The canine and feline kidneys are paired organs that lie in the retroperitoneal space just ventral to the first four lumbar vertebrae. They lie lateral to the aorta and vena cava. The right kidney is located more cranial than the left and is often in contact with the caudate lobe of the liver. The adrenal gland is located just cranial to the kidneys, although a clear plane of dissection is almost always present between these organs. The renal hilus is the origin of the ureter, renal artery, and vein. The renal artery and vein are branches off the aorta and caudal vena cava but show significant natural variation among individuals with branching or multiple renal arteries and veins common in both species.^30,31 The cranial abdominal artery passes over the adrenal gland and then dives dorsal to the cranial pole of the kidney. This vessel can be encountered during TLU. Recently, a survey of anatomic variations in ureteral anatomy in cats has been performed showing that circumcaval ureters are common in cats, occurring in approximately one third of those evaluated.³² The ureters lie dorsal to the internal spermatic vessels and the vas deferens over which they pass approximately 2 cm cranial to the bladder. In females, the ureters pass dorsal to the ureterovarian artery and vein in a similar location. During resection of the more distal aspects of the ureter, dissection around these structures is necessary. The ureters join the lateral ligaments of the bladder before entering the bladder at the ureterovesicular junction on the dorsolateral surface of the bladder just caudal to the neck.

Patients that might be candidates for TLU can have a plethora of underlying renal diseases. In many cases, they may be older patients with important comorbidities that need to be assessed. One of the most important parameters to evaluate is overall renal functional reserve because many renal pathologies are bilateral and affect the contralateral (unresected) kidney to varying extents. A complete blood count, biochemical screen, and urinalysis with urine culture and bacterial culture and sensitivity should be performed in all cases. Serum creatinine is a relatively insensitive test for detection of kidney damage, and significant elevations are only detected when 60% to 75% of nephrons have been lost. In patients in which TLU is being considered, a more sensitive test for early renal disease and especially the relative loss of filtration ability from each kidney is vital. This can be obtained using a variety of tests, including glomerular filtration rate (GFR) testing, determination of fractional excretion of electrolytes, or assays of urinary biomarkers. Global GFR calculation provides a summated measure of filtration from both kidneys and has been validated in dogs and cats using a variety of methods.³³ However, in patients in which TLU is being contemplated, a per-kidney GFR is more useful to predict the prognosis for renal function in the postoperative period. Per-kidney GFR can be calculated using scintigraphic means.^34,35 or contrast-enhanced computed tomography (CT).³⁶ If urinary tract infection is detected from a urinalysis performed preoperatively, treatment based on the results of culture and susceptibility testing should be initiated. If the patient’s clinical status allows, preoperative treatment with an appropriate antibiotic is recommended for 1 to 2 weeks before surgery.

Diagnostic imaging of the urinary tract is also critical in these cases to evaluate the extent and severity of disease, to assess for comorbidities and metastatic disease in the case of malignancy, and to provide vital information for surgical planning. Plain radiography provides relatively insensitive information for assessment of renal pathology but may give a rough idea of kidney size and may highlight radiopaque lithiasis at different locations within the urinary tract. Abdominal ultrasonography is extremely useful for assessment of renal and ureteric pathology. The presence and extent of mass lesions, degree of hydronephrosis and hydroureter, and evidence of dysplasias should be detectable. It also allows ultrasound-guided aspiration of any lesions that are evident and recovery of samples for bacterial culture and susceptibility testing by cystocentesis or pyelocentesis. Contrast-enhanced computed tomography (CE-CT) is often recommended in small animals that are being considered for TLU because it provides the surgeon with an assessment of lesion dimensions, location, and the relationship of any mass lesions to surrounding organs. CE-CT also allows evaluation of any associated lymphadenopathy that may be clinically important for disease staging and surgical planning.

Relatively little data are available for TLU in clinical patients, so making strict case selection guidelines at this point in the development of the technique is challenging.²⁸ The author suggests that case selection be made very carefully, especially in the early part of a surgeon’s learning curve, because TLU represents one of the more challenging laparoscopic interventions. The author’s group as well as others have found that laparoscopic removal of grossly normal kidneys in research animals or animals with diseased kidneys but without gross morphologic change to their kidneys is relatively simple and not associated with prolonged surgical times.^27,28 In clinical patients with distortion of the kidney by larger renal masses, hydronephrosis, or hydroureter, surgeons should select cases cautiously to avoid a high conversion rate and significant morbidity. At this time, appropriate case selection for TLU includes modestly sized primary renal neoplasms, chronic renal failure with infection, renal dysplasia, and idiopathic renal hematuria. Note that other options may be available for some of these conditions that may not necessitate TLU in these patients. Contraindications for TLU at this point in time include large renal masses (>5–7 cm), severe hydronephrosis or hydroureter, or pyelonephritis with abscessation or if there is any infection that extends beyond the renal capsule. In clinical cases, preoperative imaging with ultrasonography and preferably CT (or magnetic resonance imaging) is very helpful in ruling out conditions that might make a laparoscopic approach undesirable. As more experience is gained with the technique, the case selection criteria for TLU may change.

The hair is liberally clipped from the lateral abdomen of the patient on the affected side. The clip extends from the transverse spinous processes of the spine to the mid-abdominal area on the contralateral side. Cranially, the clipped area extends to the midthorax, and caudally it extends to the perineal area. The whole area is aseptically prepared for surgery, including an aseptic wash of the prepuce in male dogs.