A 4.5-year-old intact female Labrador retriever was presented to The Ohio State University Veterinary Teaching Hospital (OSU) for evaluation of a nonhealing wound on the left caudal flank. The farm dog spent about 90% of its time outdoors.
A left flank abscess had initially been noted by the owner and diagnosed by the referring veterinarian about two years before presentation to OSU. Treatment by the referring veterinarian had included débridement of the abscess and antimicrobial therapy (cephalexin, orbifloxacin, and ciprofloxacin used in combination or individually during various treatment episodes) based on the results of bacterial culture and antimicrobial sensitivity testing of representative tissue samples that had also been submitted for histologic evaluation.
Local surgical exploration and débridement had not revealed a nidus of infection. Histology had revealed chronic, focally extensive necrotizing pyogranulomatous dermatitis with sinus tracts, cavitations, and fibrosis. Aerobic bacterial culture results had revealed Pseudomonas aeruginosa and Streptococcus uberis. The swelling and drainage would diminish with the antimicrobial therapy, but these signs would return shortly after the antibiotic course ended.
Figure 1. The cutaneous draining tracts in the dog's left flank on presentation.
Physical examination and diagnostic testing
On initial physical examination at OSU, the dog had no abnormalities other than a series of draining tracts in its left flank with a small amount of caseous exudate (Figure 1). The dog weighed 80.2 lb (36.4 kg), with a body condition score between 2 and 3 (out of 5). The results of the complete blood count (CBC) and serum chemistry profile were unremarkable except for an increased globulin concentration (3.6 g/dl; reference range = 2.2 to 2.9 g/dl).
Differential diagnoses for an increased globulin concentration include chronic antigenic stimulation secondary to infectious or inflammatory disease, immune-mediated disorders, neoplasia, and idiopathic causes (macroglobulinemia and benign monoclonal gammopathy). Because the globulin concentration was only mildly elevated and infection or inflammation was suspected to be the cause, protein electrophoresis and other diagnostics were not pursued to rule out other differential diagnoses of hyperglobulinemia.
Figure 2. A longitudinal ultrasonogram of the foreign body and associated draining tract. The hyperechoic linear foreign body is between the + signs. The aorta is not seen in this image.
Cytologic evaluation of the fluid draining from the wound revealed a septic exudate. Most of the cells were degenerate neutrophils with multiple types of intracellular and extracellular bacterial rods and cocci. No other etiologic agents were found.
The results of an abdominal radiographic examination were normal, but because of the location of the skin lesion, abdominal ultrasonography was performed to rule out a retroperitoneal abscess (Figures 2 & 3). Intra-abdominal structures were normal. However, a 4-cm long, linear hyperechoic structure was seen in the left midlumbar hypaxial musculature, running parallel to the vertebral column and within 1 cm of the aorta. The soft tissues surrounding the foreign body were hypoechoic. A 7-cm diameter hypoechoic linear tract extended from the hyperechoic structure to the draining skin lesions of the left flank. The final ultrasonographic diagnosis was a retroperitoneal linear foreign body within the hypaxial musculature.
Figure 3. A transverse ultrasonogram of the foreign body (FB) and associated draining tract.