Ureteronephrectomy is the most commonly performed surgical procedure of the kidney. It is indicated when one of the kidneys is detrimental to the animal's health whilst the function of the contralateral one is adequate to sustain life. This frequently occurs in cases of advanced hydronephrosis – usually secondary to obstruction of the ureter or the renal pelvis. Whenever possible the kidney is spared, and alternative procedures are performed to resolve the obstruction. Nephrotomy and pyelotomy are rarely performed, and recently have been associated with or superseded by ureteral stenting. All the latter procedures are technically challenging, and require advanced expertise and facilities.
The most frequently performed surgical procedure of the upper urinary tract is ureteronephrectomy. This procedure is considered relatively easy to perform for soft tissue surgeons with a certain degree of experience in abdominal surgery. Partial nephrectomy is more complicated, and carries with it the risk of severe post-operative haemorrhage. It is therefore seldom indicated, and should be considered only when the disease (benign neoplasia or traumatic damage) is confined to a single kidney pole and in patients with suboptimal function of the contralateral kidney. Because of these considerations, partial nephrectomy will not be considered in this article; the reader will be able to find descriptions of its surgical technique in textbooks.
Other, less commonly performed, procedures are nephrotomy and pyelotomy, usually undertaken for removal of uroliths. These are considered advanced procedures, and, as well as causing some degree of kidney damage, are more likely to be followed by temporary or permanent complications. Recently, minimally invasive techniques to maintain urine outflow from the renal pelvis have become more readily available in veterinary medicine, and offer a better alternative to ureterotomy and pyelolithotomy in selected cases.
The kidneys and ureters are located in the retroperitoneal space ventral to the lumbar vertebrae and sublumbar muscles. The right kidney, which is more firmly attached, lies more cranially, with its cranial pole associated with the renal fossa of the caudate liver lobe. The left kidney is more mobile, and is located slightly caudally to the last rib. A fibrous capsule surrounded by adipose tissue covers the kidneys, and together with subperitoneal connective tissue keeps them in place (Fig. 1). The fibrous capsule of a normal kidney is easily dissected from the kidney itself, except at the hilus, where it is reflected inwards to cover the renal pelvis and the exiting structures (blood vessels and ureter).
The kidney parenchyma is formed by an external cortex, where the renal corpuscles are situated, and an internal medulla. Here run the tubuli and the ducts that carry the urine to the renal pelvis. This is a funnel-shaped structure that receives the urine and passes it into the ureter. The pelvis is elongated in a cranio-caudal direction, and extends into the renal parenchyma with five or six diverticula.
Blood supply to the kidneys comprises approximately 25% of the cardiac output. The renal artery comes directly from the aorta and usually bifurcates in dorsal and ventral branches. The site and number of divisions is variable: numerous branches or double vessels can be present. In particular, in 12–15% of dogs, there are multiple left renal arteries. Blood exits the kidney through the renal vein, which joins the caudal vena cava to the right of the midline. The left ovarian or testicular vein typically drains into the renal vein instead of inserting directly into the caudal vena cava.
Urine collects into the ureters, which leave the kidneys at the hilus and run retroperitoneally towards the urinary bladder. In their distal course, the ureters in the female pass beneath the broad uterine ligament (or beneath the vas deferens in the male), between the two peritoneal layers forming the lateral ligaments of the bladder, then tunnel through the bladder submucosa and open at the trigone with two slit-like orifices.
Evaluation of the patient's renal function is extremely important before performing surgery of the upper urinary tract. In almost all cases renal dysfunction is already present, and anaesthetic agents, haemorrhage and surgery itself may worsen the situation. The minimum data required to assess renal function includes blood and urine analysis; however, these methods are not very sensitive, as the relevant parameters (blood creatinine and urea nitrogen levels, urine specific gravity) remain within normal limits until approximately 67% of kidney function has been lost.
To ascertain the presence of early kidney disease it is necessary to assess glomerular filtration rate (GFR). The most accurate method to measure GFR is renal scintigraphy, which uses radiolabeled markers and monitors their renal excretion over time using a gamma camera. Renal scintigraphy allows determination of the individual contribution of each kidney to the overall GFR, and becomes very useful before nephrectomy. Unfortunately, access to renal scintigraphy is limited, and consequently alternative methods of GFR evaluation have been developed. In particular, plasma clearance techniques are quite practical, since they only require multiple blood sampling. Iohexol clearance or exogenous creatinine clearance can be used; the latter, although less accurate, is the most practical. Although these are not routinely used, the surgeon should request them when bilateral renal disease is suspected and nephrectomy is planned.
Anaesthetic protocols, drug doses and frequency of administration must be tailored to the individual patient, depending on the degree of renal compromise. A word of caution must be sounded regarding the use of non-steroidal anti-inflammatory drugs – these should generally be avoided in cases of renal impairment. Peri-operative antibiotics are generally advised when uraemia or ureteral obstruction are present, even in the absence of evident infection; however, they should be withheld until after collection of samples for culture.
Circulating volume and plasma electrolyte imbalances should be corrected before anaesthesia. Osmotic diuresis is initiated before surgery to protect renal function, and urine output should be monitored using a urinary catheter connected to a closed collection system. This monitoring helps to avoid fluid overload, which can occur, especially in cats, in the pre- and post-operative period.
Monitoring of blood pressure and of cardiac activity is likewise recommended. Although auto-regulation maintains kidney blood flow if systemic blood pressure is between 75–160 mmHg, values below this range can cause renal vasoconstriction and consequent reduction of urine formation in the short term, and of ischemic damage in the longer term, and should be avoided.
Complete removal of kidney and ureter is indicated in cases of unilateral disease when the presence of the non-functional kidney is detrimental to the animal's health. This most commonly occurs in cases of advanced hydronephrosis (Fig. 2) and is usually secondary to obstruction of the ureter or of the renal pelvis. Other indications for ureteronephrectomy include:
• neoplasia of the kidney, ureter or adjacent organs (Fig. 3)
• chronic pyelonephritis refractory to medical treatment
• idiopathic renal haemorrhage
• ureteral abnormalities that defy surgical repair (such as stricture, rupture or avulsion).
Nephrectomy should be considered a pragmatic solution for unilateral ureteric trauma, given the certain outcome, if the contralateral kidney and ureter are known to be unaffected. It can also be used to manage unilateral ectopic ureter, even in the absence of hydronephrosis, if ureteric transplantation is impractical, and the contralateral ureter is proven to be normal. For the animal to be a candidate for nephrectomy, contralateral kidney function must be able to provide glomerular filtration rate adequate to sustain life. Another prerequisite is the absence of metastases in cases of neoplasia.
Ideally, individual contribution of each kidney to glomerular filtration rate should be determined before nephrectomy. Since renal scintigraphy is not readily available, intravenous urography may be performed to provide a crude assessment of single kidney function (Figs. 4a and 4b).
Although the following description refers to the removal of a (relatively) normal kidney and ureter, it is important to remember that in many instances the kidney architecture and anatomy will no longer be normal; similarly, neovascularisation may be present.
In those cases the surgeon will have to adapt the technique to the specific circumstances. A surgical assistant is mandatory for this procedure.
The kidney can be approached either via a midline coeliotomy or by incising the flank caudal to the last rib. Although the latter approach allows better access to a single kidney, midline coeliotomy is preferred because it grants better visualisation of the abdominal cavity. This is important in that it helps to allow evaluation of the presence of metastases in cases of neoplasia, and also in order to inspect both ureters and the bladder.
The left kidney is visualised by reflecting the mesocolon medially and using it to contain the intestinal loops (Fig. 5), this is called the colonic manoeuvre. The right kidney is exposed by lifting the descending duodenum and using its mesentery to keep the intestines out of the surgical field, the duodenal manoeuvre. The exposed viscera and the margins of the incision are protected by moistened laparotomy swabs.
In most instances, the kidney can be removed after capsular stripping: the peritoneum overlying the kidney is lifted and incised with scissors and the kidney is then freed using blunt dissection (Fig. 6). Sharp incision may be necessary if, owing to the disease process, the peritoneum firmly adheres to the kidney capsule. Haemorrhage from capsular vessels is usually minimal and easily controlled with pressure or diathermy. In cases of renal neoplasia, or when the kidney disease has caused dense attachments of the capsule to the parenchyma, the incision is made through the peritoneum to provide a margin around the kidney so that the capsule is removed with the kidney. The assistant supports the kidney during the remainder of the dissection.
Reflection of the hilar fat, together with gentle medial retraction of the kidney, allows visualisation of the vessels and ureter on the dorsal aspect of the hilus. It is important to identify all extra-renal branches of the renal artery and/or multiple vessels, which are often present, especially in the left kidney. The artery is isolated by careful blunt dissection. Use of right-angled forceps is recommended for this. The artery is double ligated close to the aorta, using synthetic absorbable suture material; for added security against slipping, it is advisable to apply the most distal ligature as transfixing. An excellent alternative is the use of vascular clips. The vein is then ligated in similar fashion.
In intact animals, the left ovarian or testicular vein, which drains into the left renal vein instead of the caudal vena cava, is identified and preserved by ligating the renal vein distal to it. Ligating the renal artery and vein separately prevents formation of an arteriovenous fistula. However, in smaller patients, or if the anatomy is grossly distorted by the disease process, it may be safer to ligate the vessels en masse to minimise the risk of damaging them with consequent haemorrhage. The likelihood of developing an arteriovenous fistula is in fact limited, and there are no cases reported in the veterinary literature.
After vessel transection, the ureter is freed to the level of the bladder with gentle traction (Fig. 7), and ligated close to the trigone using synthetic absorbable suture material. Once resected, the ureter can be pulled free from the retroperitoneal tissue deep to the reproductive tract and removed together with the kidney. Closure of the abdomen is routine.
NEPHROTOMY AND PYELOLITHOTOMY
These procedures are usually performed to remove uroliths located in the renal pelvis. Medical dissolution is possible for struvite uroliths, but this is not always successful, may take weeks and carries a small risk of ureteral obstruction from uroliths reduced in size. However, on balance medical treatment is associated with less morbidity than surgical removal of this stone type. In recent years there has been a large increase in the incidence of oxalate uroliths, which are not amenable to medical treatment. Surgical removal of nephroliths is therefore considered in patients with deteriorating renal function, uroliths not amenable to dissolution or when there is severe pain or infection. This can be a difficult clinical decision however – these surgical interventions carry a significant morbidity. Another rare indication for nephrotomy is the exploration of the renal pelvis for investigation of neoplasia or haematuria.
In the normal kidney the renal pelvis is small and surrounded by renal parenchyma: direct access to it is possible only when it is dilated. In many cases, however, the renal pelvis can be accessed only through nephrotomy. In cases of severe hydronephrosis nephrotomy is best avoided, however, as the abnormal parenchyma may not hold sutures properly (Fig. 8), thus causing post-operative leakage of urine into the abdomen. In any event, it is rarely appropriate in these cases.
Nephrotomy causes a temporary 25–50% decrease in renal function; consequently, if bilateral procedures are necessary, they need to be staged at 4–6 week intervals. A variable degree of permanent dysfunction is also expected, and the surgeon must be clear that a long-term benefit of nephrotomy, compared to a conservative approach or nephrectomy, is possible.
After having accessed the kidney and isolated the renal vessels as previously described, temporary vessel occlusion is necessary to achieve haemostasis. This can be performed manually by an assistant, or mechanically by using an atraumatic vascular clamp or a tourniquet. In any case, duration of ischemia should not exceed 20 minutes. Whenever possible, isolation and occlusion of the renal artery alone allows venous drainage from the kidney, thus further decreasing the amount of blood in the surgical field and increasing kidney pliability.
The convex lateral surface of the kidney is exposed, and the kidney is stabilised within the grasp of the surgeon's non-dominant hand. The renal capsule is sharply incised longitudinally on the midline, for approximately two thirds of the renal length, leaving the cranial and caudal poles intact. The renal parenchyma is then bluntly separated using forceps or the scalpel handle, thus minimising the damage to small parenchymal vessels. Larger vessels (arcuate or interlobar) are occasionally present and these must be severed after ligation. Diathermy is not used, as it severely damages the renal parenchyma.
Forceps are used to spread the incision edges and to grasp and remove the urolith gently, trying to avoid its fragmentation (Fig. 9). A small-diameter soft catheter is then used to flush the diverticula and the ureter with saline solution in order to remove smaller uroliths and to confirm patency. Samples (urine and tissue) are taken from the renal pelvis and submitted for bacterial culture; the urolith is submitted for mineral analysis and bacteriology.
Nephrotomy closure is achieved by apposing the two sides of the incision with digital pressure for five minutes while blood flow is restored and a simple continuous suture is placed in the renal capsule. Usually this is sufficient to achieve haemostasis, and at the same time avoids unnecessary damage to the nephrons. Only in rare cases is it necessary to use mattress sutures through the kidney cortex.
The kidney is replaced in its original position, ensuring that 180° rotation has not occurred. Renopexy is performed, placing a few tacking sutures between the renal capsule and the sublumbar musculature to prevent post-operative rotation or kinking of the renal pedicle.
If the renal pelvis and proximal ureter are sufficiently dilated, uroliths can be removed with pyelolithotomy. This procedure does not damage the kidney parenchyma, nor does it require vascular occlusion. It is therefore generally preferred whenever renal pelvic dilation is present. However, although pyelolithotomy causes less damage to kidney function than nephrotomy, it still carries with it the risk of post-operative ureteral leakage and stenosis and of urolith reformation.
The kidney should be isolated as for nephrotomy, and then rotated to expose its dorsal surface, as the renal vessels overlie the ventral aspect of the renal pelvis. The nephrolith is removed with forceps after longitudinal incision in the pelvis and proximal ureter (Fig. 10). Saline is then flushed into the pelvis and ureter, and the latter is catheterised to ensure patency. The pyelotomy incision can now be sutured in a continuous pattern with 4/0 or 5/0 synthetic absorbable material. Use of surgical loupes facilitates accuracy of the suture.
After having returned the kidney to its original position, renopexy avoids rotation in the post-operative period, with consequent occlusion of the renal vasculature and ureter.
Double-pigtail ureteral stents are multi-fenestrated catheters made of a soft and biocompatible polyurethane compound, with a pigtail loop at each end to prevent migration.
They are commonly used in human patients with ureteral disorders, and, since 2006, placement of ureteral stents has also been performed in dogs and cats as a long-term treatment for various causes of ureteral obstructions (ureteral or trigonal obstructive neoplasia, ureteroliths, ureteral strictures, tears or spasm) (Fig. 11). Stenting can also be combined with, or precede, urolith removal. It may be used to decrease surgical tension on the ureter when applied concurrently to ureteral resection and anastomosis, and prevents oedema and leakage in the post-operative period. Stents are also used in association with extracorporeal shockwave lithotripsy and percutaneous nephrolithotomy to avoid ureteral obstruction caused by urolith fragments.
Stents divert urine from the renal pelvis into the urinary bladder (urine passes through and around the stent), thus bypassing ureteral obstructions; furthermore, the presence of the stent causes progressive passive ureteral dilation, which allows passage of previously obstructive ureteroliths. Ureteral stents are well tolerated in the long term (they have been left in place for over four years so far without problems).
In dogs, ureteral stents are most often placed in a retrograde direction through the ureteral orifice at the uretero-vesicular junction, under cystoscopic and fluoroscopic guidance, but can also be placed in an anterograde manner, percutaneously or at surgery. In cats, due to their smaller size, they are usually placed surgically, via pyelocentesis (anterograde), or, less commonly, via cystotomy (retrograde).
Surgical placement is minimally traumatic to the kidney. After midline coeliotomy the surgeon performs pyelocentesis with a needle or over-the-needle IV catheter (18–22 G depending on the size of the patient). A guidewire (Fig. 12) is passed down the ureter and exits the bladder through a small cystotomy wound. The stent is advanced in a retrograde fashion over the wire (Fig. 13) in order to minimise the size of the kidney puncture. If necessary, a ureteral dilator can be inserted over the guidewire in a retrograde manner. Once placed, the proximal loop of the stent is located inside the renal pelvis, the shaft runs through the ureteral lumen and the distal loop curls inside the urinary bladder (Fig. 14). The stent can be left in place indefinitely, unless infection or patient discomfort develops.
Intravenous fluid therapy is continued until the patient is able to maintain hydration; this is especially important after nephrotomy, pyelotomy and ureteral stenting, in order to prevent hypotension and to flush out blood clots that could cause obstruction. Furthermore, an increase in urine output is frequently present following relief of urinary obstruction, and may lead to dehydration, hypokalaemia and hyponatraemia if fluid therapy is not adequately provided.
Serial biochemistry parameters are measured and urinalysis performed to detect early complications and monitor treatment progress. Urine output may also need to be monitored if there are concerns about urine production.
Antibiotics, based on culture and sensitivity, are administered for 3–4 weeks post-operatively if urinary tract infection is present and long-term antibiotic therapy may be necessary to eliminate infection in cases of kidney damage. Opioid analgesics are administered in the immediate post-operative period; multimodal analgesia will include non-steroidal anti-inflammatories whenever appropriate. Administration of analgesics and antibiotics must take possible decreased renal filtration into account.
Rest is recommended in the immediate post-operative period; a restraint device such as an Elizabethan collar is helpful in preventing self-trauma.
The most common complications of kidney surgery are haemorrhage, urine leakage, and renal failure.
Haemorrhage from major renal vessels may cause severe blood loss, leading to rapid patient deterioration. However careful technique should minimise the risk of ligature displacement. Minor haematuria is to be expected for a few days after nephrotomy.
Urine leakage is typically secondary to an increase in hydrostatic pressure at the site of a suture, or to inaccurate suture placement. It usually occurs within the first 3–5 post-operative days. Early detection is critical to avoid severe metabolic derangement and chemical peritonitis. Urine production may remain adequate, however weight gain will occur as fluid is retained in the abdominal cavity. Diagnosis of uroabdomen is confirmed by abdominal ultrasound and abdominocentesis. Incorporation of the submucosa when suturing the renal pelvis, accurate ligation of the ureter at ureteronephrectomy and forced diuresis of the upper urinary tract in the post-operative period (to flush out blood clots that may cause occlusion) help to prevent leakage.
Renal failure may be caused by overlooked pre-existent dysfunction or by anaesthetic-induced renal damage. As previously stated, accurate evaluation of kidney function is mandatory before kidney surgery, including tests to assess the presence of IRIS stage I disease and contribution of individual kidneys to overall GFR before ureteronephrectomy.
Infection is also a possible complication of renal surgery, in particular when uroliths are present.
Other complications are more specific to single procedures: in cases of nephrotomy or pyelotomy there is risk of obstruction secondary to inflammation (in the early post-operative period) or to stricture formation (weeks to months after surgery). Since the degree of renal injury is directly proportional to the duration of urinary obstruction, early diagnosis and resolution are essential. Unfortunately, detection of early unilateral obstruction can be challenging if contralateral renal function is normal.
Another common complication after nephrotomy or pyelolithotomy for urolithiasis is recurrence of urolith formation (or failure to achieve complete removal). Diagnostic imaging is recommended after surgery to confirm that all uroliths have been removed, and serial radiographs are recommended every 3–6 months thereafter. Abdominal radiography is an adequate diagnostic tool because upper urinary tract uroliths are usually composed of radiopaque calcium oxalate or struvite.
Renal torsion because of failure to perform a pexy of the kidney after mobilisation is also possible.
Finally, complications of ureteral stenting are usually minor, and include short-term self-limiting dysuria, and, rarely, stent migration. Chronic mild haematuria and urinary tract infection have also been reported.
Prognosis after surgery to the kidney depends on the underlying disease. Ureteronephrectomy is the only treatment that improves survival in cases of primary renal tumour. When the procedure is performed for hydronephrosis, nephrectomy has not been found to be detrimental to the remaining kidney (Gookin et al., 1996).
In cases of nephrotomy/pyelotomy for relief of urinary obstruction, recovery of renal function depends on duration and degree of the obstruction itself, and function can be restored if obstruction is relieved within several days. However, after nephrotomy there is a temporary deterioration in kidney function, and ureteral obstruction following nephrotomy has also been documented in a study (King et al., 2006). Neither of these problems is easily handled in cases of contralateral renal dysfunction.
Persistent azotaemia is a widespread problem even after successful intervention to the upper urinary tract, especially in cases of obstruction; however, if confined within IRIS Stages 1–2, and with careful post-operative monitoring, a relatively long survival time can be expected.
Recurrence of urolithiasis after surgical removal is also common: it is therefore essential that the patient is prescribed an appropriate regime aimed toward prevention of urolith formation.
Renal surgery is performed in dogs and cats for treatment of urolithiasis and other causes of obstruction, or for resection of neoplasia. Clinicians can be faced with various challenges when performing these operations, due to the small size of some structures, or because patients are often in a critical condition, and complications can be life threatening. Careful patient pre-operative evaluation and post-operative monitoring, together with attention to surgical detail, are prerequisites to successful outcomes.