Typical bacteria associated with abscesses include Staphylococcus species, Streptococcus species, facultative and obligate anaerobes, Actinomyces pyogenes (recently reclassified as Arcanobacter pyogenes), Bacteroides species, Escherichia coli, Enterobacter species, Pasteurella multocida, Proteus mirabilis, and Pseudomonas aeruginosa.1,3 Although less frequently diagnosed, mycoplasma infections must also be ruled out. The cause of the abscess and the character
of the discharge must be considered when determining the most likely pathogen and most appropriate antimicrobial therapy.
In this case, Actinomyces species and Nocardia species were suspected because of the caseous discharge from the flank wound and the propensity for these microbes to produce
exudates containing sulfur granules. In addition, Actinomyces species and Nocardia species are often found in mixed populations of infections and are commonly associated with foreign bodies.
A foreign body can be identified by using palpation, radiography (plain and computed tomography), fistulography, ultrasonography,
magnetic resonance imaging, or surgical exploration.1,2,4-6 Plain radiography should be performed first to rule out radiopaque foreign bodies, involvement or infection of osseous structures
(periosteal reaction), gas-containing radiolucency, and soft tissue swelling.4,7 Ultrasonography has been shown to be an effective tool for diagnosing nonradiopaque foreign bodies in animals.1,4,8,9 In addition, although fistulography and sinography are effective, they have less sensitivity for diagnosing foreign bodies. 2,4,5
A CBC, a serum chemistry profile, cytology, bacterial and fungal culture, and antimicrobial sensitivity testing should be
used as baseline tests for an animal presenting with an abscess of unknown origin. Histology should also be performed to rule
out a neoplastic process.
Cutaneous sinus tracts from the lumbar, paralumbar, and caudal flank in animals are commonly associated with peritoneal or
retroperitoneal foreign bodies.7 This association may occur because the hypaxial musculature converges in this region, the body tends to wall off and exteriorize
local inflammatory insults, and draining fluid tends to follow the path of least resistance to the skin surface.
Wood fragments, thorns, cocktail sticks, grass, grass awns, surgical swabs, and nonabsorbable sutures have all been reported
as common foreign bodies that lead to chronic draining sinus tracts.2,7 The average duration of clinical signs associated with chronic draining tracts before referral to a surgical specialist
is 9.8 months (range = 0.5 to 33 months).2 And the referring veterinarian performs an average of two (range = one to five) surgical procedures before referral to a
In the human medical literature, an abundance of information regarding spontaneous cutaneous skin fistulae resulting from
a retroperitoneal or abdominal nidus is available. Typically these draining tracts will exit the patient in the caudal flank,10-25 chest wall,26 gluteal area,27 or thigh.28 The nidus for infection in these reported cases in people included a retroperitoneal pseudomyxoma,10 gastrointestinal tract disease,12,13,17,25,27-29 skeletal disease,12,13,15,23 urinary or reproductive tract disease,12,13,16,23,24 surgical complication after laparoscopic cholecystectomy,14,19 surgical complication after hemorrhoidectomy,11 idiopathic disease,18 and unspecified disease.20,22 People with psoas or flank abscesses are often characterized as having a psoas sign—a triad of fever, flank swelling or pain, and pain or decreased range of motion in the ipsilateral hip.
The clinical approach to chronic draining tracts and skin sinuses should include a thorough history, a physical examination,
blood evaluation, cytology, histology, bacterial and fungal culture and antimicrobial sensitivity testing (aerobic and anaerobic),
radiography, and advanced imaging if appropriate. A flank abscess in animals should evoke high clinical suspicion of a retroperitoneal
or dorsal abdominal musculature nidus as a source of the cutaneous fistula or flank swelling.
Although not illustrated in its entirety in this case, the psoas triad (seen in people) of fever, flank swelling or pain,
and pain or decreased range of motion of the ipsilateral coxofemoral joint can further increase clinical suspicion of a flank
abscess and a concurrent retroperitoneal or abdominal nidus. This case also illustrates the use of intraoperative ultrasonography
to help identify, locate, and remove a deep retroperitoneal foreign body.
This case report was provided by Mathieu M. Glassman, VMD, and Daniel D. Smeak, DVM, DACVS, Department of Veterinary Clinical
Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio. Dr. Glassman’s present address is Friendship
Hospital for Animals, 4105 Brandywine St. N.W., Washington, D.C. 20016.