Clinical Exposures: Incidental finding of renal agenesis in a cat

An approximately 2-year-old feral female domestic shorthaired cat weighing 6.1 lb (2.8 kg) was presented to a spay and neuter clinic for a routine ovariohysterectomy. The cat was fractious and bright, alert, and responsive. The physical examination findings were unremarkable, but cytologic examination of an ear swab sample revealed a mite infestation (Otodectes cynotis). The results of a rapid ELISA test for feline heartworm, feline leukemia virus, and feline immunodeficiency virus were negative.

Figure 1. A ventrodorsal urogram obtained five minutes after intravenous injection of an iodinated positive contrast medium in a 2-year-old cat. Note the well-defined right kidney and ureter and the absence of the left kidney.

OVARIOHYSTERECTOMY

Anesthesia was induced with xylazine and ketamine given intramuscularly. The cat was intubated, and anesthesia was maintained with isoflurane in oxygen. Perioperatively, 125 ml of lactated Ringer's solution was administered subcutaneously as a bolus to maintain hydration. Intraoperatively, the cat's heart rate and rhythm, respiration, and temperature were monitored manually. Electrocardiography and pulse oximetry were also used to monitor the patient.

A ventral midline celiotomy was performed. Exteriorizing the uterus revealed only one completely developed right ovary and a normally developed right uterine horn with good vascularity leading to a normal cervix. The contralateral uterine horn was absent. A thorough abdominal exploration revealed that the left ovary was embedded and masked in anterior abdominal fat caudal to the spleen; the ovary had auxiliary blood vessels from adjoining fatty tissues. Both ovaries were fully developed and had the same size and shape. Further exploration revealed the absence of a left kidney. Visualization of the abdominal organs was unremarkable. An ovariohysterectomy was performed. The abdominal incision site was closed in a routine manner with 3-0 polydioxanone suture.

Recovery was uneventful. Postoperatively, analgesia was maintained by buprenorphine (0.02 mg/kg intramuscularly). A postoperative survey radiographic examination confirmed no other thoracic, abdominal, or pelvic organ defects.

RECOVERY

The following day, the cat was bright, alert, and responsive and had a good appetite. Its temperature, pulse, and respiratory rate were normal. A complete blood count and serum chemistry profile revealed leukocytosis (total WBC = 28.91 x 103 /µl; reference range = 5.5 to 19.5 x 103 /µl), hyperglycemia (glucose concentration = 180 mg/dl; reference range = 70 to 150 mg/dl), hypoalbuminemia (albumin concentration = 1.8 g/dl; reference range = 2.2 to 4.4 g/dl), hyponatremia (sodium concentration = 139 mEq/L; reference range = 142 to 164 mEq/L), and a decreased total protein concentration (4.9 g/dl; reference range = 5.4 to 8.2 g/dl). These abnormalities were attributed to postsurgical stress.

IMAGING

To confirm the anatomical structure and assess the qualitative function of the existing kidney, an intravenous excretory urographic examination was performed the next day. A radiograph was obtained five minutes after intravenous injection of an iodinated positive contrast agent. The left kidney, ureter, and renal artery were not visualized; the right kidney and ureter were normal in size and shape (Figure 1). Most of the contrast agent was excreted into the urinary bladder within 15 minutes, which confirmed normal renal architecture and effective glomerular filtration.

On an ultrasonographic examination performed four days after surgery, the right kidney was normal in size (4.35 cm long and 2.43 cm wide) and had a regular echo texture and renal pelvis. The bladder was full and had hypoechoic urine. The mucosal and muscular layers and trigonal areas appeared normal. The liver, stomach, intestines, mesenteric lymph nodes, pancreas, adrenal glands, and spleen appeared normal.

Histologic examination of the reproductive organs removed during the ovariohysterectomy was not conducted, although it is prudent to examine these tissues histologically to help describe the type of anomaly in these animals.

FOLLOW-UP

The cat was discharged to a foster home six days after surgery. The ear mite infestation was treated with 0.01% ivermectin otic suspension. The cat was eventually adopted, and its health has been periodically monitored. In a recent biannual check-up, complete blood count and serum chemistry profile results revealed no abnormalities.

DISCUSSION

Renal agenesis or dysplasia has been reported in dogs, cats, and people.1-3 Although unilateral agenesis as occurred in this case is rarely noted, it can cause compensatory hypertrophy in the existing kidney; bilateral agenesis is fatal. Invariably, renal agenesis leads to genital tract malformation.

During embryonic development, the kidneys, urinary tract, and most of the reproductive organs arise in the intermediate mesoderm between the somites and the lateral plate. Three stages of renal development recapitulate evolution of the kidney: pronephros, mesonephros, and metanephros. Urogenital system development in mammals requires the coordinated differentiation of two distinct tissues—the ductal epithelium and the nephrogenic mesenchyme—both derived from the intermediate mesoderm of the early embryo. The former gives rise to the genital tracts, ureters, and kidney collecting duct system, whereas mesenchymal components undergo epithelial transformation to form nephrons in both the mesonephric (embryonic) and metanephric (definitive) kidney.4

Pax-2 is a transcriptional regulator gene of the paired-box family and is widely expressed during the development of both ductal and mesenchymal components of the urogenital system. If the Pax-2 gene is dysfunctional, the ureters, inducers of the metanephros, are absent, so kidney development does not occur.4 Mesenchyme of the nephrogenic cord fails to undergo epithelial transformation and is unable to form tubules in the mesonephros.4

In people, unilateral renal agenesis may have a noncystic fibrosis-mediated genetic basis that leads to abnormal development of the entire mesonephric duct at around seven weeks of embryonic development. Unilateral renal agenesis is compatible with normal life if the other kidney is normal; however, if contralateral dysplasia or hypoplasia is present, renal failure ultimately develops.5

The etiopathogenesis of renal agenesis in small animals is uncertain. A familial genetic predisposition for the condition has been reported in Shetland sheepdogs and Doberman pinschers.2 Because of close associations in the development of the urogenital system, findings of abnormal or absent vas deferens, epididymal tails, or uterine horns at the time of castration or ovariohysterectomy should arouse suspicion of concurrent unilateral renal agenesis. Because unilateral renal agenesis is compatible with normal life, specific therapy is not indicated unless reduced renal function ensues.

To our knowledge, only a few reports of aplasia of a uterine horn and ipsilateral renal agenesis occur in the literature.6,7 One cat with renal agenesis and segmental aplasia of the right uterine horn had initially been presented for evaluation of acute vomiting, depression, and constant shivering.7 The authors of the report did not observe any functional or anatomical defects in the existing left kidney except enlargement.

High-volume spay and neuter facilities may encounter reproductive organ development anomalies more frequently than traditional veterinary practices. Monitoring kidney and urinary tract function after adoption is necessary to ensure a good quality of life in organ- (kidney-) deficient animals. Breeding such animals is discouraged as the offspring may be predisposed to genetic disorders. The baseline information collected is of benefit for future therapeutic considerations. An incidental finding of renal aplasia also suggests that a thorough exploration of the abdominal cavity be done to avoid leaving functional ovaries, which postoperatively may result in the animal developing estrous cycles, ectopic pregnancy, or pyometra.

ACKNOWLEDGMENT

We are grateful to John E. Ledoux, VMD, in Atkinson, N.H., for performing and interpreting the abdominal ultrasonographic examination. We are also grateful for the assistance of technicians Shelby Page, Melanie Norman, Nicole Willis, and Lori Wyatt at Main Street Animal Hospital in Bradford, Mass. The help of Sarah Ingram, DVM, in preparing the manuscript is highly appreciated. We thank Barbara Cusick, president of the Animal Rescue Merrimack Valley in Bradford, Mass., for providing foster care to Gracie, the cat featured in this case.

Tumkur Narasimhan, DVM, MS, PhD

Yassine Absar, DVM

Main Street Animal Hospital

839 South Main St.

Bradford, MA 01835

REFERENCES

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2. Hoskins JD. The urinary system. In: Veterinary pediatrics: dogs and cats from birth to six months. 3rd ed. Philadelphia, Pa.: WB Saunders Co, 2001; 371-395.

3. Morita T, Michimae Y, Sawada M, et al. Renal dysplasia with unilateral renal agenesis in a dog. J Comp Pathol 2005;133(1):64-67.

4. Torres M, Gomez-Pardo E, Dressler GR, et al. Pax-2 controls multiple steps of urogenital development. Development 1995;12 (12); 4057-4065.

5. Maxie MG. The urinary system. In: Jubb KVF, Kennedy PC, Palmer N, eds. Pathology of domestic animals. 4th ed. San Diego, Calif.: Academic Press, 1993;447-538.

6. Aiello SE. Urinary system. In: The Merck veterinary manual. 8th ed. Whitehouse Station, N.J.: Merck and Co Inc, 1998; 1130-1157.

7. Chang J, Jung JH, Yoon J. et al. Segmental aplasia of the uterine horn with ipsilateral renal agenesis in a cat. J Vet Med Sci 2008;70(6):641-643.