Daniel J. Brockman, BVSc, CVR, CSAO, DACVS, DECVS, FHEA, MRCVS
The right kidney is more cranial than the left and attached to the liver by the hepatorenal ligament. Both kidneys are retroperitoneal with a hilus at their medial aspect, where the renal vessels and the ureters enter and exit. In most dogs the right renal artery is single but in about 13% of dogs the left renal artery is a paired structure. The gonadal vein enters the left renal vein. The renal vein is cranial and ventral to the artery; the ureter is the most caudal of the three. They may be seen on plain film radiographs but their visibility is enhanced following intravenous administration of iodinated contrast agent. Ultrasonography can be used to give anatomical information about the kidneys. Relative renal function can be estimated most accurately using renal scintigraphy, but this is still not a very sensitive investigative tool.
Both the ureters are fibromuscular organs that travel in the retroperitoneum until they join the bladder wall within peritoneal reflections (the lateral ligaments of the bladder). The transport of urine to the bladder from the renal pelvis is an active process brought about by peristalsis. Unless they are abnormal (dilated) these can only be imaged by excretory urography.
Two lateral (umbilical vein remnants) and one ventral ligament (urachal remnant) meet at the trigone where the two ureters enter at an oblique angle in the dorsolateral wall forming a small, slit-like opening in the mucosal epithelium. The bladder is an extremely distensible muscular organ with sympathetic (hypogastric nn), parasympathetic (pelvic nn), and somatic (pudendal nn) innervation. The bladder is often divided, arbitrarily, into the neck (trigone) and body. The urine-filled bladder is a good subject for ultrasound evaluation. Useful radiographic studies include negative contrast cystography, positive contrast cystography, and double contrast cystography.
The urethra is a muscular tube extending from the bladder neck to the vagina in female dogs or tip of the penis in male dogs. There are skeletal muscle fibres at the proximal urethra under somatic control; the remainder of the urethral wall contains smooth muscle fibres under autonomic control. It can be imaged in the male dog by retrograde urethrography and in the female dog by retrograde vaginourethrography or voiding cystourethrography.
Neoplasia of the Urinary Tract
Primary tumours of the kidney are rare and account for about 1% of all malignant canine neoplasms. The kidneys are common sites for metastatic disease. Benign neoplasms are rare and may not even be recognised clinically if they are slow growing.
The most common malignant neoplasms of both cats and dogs are renal carcinoma and nephroblastoma.
Renal carcinoma: Early signs are nonspecific and include haematuria, recurrent or intractable urinary tract infection. Unfortunately, however, the condition may go unnoticed until a large abdominal mass is evident (and metastasis has occurred). Occasionally renal carcinoma is associated with a paraneoplastic syndrome involving other organ systems. Therefore, anaemia, fever, anorexia, weight loss, and DIC may be seen. Rarely do these cause renal failure. Metastasis occurs to the lungs, LN, liver and brain.
Nephroblastoma: These are congenital tumours which are usually unilateral. The neoplasm has been reported in a two-month-old dog but is often not apparent clinically until the animal is several years old. Clinical features of this disease are similar to those for carcinoma. Metastasis is via lymphatic and venous systems to lungs, liver, etc., as well as local invasion.
Fibrosarcoma, leiomyoma/sarcoma, cystadenoma, transitional cell & squamous cell carcinoma: All seen occasionally but rare.
The clinical features may include persistent haematuria, urinary tract infection, and palpable abdominal mass. Logical investigation must include serum biochemistry, haematology, urinalysis (including sediment evaluation), abdominal and thoracic radiography, and abdominal ultrasound or contrast CT. Percutaneous renal biopsy can be performed with or without ultrasound guidance but whenever primary renal neoplasia is suspected, in all but critically ill patients, excisional biopsy is the treatment of choice.
The presence of a neoplasm is confirmed at exploratory laparotomy and excision (ureteronephrectomy) is performed via a ventral midline incision or a combined ventral and paracostal incision depending on the size of the mass.
Since early diagnosis is not often achieved, malignant tumours of the kidney carry a poor prognosis. Chemotherapy offers some hope and has been shown to be helpful in people with nephroblastomas.
Neoplasia of the Ureter
These are rare, the most common one being transitional cell carcinoma but can be of smooth muscle origin. Hydronephrosis and pyelonephritis can develop secondary to ureteral obstruction.
Storage of urine in the bladder may expose the epithelium to carcinogens for prolonged periods of time, thereby accounting for the increased frequency of neoplasms at this site more than any other site in the urinary tract. Common sites are around the bladder neck or at the cranial pole of the bladder but can originate from anywhere.
Rhabdomyosarcoma - juvenile
Clinical Features and Diagnosis
Most urinary cystic neoplasms show only subtle disease early in the process such as intermittent haematuria and stranguria. Polyuria, stranguria, dysuria and haematuria will become more consistent as the disease progresses. Note again that these signs are nonspecific. Investigation of these patients must involve serum chemistry, haematology, urinalysis (including sediment) and imaging of the urinary tract. Positive contrast urethrography; negative, positive and double contrast cystography; and excretory urography may be helpful. Careful and skilled ultrasound examination can obviate the need for many of these contrast radiographic studies. Contrast-enhanced CT or MRI can both be useful in the diagnosis and staging of these tumours.
Be aware that bladders with neoplasms will have a urinalysis consistent with UTI (because this is usually a concurrent process) and tumour cells may be seen in the urine sediment. Reactive transitional cells may also be present in the sediment of urine from animals without neoplastic disease.
Occasionally ureteric and urethral obstruction can lead to the development of post renal failure by causing hydroureter and pyelonephritis. Much less commonly acute obstruction and post renal failure develop.
Biopsy by cystoscopy or at laparotomy is required for a definitive diagnosis. If laparotomy is undertaken internal iliac and sublumbar lymph nodes should be carefully examined and removed if enlarged.
Bladder neoplasia is often advanced when the diagnosis is made and excision is not feasible without urinary tract diversion. Even when the situation looks favorable for surgery (cranial pole mass) clean surgical margins are rarely achieved. The use of intraoperative radiotherapy, local and systemic chemotherapy have been used but definitive proof of efficacy is lacking and local recurrence and the development of distant metastases are common. Nonsteroidal drugs (piroxicam and meloxicam) can produce dramatic palliative effects by either directly reducing the mass of neoplastic cells or by reducing perineoplastic inflammation. The author would recommend at least trial therapy with one of these and currently uses the licenced meloxicam for this.
Technique for Ureteronephrectomy
Generous ventral midline incision from just caudal to the xiphoid to beyond the umbilicus. The left kidney is found by elevating the colon, thereby reflecting the remaining small intestine to the right which is held in place by the mesocolon. The right kidney is found by locating the descending duodenum and using the mesoduodenum to reflect the other abdominal structures in a similar way. The kidney is packed off with moist laparotomy towels and the perirenal fascia stripped from the capsule by blunt dissection. The renal vessels and ureter are identified and the renal artery is dissected free and ligated close to the aorta (prevents blind sac for thrombus to form); the renal vein is treated similarly. Both should be double ligated with silk or PDS. The ureter is then dissected free as close to its attachment to the bladder as possible and divided between ligatures (prevent blind sac as focus for infection). Gentle traction on the kidney should then pull the ureter out to complete the removal. Closure is routine.
Nephrolithiasis and Ureterolithiasis
History, Clinical Features, and Diagnosis
In man, renal and ureteric calculi are believed to be among the most painful conditions known. This discomfort may be evident in animals as abdominal splinting and depression, or a change in temperament, or may even mimic spinal pain. Most renal and ureteric stones, in animals, are discovered during investigation for persistent UTI, pyuria and polyuria.
Medical therapy is well established for the dissolution of struvite calculi but may not be helpful for all types of stone. Postoperative medical therapy is, however, very important. Initial antibiotic therapy based on cultures taken at surgery should be continued for prolonged periods (4–6 weeks). Urinary pH can be modified by a change in the diet and by drugs.
Noninvasive treatment of non-obstructive stones (lithotripsy), although effective, is not available to many. Surgical removal of renal stones is indicated if there is a persistent UTI, if they are obstructing the renal pelvis, or if they are increasing in size despite medical therapy, and can be performed via a ventral midline coeliotomy. The affected kidney is identified and its vessels dissected so as to allow the placement of a temporary non-crushing clamp or ligature. This clamp must be tight enough to prevent flow through the artery as well as the vein! (an assistant's fingers make a satisfactory atraumatic clamp). An incision is made through the peritoneum at the greater curvature of the kidney and continued through the cortex, medulla into the renal pelvis. The stone is gently removed and the pelvis flushed with copious amounts of sterile saline. The kidney is closed using sutures in the renal capsule (including the peritoneum). The renal vessels are then released and the kidney observed.
Alternatively, if the renal pelvis is dilated, stones within the pelvis can be accessed without damaging the renal parenchyma. The technique is called pyelotomy or pyelolithotomy, if stones are to be removed. The kidney is mobilized by dissecting the perirenal fascia free of the peritoneum. The kidney is then reflected medially, exposing the dorsal aspect of the renal pelvis. The renal pelvis is incised and the stone(s) removed. The pelvis is then flushed with sterile saline and closed using fine sutures of Prolene or PDS.
It is not common to find ureteral stones in dogs; however, ureteral obstruction in cats with calcium oxalate uroliths is becoming a more common condition. The presence of ureteroliths can be devastating for the associated kidney. Surgical removal can be done in dogs, with the help of magnification loupes and best achieved via a ventral midline laparotomy. The stone is identified and preferably a transverse incision is made in the ureter over the urolith to allow its removal. This should be closed with fine (5-0 or 6-0) nonreactive suture material in a simple interrupted pattern that does not penetrate the lumen (whenever possible). PDS or Prolene would be suitable.
Ureterolithiasis management in cats is problematic because of the size of the ureter and the severity of renal obstruction/renal compromise that these animals are presented with. Poor results with the technically demanding ureterotomy surgical techniques have led to the development of intra-ureteric stents and extra-anatomical ureteric bypass catheters. Both of these should be considered palliative and investigational until further data on their use is published.
Congenital Abnormalities of the Urinary Tract
Ureteric Ectopia and Ureterocele
An anomaly resulting from poor differentiation of the mesonephric ducts and the ureteric bud results in one or both ureters entering the prostate, seminal vesicles, urethra or vagina. Breed and familial predisposition for Siberian huskies and Golden retrievers has been suggested. It is commonly associated with other congenital abnormalities such as hydronephrosis, short urethra, disorders of the bladder sphincter mechanism, renal hypoplasia and hydroureter. Ureterocele is a dilatation of an intracystic portion of the (usually ectopic) ureter. This may be associated with a duplex urine collection system (i.e., two renal pelvises and two ureters from the same kidney). The condition is usually treated in a similar manner to other cases of ectopia but may require excision of the redundant collection system.
History and Clinical Features
This is most commonly diagnosed in female dogs that have had a dribbling incontinence since birth. Affected animals commonly can void small amounts of urine normally but often dribble constantly and have staining of the perivulval skin and hair and occasionally dermatitis on the ventrum. It has also been seen in aged female dogs with late-onset incontinence, and in the cat. It is relatively infrequently diagnosed in males but may be just as common. Ectopia causes incontinence less frequently in males probably because of the length of the urethra and urethralis muscle (and therefore the sphincter mechanism). If incontinence does not occur, hydronephrosis and/or pyelonephritis may be the presenting disease.
A cystocentesis or catheter urine sample should be obtained for urinalysis, culture and sensitivity. Routine CBC and serum chemistry should be performed. The diagnosis of ureteric ectopia is confirmed radiographically, under general anaesthesia, by excretory urography (fluoroscopy is helpful) and/or retrograde vaginourethrography. Remember to prepare the patient adequately for this study (i.e., several enemas). Urethrocystography may also aid diagnosis of ureteric ectopia in female dogs.
Prior to surgery any infection in the bladder should be appropriately treated. A ventral midline incision and ventral cystotomy are performed. The trigone is carefully examined for any ureteral orifices. (Be gentle; the urothelium becomes oedematous very easily.) If found, the ureter(s) should be catheterised using a soft rubber catheter. The ectopic ureters usually join the bladder in a normal position and tunnel caudally in the submucosa to open in the distal urogenital tract. Occasionally two openings will be present, one in the bladder and one more distal; the ureteric orifice should therefore be probed in both directions. Once ectopia is confirmed the only treatment to be considered is ureteronephrectomy or some type of ureteroneocystostomy (reimplantation). If the kidney or ureters are involved in advanced disease, but involvement is unilateral, removal is more satisfactory.
Endoscopic Laser Ablation
Recently reported in a small number of dogs with similar results to surgical therapy but much lower morbidity because it is much less invasive.
1. Persistent UTI: Requires careful monitoring and therapy. If persists, could be hydroureter & hydronephrotic kidney acting as a reservoir for infection; therefore, ureteronephrectomy will be needed.
2. Persistent incontinence: Could be due to re-canalisation of a submucosal tunnel or a poor sphincter mechanism; occasionally poor vaginal conformation causes pooling of urine at urination which then slowly leaks out. A repeat radiographic study may help determine the problem; also a voiding cystogram will show any functional abnormality of the vagina.