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CT/MRI

4-year-old castrated male Labrador Retriever

July 1, 2014
Alex zur Linden DACVR, University of Guelph, ON Canada

Presented on ER for left orbital foreign body

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History

A 4 year old castrated male Labrador Retriever presented on emergency for a left orbital foreign body. Emergency surgery was performed to remove a 2 cm long wooden stick that did not penetrate the globe but extended through the conjunctiva laterally. Patient presented 20 days later for increased discharge from the left eye and ventral strabismus. Examination at this time revealed severe left ventral strabismus, severe enophthalmos, blepharospasm and a mucopurulent ocular discharge. A normal direct and indirect PLR was present. The left eye did not have normal physiologic nystagmus and appeared ‘frozen’ in place. The right eye was normal.

Technique

  • MRI of the head, 1.5 T magnet, GE Signa

Sequences:

  • Dorsal T2-W images (TE 80.8 ms, TR 5166.7 ms, 3 mm slice thickness)
  • Transverse T2-W images (TE 92.2 ms, TR 5550 ms, 4 mm slice thickness)
  • Left oblique sagittal T1-W images (TE 12.5 ms, TR 500 ms, 3 mm slice thickness)
  • Transverse T1-W images (TE 10.1 ms, TR 500 ms, 4 mm slice thickness)
  • Post contrast T1-W images with fat suppression in transverse, dorsal and oblique sagittal planes obtained after intravenous injection of 0.2 ml/kg (0.1 umol/kg) gadopentate dimeglumine.

T2w dor

T2w tra

T1w transverse

T1w oblique parallel to left optic nerve

T1w +C transverse

T1w +C oblique, parallel to the left optic nerve

T1w +C dorsal

Within the left retrobulbar space, ventral to the optic nerve, axial to the left maxillary artery, at the plane of the vertical ramus of the mandible between the temporomandibular joint and the zygomatic salivary gland, is a flat, rectangular shaped structure. This structure has a strong T1 hyperintensity and mild T2 hyperintensity in comparison to the adjacent musculature. This structure has linear striations within it and measures ~ 0.2 cm in width, 1 cm in height and 2.5 cm in length. There is a moderate amount of T2 hyperintense and markedly contrast enhancing tissue surrounding the structure that extends ventral to the left maxillary artery and abuts the left medial pterygoid muscle dorsally, compressing it and mildly displacing it ventrally. At the caudoventral most aspect of these hyperintensity changes, dorsal to the left medial pterygoid muscle, is a focal 4 mm diameter pocket of free fluid that suppresses on FLAIR sequence (images not shown). The left globe is rotated ventrally on all sequences

  1. Rectangular shaped T1 hyperintense structure, left ventral retrobulbar space.
  2. Marked contrast enhancing tissues surrounding the structure with a focal small fluid pocket.

These findings are consistent with a foreign body, suspected to be a fragment of a wooden stick, with surrounding inflammation/infection.

Follow-up and Discussion

The dog went to surgery for removal of the foreign body. The surgeons resected the zygomatic arch and replaced it following surgery, liberated the masseter muscle from the mandible, and resected the vertical ramus to the level of the TMJ to facilitate access to the ventral orbit caudal to the globe. The foreign body was located within the bulbar sheath and was difficult to access due to its location axial to the maxillary artery. The left globe was surgically released but remained slightly deviated ventrally. Orbital tissue was removed and submitted for histopathology that revealed orbital granulation tissue with pyogranulomatous cellulitis and intralesional plant material. Aerobic and anaerobic cultures were negative.

A previous article described characteristic findings of wooden foreign bodies as geometric, markedly hypointense structures on both T1 and T2 weighted sequences surrounded by a thick rim of vascular soft tissue and sometimes a small amount of fluid (1). A case series in humans revealed all wooden foreign bodies to be hypointense (2). A case report in a human revealed at 10 days post-injury a wooden foreign body in the brain was T1-hypointense, that became T1-hyperintense at 64 days post-injury(3). A case report in a dog identified a wooden foreign body that was cylindrical and iso- to hyperintense compared to the adjacent musculature (4). The MR imaging characteristics of wood appear to vary from hypointense on T1W and T2W to hyperintense. It has been suggested that the T1 and T2 values of wood may elongate with time due to absorption of exudate and hematoma (5). The type of wood, any coatings or treatment on the wood, or if the wood is present within an abscess versus a granuloma, may affect the imaging characteristics of wood. Regardless of the intensity changes, the geometric shape of all reported wooden foreign bodies is a common finding.

This case also demonstrates the usefulness of oblique sagittal plane sequences in the plane of the optic nerve when evaluating the retrobulbar space.

References

  1. Dobromylskyj MJ, Dennis R, Ladlow JF and Adams VJ. The use of magnetic resonance imaging in the management of pharyngeal penetration injuries in dogs. Journal of Small Animal Practice, Vol 49, 2008, 74-79.
  2. Peterson JJ, Bancroft LW, Kransdorf MJ. Wooden Foreign Bodies: Imaging Appearance. AJR: 178, March 2002.
  3. Smely C, Orszagh M. Intracranial transorbital injury by a wooden foreign body: re-evaluation of CT and MRI findings. British Journal of Neurosurgery 1999; 13(2): 206-211.
  4. Potanas CP, et al. Ultrasonographic and Magnetic Resonance Imaging Diagnosis of an Oropharyngeal Wood Penetrating Injury in a Dog. J Am Anim Hosp Assoc 2011; 47, e1-6.
  5. Ochiai H et al. Neuroimaging of a Wooden Foreign Body Retained for 5 months in the Temporalis Muscle Following Penetrating Trauma with a Chopstick. Neurol Med Chir (Tokyo) 39, 744-747, 1999

Foreign body postop