding central hypointensity (coagulative necrosis, fibrin, and mucin

Doughnut sign on T1shows a low signal intensity rim surrounding an irregular or ovoid center of even lower signal intensity.

CEMR-same as CT The peripheral washout sign, in which the peripheral rim is hypointense to the center of the

lesion, can also be seen on delayed enhanced images (sensitivity of 25% and a specificity of 100% for the diagnosis of malignancy using this sign)

High signal intensity on T1-weighted sequences has also been described for various metastatic lesions and is presumably related to the internal content of a paramagnetic substance.

High T1 signal intensity is not specific for malignancy. This appearance can be seen with metastases from 1. melanoma (melanin, extracellular methemoglobin), 2. colonic adenocarcinoma (hemorrhage or coagulative necrosis), 3. ovarian adenocarcinoma (protein), 4. multiple myeloma (protein), and 5. pancreatic mucinous cystic tumor6. hemorrhagic metastases (eg, lung, kidney, testicle)

pancreatic neuroendocrine tumour: a metastasis with a fluid-fluid level on MRI is characteristic of a neuroendocrine tumour metastasis

perilesional fat deposition has been specifically described with hepatic metastases from a primary pancreatic insulinoma and is thought to be related to the effects of insulin, that is, the inhibition of fatty acid oxidation and the promotion of hepatocyte triglyceride accumulatio

Varieties

Calcified metastases-Calcification may be present with metastases from mucinous gastrointestinal tract tumors and from primary ovarian, breast, lung, renal, and thyroid cancer

Calcified mets from CRC, 51y/F

•Nonenhancing•Amorphous calcification

Cystic Metastases

Two mechanisms- hypervascular metastatic tumors with rapid growth may lead

to necrosis and cystic degeneration. This mechanism is frequently demonstrated in metastases from neuroendocrine tumors, sarcoma, melanoma, and certain subtypes of lung and breast carcinoma . Contrast-enhanced CT and MR imaging typically demonstrate multiple lesions with strong enhancement of the peripheral viable and irregularly defined tissue.

Second, cystic metastases may also be seen with mucinous adenocarcinomas, such as colorectal or ovarian carcinoma . Ovarian metastases commonly spread by means of peritoneal seeding rather than hematogenously.Therefore, they appear on cross-sectional images as cystic serosal implants on both the visceral peritoneal surface of the liver and the parietal peritoneum of the diaphragm

Hemorraghic mets Hepatic metastases from lung carcinoma, renal carcinoma,

and melanoma are the most frequent types to cause hepatic bleeding

Hemoperitoneum is more frequently seen in association with primary liver tumors, which have greater vascularity than metastatic lesions. The latter tend to be more fibrotic with a poorer blood supply. Fever and leukocytosis, perhaps secondary to tumor necrosis, may be part of the clinical presentation 

the diagnosis of hemorrhagic metastasis is suggested if blood is identified in one or more liver lesions in a patient with known hepatic metastases or a known primary tumor elsewhere 

If the hemorrhage is severe, a subcapsular hematoma or hemoperitoneum may also be noted.

Hemorrhagic metastases from malignant melanoma

NCCT T1 T2

Solitary metastases from Ca sigmoid

T1

T2

Fiesta

T2FS

Differential diagnosis

Hypovascular metastases have to be differentiated from cysts,focal fatty infiltration and abscesses

Cyst

Thin wall No internal architecture Non enhancing CT hypodense(fluid attenuation) MRI-TI hypo,T2 hyper

abcesses clinical symptoms coalescent, grouped appearance thick-walled lesions Homogenous low internal attenuation

increased peripheral rim enhancement, which is secondary to increased capillary permeability in the surrounding liver parenchyma (the “double target” sign)

Perilesional edema is seen on T2-weighted MR images in 50% of

abscesses, although it may also be seen in 20%–30% of patients with primary or secondary hepatic malignancies

An additional sign pointing to liver abscesses is the presence of air densities inside the lesions

Arterial-phase contrast-enhanced CT scan shows a cystic lesion with high attenuation of the surrounding normal liver parenchyma (arrows) due to hyperemia (the double target sign).

Focal Fatty change focal fatty infiltration of the liver does not display mass

effect, and branches of the hepatic and portal veins traverse it without change in their course,show poorly delineated margins and enhance ment similar to or less than normal liver.

characteristically occurs in specific areas (eg, adjacent to the falciform ligament or ligamentum venosum, in the porta hepatis, and in the gallbladder fossa)

MRI can help-T1/T2 Hyperintense with supression on out of phase images

Nodular Focal fatty infiltration Nodular Focal fatty infiltration can simulate

metastases.  masslike lesions in a diffusely fatty liver that are

well seen only on opposed-phase MRI during an examination that includes T2-weighted and dynamic gadolinium enhanced sequences may represent nodular fatty sparing in the appropriate clinical setting. IN

PHASEOUT PHASE

Metastases in fatty liver fatty liver can also obscure metastases. 

On a contrast enhanced CT hypovascular lesions can be obscured if the liver itself is lower in density due to fat deposition. On a NECT these lesions usually are better depicted

PVP Plain

THAD/THID

Focal perfusion artefacts-either nontumorous arterioportal shunts or obstruction of distal parenchymal portal venous flow

which are usually wedge-shaped and located peripherally with undisplaced internal vasculature

Location-segment 4

`lesions'' are not visible on pre-contrast imaging, nor on delayed post- contrast images

polymorphous transient hepatic intensity differences due to anomalous venous supply and drainage by right gastric vein. Axial gradient-echo T1-weighted gadolinium-enhanced arterial phase MR images

Sectorial THAD

Hypervascular metastases have to be differentiated from other hypervascular tumors that can be multifocal like hemangiomas, FNH, adenoma and HCC. 

Hemangiomas

3 Patterns of enhancement On Arterial phase show discontinous nodular peripheral enhancement

with almost complete centripetal fill in on subsequent phases. Large hemangiomas may have central areas of hemorrhage or

fibrosis that do not fill in with contrast material. smaller than 1 cm usually show uniform early enhancement on CT

and MRI

Enhancement matches blood pool

A greater signal intensity on T 2 is seen, higher than metastasis

When a longer echo time(TE>160) is used benign lesions tend to retain high signal intensity, while metastases typically show some reduction

Multiple hemangiomasT1 T

2

Arterial

15 min delayed

decision algorithm helpful in evaluating hypervascular liver lesions

In the End….. Metastases are the most common malignant liver lesions

Two Types-Usually HYPOVASCULAR and HYPERVASCULAR

Easily Differentiated-clinical setting and systematic analysis

Benign or Malignant- incidental lesions in patients with no suspicion of primary malignancy are almost invariably benign , but small lesions seen in patients undergoing staging procedures or surveillance following treatment of primary malignancy turn out to be metastases in about 10% of cases

Small mets can be a challenge to pick up and characterize

With current imaging technology, we should detect virtually all liver metastases 2 cm or larger in size, and most of those 1-2 cm in size

Even with optimum imaging, at present we detect only about one-half of metastatic nodules smaller than 1 cm in patients undergoing liver resection and pathological correlation.

Thank You !