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Neuroradiology Case of the Week

Case 271

Ashwani K. Sharma, MD, Brian Sorensen, MD,
and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 42-year-old male who presented with head trauma and left orbital saw injury.

Imaging Findings: Plain x-rays are fairly accurate in detecting metallic foreign bodies. CT detects the location of metallic foreign body in the orbit. CT is also useful in detecting when multiple foreign bodies are present, or when it remains uncertain whether a radiologically proven foreign body is intraocular. Finally, if a non-radiopaque intraocular foreign body (IOFB) is still strongly suspected following negative CT imaging, other imaging modalities such as ocular ultrasound or magnetic resonance imaging may need to be considered.

Diagnosis: Orbital foreign body injury (saw)

Discussion: Orbital radiography (plain and computed tomography (CT) imaging) to detect and/or localize intraocular foreign bodies (IOFBs) is commonly performed on ophthalmic patients with a history of exposure to high-velocity particles. The booklet 'Making the Best Use of a Department of Clinical Radiology' issued by the Royal College of Radiologists (MBUR RCR) [1] states that a single 'soft' lateral X-ray is the only projection required to exclude a metallic foreign body, and that images with eye movement are indicated only in those cases where the intraocular position of a radiologically proven foreign body is uncertain. These guidelines also suggest that CT orbital imaging in cases or suspected cases of IOFB should be undertaken only when the plain orbital radiograph fails to show a strongly suspected foreign body, which may not be metallic, when multiple foreign bodies are present, or when it remains uncertain whether a radiologically proven foreign body is intraocular. The MBUR RCR guidelines aim to limit patients' exposure to radiation and to reduce non-contributory yet costly examinations in the Accident and Emergency and/or Radiology Departments.
     Previous reports have shown that CT orbital imaging is superior to orbital plain orbital radiography for the detection and localization of IOFBs, although CT is associated with greater exposure to radiation than plain radiography [2].
     According to some authors [3], where there is clinical evidence of ocular penetration but an IOFB is not clinically visible, CT imaging is necessary irrespective of the result of the preceding plain orbital radiograph. This is so for two reasons. First, CT imaging would identify an IOFB that might have gone undetected on orbital plain X-ray. Second, when an IOFB is demonstrated on the plain orbital radiograph, CT imaging would be necessary for its accurate localization.

References:

1. Royal College of Radiologists. Making the Best Use of a Department of Clinical Radiology. Guidelines for Doctors, 5th ed. London, 2003.
2. Etherington RJ, Hourihan MD. Localisation of intraocular and intraorbital foreign bodies using computed tomography. Clin Radiol. 1989 Nov;40(6):610-4. [Medline]
3. Saeed A, Cassidy L, Malone DE, Beatty S. Plain X-ray and computed tomography of the orbit in cases and suspected cases of intraocular foreign body. Eye. 2007 Jun 8; [Epub ahead of print]. [Medline]