Urologic complications of kidney transplantation

1. Introduction

Urologic complications are an important cause of morbidity after kidney transplantation. Although their frequency has decreased thanks to advances in organ procurement, reconstructive techniques, and postoperative management, they remain a potentially reversible cause of graft dysfunction and loss.

Their relevance is particular because the transplanted kidney is often the only functioning renal organ, and it is in an immunosuppressed patient.

In addition, graft denervation alters the clinical presentation of some complications. A ureteral obstruction may manifest only as a rise in creatinine, without colicky pain.

The main complications include:

• Urinary fistula and urinoma.
• Ureteral necrosis.
• Ureteral stricture and obstruction.
• Lymphocele and other compressive collections.
• Hematuria and obstruction by clots.
• Urinary tract infections.
• Vesicoureteral reflux.
• Graft stone disease.
• Urinary retention and bladder dysfunction.

2. Classification of complications

The division by timing is useful, although not absolute.

Complication	Typical presentation	Main mechanism
Urinary fistula	Early	Anastomotic failure or ischemia
Ureteral necrosis	Early	Vascular compromise
Early obstruction	Days or weeks	Edema, clots, kinking, or compression
Ureteral stricture	Weeks to months, or late	Ischemia and fibrosis
Lymphocele	Weeks to months	Lymphatic accumulation
Hematuria	Early or late	Surgical bleeding, infection, or other injuries
Urinary tract infection	Any time	Anatomic factors, devices, and immunosuppression
Vesicoureteral reflux	Variable	Characteristics of the anastomosis and the bladder
Stone disease	Usually late	Metabolic, infectious, or anatomic factors
Urinary retention	Early or late	Bladder outlet obstruction or bladder dysfunction

3. Prevention: pretransplant urologic evaluation

Some urinary complications can be anticipated through an adequate evaluation of the recipient. Planning should not be limited to determining whether the patient has an anatomically present bladder: it must establish whether that bladder is able to store urine at safe pressures and empty adequately.

Medical history

Investigate:

• Etiology of chronic kidney disease.
• History of vesicoureteral reflux.
• Recurrent urinary tract infections.
• Stone disease.
• Bladder outlet obstruction.
• Previous urologic surgery.
• Neurogenic bladder.
• Urinary tract malformations.
• Hematuria.
• Prolonged anuria.
• History of urologic tumors.
• Need for intermittent catheterization.

Anatomic and functional evaluation

Depending on the history, the following may be required:

• Renal and bladder ultrasound.
• Measurement of post-void residual.
• Uroflowmetry.
• Voiding cystourethrography.
• Cystoscopy.
• Urodynamic study.
• CT for specific anatomic situations.

Urodynamics is not mandatory in all candidates, but it becomes especially important in cases of neurogenic bladder, low compliance, complex voiding disorders, or suspected high-pressure storage.

Low-capacity bladder

Patients who are anuric for prolonged periods may have a small, underused bladder. A distinction should be made between:

• Low-capacity but compliant bladder: its capacity may increase progressively once urine production is restored.
• Low-capacity, high-pressure bladder: it may pose a risk to the upper urinary tract and the graft.

A single bladder capacity value should not be used as an absolute criterion to accept or reject a conventional reconstruction.

Bladder outlet obstruction

In older men, prostatic hyperplasia can become relevant after transplantation, once urine production is restored. A previously minimally symptomatic obstruction may manifest with retention, elevated residual volume, infection, or impaired graft drainage. Its evaluation and treatment should be planned according to risk and the clinical situation.

4. Pathophysiologic basis of ureteral complications

Blood supply of the transplanted ureter

The graft ureter depends fundamentally on the proximal blood supply that is preserved during renal procurement. Excessive dissection of the periureteral tissue can interrupt small vessels and compromise the viability of the distal segment. This explains why ischemia plays a role both in the development of early fistulas and in later strictures.

Technical factors

Potentially modifiable factors include:

• Excessively long ureter.
• Extensive dissection of periureteral tissue.
• Anastomosis under tension.
• Ureteral kinking.
• Muscular tunnel that is too tight.
• Injury to the mucosa or ureteral wall.
• Blood supply problems of the lower pole.
• Unfavorable graft position.
• Unrecognized distal obstruction.

Prevention during implantation

The principles are:

1. Preserve the periureteral tissue, including the peripelvic fat and the ureteral adventitia.
2. Use a ureter of adequate length.
3. Resect clearly devitalized tissue.
4. Avoid tension and torsion.
5. Perform a watertight anastomosis.
6. Ensure urinary drainage.
7. Use a double-J stent according to protocol and the circumstances of the case.

5. Urinary fistula and urinoma

Definition

A urinary fistula is the abnormal escape of urine outside the excretory tract. When urine accumulates in a delimited space around the graft, a urinoma forms. It is an especially important complication in the first weeks after transplantation.

Etiology

• Failure of the ureterovesical anastomosis: suture defects, tension, or technical problems.
• Ischemia and ureteral necrosis: loss of blood supply can cause partial or complete necrosis of the distal ureter.
• Distal obstruction: increased intraluminal pressure can promote leakage of urine through a vulnerable area.
• Injury to the renal pelvis or ureter: it can occur during procurement, bench surgery, or implantation.

Clinical manifestations

• Increased output from the surgical drain.
• Clear fluid leaking from the wound.
• Decreased urine output through the Foley catheter.
• Pain or distension in the iliac fossa.
• Perigraft collection.
• Rise in creatinine.
• Fever or infection of the collection.

A significant leak can raise serum creatinine through reabsorption of urinary components, in addition to compromising graft function.

Diagnosis

Ultrasound. It allows identification of a fluid collection and assessment of its size and relationship to the graft. However, it does not always distinguish urinoma, lymphocele, or seroma.

Drain fluid creatinine. It is one of the most useful tests. A concentration clearly higher than the serum level suggests that the fluid contains urine. There is no single numerical ratio applicable to all scenarios, because interpretation depends on renal function, dilution, and time since onset.

Contrast studies. These may include:

• Cystography, if a bladder leak is suspected.
• Antegrade pyelography.
• CT studies with an excretory phase when appropriate.
• Selected nuclear medicine studies.

Antegrade pyelography can be particularly useful when a nephrostomy is placed, because it allows identification of the location and extent of the leak.

Treatment: when conservative and when surgical?

The decision depends on four variables:

1. Magnitude of the leak.
2. Viability of the ureter.
3. Presence of obstruction.
4. Presence of infection or a significant collection.

Small leak, no evident necrosis. Treatment with urinary decompression and drainage, with close surveillance, may be considered. The tools include a urinary catheter, double-J stent, percutaneous nephrostomy, and urinoma drainage. The choice depends on the location and on the possibility of achieving effective drainage.

Significant or persistent leak. A relevant anatomic failure should be suspected. Ureteral necrosis, extensive dehiscence, or a leak that is not controlled with urinary diversion may require surgical reconstruction.

Ureteral necrosis. The repair must use viable tissue. It may be necessary to resect the ischemic segment and perform a new ureteroneocystostomy, ureteroureterostomy, or pyeloureterostomy.

6. Ureteral necrosis

Ureteral necrosis deserves to be considered a specific entity because it determines the reconstructive strategy.

Mechanism

Interruption of the blood supply can lead to necrosis of the distal ureter. The compromise may be partial or extend to proximal segments. Necrosis may initially manifest as a urinary leak and later be associated with stricture.

Predisposing factors

• Excessive dissection.
• Loss of periureteral tissue.
• Injury to lower pole vessels.
• Ureter that is too long.
• Compromised graft perfusion.
• Injuries during procurement.

Diagnosis

Suspicion may arise from a persistent fistula or an early urinary collection. The true extent of devitalized tissue may not be completely defined by imaging. In certain cases, ureteral viability must be assessed directly during surgical exploration.

Principles of treatment

• Do not preserve clearly necrotic tissue.
• Avoid anastomosis under tension.
• Reconstruct with well-vascularized segments.
• Select an alternative technique when the remaining length is insufficient.
• Ensure urinary drainage and infection control.

The choice between bladder reimplantation, ureteroureterostomy, and pyeloureterostomy depends on the viable length and the recipient's anatomy.

7. Ureteral obstruction and graft stricture

Urinary tract obstruction is one of the most relevant urologic complications of kidney transplantation, both because of its frequency and because of the possibility of irreversible deterioration of graft function if it is not recognized in time. It is essential to distinguish two situations:

• Early ureteral obstruction: it may be transient or secondary to a correctable mechanical problem.
• Established ureteral stricture: it implies a persistent reduction in caliber, usually associated with fibrosis or ischemia.

Etiology of early obstruction

• Edema of the ureterovesical anastomosis.
• Intraluminal clots.
• Kinking of the ureter.
• Compression by hematoma or lymphocele.
• Excessively narrow anastomosis.
• Compressive muscular tunnel.
• Preexisting graft stone disease.
• Problems related to the double-J stent.

Etiology of late stricture

• Ureteral ischemia: the most important mechanism in many distal strictures.
• Anastomotic fibrosis: scarring that progressively reduces the caliber.
• Persistent extrinsic compression: lymphocele, fibrosis, or collections.
• Previous ureteral injury: manipulation, reconstructions, or endourologic procedures.
• Inflammatory or infectious disorders: they may contribute in certain cases.

Anatomic classification

The location determines the treatment.

Location	Reconstructive consideration
Ureterovesical anastomosis	Reimplantation or selected endourologic treatment
Distal ureter	Bladder reimplantation or use of the native ureter
Mid ureter	Reconstruction according to viable length
Proximal ureter	Selected ureteroureterostomy or pyeloureterostomy
Extensive stricture	Complex reconstruction with alternative tissue

It is also necessary to describe whether the stricture is short or long, complete or partial, single or multiple, and whether viable ureteral tissue exists.

Clinical presentation

Unlike obstruction of a native kidney, graft stricture may occur without renal colic. The usual presentation may include:

• Progressive rise in creatinine.
• Decreased urine output.
• Hydronephrosis detected on ultrasound.
• Urinary tract infection.
• Functional deterioration without specific symptoms.

Sometimes the diagnosis is made during routine follow-up.

Diagnosis

Ultrasound. It is the initial study. It allows identification of pelvicalyceal dilation, collections, and other graft abnormalities. However, not every dilation represents a significant obstruction: residual dilation or dilation related to reflux may exist, especially in distended bladders.

Bladder evaluation. Before concluding that a stricture exists, one must verify catheter patency (if one is in place), bladder volume, post-void residual, the presence of retention, and the possibility of reflux.

Diuretic renogram. It can provide functional information on drainage, although its interpretation is more difficult when graft function is impaired.

Antegrade pyelography. It allows definition of the level of obstruction, the length of the lesion, and whether contrast can pass. It is particularly useful when a nephrostomy has been placed.

CT studies. They can identify stones, extrinsic compression, or complex anatomic abnormalities.

When to place a nephrostomy?

Percutaneous nephrostomy is a fundamental tool for decompressing the graft's urinary tract. It should be considered especially in the setting of:

• Obstruction with significant deterioration of renal function.
• Obstruction associated with infection.
• Inability to achieve retrograde drainage.
• Complex stricture.
• Need to define the lesion anatomically.
• Failure of a ureteral stent.

In the presence of infection and obstruction, decompression is an urgent priority, together with antimicrobial treatment and clinical support.

Endourologic treatment

The options include balloon dilation, endoureterotomy in selected cases, and placement of ureteral stents. Success depends on the length of the stricture, time since onset, degree of fibrosis, ischemic etiology, location, and prior treatments.

Short strictures that are not completely obliterative may be better candidates for endourologic treatment than long or recurrent strictures. Endourologic treatment should not be repeated indefinitely when there is an anatomic lesion that requires reconstruction.

Surgical reconstruction of the stricture

• New ureteroneocystostomy: it may be appropriate for a distal stricture when enough viable ureter exists to reach the bladder without tension.
• Ureteroureterostomy: it allows use of the recipient's native ureter. It may be especially useful when the graft ureter does not reach the bladder or when direct bladder reconstruction is not advisable.
• Pyeloureterostomy: it may be indicated when the graft ureter is very short, extensively damaged, or not viable.
• Complex reconstructions: in exceptional cases, other techniques may be required, depending on the recipient's anatomy, previous surgeries, and reconstructive experience.

Video clinical case: graft ureteral stricture

The following video presents a clinical case of ureteral stricture in a kidney transplant, as an example of the evaluation and decision-making described in this section.

8. Perigraft collections: urinoma, lymphocele, and hematoma

Perigraft collections can cause direct complications or complications secondary to compression of the urinary tract and vessels. Identifying them requires considering the time of onset, the characteristics of the fluid, and the impact on the graft.

Differential diagnosis

Characteristic	Urinoma	Lymphocele	Hematoma
Origin	Urinary leak	Lymphatic leak	Bleeding
Onset	Usually early	Often weeks later	Usually early
Fluid creatinine	Higher than serum, depending on dilution	Similar to serum	Variable
Ultrasound	Fluid collection, often anechoic	Usually fluid	Variable echogenicity depending on evolution
Complication	Infection, persistent leak	Ureteral or venous compression	Compression and bleeding

Ultrasound provides guidance, but it does not always establish the type of collection on its own.

Lymphocele

It is an accumulation of lymphatic fluid related to dissection of the recipient's iliac vessels or of the graft's lymphatic tissue. It can appear weeks after transplantation.

Manifestations:

• Asymptomatic ultrasound finding.
• Ureteral compression and hydronephrosis.
• Lower limb edema.
• Venous compression.
• Deterioration of renal function.
• Pain or sensation of a mass.

Diagnosis. Ultrasound allows identification of the collection. In selected cases, CT may be required to define anatomic relationships. Analysis of fluid obtained by puncture helps rule out urinoma and infection.

Treatment. A small, asymptomatic lymphocele can be observed. A symptomatic or compressive lymphocele requires consideration of drainage. The options include:

• Percutaneous drainage.
• Drainage combined with sclerotherapy in selected cases.
• Laparoscopic or open surgical fenestration.
• Other techniques aimed at controlling the lymphatic leak in specialized centers.

Aspiration alone carries a risk of recurrence and is generally not the best definitive strategy for a persistent lymphocele.

Laparoscopic fenestration of the lymphocele

The goal is to create a wide, durable communication between the lymphocele and the peritoneal cavity to allow the fluid to be reabsorbed. Technical considerations:

1. Review the images and the relationship to the graft.
2. Identify the location of the vessels and the ureter.
3. Confirm that the collection is a lymphocele and not a urinoma or abscess.
4. Plan a safe access.
5. Create an adequate peritoneal window.
6. Avoid injury to the graft, vascular pedicle, and urinary tract.
7. Assess the risk of recurrence.

Perigraft hematoma

It can cause ureteral, vascular, or parenchymal compression. Management depends on its size, growth, hemodynamic stability, signs of infection, and impact on the graft. Not all hematomas require evacuation.

9. Hematuria after kidney transplantation

Hematuria can be a manifestation of surgical, infectious, vascular, or neoplastic complications.

Early hematuria

It may be related to:

• Surgical manipulation.
• Bleeding from the urinary anastomosis.
• Catheter trauma.
• Clots in the urinary tract.
• Coagulation disorders.
• Graft injuries.

Mild hematuria may resolve spontaneously. Heavy hematuria can cause obstruction by clots, retention, and impaired graft drainage.

Evaluation

Hemodynamic stability, hemoglobin, renal function, catheter patency, the presence of clots, infection, and ultrasound findings should be assessed.

Treatment

Depending on severity, the following may be required:

• Surveillance.
• Maintaining adequate bladder drainage.
• Bladder irrigation when indicated.
• Clot evacuation.
• Cystoscopy.
• Treatment of the identified cause.

Late hematuria

The possibility of the following should be investigated:

• Urinary tract infection.
• Stone disease.
• Urothelial neoplasia.
• Prostatic disease.
• Vascular lesions after biopsy.
• Other graft diseases.

10. Urinary tract infections in the kidney transplant recipient

Urinary tract infections are especially important because of immunosuppression and the possibility of directly affecting the graft. Urinary devices, diabetes, anatomic abnormalities, and exposure to resistant organisms are relevant factors.

Risk factors

• Immunosuppression.
• Urinary catheter.
• Double-J stent.
• Diabetes.
• Vesicoureteral reflux.
• Urinary obstruction.
• Stone disease.
• Elevated postvoid residual.
• Functional bladder abnormalities.
• History of infections with multidrug-resistant organisms.

Clinical classification

• Asymptomatic bacteriuria: bacterial growth in urine without symptoms attributable to infection.
• Cystitis: symptomatic infection of the lower urinary tract.
• Graft pyelonephritis: infection involving the upper urinary tract that can cause functional deterioration.
• Urosepsis: urinary tract infection associated with potentially severe organ dysfunction.

Diagnosis

In symptomatic patients, the following should be considered:

• Urine culture.
• Complete blood count.
• Renal function.
• Evaluation of inflammatory markers depending on context.
• Blood cultures in the setting of high fever, sepsis, or suspected bacteremia.
• Ultrasound if there is functional deterioration, suspected obstruction, or an unfavorable course.

Asymptomatic bacteriuria

Management depends on the time since transplantation, the planned urologic procedures, and the patient's characteristics. It is important to distinguish late asymptomatic bacteriuria from symptomatic infection.

In stable kidney transplant recipients, more than one or two months after transplantation, contemporary recommendations generally advise against routine treatment of asymptomatic bacteriuria, except in particular situations. In the earliest postoperative period there is greater uncertainty, and local protocols should be considered.

Treatment of symptomatic infection

It should be based on clinical severity, time since transplantation, prior cultures, local epidemiology and resistance, renal function, interactions with immunosuppressants, and the presence of obstruction or devices. Antimicrobial treatment should be coordinated with nephrology and infectious disease when complexity requires it.

Infection associated with obstruction

The combination of infection and urinary obstruction is an emergency. Administering antibiotics is not enough if an infected, obstructed collecting system persists. Urgent drainage by nephrostomy or ureteral stent should be considered, depending on anatomy and technical feasibility.

11. Graft vesicoureteral reflux

Vesicoureteral reflux is the retrograde passage of urine from the bladder into the ureter and collecting system of the graft. It can be seen after a ureteroneocystostomy, especially if the antireflux mechanism is insufficient.

Is all reflux pathologic?

No. The presence of isolated reflux does not necessarily imply renal damage or require surgical correction. Its clinical importance depends on:

• Grade of reflux.
• Recurrent urinary tract infections.
• Episodes of pyelonephritis.
• Graft function.
• Bladder pressures.
• Presence of obstruction.
• Voiding abnormalities.

Diagnosis

Voiding cystourethrography can demonstrate and grade reflux. It should not be ordered routinely in all recipients without a clinical indication. It may be considered in the setting of recurrent pyelonephritis, suspected significant reflux, or anatomic and functional abnormalities.

Treatment

• Asymptomatic reflux: usually observation.
• Reflux associated with recurrent infections: first evaluate and treat modifiable factors, including post-void residual, obstruction, bladder dysfunction, and stone disease.
• Persistent, clinically significant reflux: consider correction in selected cases.

The options may include endoscopic treatment with bulking agents, revision of the ureteroneocystostomy, or ureteroureterostomy with the native ureter in appropriate situations. Endoscopic treatment has variable results and does not always resolve high-grade reflux.

12. Stone disease in the transplanted kidney

Graft stone disease has particular characteristics because of its anatomy, location, and denervation.

Etiology

• Stones present in the graft since donation.
• Persistent hyperparathyroidism.
• Metabolic abnormalities.
• Recurrent urinary tract infection.
• Urinary stasis.
• Foreign bodies.
• Sutures or clips exposed to the urinary tract.
• Ureteral stricture.
• Disorders of calcium and uric acid metabolism.

Clinical presentation

Unlike stone disease in a native kidney, colicky pain may be absent. The manifestations may be:

• Rise in creatinine.
• Hematuria.
• Urinary tract infection.
• Hydronephrosis.
• Decreased urine output.
• Incidental finding.

Graft denervation explains part of this atypical presentation.

Diagnosis

• Ultrasound: useful for identifying hydronephrosis and visible stones.
• Noncontrast CT: it allows definition of the location, size, density, and number of stones.

The choice should take into account the diagnostic need and radiation exposure.

Treatment

The choice depends on the size and location of the stone, the presence of obstruction, infection, the anatomy of the urinary reconstruction, graft function, and endoscopic accessibility.

• Retrograde ureteroscopy: it can be technically difficult because of the location and orientation of the graft ureteral meatus. Flexible ureteroscopes can facilitate access.
• Retrograde intrarenal surgery: an alternative for certain kidney stones, provided that access to the graft's urinary tract is possible.
• Percutaneous nephrolithotomy: it can be used for larger stones or when retrograde access is unfavorable. The superficial location of the graft can facilitate certain aspects of access, but it requires careful planning to avoid bowel and vascular injury.
• Extracorporeal shock wave lithotripsy: it may be considered in selected cases depending on size, location, and the likelihood of fragment clearance.

Infected obstructive stone disease

It is a urologic emergency. The priority is:

1. Resuscitation and sepsis assessment.
2. Appropriate antibiotics.
3. Urgent decompression.
4. Definitive treatment of the stone disease after the infection is controlled.

13. Urinary retention and lower urinary tract dysfunction

Recovery of diuresis after transplantation can reveal voiding disorders that previously had little clinical expression.

Causes

• Obstructive prostatic hyperplasia.
• Urethral stricture.
• Detrusor dysfunction.
• Neurogenic bladder.
• Retention related to anesthesia and medications.
• Clots.
• Previous anatomic abnormalities.

Consequences for the graft

• Elevated bladder pressure.
• Reflux.
• Hydronephrosis.
• Urinary tract infection.
• Impaired ureteral drainage.
• Risk to a recent anastomosis.

Diagnosis

Clinical evaluation, bladder ultrasound, post-void residual, uroflowmetry when appropriate, and selected urodynamic studies.

Treatment

Management depends on the cause. It may include:

• Bladder drainage.
• Pharmacologic treatment of prostatic obstruction.
• Intermittent catheterization.
• Correction of urethral stricture.
• Surgical treatment of bladder outlet obstruction in selected patients.

14. Salvage surgical reconstruction

This section integrates the knowledge from the urinary reconstruction lesson with the treatment of complications.

When to abandon endourologic treatment?

Definitive reconstruction should be considered in the setting of:

• Extensive stricture.
• Complete obstruction.
• Ureteral necrosis.
• Persistent fistula.
• Recurrence after endourologic treatment.
• Unfavorable anatomy.
• Need to maintain prolonged drainage without a definitive solution.

The decision depends on the patient's condition, graft function, and the team's experience.

Preoperative evaluation

Before reconstructing, the following must be known:

• Location of the lesion.
• Length of viable ureter.
• Anatomy of the renal pelvis.
• Position of the graft.
• Relationship to the iliac vessels.
• Bladder capacity and function.
• Condition of the native ureter.
• Presence of infection.
• Previous surgeries.

Choice of technique

Situation	Alternative to consider
Distal fistula with viable proximal ureter	New ureteroneocystostomy
Short distal stricture	Selected endourology or reimplantation
Short ureter and viable native ureter	Ureteroureterostomy
Extensive necrosis of the graft ureter	Pyeloureterostomy with native ureter
Compressive lymphocele	Drainage or fenestration, depending on the case
Complex bladder anatomy	Individualized reconstruction

Surgical principles

The repair must meet the same principles as primary reconstruction: viable tissue, adequate blood supply, tension-free anastomosis, absence of torsion, and effective drainage. Salvage surgery adds difficulties: fibrosis, adhesions, proximity of the vascular pedicle, and distortion of the anatomic planes. Planning with imaging and the availability of alternative techniques are essential.

Open, laparoscopic, and robotic surgery

Open reconstruction remains an important option, especially in urgent situations or with complex anatomy. Laparoscopy and robotic surgery can be used in experienced centers for selected reconstructions. The choice of approach should not take precedence over the vascular and urinary safety of the graft.

Algorithm A. Management of urinary fistula

Suspected urine leak → ultrasound + fluid creatinine + clinical evaluation → determine extent, location, infection, and ureteral viability.

• Limited leak, viable ureter → urinary decompression ± drainage of the collection and close monitoring.
• Necrosis, extensive dehiscence, or failed drainage → surgical revision and reconstruction with viable tissue.

Algorithm B. Hydronephrosis and functional deterioration of the graft

Functional deterioration + hydronephrosis → assess the bladder, patency of devices, infection, and degree of obstruction. Significant obstruction with clinical repercussions?

• Not confirmed → complete the functional and anatomic evaluation; follow-up according to clinical course.
• Yes → decompress when appropriate, especially if there is infection or significant deterioration; define location, length, and cause; then selected endourologic treatment or definitive reconstruction.