British Journal of Radiology (2004) 77, 77-78
© 2004 British Institute of Radiology
doi: 10.1259/bjr/10205817
A summer trip
N Mulholland, MA, MRCP
and
S Connor, MRCP, FRCR
Department of Neuroradiology, Kings College Hospital, Denmark Hill, London SE5 9RS, UK
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Introduction
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A 91-year-old woman presented to the accident and emergency department in June following a fall in the garden earlier that day. She presented with poor vision in the right eye. She had no past medical history of note. On examination, her Glasgow Coma Scale was initially 13/15 but improved to 15/15. She was found to have a tense eye with proptosis and conjuctival chemosis. Extraocular movements were minimal. She exhibited no perception of light in the right eye, a relative afferent pupillary defect and absent corneal sensation.
She was referred for CT of the orbits, with 3 mm section thickness (Figure 1
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What does the CT show? What is the diagnosis?
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Answer
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Axial CT of the orbits photographed with window width 450 and level 35 revealed an area of low density indistinguishable from air adjacent to a fracture of the right greater wing of sphenoid and further low density areas within the anteromedial orbit. Patchy intraconal and extraconal high density areas felt to represent intraorbital haematoma were noted. The patient was transferred to a neurosurgical and ophthalmology unit. Subsequent review of the images using a window width of 2000 demonstrated that the abnormalities were not due to air (Figure 2a - see arrows). It represented a geometric area of low density with a linear internal texture consistent with a retained wooden intraorbital foreign body (IFB) (Figure 2b - see arrowhead). This was confirmed at operation to be a wooden cane measuring 1.5 x 4.2 cm. Further small pieces of wood, grass and haematoma were also removed. The aetiology of the blindness was thought to be direct optic nerve injury and likely to be irreversible.
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Figure 2. Axial CT sections through (a) the mid and (b) superior orbits demonstrate areas of low density (arrow) representing intraorbital wooden foreign body.
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This report illustrates the potential misinterpretation of wooden IFBs as intraorbital air [1]. The appearance of wooden foreign bodies at CT is very variable and depends on the degree of hydration [2], presence of paint [3], whether it is fresh or dry and the time interval between injury and examination. The CT density of wood has been described as ranging from -984 HU to +110 HU [1] and is particularly dependent on the air or water content of the cellulose matrix [2]. Quantitative assessment of the Hounsfield numbers may prove difficult with small wooden fragments due to partial volume effects. However, the geometric interface between the area of low attenuation and the orbital soft tissues together with the linear shape may imply the presence of a wooden foreign body. More importantly, rather than using standard window settings, the use of wide window widths (up to 1000 HU) should be used to distinguish intraorbital wood from air [1, 4].
Due to the increased availability of CT and its ability to detect associated abnormalities such as fractures and abscesses, it seems appropriate to use this as the imaging method of choice. If CT is negative and there is a high clinical suspicion of a wooden IFB, then MRI is sometimes helpful [5]. However, there may remain difficulty in differentiating dry wood from gas [4].
Although external wounds may be minimal, the porous organic nature of wooden IFBs and possible microbiological contents lead to almost certain abscess formation and severe visual sequelae if left untreated and most surgeons suggest early treatment. In the pre-antibiotics era mortality was as high as 25% [6]. We reiterate the importance of optimizing the image contrast with wide window width when using CT to detect the presence of wooden foreign bodies in the setting of penetrating orbital trauma.
Received for publication March 18, 2003.
Accepted for publication April 24, 2003.
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References
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- Ho VT, McGuckin JF Jr, Smergel EM. Intraorbital wooden foreign bodies: CT and MR appearance. AJNR Am J Neuroradiol 1996;17:134–6.[Abstract]
- Hansen JE, Gudemna SK, Holgate RC, Saunders RA. Penetrating intracranial wood wounds: clinical limitations of computerised tomography. J Neurosurgery 1998;68:753–6.
- Myllyla V, Pyhtinen J, Paivansalo M, Tervonen O, Korskela P. CT detection and location of intraorbital foreign bodies: experiments with wood and glass. ROFO 1987;146:6390–430.
- McGuckin JF Jr, Akhtern N, Ho VT, Smergel EM, Kubacki EJ, Villafana T. CT and MR evaluation of a wooden foreign body in an in vitro model of the orbit. AJNR Am J Neuroradiol 1995;17:129–33.
- Smely C, Orszagh M. Intracranial transorbital injury by a wooden foreign body: re-evaluation of CT and MR findings. Br J Neurosurg 1999;13:206–11.[Medline]
- Linberg JV. Management of orbital trauma. Duanes clinical ophthalmology, Vol 87. Philadelphia: JB Lippincott, 1994:11–5.
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