Urologic Considerations in the Kidney Transplant Patient
Nick G. Cowan
PRETRANSPLANT UROLOGIC CONSIDERATIONS
A renal allograft must have three components to function properly: inflow of blood, outflow of blood, and urinary drainage.
Suitable arterial targets for revascularization may be assessed pretransplant with a thorough vascular examination (pulses), abdominal ultrasound (U/S) with duplex, or computed tomography (CT) abdomen/pelvis.
Transplant candidates with a history of peripheral vascular disease, amputations, claudication, or long-standing diabetes may warrant a more thorough vascular examination because significant atherosclerosis is more likely.
Candidates with a history of multiple groin catheters may also warrant a more detailed vascular examination with dedicated venous imaging to ensure a venous target exists because sclerosis of the iliac venous system can occur.
An ideal bladder for renal allograft drainage is one which has adequate storage volume (at least 300-400 mL), normal compliance (low pressures with filling and voiding), and complete emptying (postvoid residuals <50 mL).
Bladders that were otherwise healthy but have not been used for many years will typically have a low capacity immediately posttransplant (<200 mL) but will most often return to their predialysis capacity over the course of the first year posttransplant. Patients will often have urinary frequency immediately posttransplant as a result of this diminished capacity.
Patients with a history of neurogenic bladder, urinary incontinence, or other bladder anomalies must be carefully evaluated preoperatively to ensure their bladders are “safe” for transplantation (ie, normal compliance, capable of emptying).
Allograft urinary drainage is typically performed with a ureteroneocystostomy (donor ureter is connected to native bladder [Figure 12-1]) but may also be accomplished by connecting the transplant ureter to a native kidney ureter (known as the ureteroureterostomy) if necessary, although the rates of stricture are higher with this approach.
THE IMMEDIATE POSTTRANSPLANT PERIOD
Posttransplant bladder spasm
Patients may suffer from painful involuntary bladder contractions postoperatively due to the presence of the Foley balloon or ureteral stent.
A bladder spasm typically manifests as episodic lower abdominal cramping and leakage around the Foley catheter.
Initial management involves ensuring the catheter is draining properly and no residual urine remains in the bladder (obtain bladder scan).
Medical management involves oral anticholinergics (oxybutynin 5 mg orally, three times a day as needed) and/or suppositories (belladonna and opium 16.2 mg/30 mg every 12 hours as needed).
For severe cases refractory to medical management, consideration may be given to early stent or Foley catheter removal.
Allograft hydronephrosis may be reported as mild, moderate, or severe. If present, discussion with the transplant surgeon and/or urologic consultation should be pursued.
Allograft hydronephrosis should be assessed in the setting of an empty bladder to rule out urine reflux as the cause of dilation.
U/S is typically used for initial assessment.
Technetium-99m mercaptoacetyltriglycine (MAG3) nuclear function testing with furosemide washout and calculation of a t1/2 can be an adjunct test in equivocal cases of hydronephrosis to determine if urinary obstruction is present. This test should be performed with a urinary catheter in place.
Contrast studies including antegrade or retrograde pyelograms can help elucidate the cause of the hydronephrosis (eg, stricture, stone).
Most common major urologic complication following renal transplantation1
Occurs in an estimated 3% of transplant recipients2
Most often results from distal ureteral ischemia leading to fibrosis of the ureteric intima
Onset of ureteral stricture can occur anytime between a few weeks to months after transplant.
Ureteral stricture rates are lowest in recipients who are stented at the time of transplant.
Patients may be clinically asymptomatic as the allograft is denervated and the diagnosis suspected only due to the presence of a rising creatinine and allograft hydronephrosis.
Suspected in the presence of moderate to severe allograft hydronephrosis (best demonstrated by CT of kidneys, ureter, and bladder [KUB] or allograft U/S) despite the presence of a Foley catheter, which rules out reflux as the cause of hydronephrosis
The diagnosis may be confirmed with an antegrade nephrostogram via a percutaneous allograft nephrostomy tube or retrograde pyelogram via cystoscopy.
MAG3 nuclear renal scan with furosemide washout showing an elevated t1/2 (>20 minutes). Note that the result of this test is often equivocal (t1/2 >10 minutes but <20 minutes).
Depends on stricture length and suspected etiology (ischemic, external compression, BK viral infection)
Options include endoscopic stricture incision and/or dilation, stenting, or open reimplantation.
Second most common major urologic complication following renal transplantation
Patients may present with pain (often severe pain) over the allograft and clear fluid draining from their wound.
If a surgical drain is present, rising serous output may indicate a urine leak.
Diagnosis may be confirmed with a CT cystogram, plain film cystogram, or voiding cystourethrogram (VCUG) demonstrating urine extravasation.
Low-volume urine leaks (low drain output, minimal extravasation on cystogram) may be successfully managed with prolonged ureteral stenting and Foley catheter drainage (typically 1-3 weeks). A repeat cystogram should be performed to confirm resolution of the leak prior to catheter removal.
Renal artery stenosis
Patients will often be asymptomatic.
Presence of renal artery stenosis is often suspected when there is/are unexplained allograft dysfunction, new onset or difficult to control hypertension, and/or bruit over the allograft.
Diagnosis is suspected when a duplex U/S shows elevated renal allograft vascular velocities (>200-250 cm/s) or elevated peak systolic velocity ratio between the iliac and renal arteries (>3.0-3.5).
CT angiogram, magnetic resonance (MR) angiogram, or angiography showing a stenosis of >50% of intraluminal diameter may be used to confirm the diagnosis.
Note that elevated anastomotic velocities on duplex U/S are typical in the early postperiod but should normalize by approximately 3 months posttransplant. Trending the anastomotic velocity to ensure a decreasing trend may be all that is necessary for an incidental finding of elevated vascular velocities in the early posttransplant period.3
Consultation with the surgeon who performed the transplant is essential because he or she may have insight into the specific vascular anatomy of the donor kidney and recipient vasculature.