Penetrating orbital injury: Pearls for case evaluation, management

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Evaluation and management of penetrating orbital injuries is largely guided by knowledge about the foreign body and is improving with advances in imaging technology.

By Cheryl Guttman Krader; Reviewed by James C. Fleming, MD

Memphis, TN-The need for intervention in patients with an intraorbital foreign body depends on the ability to localize the retained material and determine the full extent of injury. Success with each of these measures depends on knowledge of the physics of traumatic injuries, features of orbital anatomy, and the unique characteristics of different foreign body materials and imaging modalities.

Understanding of the physics of traumatic injuries is the basis for understanding the extent of intraocular damage, said James C. Fleming, MD, chairman, Department of Ophthalmology, and the Philip M. Lewis Professor of Ophthalmology, University of Tennessee Health Science Center, Hamilton Eye Institute, Memphis, TN.

Dr. Fleming explained that the object’s mass and velocity affect its ability to penetrate orbital tissues as well as the cavitation effect that is produced, which will determine if there is damage disseminated distant from the site where the foreign body lies.

In terms of anatomic considerations, Dr. Fleming pointed out that the orbit is a conically-shaped compartment with internal structures, including extraocular muscles and a septal system. Foreign bodies entering the conical orbit are driven back to the apex, and trauma from a penetrating foreign body to the extraocular muscles and septal system can affect ocular movement.

Foreign body characteristics

The composition of the foreign body determines its visibility on imaging and reactivity within the orbit. Although foreign bodies can be classified based on whether they are inorganic (metal, glass, fiberglass, plastic) or organic (plant material), no generalizations can be made based on those categorizations.

Among inorganic materials, even minimally sized metallic foreign bodies can be detected with plain radiography. Plastic and fiberglass look like air, and the identification of glass fragments depends on their size and whether the glass contains lead or is colored because of metal content (e.g., cobalt or gold).

Dry wood is relatively easy to detect on a CT or MRI where it looks like linear air but with a cylindrical shape. Discriminating between air and wood on CT scan requires proper setting and understanding of the monitors of the display scale and using “lung” presets on the CT scan views. As another clue, “linear air” associated with the presence of dry wood will remain if imaging is repeated after a few days, but will have disappeared if it was only air.

However, due to its water content, green wood is difficult to find with either CT or MRI.

“Inflammation will be seen surrounding retained wood and that can be identified with gadolinium enhancement,” Dr. Fleming said. “So, we are almost doomed to identifying green wood on imaging only after waiting for inflammation to set up.”

He added that looking for delayed inflammation with repeat imaging is probably also the best way to determine complete success in removing wood foreign bodies.

Whether it is necessary to remove an intraocular foreign body depends in part on the material. Glass, plastic, and many metals are inert and therefore can be left alone if they are not causing problems or anticipated to lead to issues based on their resting location.

The exceptions to this rule are in cases of metallic foreign bodies made of pure copper, iron, or lead in its pure form, and for patients with any metallic foreign body needing MRI of the head in the future.

Surgical tips

When extracting foreign bodies, Dr. Fleming recommended placing a ribbon retractor or some other instrument behind the fragments whenever possible to prevent them from being propelled posteriorly during the retrieval attempt. He also advised following the missile track carefully to find the terminal site of injury and to anticipate that multiple fragments are retained.

Intraoperative stereotactic localization with preoperative CT or MRI may not be helpful in guiding foreign body extraction since soft tissue landmarks can change intraoperatively and cannot be tracked. “C” arm localization may be better, but it provides limited soft tissue differentiation.

However, intraoperative MRI and CT systems are now available that allow for real-time imaging in the operating room or intensive care unit.

James C. Fleming, MD

E: jflemin4@uthsc.edu

James C. Fleming, MD, reviewed these principles in his delivery of the Wendell Hughes Lecture at the 2013 meeting of the American Academy of Ophthalmology. Dr. Fleming has no relevant financial interests to disclose.

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