The gastrointestinal system runs all the way from the mouth to the rectum and anus. Gastrointestinal imaging is a diagnostic modality that helps in the identification of an abnormality in the GIT. In some cases, it is not definitive but helps in the determination of pathology. It is important that one knows the general anatomy of the GIT and the various pathologies affecting it and how they present. As mentioned earlier, gastrointestinal imaging in some cases does not lead to a definitive diagnosis. Many GIT conditions can be spotted through imaging, but a detailed history and examination are vital in determining the exact disease or its cause.
The common modalities of imaging that help in the diagnosis of GIT pathology are abdominal radiography, abdominal ultrasound, computed tomography, magnetic resonance imaging (MRI) and angiography. A method may be preferred to another depending on the presenting complaint and the suspected organ damaged. For example, a CT scan is preferred to and abdominal radiograph when the liver or kidneys are suspected to be causes of disease. An abdominal ultrasound is the first line diagnostic modality in instances of abdominal trauma. A FAST (Focused Assessment with sonography for trauma) ultrasound is used in the assessment of abdominal trauma.
Contrast material is sometimes needed to help in visualization of the GIT. Contrast material may be administered orally, intravenously, or as enemas. Contrast medium commonly used in GIT is Barium Sulphate, and it may be administered orally as a swallow or as an enema. Gadolinium is used as contrast in magnetic resonance imaging, and it is administered intramuscularly. Contrast studies are accurate, safe and less expensive, but there are some contraindications to use of contrast.
Radiocontrast is contraindicated in patients who get a severe reaction from contrast and those with renal failure. Patients on pharmacologic treatments, most notably beta blockers, aminoglycosides, vancomycin, amphotericin B, metformin, NSAIDs and interleukin 2, have to temporarily stop their medication before contrast imaging because these agents are nephrotoxic and thus an increased risk of adverse reactions. Low dose contrast should be used, and massive fluid intake should be encouraged before and after contrast administration. Contrast-induced nephropathy is common because contrast media are excreted majorly through glomerular filtration. High doses of contrast are risky especially in patients who are at risk of kidney dysfunction, and it has been isolated as a cause of mortality.
Imaging of the abdomen is very useful in the determination of an abnormal abdomen. Imaging has been a massive breakthrough in the diagnosis of various malignancies of the GIT such as gastric cancer, small intestine cancers, colorectal malignancy, liver and biliary tract cancers and kidney cancers. Imaging is also used to monitor the progress of therapy in malignancy. Gastrointestinal imaging is essential when malignancy is involved. Not only neoplastic conditions are diagnosed through radiography, but other non-neoplastic conditions such as congenital abnormalities, inflammatory conditions of the GIT such as Crohn’s disease and Ulcerative colitis, bleeding in the GIT and gas patterns in the abdomen.
The value of abdominal imaging in diagnosis should never be underestimated.