For abdominal hernia diagnosis, is a computed tomography (CT) scan performed with or without contrast?

From the Guidelines

For abdominal hernias, a CT scan with intravenous contrast is the preferred initial imaging modality, as it provides optimal evaluation of the hernia contents, potential complications, and surrounding anatomical structures. The use of IV contrast enhances vascular structures and can identify inflammation or ischemia, which is crucial in diagnosing complications like strangulation or bowel obstruction 1. According to the American College of Radiology, CT abdomen and pelvis with IV contrast is usually appropriate for the initial imaging of suspected small-bowel obstruction, which can be a complication of abdominal hernias 1.

When considering the use of contrast, it's essential to weigh the benefits against potential contraindications, such as renal impairment or contrast allergies. However, in the absence of such contraindications, IV contrast is preferred for its ability to provide detailed information about the hernia and surrounding structures. Oral contrast can also be useful in delineating bowel loops, but the primary focus is on the use of IV contrast for optimal evaluation.

In emergency situations where time is critical, or in patients with contraindications to contrast, a non-contrast CT may be performed, but this should be decided on a case-by-case basis by the radiologist and referring physician, taking into account the specific clinical scenario, suspected complications, and patient factors 1. The importance of contrast in CT scans for abdominal conditions is underscored by studies that show non-contrast CT holds poorer performance compared to CT with IV contrast, particularly in assessing inflammation and complications associated with conditions like Crohn's disease 1.

Key points to consider include:

• The use of IV contrast in CT scans for abdominal hernias provides optimal evaluation of the hernia contents and surrounding structures.
• IV contrast is crucial in diagnosing complications like strangulation or bowel obstruction.
• Contraindications to contrast, such as renal impairment or allergies, must be considered on a case-by-case basis.
• In emergency situations or with contraindications, non-contrast CT may be an alternative, but with potentially reduced diagnostic accuracy.

From the FDA Drug Label

Visualization of the joint spaces, uterus, fallopian tubes, peritoneal herniations, pancreatic and bile ducts, and bladder can be accomplished by direct injection of contrast medium into the region to be studied. For a hernia of the abdomen, CT with contrast may be used to visualize peritoneal herniations, as it allows for direct injection of contrast medium into the region to be studied 2.

• Key points:
  • Iohexol is well tolerated and readily absorbed if leakage into the peritoneal cavity occurs
  • The use of appropriate iodine concentrations assures diagnostic density
  • Direct injection of contrast medium into the region to be studied can be used to visualize peritoneal herniations.

From the Research

CT Scan for Hernia Abdomen

• The decision to use contrast or not in a CT scan for hernia abdomen depends on various factors, including the patient's renal function and the presence of risk factors for contrast-induced nephropathy (CIN) 3, 4, 5.
• Studies have shown that the incidence of CIN is low in patients with normal renal function, but it can be higher in patients with pre-existing renal impairment or other risk factors 3, 5.
• The use of intravenous contrast agent can provide valuable diagnostic information, especially in cases where mesenteric ischemia is suspected 3.
• A study published in 2005 found that the use of Valsalva's maneuver during MDCT can aid in the detection and characterization of abdominal wall hernias, and that a single scan obtained during Valsalva's maneuver can be sufficient to detect 100% of anterior abdominal wall hernias identified on CT 6.
• Another study published in 2018 found that CT signs such as bowel wall thickening, mucosal hypoenhancement, and pneumatosis can be highly specific for ischemia in the setting of bowel obstruction, but that none of the evaluated CT signs were found to be highly sensitive 7.

Risk Factors for Contrast-Induced Nephropathy

• Risk factors for CIN include pre-existing renal impairment, diabetes, advanced age, vascular disease, and the use of certain concurrent medications 3, 4, 5.
• Patients with a stable serum creatinine level less than 1.5 mg/dL are considered to be at low risk for CIN 3.
• The use of low-osmolality iodinated contrast material can reduce the risk of CIN, but it is still important for radiologists and referring physicians to be aware of the risk factors and take preventive measures 3, 4, 5.