What type of computed tomography (CT) scan, with or without intravenous contrast, is indicated to evaluate for a metallic foreign body near the orbits?

From the Guidelines

To evaluate for a metallic foreign body near the eyes, a non-contrast CT scan of the orbits should be ordered, as it is the most accurate method for detecting metallic foreign bodies, with a sensitivity of 94.9%. This recommendation is based on the most recent and highest quality study, which found that CT scans are the most useful imaging modality in evaluating orbital trauma, and that contrast is not necessary for detecting metallic foreign bodies 1.

The use of non-contrast CT scans is preferred because metallic foreign bodies are high-density objects that appear as bright white objects on the images, making them easily detectable without the need for contrast enhancement. Additionally, the use of contrast may obscure small metallic fragments, making it more difficult to detect them.

Some key points to consider when ordering a CT scan for a metallic foreign body near the eyes include:

• Using thin-slice (1-2 mm) axial CT images without contrast enhancement
• Informing the radiologist about the specific concern for a metallic foreign body so they can use appropriate protocols and window settings to optimize detection of even small metallic fragments
• Avoiding MRI until the presence of metal has been ruled out, as the magnetic field could cause movement of the metallic object and potentially cause further damage to ocular structures 1.

It is also important to note that CT scans are the preferred imaging modality in the initial evaluation of orbital trauma, and that MRI may be used as a supplementary imaging modality to provide more detailed information about the globe and optic nerves 1. However, in the case of a suspected metallic foreign body, a non-contrast CT scan is the most appropriate initial imaging modality.

From the Research

CT Scan for Metallic Foreign Body Near the Eyes

To evaluate for a metallic foreign body near the eyes, a CT scan without contrast is typically ordered. The following points highlight the rationale behind this choice:

• A CT scan is the first-line imaging method for patients with suspected intraocular foreign bodies (IOFBs) 2.
• CT scans can detect metallic foreign bodies and provide information on their size and location, which is helpful in determining the surgical approach 2.
• Non-contrast CT scans are usually sufficient for detecting metallic foreign bodies, as they are typically visible due to their high density 3, 4.
• The use of contrast is not necessary for detecting metallic foreign bodies and may not provide additional useful information in this context.

Key Considerations

Some key considerations when ordering a CT scan for a metallic foreign body near the eyes include:

• The patient's history of injury or occupation, which may increase the risk of a metallic foreign body 5.
• The presence of symptoms such as acute pain, blurring of vision, or tearing, which may indicate the presence of a foreign body 3.
• The importance of careful interpretation of CT scans to avoid missing small foreign bodies, such as tiny iron dust fragments 2.