MRI SCAN

What is an MRI scan?

 

MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s.
The MRI scan uses magnetic and radio waves, meaning that there is no exposure toX-rays or any other damaging forms of radiation.

How does an MRI scanner work?

 

The patient lies inside a large, cylinder-shaped magnet.
Radio waves 10,000 to 30,000 times stronger than the magnetic field of the earth are then sent through the body. This affects the body's atoms, forcing the nuclei into a different position.
As they move back into place they send out radio waves of their own.
The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals.
Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above.

What does an MRI scan show?

 

Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body.
The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter.
By changing the timing of the radiowave pulses it is possible to gain information about the different types of tissues that are present.
An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be used to find out if it has spread into nearby brain tissue.
The technique also allows us to focus on other details in the brain. For example, it makes it possible to see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of oxygen after a stroke.
The MRI scan is also able to show both the heart and the large blood vessels in the surrounding tissue. This makes it possible to detect heart defects that have been building up since birth, as well as changes in the thickness of the muscles around the heart following a heart attack. The method can also be used to examine the joints, spine and sometimes the soft parts of your body such as the liver, kidneys and spleen.

How does an MRI scan differ from a CT scan?

 

With an MRI scan it is possible to take pictures from almost every angle, whereas aCT scan only shows pictures horizontally. There is no ionizing radiation (X-rays) involved in producing an MRI scan. MRI scans are generally more detailed, too. The difference between normal and abnormal tissue is often clearer on the MRI scan than on the CT scan.

How is an MRI scan performed?

 

The scan is usually done as an outpatient procedure, which means that the patient can go home after the test. During the scan it is important to lie completely still. For this reason it might be necessary to give a child an anaesthetic before they are tested.
Since you are exposed to a powerful magnetic field during the MRI scan, it is important not to wear jewellery or any other metal objects.
An MRI scan is not suitable for the patient if they have electrical appliances, such an a ear implant, implantable cardioverter defibrillator or pacemaker, or have any metal in their body such as surgical clips.
But orthopaedic metal ware, such as artificial hips or bone screws, are not normally a problem.

Is an MRI scan dangerous?

 

There are no known dangers or side effects connected to an MRI scan. The test is not painful; you cannot feel it. Since radiation is not used, the procedure can be repeated without problems. There is a small theoretical risk to the foetus in the first 12 weeks of pregnancy, and therefore scans are not performed on pregnant women during this time.
Because patients have to lie inside a large cylinder while the scans are being made some people get claustrophobic during the test. Patients who are afraid this might happen should talk to the doctor beforehand, who may give them some medication to help them relax.
The machine also makes a banging noise while it is working, which might be unpleasant.



                    Liver Tumours

  1. Liver tumours are benign or malignant; malignant tumours can be primary or secondary.
  2. In Europe and the USA, a solitary lesion in the liver is more likely to be a metastatic carcinoma than a primary liver tumour.1
  3. In 2000, it was estimated that liver cancer was the 5th most common malignancy in men and the 8th most common in women worldwide.2
  4. The incidence of primary liver cancers in developed countries seems to be increasing. This is related to hepatitis B and C infection, which peaked in incidence in the 1950s to 1980s.2
  5. Hepatitis B and C infection accounts for over 80% of liver cancer worldwide. Introduction of hepatitis B vaccination programmes and blood and blood product screening for the viruses has the potential to reduce this.2
Benign liver tumours

Haemangioma

  • The most common benign liver tumour in adults and children.3,4
  • In children:4
    • Commonly occurs within first 6 months of life.
    • Can be small and found incidentally on imaging for another reason. Large cavernous haemangiomas can also occur and may reach 8 to 10 cm in diameter.
    • A subgroup of haemangioma, known as haemangioendothelioma, is found in infants.
    • Can present with abdominal distension and high-output cardiac failure. Cutaneous haemangiomas may co-exist.
    • Sequestration of platelets and a consumptive coagulopathy can rarely occur.
    • Usually regress within first 2 years of life.
    • Treatment only needed if high-output cardiac failure or platelet sequestration. Steroid and interferon treatment, surgical excision and hepatic artery embolization are all treatment options.
  • In adults:
    • Are usually small and found incidentally on imaging for another reason.
    • Rarely lead to symptoms which include abdominal pain. Also have potential to rupture, causing shock.
    • Thought to be congenital and may enlarge under the influence of oral contraceptives5 but usually regress when they are stopped. Can also grow during pregnancy.
    • Can bleed profusely if attempt is made at liver biopsy.
    • If they require removal, are not usually amenable to simple excision of the tumour and a whole lobe of the liver must be removed.
    • Thrombocytopenia, hypofibrinogenaemia and microangiopathic haemolytic anaemia can occur.3

Hepatic adenoma

  • Also usually asymptomatic and found incidentally, either as a mass on physical examination or during imaging for another reason.
  • Can occur in adolescent girls.
  • Occasionally presents with abdominal pain and intraperitoneal bleeding.3
  • Liver function is not usually affected.
  • Most cases have occurred in women who have been taking the contraceptive pill for 5 years or more.3
  • Hepatic adenoma and adenocarcinoma may also be associated with the use of anabolic steroids.6
  • Can be seen as solitary, or sometimes multiple, vascular masses on hepatic arteriography.
  • There is about a 5% chance of malignant change to hepatocellular carcinoma and a risk of intraperitoneal bleeding so they are best removed.

Focal nodular hyperplasia

  • More common in women.3 Can occur in adolescent girls.
  • Not prone to malignant change.4
  • Rupture and haemorrhage has occasionally been reported.3 Because of this, some advocate excision. Others just monitor regularly using imaging.
  • Can be distinguished from hepatic adenoma by careful imaging and liver biopsy.

Ø     Other benign tumours

Ø      Very rare. Include:
Ø      Fibroma
Ø      Lipoma
Ø      Leiomyoma
Ø      Cystadenoma
Ø      Primary carcinoma of the liver

Ø     Hepatocellular carcinoma (HCC)

Ø      See separate Hepatocellular Carcinoma article.
Ø      There are about 1500 deaths per year from HCC in the UK and its incidence appears to be rising.7
  • The majority of cases worldwide are related to hepatitis B and C virus infection. There are also associations with alcohol, haemochromatosis and primary biliary cirrhosis.
  • HCC is the second most common hepatic malignancy in children:4 It usually occurs in children with pre-existing liver disease (hepatic fibrosis and cirrhosis) secondary to e.g. metabolic liver disease, viral hepatitis, chemotherapy or total parenteral nutrition.
  • Presentation is with abdominal pain, abdominal mass, weight loss and anaemia.
  • Lung and lymph node metastases are common.
  • Resection and chemotherapy is the mainstay of treatment but many tumours are unresectable at presentation.
  • Prognosis is generally poor.

Hepatoblastoma

  • Commonest hepatic malignancy in children (although still uncommon compared to other solid tumours).8
  • Extremely rare in adults.9
  • Usually presents as abdominal mass and distension, vomiting, anaemia and failure to thrive in a child under the age of 3.
  • Alpha fetoprotein levels are raised and can be used to monitor response to treatment.
  • There are associations with hemihypertrophy, Beckwith-Wiedemann syndrome and familial adenomatous polyposis syndrome.
  • Pulmonary metastases are common.
  • Treatment is with resection and chemotherapy (which may be required before surgery to shrink the tumour).
  • Liver transplantation has been used in children with non-resectable tumours.9
  • With complete tumour resection and the use of adjuvant chemotherapy, survival rate can be 100%.9
  • A poor prognosis is associated with large tumour size, multifocal disease, extrahepatic disease and metastatic spread.8

Cholangiocarcinoma

  • This is a carcinoma that arises in the biliary tree anywhere from the small intrahepatic ducts to the distal common bile duct. It is most commonly found near the junction of the left and right hepatic ducts.
  • It presents by causing obstruction to the flow of bile with subsequent obstructive jaundice, pale stools and dark urine.
  • There is a separate article on Cholangiocarcinoma.

Other tumours

Ø      malignant liver Other rare primary tumours include:
Ø      Fibrosarcoma
Ø      Angiosarcoma
Ø      Leiomyosarcoma
Ø      Lymphoma

Secondary carcinoma of the liver

  • Lymph nodes are the commonest site for metastatic malignant spread with the liver next in frequency.
  • The vulnerability of the liver for metastatic disease may be related to the fact that it is the largest organ in the body and it filters blood from both the systemic and portal systems. Humoral factors promote cell growth and blood flow is second only to the lungs.
  • Most liver metastases are multiple and affect both lobes. Single metastases occur in only 10%.1
  • The commonest primary sites for hepatic metastases are colorectal, stomach, pancreas, breast, lung and eye.1
  • In children the commonest primaries are neuroblastoma, Wilm's tumour and leukaemia.1
  • Most tumours that have spread to the liver have metastasised to other sites as well.
  • Ultrasound, CT, MRI and positron emission tomography may all be used as imaging techniques. CT seems to be most widely used and the imaging technique of choice.
  • Biopsy is needed for a histological diagnosis. However, biopsy can lead to needle tract metastases and some argue that in Western populations where primary liver tumours are rare, investigation should focus on finding a primary source when investigating malignant liver lesions.10

Clinical features

  • Hepatomegaly and ascites are common clinical features that accompany liver metastases. Nodularity may be palpable along the enlarged liver edge. Ascites indicates wide dissemination and a poor prognosis.
  • Liver function tests may not always be abnormal.
  • Large metastases may block bile ducts and cause jaundice, malaise, anorexia and loss of weight.

Management

  • Partial hepatectomy to remove a single deposit may prolong survival and even lead to cure in some cases.3
  • Minimally invasive treatments, including radiofrequency ablation, have also been used in the treatment of metastatic hepatic deposits.11 However, more trials are needed to look at its effectiveness.12
  • NICE have advocated the use of laparoscopic liver resection for a solitary liver metastasis, HCC and for benign liver tumours and cysts.13 Radiofrequency-assisted liver resection is also supported by NICE.14
  • Chemotherapy may also be a treatment option depending on the primary site. However, if there is coexisting extensive extrahepatic disease, prognosis is usually guarded.

Prognosis

Ø      Deposits from colorectal cancer seem to have a better prognosis.3
Ø      People with secondary liver carcinoma do not usually die as a direct result of the liver metastases but for some other reason, for example a chest infection or renal impairment.3




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