• View in gallery
    Figure 1

    Precontrast (A and B; bone window [window width, 4,000 HU; window level, 500 HU]) and approximately 2 minutes postcontrast (C and D; soft tissue window [window width, 400 HU; window level, 50 HU]) dorsal (A and C) and transverse (B and D) CT images of the right manus of a 4-year-old 19.1-kg female spayed German Shorthaired Pointer with nonhealing wounds and purulent discharge adjacent to the surgical site of en bloc resection performed 1 month earlier for an ulcerative soft tissue mass protruding from the dorsal aspect between digits 3 and 4. Lateral is toward the left in all images; dorsal is toward the top in B and D. The lines across the dorsal plane images represent the plane of transverse images.

  • View in gallery
    Figure 2

    Same images as in Figure 1. A and B—A mineral-dense structure (white arrow) is in the soft tissues, palmar to the third and fourth metacarpal bones and proximal phalanges. There is also mild, smoothly marginated, multifocal, periosteal new bone formation along the third and fourth metacarpal bones (arrowheads). C and D—There is heterogeneously contrast-enhancing fluid and soft tissue dense material (open black arrows) that surrounds a foreign body and tracks dorsally between the third and fourth metacarpal bones and communicates with the nonhealing wounds on the dorsal aspect of the paw.

  • 1.

    Ober CP, Jones JC, Larson MM, et al. Comparison of ultrasound, computed tomography, and magnetic resonance imaging in detection of acute wooden foreign bodies in the canine manus. Vet Radiol Ultrasound. 2008;49(5):411418.

    • Search Google Scholar
    • Export Citation
  • 2.

    Aras MH, Miloglu O, Barutcugil C, et al. Comparison of the sensitivity for detecting foreign bodies among conventional plain radiography, computed tomography, and ultrasound. Dentomaxillofac Radiol. 2010;39:7278.

    • Search Google Scholar
    • Export Citation
  • 3.

    Pattamapaspong N, Srisuwan T, Sivasomboon C, et al. Accuracy of radiography, computed tomography and magnetic resonance imaging in diagnosing foreign bodies in the foot. Radiol Med (Torino). 2013;118:303310.

    • Search Google Scholar
    • Export Citation
  • 4.

    Tollefson CR, Hiebert EC, Lee AM, et al. What is your diagnosis? J Am Vet Med Assoc. 2018;253(11):14051407.

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What Is Your Diagnosis?

Christine M. MesecherDepartment of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS

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Christopher R. TollefsonDepartment of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS

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Marc A. SeitzDepartment of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS

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Abstract

In collaboration with the American College of Veterinary Radiology

Abstract

In collaboration with the American College of Veterinary Radiology

History

A 4-year-old 19.1-kg spayed female German Shorthaired Pointer was reevaluated because of nonhealing wounds with purulent discharge adjacent to the surgical site of en bloc resection performed 1 month earlier for an ulcerative soft tissue mass protruding from the dorsal aspect between digits 3 and 4 of the right forelimb. Nine months prior, the dog returned home with a stick protruding from the right forepaw after roaming around the owner’s property. The wound did not heal, and the dog had mild chronic lameness despite antimicrobial treatment and the primary veterinarian performing 3 exploratory surgeries. Before en bloc resection, cytologic examination of a fine-needle aspirate sample of the mass revealed a moderate number of degenerate neutrophils with occasional phagocytized rod-shaped bacteria. Radiography revealed a convex, smoothly marginated, soft tissue opaque mass (approximately 2.5 X 0.5 cm) that bulged from the dorsal soft tissues at the level of the mid to distal diaphyses of the third and fourth metacarpal bones, widening of the corresponding interdigital space, and mild smoothly marginated periosteal proliferation along the lateral and dorsal aspects of the mid diaphysis of the third metacarpal bone (not shown), and the owner declined CT. Histologic examination of resected tissues revealed dermal fibrosis and granulation tissue with no apparent inciting cause. There was no evidence of fungal organisms or neoplasia, and the lesion appeared completely excised on the sampled sections. Antimicrobials (amoxicillin, 21 mg/kg, PO, q 8 h, for 6 weeks; and cefpodoxime, 10 mg/kg, PO, q 24 h, for 6 weeks) were prescribed to treat Actinomyces spp and Enterobacter cloacae, respectively, based on results from bacterial culture and susceptibility testing.

On recheck examination, the dog was bright and alert, had no sign of lameness, but had nonhealing wounds with purulent discharge adjacent to the surgical site on the right forepaw. The remaining findings were unremarkable. The dog was sedated with dexmedetomidine (5.0 µg/kg, IV) and hydromorphone (0.02 mg/kg, IV) and then positioned in sternal recumbency for CT (Aquilion 16, Toshiba) of the right manus with imaging settings of 50 mA, 120 kVp, 2,500-ms exposure time, 0.5-mm slice thickness, and 512 X 512 matrix with a high-spatial-frequency bone algorithm (FLO3 convolutional kernal) before and approximately 2 minutes after the administration of a nonionic iodinated contrast agent (ioversol [Optiray 320, Libel-Flarsheim Co], 700 mg/kg, IV; Figure 1).

Figure 1
Figure 1
Figure 1
Figure 1
Figure 1

Precontrast (A and B; bone window [window width, 4,000 HU; window level, 500 HU]) and approximately 2 minutes postcontrast (C and D; soft tissue window [window width, 400 HU; window level, 50 HU]) dorsal (A and C) and transverse (B and D) CT images of the right manus of a 4-year-old 19.1-kg female spayed German Shorthaired Pointer with nonhealing wounds and purulent discharge adjacent to the surgical site of en bloc resection performed 1 month earlier for an ulcerative soft tissue mass protruding from the dorsal aspect between digits 3 and 4. Lateral is toward the left in all images; dorsal is toward the top in B and D. The lines across the dorsal plane images represent the plane of transverse images.

Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.19.12.0647

Formulate differential diagnoses, then continue reading.

Diagnostic Image Findings and Interpretation

In the soft tissues palmar to the right third and fourth metacarpal bones and proximal phalanges, there was an irregularly marginated, lancet-shaped, well-demarcated, peripherally mineral-dense, non–contrast-enhancing structure (approximately 0.3 X 0.4 X 3.5 cm; Figure 2). On precontrast images viewed in a soft tissue window (window width, 400; window level, 50), this structure was hyperdense (ranging between 130 and 250 HU) to the surrounding soft tissues (ranging between 50 to 80 HU). This structure was also surrounded by heterogeneously contrast-enhancing fluid and soft tissue dense material that was surrounded by a strongly contrast-enhancing rim. Additionally, this material tracked dorsally between the third and fourth metacarpal bones and communicated with the cutaneous wounds identified on physical examination. There was also mild, smoothly marginated, multifocal, periosteal new bone formation along the third and fourth metacarpal bones in the region of the abnormal soft tissues. Thus, CT confirmed the presence of a foreign body in the palmar soft tissues of the metacarpal region and reactive periostitis in the right manus.

Figure 2
Figure 2
Figure 2
Figure 2
Figure 2

Same images as in Figure 1. A and B—A mineral-dense structure (white arrow) is in the soft tissues, palmar to the third and fourth metacarpal bones and proximal phalanges. There is also mild, smoothly marginated, multifocal, periosteal new bone formation along the third and fourth metacarpal bones (arrowheads). C and D—There is heterogeneously contrast-enhancing fluid and soft tissue dense material (open black arrows) that surrounds a foreign body and tracks dorsally between the third and fourth metacarpal bones and communicates with the nonhealing wounds on the dorsal aspect of the paw.

Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.19.12.0647

Treatment and Outcome

The patient underwent a fifth surgical procedure to remove the foreign body. The foreign body was a small sliver of wood, likely originating from the historically reported stick that impaled the patient’s right paw. At last follow-up 11 months after surgery, the owners reported no further recurrence of the mass or draining tracts.

Comments

Cutaneous and musculoskeletal foreign bodies are common in veterinary species.1 In dogs and cats, the distal extremities are most commonly affected.1 Most of the soft tissue and osseous changes that occur with chronic foreign bodies are relatively nonspecific. Ergo, definitive diagnosis relies on the identification of the offending material on imaging studies.13

Radiography is readily available in most veterinary hospitals and hence the most common first-line imaging modality. Mineral, metal, glass, and larger recently acquired wooden foreign bodies are usually identifiable on radiographs.2 Orthogonal and oblique projections increase the likelihood of detection; however, foreign bodies are capable of unpredictable migration, presenting an additional challenge if their location falls outside of the selected field of view. Unfortunately, wood or other plant material is the most common type of foreign body in veterinary species, and the material is usually inconspicuous on radiographic images when located in soft tissues because of a small size or when chronic in nature.1,2 Subcutaneous gas resulting from acute penetration or gas-producing bacteria can sometimes act as a negative contrast agent, improving visualization of part or all of the foreign body4; however, this finding was not present for our patient. For the dog of the present report, the differential diagnoses for the persistent mass and described radiographic findings included an occult foreign body, fungal granuloma, or a bacterial etiology (eg, abscess or cellulitis) not sensitive to the previously prescribed antimicrobials. Reactive periostitis was considered most likely for the smoothly marginated periosteal proliferation along the third metacarpal bone; however, early osteomyelitis could not be entirely excluded.

As underscored by findings in our patient, when radiography does not identify the inciting cause, more advanced and accurate imaging modalities should be pursued, such as CT, ultrasonography, or MRI.2,3 Unlike radiography, CT is ideal for both the diagnosis and surgical planning for removal of various foreign bodies.2,3 A primary advantage of CT, compared with radiography, is its superior contrast resolution. Computed tomography eliminates superimposition and thereby improves the delineation of size, shape, and location of structures.2 It also allows differentiation of more subtle differences in density (in HUs) of tissues and structures, as evident for the dog of the present report. The density of wooden foreign bodies varies drastically and depends on the hardness of the wood, its water content, and its duration in the patient.1 In general, recently acquired wooden foreign bodies are hypodense to surrounding muscle, whereas wooden foreign bodies of longer duration are iso- to hyperdense due to their absorption of water secondary to edema and inflammation or because of dystrophic mineralization.1,3 The foreign body in our patient was hyperdense, compared with the surrounding soft tissues, likely explained by dystrophic mineralization given the chronicity of the foreign body.

The ability to detect wood foreign bodies with CT improves with ≥ 1 of the following conditions. First, the foreign body is composed of a material that attenuates differently than the surrounding soft tissues. Second, the region of interest can and should be viewed in multiple windows (eg, soft tissue, bone, or lung) and reconstructed imaging planes. Finally, if a foreign body is not seen on initial image sets, repeat imaging after IV injection of an iodinated contrast agent can potentially improve conspicuity by delineating subtle soft tissue changes that occur with edema, inflammation, cellulitis, and abscess formation. For the dog of the present report, pre- and postcontrast CT was integral to achieving a definitive diagnosis and localizing the foreign body to guide successful surgical removal. Although the foreign body was easily seen on precontrast image sets, contrast agent administration allowed for better surgical planning by delineating the secondary soft tissue changes and the draining tract.

Ultrasonography is also superior to radiography in identifying wood foreign bodies and arguably less expensive and more readily available than CT. However, given the palmar location of the foreign body in our patient, it was unclear whether ultrasonography could have provided a definitive diagnosis prior to pursuing CT with contrast due to the potential for poor transducer contact and distal acoustic shadowing from the pad surfaces.1 Additionally, MRI may be a useful tool in identifying soft tissue foreign bodies with reportedly similar detection rates as CT.1,3 However, CT may be superior for more chronic foreign bodies because their increased water content causes a hyperintense signal on MRI that resembles and blends into surrounding edema and inflammation. Furthermore, the limited availability and higher cost of MRI, compared with other modalities, limit its clinical utility.

In summary, CT with the administration of a contrast agent was integral to diagnosing and locating the foreign body and guiding its successful surgical removal. In cases where results of radiography are equivocal, CT, ultrasonography, or MRI are all reasonable next steps, each with distinct advantages and disadvantages. However, CT may be superior when a foreign body is located in the distal aspect of an extremity or it has been present for a longer duration.

References

  • 1.

    Ober CP, Jones JC, Larson MM, et al. Comparison of ultrasound, computed tomography, and magnetic resonance imaging in detection of acute wooden foreign bodies in the canine manus. Vet Radiol Ultrasound. 2008;49(5):411418.

    • Search Google Scholar
    • Export Citation
  • 2.

    Aras MH, Miloglu O, Barutcugil C, et al. Comparison of the sensitivity for detecting foreign bodies among conventional plain radiography, computed tomography, and ultrasound. Dentomaxillofac Radiol. 2010;39:7278.

    • Search Google Scholar
    • Export Citation
  • 3.

    Pattamapaspong N, Srisuwan T, Sivasomboon C, et al. Accuracy of radiography, computed tomography and magnetic resonance imaging in diagnosing foreign bodies in the foot. Radiol Med (Torino). 2013;118:303310.

    • Search Google Scholar
    • Export Citation
  • 4.

    Tollefson CR, Hiebert EC, Lee AM, et al. What is your diagnosis? J Am Vet Med Assoc. 2018;253(11):14051407.

Contributor Notes

Corresponding author: Dr. Seitz (marc.seitz@msstate.edu)