Veterinary Diagnostic Imaging

History and clinical signs

A 2-year-old, neutered male, Labrador retriever was referred from northern Ontario with a history of several wounds in the ventral region of the neck that had had chronic discharge over a 6-mo period. The dog also exhibited unresolved left foreleg lameness. Six months prior, the dog was treated for accidentally impaling itself with a sharp stick while running and playing fetch with its owner. At the time of the injury, the owner removed an approximately 15-cm long stick from a penetrating wound in the dog’s pharynx. Most of the plant material removed initially was deeply embedded into the ventral musculature of the neck. Two large draining tracts developed soon afterwards along the ventral aspect of the neck. The referring veterinarian had attempted to treat the fistulous tracts in 2 separate exploratory surgeries, using drainage tubes, and had placed the dog on 4 separate courses of different antibiotics; amoxicillin (Apo. Aoxi; Apotex, Toronto, Ontario), 20 mg/kg bodyweight (BW), PO, q12h, enrofloxacin (Baytril; Bayer HealthCare, Toronto, Ontario), 5 mg/kg BW, PO, q12h, clindamycin (Novopharm, Toronto, Ontario), 10 mg/kg BW, PO, q12h, and marbofloxacin (Zenequin; Pfizer Animal Health, Kirkland, Quebec), 2.75 mg/kg BW, PO, q24h, with no response. Fluid discharged from the fistulous tracts could not be cultured and sensitivity tested, since this type of testing was not locally available to the veterinarian.

The volume of discharge from the tracts was significant, but it could be managed by the owners of the dog, whose primary concern was their pet’s foreleg lameness and quality of life. Keeping this in mind, and in an attempt to avoid a 3rd and potentially aggressive exploratory surgery, the veterinarian referred the dog for further diagnostic imaging. There was a suspicion that a fragment of the original organic material was still imbedded in the neck. It was hoped that further diagnostic imaging would help to localize the foreign body and, thereby, minimize the risks associated with surgical removal. As any remaining plant material had, by this time, been present in the body for almost 6 mo, there was some consideration as to which imaging modality would best identify the offending organic mass. After this length of time, the plant material would have been subjected to the effects of inflammation and might not have maintained its integrity.

The recommendation was for: an ultrasonographic examination (ATL HDI 5000; Philips Medical Systems, Markham, Ontario) first, due to its lower cost, with a Spiral Computed Tomography (CT) scan (Toshiba Express CT Scanner; Toshiba Medical Systems, Markham, Ontario) to follow if the 1st examination was either undiagnostic or inconclusive. Before any type of imaging was commenced, 2 rubber feeding tubes (Sovereign; Tyco Healthcare Group LP, Mansfield, Massachusetts, USA) were advanced into the largest of the fistulous tract openings until they met with resistance to provide multiple reference points on each of the examinations. The investigative ultrasonographic examination, using an L12-5 probe, outlined a diffuse area of inflammation in the caudoventral aspect of the neck that was surrounded by vessels on 3 fronts (Figure 1). There was no direct visualization of a foreign body.

Figure 1.

A color Doppler ultrasonographic image demonstrating a hypoechogenic area (arrowheads) that represents the cranial margin of the inflammatory tissues surrounding the organic foreign body. Note the proximity to the jugular vein (long arrow).

A Spiral CT examination with contrast (Omnipaque 350; Amersham Health, Oakville, Ontario) was initiated to further outline any abnormal densities and to demonstrate their relationship with the surrounding vasculature. The CT examination clearly illustrated a linear foreign body outlined by a radiolucent contour, similar to that previously described with respect to a wooden foreign body (1,2). The CT examination indicated that the foreign body was in the sternocephalic muscle mass, just ventrolateral to the positioning of the cranially placed tube and transecting the caudally placed one (Figures 2 and 3). The organic density was 1.5 cm lateral to the outer wall of the trachea at its center, and at a total depth of 3.4 cm from the incision line of the most probable surgical approach (Figures 2 and 3).

Figure 2.

A) A 2-mm thick contrast enhanced CT image demonstrating the hollow wooden fragment (long arrow) and the surrounding inflammatory tissues (arrow heads). The 2 curved arrows outline the rubber tubes that were placed pre-operatively to help localize the lesion. B) Color 3D CT reconstruction in the same area as in the image to the left. Note that the extent of the inflammatory tissue (arrowheads) is more clearly outlined. The fenestrated rubber tubes are also more prominent and easily identified.

Figure 3.

This collage includes 2 CT reconstructions: A) is a lateral view of the neck. The linear lesion surrounded by arrows illustrates the wooden foreign object and its hollow center, B) is the same object as seen in a coronal projection. C) a photograph of the wooden fragment (white arrow) as presented during surgery following careful blunt dissection. The orange rubber tubing is seen to the side of the foreign body.

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Discussion

Our clinical diagnosis was that of a 9-cm wooden foreign body (Figure 3) lodged in the sternocephalic muscle in the caudal part of the neck. Multidetector CT and magnetic resonance imaging (MRI) have been described as being useful in localizing foreign bodies as small as 0.1-mm steel wire seen as intraocular densities in small animals (3,4). Spiral CT was used to locate porcupine quills in the thorax of a dog that had punctured and resulted in the eventual collapse of a lung lobe (unpublished observations). This had resulted in an acute episode of pneumothorax. The capability of CT to detect foreign bodies of plant origin in difficult to localize areas, such as the spinal canal, has also been reported (5).

After the CT images and 3D reconstructions (Figure 3) had been evaluated, the surgery planned for the localization, exposure, and removal of the wooden foreign body was uneventful with minimal soft tissue trauma. Samples for culture and sensitivity testing (Vita-Tech, Markham, Ontario) were taken directly from the surgical site; a scanty growth of both Corynebacterium spp. and Enterococcus faecalis was recorded. Both were sensitive to ampicillin, penicillin, and enrofloxacin. A pair of Penrose drains was placed for 3 d following the surgery, as postoperative drainage was anticipated.

The left foreleg lameness soon resolved postoperatively. We believed it was the result of intramuscular pain, secondary to a space-occupying lesion within the body of the muscle. Contracture of the injured muscle during movement of the forelimb would have resulted in the compression of the muscle fibers against the foreign body, causing sharp pain. We suspect that the outer epimysium fascial layer that envelops the body of the sternocephalic muscle would have effectively limited the ability of the tissues to compensate for the additional volume occupied by the firm foreign body. The rapid resolution of the lameness, as well as the lack of proximity of the foreign body to the brachial plexus, makes it unlikely that it was neurological in origin. Computed tomography images of the axilla show that the inflammatory tissue did not envelop the nerve roots of the brachial plexus (Figure 4), lending more weight to the suspicion that the foreleg lameness was predominantly induced through inflammatory musculoskeletal pain.

Figure 4.

A) An axial CT view near the level of the thoracic inlet. This image was created to evaluate the relationship between any of the inflammatory tissues (arrow) and the brachial plexus (curved arrow). The enhanced reactive tissue is less clearly defined, as the contrast material had already started to clear from the body through renal elimination. In some tissues, this can occur in less then 1 min. B) A 3D CT color reconstruction that better outlines the area of enhancement (arrow) and its distance from the plexus.

Advanced diagnostic imaging, such as high frequency ultrasound and Spiral CT scanning proved very useful in resolving this dog’s condition. Of particular interest is the sensitivity of the CT in outlining the wooden foreign body even 6 mo after its initial penetration of the body. Rather than “looking for a needle in a haystack,” it was indubitably preferable, to have the exact location of the offending structure prior to implementing surgery. When all of the important structures that must be avoided in the neck during an exploratory surgery are considered, going in blindly did not seem to be a viable option. The decision by the original veterinarian to refer the patient proved to be invaluable, as the hope was to accurately localize the foreign body prior to any further attempts at surgical removal.

Figure 5.

A photograph of the 9-cm wood fragment that was removed from the dog. Note that after many months of being embedded in muscle, there is very little decomposition of organic material.