what can an abdominal ct without contrast used to diagnose
When is contrast needed for abdominal and pelvic CT?
Computed tomography (CT) is one of the almost frequently utilized imaging modalities in medicine due to its ability to evaluate for a wide range of pathologies. The utilise of contrast agents, intravenous (IV) or oral, improves image quality past further delineating anatomical structures. However, contrast enhancement is not always necessary and does come with some risks. The appropriateness of contrast enhancement usually depends on the suspected diagnosis. In cases in which the diagnosis is uncertain, administration of contrast is reasonable, although the benefits should exist weighed confronting any potential risks.
INTRAVENOUS Dissimilarity
All modern IV contrast agents are iodine-based. The iodine causes increased assimilation and scattering of the incoming radiations, which serves to increase the attenuation or "brightness" of the tissue or organ.i Importantly, the IV contrast used in CT is distinct from the gadolinium-based IV contrast used in magnetic resonance imaging, meaning that there is no cantankerous-reactivity between the two, which is important if the patient is allergic to 1 of them.
4 contrast is necessary for the evaluation of whatsoever kind of vascular disease, since it allows for easy identification of the blood vessel lumen.1 In abdominal imaging, Four contrast is recommended in most cases.
ORAL Contrast
The primary benefit of oral dissimilarity is its power to distend the bowels to help distinguish them from adjacent intestinal structures.
Oral contrast comes in two forms: neutral or positive. Neutral oral contrast consists of water or a dilute, low-attenuation solution that mirrors water. Positive oral dissimilarity is an iodinated (ie, gastrografin) or barium-based solution with high attenuation that further demarcates bowel past opacification.
The appearance of multidetector CT, which offers improved resolution, has made it easier to differentiate abdominal structures without the need for the opacification with positive oral contrast. As a result, some have argued that neutral oral contrast may be preferable to positive oral contrast due to similar efficacy, cost-effectiveness, and easier patient tolerability.2
GENERAL INDICATIONS FOR Contrast Utilize IN ABDOMINOPELVIC CT
The decision to use contrast in abdominopelvic CT depends on the diagnosis suspected.
IV contrast is recommended in well-nigh cases (Table i).three It is useful in the evaluation of infection (appendicitis, colitis, diverticulitis, pyelonephritis) (Figure 1); inflammation (pancreatitis, inflammatory bowel disease), masses and malignancies; and vascular abnormalities (gastrointestinal bleeding, aortic autopsy, abdominal aortic aneurysm). Yet, Iv contrast is not necessary to diagnose bowel perforations, nephrolithiasis, or hematomas.
Table one
Indications for intravenous contrast in intestinal and pelvic computed tomography
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Effigy i
Computed tomography with intravenous dissimilarity enhancement in a patient with right-lower-quadrant abdominal pain. Centric (A) and coronal (B) views reveal diffuse mural and periappendiceal edema, with thickening of the appendix (cherry arrows). Fibroid calcification within the appendix (xanthous arrow) probable represents an appendicolith.
In vascular imaging, the study of choice is CT angiography, which is timed so that the image is taken when the Four dissimilarity reaches the arterial system, making it easier to place active bleeding.
The utilize of oral dissimilarity is more controversial.four–6 No clear consensus exists on the need for oral contrast, and adept opinion ofttimes drives current practices with regard to oral contrast employ at academic medical centers.6 In general, when the master reason for CT is to evaluate the liver, gallbladder, pancreas, spleen, adrenal glands, or urinary tract, oral contrast is unnecessary.
Alternatively, when evaluating the gastrointestinal lumen or bowel wall, oral contrast may be beneficial (Figure 2). However, oral contrast is not needed in the diagnosis of appendicitis or diverticulitis, even though both are luminal disorders.five
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Figure 2
Computed tomography with a neutral oral contrast amanuensis. Axial (A) and coronal (B) views reveal multiple loops of dilated bowel (red arrows) with a transition signal—ie, site of sudden luminal narrowing (yellow arrows)—in the left lower quadrant, findings consistent with a minor-bowel obstruction.
Bowel "illumination" accomplished with positive oral contrast is useful when searching for "breaks" in the bowel wall, such as what would be seen with fistulas and perforations, or for identifying fluid collections or abscesses between loops of opacified bowel.
Conversely, neutral oral contrast is preferred when evaluating for mural abnormalities or a suspected gastrointestinal drain, equally positive dissimilarity will opacify and mask the luminal surface, making it challenging to identify the haemorrhage source.4
In patients presenting with nonspecific abdominal complaints, some would argue that the addition of the use of oral dissimilarity optimizes the diagnostic yield of abdominal CT.6 Woolen et al found that 89% of patients would prefer oral contrast if it had any diagnostic benefit.seven Thus, in patients undergoing abdominal CT for vague or nonspecific complaints, the addition of oral contrast to the written report appears reasonable.
Adverse EFFECTS OF Dissimilarity
4 contrast carries a run a risk of an allergic reaction (incidence 0.6%), which can manifest as urticaria, pruritus, bronchospasm with wheezing, or anaphylactic stupor.viii Several premedication regimens consisting of a steroid with or without an antihistamine are bachelor for at-take chances patients (Table 2).eight
TABLE ii
Premedication regimens for patients allergic to intravenous contrast
Take a chance of nephropathy
Another business concern with Iv contrast is its apply in patients with underlying renal illness. These patients are at risk for developing contrast-induced nephropathy (CIN), which is an acute kidney injury (AKI) that develops inside 48 hours of IV contrast administration. The diagnosis is fairly controversial, with some studies having found like rates of AKI in patients undergoing CT with and without Four contrast.ix Iv contrast is considered unlikely to cause nephropathy in patients with normal renal function, simply can crusade CIN in those with impaired renal office.viii
Electric current guidelines for IV contrast administration are based on the estimated glomerular filtration rate (eGFR).eight,9 In general, patients with an eGFR of at least thirty mg/dL tin receive Four dissimilarity, whereas those with an eGFR less than thirty mg/dL (corresponding to stage iv chronic kidney disease) are at high hazard for renal failure. In these patients, a discussion should exist held regarding the high probability of progression to end-stage renal disease, requiring dialysis.
Preventive measures to minimize the gamble of contrast-induced nephropathy involve giving Four fluids at 100 mL/hour for 6 hours before and subsequently contrast administration.viii,ix Historically, sodium bicarbonate and N-acetylcysteine have been used as adjunctive agents, although there is a lack of evidence supporting their employ.8,9
Risks of oral dissimilarity agents
Oral dissimilarity is generally safety and well tolerated, although some patients can experience bothersome symptoms. Neutral contrast agents may contain osmotically agile substances that can promote loose stools or diarrhea. Of the positive oral contrast agents, iodinated agents should be avoided in patients at chance for aspiration, every bit they can cause aspiration pneumonitis. Barium-based oral contrast agents should exist avoided in patients with suspected perforations (tin crusade mediastinitis or peritonitis) or bowel obstruction, equally retained barium tin harden to form a "barolith," worsening the obstacle and requiring endoscopic or even surgical removal.x
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Source: https://www.ccjm.org/content/87/10/595
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