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Role of CT in Colorectal Cancer |
Screening Techniques for Colorectal Cancer
Colorectal cancer, the second leading cause of cancer death in the U.S., is particularly amenable to screening since the disease evolves from small, premalignant polypoid masses detected via a variety of examinations:
- The hemoccult test to check for blood in stool
- Barium enema
- Colonoscopy
- Helical CT ("virtual" colonoscopy)
The hemoccult test is the most widely available and easily implementable test. It is also the least accurate and specific.
Air contrast barium enema is minimally invasive and requires no sedation. The technique has only modest sensitivity (50%-80%) for polyps <1 cm or for Dukes Stage A and B cancers (55%-85%). The low sensitivity is due to inadequate visualization of bowel segments and errors of interpretation. The increasing utilization of endoscopic techniques is causing a decline in the numbers of patients referred for double contrast barium enemas.
The current gold standard-colonoscopy-misses 15%-20% of polyps <1 cm and up to 6% of larger lesions. It should also be noted that colonoscopy is an invasive technique associated with a varying level of morbidity depending upon the experience level of the endoscopist, and the patient's clinical condition. An advantage of colonoscopy over CT colongraphy is that both visual diagnosis and biopsy of suspicious polyps can be performed in one procedure.
Thus, there are hopes for the noninvasive helical CT technique which uses "virtual reality" computer visualization. The patient must undergo pre-imaging bowel preparation similar to the protocol prior to colonoscopy. The colon is then inflated with air or carbon dioxide before imaging begins.
Ongoing multicenter trials will eventually determine if helical CT is cost effective and accurate enough to replace invasive colonoscopy as the gold standard in this regard. It should also be noted that MRI colonoscopy is also undergoing extensive evaluation with some impressive preliminary results.
Staging Primary Colon Cancer
The initial immediate therapy for colon cancer is wide surgical resection of the involved segment and removal of regional lymph nodes. Risk of recurrence increases with initial spread (e.g., 5% in lesions confined to the mucosa or submucosa but 25% or higher for tumors extending in to the pericolonic fat). Adenopathy is a particularly ominous associated finding, greatly elevating the risks of recurrence. Recurrent disease occurs in up to 40% of patients who undergo a theoretically curative initial resection.
Cross-sectional imaging is the most useful staging protocol. Endoscopic ultrasound is a useful tumor staging tool which can also help stage surrounding nodes adjacent to the colonic wall. MRI or CT require colonic cleansing and adequate distension in order to well delineate an intraluminal tumor. Both CT and MRI are, however, powerful tools for evaluating extension beyond the bowel wall, as well as distant metastatic disease. Contrast-enhanced MRI facilitates multiplanar imaging which is particularly useful in patients with involvement of adjacent organs.
Hepatic metastases can be removed by liver resection, assuming the tumor burden in the liver is not too high. Therefore, it is critical to fully delineate the number of lesions and their precise locations. CT and MRI both offer excellent noninvasive alternatives, as opposed to the gold standard arterial portography and intraoperative sonography. MRI with conventional contrast-enhanced techniques with gadolinium agents like MAGNEVIST ®(gadopentetate dimeglumine) are continually being refined, as well.
While extrahepatic disease in the abdomen and peritoneal spread can both be assessed equally well by MRI or CT, lung lesion detection is most reliably performed by CT.
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INDICATIONS and IMPORTANT SAFETY INFORMATION
MAGNEVIST® (gadopentetate dimeglumine) Injection
INDICATIONS AND USAGE
Central Nervous System: MAGNEVIST® (gadopentetate dimeglumine) Injection is indicated for use with magnetic resonance imaging (MRI) in adults, and pediatric patients (2 years of age and older) to visualize lesions with abnormal vascularity in the brain (intracranial lesions), spine and associated tissues. MAGNEVIST Injection has been shown to facilitate visualization of intracranial lesions including but not limited to tumors.
Extracranial/Extraspinal Tissues: MAGNEVIST is indicated for use with MRI in adults and pediatric patients (2 years of age and older) to facilitate the visualization of lesions with abnormal vascularity in the head and neck.
Body: MAGNEVIST Injection is indicated for use in MRI in adults and pediatric patients (2 years of age and older) to facilitate the visualization of lesions with abnormal vascularity in the body (excluding the heart).
IMPORTANT SAFETY INFORMATION
WARNING: NEPHROGENIC SYSTEMIC FIBROSIS
Gadolinium-based contrast agents increase the risk for nephrogenic systemic fibrosis (NSF) in patients with:
- acute or chronic severe renal insufficiency (glomerular filtration rate < 30 mL/min/1.73m2), or
- acute renal insufficiency of any severity due to the hepato-renal syndrome or in the perioperative liver transplantation period.
In these patients, avoid use of gadolinium-based contrast agents unless the diagnostic information is essential and not available with non-contrast enhanced magnetic resonance imaging (MRI). NSF may result in fatal or debilitating systemic fibrosis affecting the skin, muscle and internal organs. Screen all patients for renal dysfunction by obtaining a history and/or laboratory tests. When administering a gadolinium-based contrast agent, do not exceed the recommended dose and allow a sufficient period of time for elimination of the agent from the body prior to any readministration.
The possibility of serious or life-threatening anaphylactic or anaphylactoid reactions, including cardiovascular, respiratory, and/or cutaneous manifestations, should always be considered. As with other paramagnetic contrast agents, caution should be exercised in patients with renal insufficiency due to the possibility of further deterioration in renal function. As with other injectable products, cases of phlebitis and thrombophlebitis have been reported; assessment of the dosed limb for the development of injection site reactions is recommended.
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.
For important risk and use information, please see the full prescribing information.
EOVIST® (gadoxetate disodium) Injection
INDICATIONS AND USAGE
EOVIST® (gadoxetate disodium) Injection is a gadolinium-based contrast agent indicated for intravenous use in T1-weighted magnetic resonance imaging (MRI) of the liver to detect and characterize lesions in adults with known or suspected focal liver disease.
IMPORTANT SAFETY INFORMATION
WARNING: NEPHROGENIC SYSTEMIC FIBROSIS
Gadolinium-based contrast agents increase the risk for nephrogenic systemic fibrosis (NSF) in patients with:
- acute or chronic severe renal insufficiency (glomerular filtration rate < 30 mL/min/1.73m2), or
- acute renal insufficiency of any severity due to the hepato-renal syndrome or in the perioperative liver transplantation period.
In these patients, avoid use of gadolinium-based contrast agents unless the diagnostic information is essential and not available with non-contrast enhanced magnetic resonance imaging (MRI). NSF may result in fatal or debilitating systemic fibrosis affecting the skin, muscle and internal organs. Screen all patients for renal dysfunction by obtaining a history and/or laboratory tests. When administering a gadolinium-based contrast agent, do not exceed the recommended dose and allow a sufficient period of time for elimination of the agent from the body prior to any readministration.
The possibility of serious or life-threatening anaphylactoid/hypersensitivity reactions with cardiovascular, respiratory and/or cutaneous manifestations should always be considered. The most common adverse reactions observed in clinical trials at the recommended dose included feeling hot, nausea and headache.
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.
For important risk and use information, please see the full prescribing information.
ULTRAVIST® (iopromide) Injection
INDICATIONS AND USAGE
ULTRAVIST® (iopromide) Injection is an iodinated contrast agent indicated for:
Intra-arterial Procedures*: 150 mgI/mL for intra-arterial digital subtraction angiography (IA-DSA); 300 mgI/mL for cerebral arteriography and peripheral arteriography; 370 mgI/mL for coronary arteriography and left ventriculography, visceral angiography, and aortography.
Intravenous Procedures*: 240 mgI/mL for peripheral venography; 300 mgI/mL for excretory urography; 300 mgI/mL and 370 mgI/mL for contrast Computed Tomography (CT) of the head and body (intrathoracic, intra-abdominal and retroperitoneal regions) for the evaluation of neoplastic and non-neoplastic lesions. The usefulness of contrast enhancement for the investigation of the retrobulbar space and of low grade or infiltrative glioma has not been demonstrated.
*For information on the concentrations and doses for the Pediatric Population [see Dosage and Administration (2.3) and Use in Specific Populations (8.4) in the full prescribing information].
IMPORTANT SAFETY INFORMATION
WARNING: NOT FOR INTRATHECAL USE
Inadvertent intrathecal administration may cause death, convulsions, cerebral hemorrhage, coma, paralysis, arachnoiditis, acute renal failure, cardiac arrest, seizures, rhabdomyolysis, hyperthermia, and brain edema.
CONTRAINDICATIONS
ULTRAVIST Injection is contraindicated for intrathecal use.
Preparatory dehydration (e.g. prolonged fasting and the administration of a laxative before ULTRAVIST Injection) is contraindicated in pediatric patients because of risk of renal failure.
WARNINGS AND PRECAUTIONS
Life-threatening or fatal anaphylactoid reactions may occur during or after Ultravist administration. Acute renal failure may occur following ULTRAVIST administration, particularly in patients with renal insufficiency, diabetes, multiple myeloma. Hemodynamic disturbances including shock and cardiac arrest may occur during or shortly after administration of ULTRAVIST. Angiography may be associated with local and distal organ damage, ischemia, thromboembolism and organ failure.
MOST COMMON ADVERSE REACTIONS
Most common adverse reactions (>1%) are headache, dysguesia, abnormal vision, chest pain, vasodilatation, nausea, vomiting, back pain, urinary urgency, injection site and infusion site reactions, and pain.
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.
For important risk and use information, please see the full prescribing information.
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