Diagnosis and successful medical management of a renal corticomedullary abscess in a dog

Abstract

A 10-year-old spayed female mixed-breed dog was brought to the Ohio State University Veterinary Medical Center because of a suspected mass located to the right kidney. The mass was diagnosed by abdominal ultrasound following a recurrent lower urinary tract infection. Abdominal computed tomography revealed 2 isoattenuating, peripherally hypoattenuating, and centrally non-contrast-enhancing nodules in the right kidney; the larger one measured 1.9 cm. Initial attempts at fine-needle aspiration were unsuccessful. The dog was returned and the mass was aspirated using ultrasound guidance under heavy sedation. Cytology confirmed the presence of septic inflammation, consistent with a renal corticomedullary abscess. The dog was administered oral enrofloxacin (15 mg/kg, q24h) after diagnosis. Ultrasound guidance was used 2 wk later, under general anesthesia, to achieve percutaneous drainage of ~0.25 mL of fluid and instillation of 5.7 mg (0.25 mL) of enrofloxacin into the abscess capsule. Two weeks after percutaneous drainage, ultrasound examination showed complete resolution of the renal corticomedullary abscess. Urine culture confirmed resolution of the urinary tract infection. To the authors’ knowledge, kidney-sparing medical management has never been successfully reported in a dog with a renal corticomedullary abscess.

Key clinical message:

Renal corticomedullary abscesses occur infrequently in dogs. Medical management is feasible and can result in complete resolution of clinical signs and imaging abnormalities.

Renal abscessation is an infrequent condition of the kidney, reported most commonly in humans (1–3). Infection can be contained to the renal parenchyma as a renal cortical or corticomedullary abscess, or between the renal capsule and parenchyma as a subcapsular abscess (2). Abscessation can form secondary to hematogenous spread of bacteria or secondary to ascending lower urinary tract infections (2–4). Subcapsular abscesses have been most frequently reported in dogs (5–13). A renal cortical abscess was reported in 1 dog, suspected to be secondary to polycystic kidney disease (14). Treatment for renal abscesses in dogs has been limited to surgical intervention, with unilateral nephrectomy, partial nephrectomy, and surgical drainage reported (7,8,11,14). Medical management with oral antibiotics has been attempted for subcapsular abscesses in dogs; however, it has ultimately been unsuccessful (9,12,13). This is the first case of a renal corticomedullary abscess in a dog that was treated successfully, to complete resolution, with medical management.

CASE DESCRIPTION

A 10-year-old spayed female mixed-breed dog was brought to the Ohio State University Veterinary Medical Center (OSU-VMC) Surgical Oncology Service for further assessment of a suspected mass associated with the caudal pole of the right kidney. The dog had been presented to the OSU-VMC Rehabilitation Service 6 wk earlier, for further treatment of elbow dysplasia and a week-long history of hyporexia, lethargy, and improving hind-limb paresis. A neurologic examination revealed tetraparesis and proprioceptive ataxia, with proprioceptive deficits seen to be worse in the hind limbs. There was pain on palpation of the caudal cervical and lumbosacral spine. Due to suspicion of a cervical myelopathy, magnetic resonance imaging of the cervical spine was recommended; however, due to improvement of the hind-limb paresis, it was elected instead to move forward with a complete blood (cell) count (CBC) and chemistry panel. The CBC revealed a mild, non-regenerative anemia [hematocrit: 37%, reference interval (RI): 40 to 59%] and an inflammatory leukogram (leukocytes: 17.43 × 10⁹/L, RI: 4.8 to 13.9 × 10⁹/L; segmented neutrophils: 15.34 × 10⁹/L, RI: 2.6 to 10.8 × 10⁹/L; band neutrophils: 0.17 × 10⁹/L). The chemistry panel documented increased alkaline phosphatase (549 IU/L, RI: 12 to 133 IU/L), hypercholesterolemia (567 mg/dL, RI: 122 to 345 mg/dL), hyperglobulinemia (3.9 g/dL, RI: 1.7 to 3.4 g/dL), and hypoalbuminemia (2.5 g/dL, RI: 3.3 to 4.2 g/dL).

The dog was seen by the primary veterinarian 2 d later due to continued anorexia. No lower urinary tract signs were reported at that time. Thoracic radiographs were obtained and an abdominal ultrasound and a urinalysis were completed. Abdominal ultrasound showed a cavitated mass associated with the caudal pole of the right kidney. Urinalysis was consistent with a urinary tract infection. Thoracic radiographs were unremarkable. The dog was administered amoxicillin clavulanic acid (13 mg/kg, PO, q12h). A urinalysis taken 5 d later showed continued evidence of a lower urinary tract infection. Culture and susceptibility examinations done at this time showed growth of Escherichia coli that was susceptible to amoxicillin clavulanate. The dog then began a 6-week course of amoxicillin clavulanate (13 mg/kg, PO, q12h).

Four days following completion of the course of amoxicillin clavulanate, the dog was brought back to the OSU-VMC Surgical Oncology Service for further workup of a suspected renal tumor. The dog was reported to be doing clinically better at this time, with no symptoms associated with a lower urinary tract infection. On presentation, the dog was bright and alert. The physical examination was overall unremarkable, except for mild cervical pain and proprioceptive deficits in all 4 limbs. A CBC and chemistry panel were taken and showed a mild, non-regenerative anemia (hematocrit: 36%, RI: 40 to 59%), increased alkaline phosphatase (649 IU/L, RI: 12 to 133 IU/L), and hypercholesterolemia (391 mg/dL, RI: 122 to 345 mg/dL). A urinalysis showed an active sediment with bacteriuria. A urine culture was submitted at that time, and further antibiotic therapy was delayed until the results were received. Four days later, the urine culture showed growth of E. coli susceptible to amoxicillin.

Due to the suspected renal mass, computed tomography (CT) of the thorax and abdomen was undertaken. A CT scan of the thorax revealed a single 3-millimeter soft-tissue nodule in the left caudal lung lobe. A triple-phase contrast abdominal CT scan identified 2 round, isoattenuating, peripherally hypoenhancing nodules with a central area of minimal contrast enhancement in the cranial and caudal cortices of the right kidney (Figure 1). The larger of these measured ~1.9 cm in diameter. The lesion in the cranial pole created a small bulge in the renal capsule. The pelvis of the right kidney was mildly dilated, measuring 3.5 mm. Both kidneys had non-contrast-enhancing linear and concave defects noted in the cortices. The cranioventral urinary bladder wall was thickened with 2 pedunculated, contrast-enhancing polypoid lesions extending from the ventral wall. Based on these findings, we ruled out renal abscesses, granulomas, and neoplasms with pyelectasia of the renal pelvis for the lesions in the right kidney. The other linear and concave defects were suspected to be renal cortical infarcts. The changes to the urinary bladder were suspected to be secondary to polypoid cystitis, with neoplasia considered less likely. The pulmonary nodule was suspected to be a granuloma or neoplastic lesion.

FIGURE 1.

A to C — Post-contrast computed tomographic images of a dog that was presented for evaluation of a renal mass. The right kidney has circular cortical lesions with isoattenuating, hypoenhancing outer rings with central regions of less contrast uptake. These are present in the cranial and caudal poles of the kidney on the sagittal view (B). A single lesion is seen within the renal parenchyma on the transverse (A) and dorsal (C) views.

Ultrasound-guided aspiration of the lesions in the right kidney was attempted; however, samples were nondiagnostic. On ultrasound examination, the lesion appeared as a hypoechoic to anechoic structure within the renal parenchyma (Figure 2). Five days later, ultrasound guidance was used under heavy sedation to successfully retrieve an aspirate from the cranial renal lesion. Cytological examination confirmed the presence of a marked septic neutrophilic inflammation with cocci, diplococci, and rare rod bacteria.

FIGURE 2.

Abdominal ultrasound image of a dog that was presented for further evaluation of a renal mass. This is a transverse view of the right kidney. In the cranial pole, there is a hypoechoic to anechoic, circular lesion. The hyperechoic focus in the lesion is a needle, inserted for purposes of aspiration.

Since cytological results confirmed the presence of a renal corticomedullary abscess, the dog was administered oral enrofloxacin, 15 mg/kg, q24h. Treatment options discussed with the owner included percutaneous drainage and antibiotic instillation or nephrectomy to remove the diseased kidney. The owner elected to move forward with percutaneous drainage, and the dog was returned 2 wk after diagnosis due to the owner’s scheduling preference. The dog was placed under general anesthesia for percutaneous drainage of the abscesses. Drainage produced only a small amount (~0.25 mL) of turbid, tan-colored material from the cranial lesion. An equal volume of 22.7 mg/mL enrofloxacin, ~5.7 mg (0.17 mg/kg), was injected into the capsules of both abscesses. The dog did well immediately after treatment and continued to receive oral enrofloxacin.

Approximately 14 d later, the dog was returned for a recheck. The dog was reported to be doing well at home, with resolution of all clinical signs. A focal ultrasound was repeated and showed resolution of the renal abscesses, with hyperechoic, non-shadowing foci in the location of the abscess. These findings were suspected to be secondary to cortical fibrosis, chronic infarcts, or dystrophic mineralization. There was no bacterial growth on urine culture recheck. The dog continued to receive antibiotics for 4 wk after negative urine culture. Six months following initial diagnosis and treatment of the abscess, the dog continued to do well clinically, with no evidence of abscess recurrence on repeated abdominal ultrasound examinations.

DISCUSSION

A renal cortical abscess has been reported in only 1 dog in the recent veterinary literature (14). However, several reports have discussed subcapsular abscesses, which may seem similar (5–13). Renal abscesses have been more frequently reported in human medicine (1–3). They can be located within the renal parenchyma, extending outside the renal capsule, or as a mixture of both (2). Clinical signs are generally vague; the dog in the previously reported case of a renal cortical abscess exhibited lethargy, weight loss, pyrexia, and vomiting (14). If the disease progresses or there is trauma to the lesion, the development of a septic abdomen is also possible (13). The dog in this case initially had vague clinical signs of lethargy, weight loss, hyporexia, and hind-limb weakness.

Abdominal ultrasound has been frequently reported as an initial diagnostic tool for dogs with renal abscesses (5–14). Ultrasound examinations of dogs and humans demonstrated a pocket of anechoic fluid with hyperechoic, gravity dependent foci throughout (2,6,13,14). This is consistent with the initial ultrasonographic findings in this dog, which were initially mistaken for a neoplastic renal lesion. The use of CT imaging was reported for 1 case in a dog with a large, subcapsular abscess, and showed a well-marginated, fluid-attenuating mass with peripheral rim enhancement (11). In human medicine, CT is a valuable method of evaluation for renal abscesses, demonstrating high sensitivity and specificity for renal abscessation (15). In humans, CT imaging of renal abscesses showed a thick, hypoenhancing outer rim surrounding a hypoattenuating center (15). This imaging is also used to more accurately assess the size of renal abscessation to help determine the best treatment options (15). Imaging in this dog was consistent with CT imaging of renal abscessation in humans.

Diagnosis of a renal abscess can be confirmed with aspiration of the lesion and cytological confirmation of septic inflammation (5–14). In addition, culture and susceptibility testing can be used to determine the causal pathogen and best antibiotic therapy (6–8,10–12,14). Pathogens reported in dogs include E. coli, Staphylococcus pseudintermedius, and Hafnia alvei (6–8,10–12,14). Escherichia coli and S. pseudintermedius are equally represented on culture in dogs (6–8,10–12,14). In humans, E. coli is reported as the most common pathogen isolated (3). Abscess culture is not always undertaken, and instead, urine culture results are used to guide antibiotic therapy in humans (2,3,16). Culture of the abscess was not done in this dog due to an initial inability to obtain enough material; however, urine culture showed growth of E. coli susceptible to both amoxicillin clavulanate and enrofloxacin. Due to better renal penetration of enrofloxacin and lack of resolution of clinical signs with amoxicillin clavulanate, enrofloxacin was selected as the antibiotic of choice.

After a diagnosis has been made, reported successful treatments in dogs have been limited to surgical management. Medical management with oral antibiotics has been attempted in 3 dogs, with 1 requiring surgical intervention following abscess rupture and development of septic peritonitis, 1 having persistent clinical signs despite antibiotic therapy, and 1 spontaneously dying before any other treatment could be employed (6,12,13). Surgical treatments in dogs have consisted of surgical debridement of the abscessed tissue or nephrectomy of the affected kidney (5–11,13,14). Most dogs do well after surgery, without reported recurrence (5–11,13,14). Nephrectomy was an option for this dog; however, medical management was used to provide a renal-sparing option. Treatment options vary in human medicine based on the type of abscess present. Current treatments consist of oral or intravenous antibiotic therapy, percutaneous drainage, surgical drainage, or nephrectomy (2,3,16). In humans, nephrectomy is reserved for kidneys that are no longer functional (2). Treatment for renal parenchymal abscesses consists of antibiotic therapy; however, abscesses > 5 cm are more amenable to percutaneous drainage (1–3,16). There are reports of complete resolution of renal abscessation in humans ~4 to 6 wk following initiation of appropriate antibiotic therapy (17). Treatment of the renal abscess in this dog was modeled after treatment of renal abscesses in humans.

The cause of renal abscessation can be challenging to ascertain. In humans, up to 43% of patients have positive urine cultures with suspected ascending infections (2). Bacteremia is also a potential cause of abscessation, with up to 40% of human patients with renal abscessation presenting with bacteremia (2). It is unclear if urinary tract infections or bacteremia are causing the abscessation or are secondary (2). Other predisposing factors in humans can include immunosuppression, diabetes mellitus, and urolithiasis (2,3). Occasionally, the cause of renal abscessation cannot be determined (2,3). In dogs, diabetes mellitus, migrating foreign bodies, abdominal surgery, pyometra, nephrolithiasis, and pyelonephritis have all been implicated (5–14). A cause for the renal abscess in this dog was not determined; however, due to recurrent urinary tract infections, it was suspected to be secondary to an ascending infection.

Renal abscessation has also been reported in cats, with 7 cases in the recent literature (18,19). There was no obvious predisposing condition reported in any cat, but all cases were diagnosed in cats with chronic kidney disease (18,19). Culture of the abscess showed growth of E. coli in 5 of the 7 reported cases (18,19). Medical management with oral antibiotics was attempted in all cases, based on bacterial susceptibility (18,19). Three of these cats responded favorably to medical management alone, with resolution of the abscess on follow-up imaging as early as 14 d following initiation of antibiotic therapy (18). Three cats underwent drainage of their abscesses: 2 had surgical drainage and debridement and 1 had percutaneous drainage (18). These 3 cats were prescribed oral antibiotics following their procedures, and the abscesses resolved (18). Only 1 cat did not respond favorably to treatment and died shortly after initiation of oral antibiotics (19).

This report details the diagnosis of a renal abscess in a dog using CT, and treatment with percutaneous drainage, local antibiotic instillation, and oral antibiotic therapy that resulted in clinical cure. The use of CT has been previously reported in the diagnosis of renal abscessation in only 1 dog with a subcapsular abscess (11). Successful medical management has not been previously described in a dog, so treatment outcomes are unknown. The dog in this case had complete resolution of the recurrent urinary tract infections and concurrent clinical signs with medical management alone. Although long-term outcome for kidney function is unknown, human literature reports continued normal renal function with abscesses treated similarly (2,3). This treatment method needs further research in a larger population of animals; however, it may be a kidney-sparing option for dogs with renal abscessation moving forward. With these limitations in mind, this case report provides the first description of a renal corticomedullary abscess in a dog diagnosed by CT, and the first description of percutaneous drainage with antibiotic instillation as a successful treatment for the abscess. CVJ