History
An 8-year-old 5-kg (11-lb) spayed female Miniature Dachshund was examined as part of a routine wellness and vaccination program. On physical examination, the dog was quiet, alert, and responsive; however, a large mass was palpated in the caudal aspect of the dog's abdomen. Results of CBC and serum biochemical analyses indicated high RBC count (9.54 × 106 RBCs/uL; reference range, 5.39 × 106 to 8.7 × 106 RBCs/uL), Hct (59%; reference range, 38.3% to 56.5%), and hemoglobin concentration (21.6 g/dL; reference range, 13.4 to 20.7 g/dL) and low blood glucose concentration (62 mg/dL; reference range, 63 to 114 mg/dL). Abdominal radiography was performed (Figure 1).
Right lateral (A) and ventrodorsal (B) abdominal radiographic images of an 8-year-old 5-kg (11-lb) spayed female Miniature Dachshund examined because of an abdominal mass palpated on physical examination performed as part of a routine wellness and vaccination program.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Right lateral (A) and ventrodorsal (B) abdominal radiographic images of an 8-year-old 5-kg (11-lb) spayed female Miniature Dachshund examined because of an abdominal mass palpated on physical examination performed as part of a routine wellness and vaccination program.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Right lateral (A) and ventrodorsal (B) abdominal radiographic images of an 8-year-old 5-kg (11-lb) spayed female Miniature Dachshund examined because of an abdominal mass palpated on physical examination performed as part of a routine wellness and vaccination program.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Abdominal radiography revealed a large, well-defined and smoothly margined soft tissue mass in the mid-through-caudal regions of the abdomen (Figure 2). The mass displaced the descending colon caudally and to the left, small intestines cranially, and spleen ventrally and was not clearly associated with the spleen or other visceral structures. Although the mass was caudal to the expected location of the right kidney, the margins of the right kidney were not evident. The stomach contained heterogenous material, consistent with food, and the T12–13 intervertebral disk appeared mineralized.
Same radiographic images as Figure 1. A large soft tissue mass (black arrows) occupies much of the caudal aspect of the abdomen and displaces abdominal organs. The silhouette of the left kidney (white arrows) is evident.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Same radiographic images as Figure 1. A large soft tissue mass (black arrows) occupies much of the caudal aspect of the abdomen and displaces abdominal organs. The silhouette of the left kidney (white arrows) is evident.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Same radiographic images as Figure 1. A large soft tissue mass (black arrows) occupies much of the caudal aspect of the abdomen and displaces abdominal organs. The silhouette of the left kidney (white arrows) is evident.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Ultrasonography revealed that the mass was caudal to the right kidney and renal artery, was well-defined, and had a hyperechoic and sacculated periphery and an anechoic center, consistent with a fluid-filled mass (Figure 3). No blood vessel supplying the mass was identified. The liver, spleen, and both kidneys were visualized ultrasonographically and appeared clinically normal. The mass did not appear to have been associated with other visceral structures.
Ultrasonographic image of the abdominal mass identified in Figure 2. There are sacculations of the hyperechoic capsule (arrowheads) that extend into the largely anechoic mass, consistent with a large fluid-filled structure that is well encapsulated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Ultrasonographic image of the abdominal mass identified in Figure 2. There are sacculations of the hyperechoic capsule (arrowheads) that extend into the largely anechoic mass, consistent with a large fluid-filled structure that is well encapsulated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Ultrasonographic image of the abdominal mass identified in Figure 2. There are sacculations of the hyperechoic capsule (arrowheads) that extend into the largely anechoic mass, consistent with a large fluid-filled structure that is well encapsulated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Treatment and Outcome
An exploratory celiotomy was performed. A large (approx 12 × 8 × 8 cm) fluid-filled structure was in the right retroperitoneal space caudal to the right kidney and renal artery and was attached dorsally to the aorta by a small-diameter, thin and flat attachment containing a vascular branch (approx 8 mm in diameter) from the aorta to the mass. There was also a tubular structure that extended caudally from the mass toward the urinary bladder; however, the caudal termination of the tubular structure was not visualized. After ligation of the vascular branch dorsally and the tubular structure caudally, the intact mass was easily removed from the abdomen. Both of the dog's kidneys were visualized and were clinically normal in appearance and location. The dog was recovered from anesthesia and treated with carprofen (1.25 mg/kg [0.57 mg/lb], PO, q 12 h for 8 days) for postoperative pain management.
Findings from histologic examination of the mass were consistent with a kidney affected by chronic hydronephrosis. The renal pelvis was markedly dilated, lined by transitional epithelium, and bordered by smooth muscle (Figure 4). The renal medulla and cortex were markedly attenuated, with the renal parenchyma width approximately 500 μm from capsule to pelvis. These findings combined with the fact that the dog also had 2 clinically normal-appearing kidneys led to a final diagnosis of hydronephrosis of a supernumerary kidney.
Photomicrographs of a section of the hydronephrotic supernumerary kidney from the dog in the previous figures. A portion of the ureter (asterisk; A) is evident. The renal pelvis (dagger; A and B) is substantially dilated with a markedly attenuated cortex (black brackets; A and B) and medulla (blue brackets; A and B). Glomeruli (long arrows; B) have tuft collapse with mesangial proliferation and are multifocally sclerotic. Tubules (short arrows; B) occasionally have intraluminal protein-rich fluid. A—H&E stain; bar = 5 mm. B— H&E stain; bar = 100 μn.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Photomicrographs of a section of the hydronephrotic supernumerary kidney from the dog in the previous figures. A portion of the ureter (asterisk; A) is evident. The renal pelvis (dagger; A and B) is substantially dilated with a markedly attenuated cortex (black brackets; A and B) and medulla (blue brackets; A and B). Glomeruli (long arrows; B) have tuft collapse with mesangial proliferation and are multifocally sclerotic. Tubules (short arrows; B) occasionally have intraluminal protein-rich fluid. A—H&E stain; bar = 5 mm. B— H&E stain; bar = 100 μn.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Photomicrographs of a section of the hydronephrotic supernumerary kidney from the dog in the previous figures. A portion of the ureter (asterisk; A) is evident. The renal pelvis (dagger; A and B) is substantially dilated with a markedly attenuated cortex (black brackets; A and B) and medulla (blue brackets; A and B). Glomeruli (long arrows; B) have tuft collapse with mesangial proliferation and are multifocally sclerotic. Tubules (short arrows; B) occasionally have intraluminal protein-rich fluid. A—H&E stain; bar = 5 mm. B— H&E stain; bar = 100 μn.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.767
Comments
When > 2 kidneys are present, the additional kidney or kidneys are considered supernumerary. Supernumerary kidneys are rare congenital anomalies of the urinary tract in humans, with fewer than 100 cases documented in the literature.1 Supernumerary kidneys develop as an outpouching of a Wolffian duct of an existing kidney or by branching from the initial ureteral bud. This supernumerary kidney has an independent or partially fused renal parenchyma, a separate renal capsule with calyces, and a separate blood supply (both venous and arterial). This should not be confused with a duplex kidney, which shares a single renal capsule, has fewer calyces than its adjoining kidney, and has a shared blood supply.2 Treatment depends on the patient's clinical signs and function of the supernumerary kidney or kidneys. In humans, there is a high incidence of hydronephrosis, renal lithiasis, pyelonephritis, and malignancies in supernumerary kidneys.3
Palpable on physical examination of the dog in the present report, the later identified supernumerary kidney was hydronephrotic. Hydronephrosis may be an incidental finding, associated with nonspecific clinical signs, or associated with renal failure, and kidneys suspected to be affected may be identified on palpation, abdominal surgery, or abdominal imaging.4 A cause for hydronephrosis was not identified in the dog of the present report but was presumably acquired because no abnormalities were detected on abdominal palpation during previous examinations as might have been expected if hydronephrosis was congenital. The renal function of the hydronephrotic kidney in the dog of present report was not known. To estimate functionality of a single kidney prior to nephrectomy, renal scintigraphy or excretory urography would have been required, but when the dog was evaluated, it was not clear that the mass was a supernumerary kidney, and therefore these advanced diagnostic procedures were not pursued.5,6
Radiography and ultrasonography were key diagnostic tools used to investigate the abdominal mass that was later diagnosed as a hydronephrotic supernumerary kidney in the dog of the present report. Additionally, diagnostic imaging facilitated in evaluating the dog's other abdominal organs, developing the treatment options, and planning the surgery. We suspected that the position of the supernumerary kidney and its ureter (caudal to the right kidney and in a fixed retroperitoneal space) obscured ultrasonographic visualization of their blood supply. We recommend that when treating animals with similar initial findings, veterinarians consider referral to a board-certified veterinary radiologist for abdominal ultrasonography and possibly advanced diagnostic imaging.
References
1. da Silva RM, Chaib Neto J, de Morais MF Jr. Supernumerary kidney with pelvic communication and a single ureter. Radiol Bras 2018;51:66–67.
2. Sureka B, Bansal K, Patidar Y. Supernumerary kidneys do exist! AJR Am J Roentgenol 2016;206:W48.
3. Bernik TR, Ravnic DJ, Bernik SF, et al. Ectopic supernumerary kidney, a cause of para-aortic mass: case report and review. Am Surg 2001;67:657–659.
4. Rousset N, Abbondati E, Posch B, et al. Unilateral hydronephrosis and hydroureter secondary to ureteric atresia, and uterus unicornis in a young terrier. J Small Anim Pract 2011;52:441–444.
5. Wehbi E, Salle A, Kanaroglou N, et al. Measurement of differential renal function by scintigraphy in hydrochronic kidneys: importance of conjugate views for accurate evaluation. J Urol 2016;195:471–475.
6. Seiler GS. Kidneys and ureters. In: Thrall DE, Widmer WR, eds. Textbook of veterinary diagnostic radiology. 7th ed. St Louis: Saunders, 2018;824.
