Upper Urinary Tract Obstruction

Pathophysiology of Obstruction

Unilateral ureteral obstruction (UUO) — triphasic

• After complete UUO, renal function is permanently lost by 6 weeks (1.5 months) — recovery on relief (canine model):
  • 7 days → 100% · 14 days → 70% · 4 weeks → 30% · 6 weeks → 0%
• Better recovery → milder obstruction, a compliant collecting system, pyelolymphatic backflow, early relief.
• Poor recovery → older age, thin cortex, increased parenchymal collagen, glomerulosclerosis.

Bilateral ureteral obstruction (BUO) — biphasic

• The initial vascular response to complete ureteral obstruction is preglomerular vasodilatation.
• Efferent arteriolar constriction is a second-phase event in bilateral obstruction only — it does not occur in unilateral obstruction.
• The first renal function parameter impaired by ureteral obstruction is water reabsorption.
• A JJ stent left > 4 weeks after chronic obstruction decreases ureteral contractility and contributes to VUR.
• Bicarbonate excretion → cortical collecting duct, by type B (β) intercalated cells —
  • Apical pendrin Cl⁻/HCO₃⁻ exchanger secretes HCO₃⁻ into urine → disposes of excess base in metabolic alkalosis.

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Post-Obstructive Diuresis (POD)

Urine output > 200 mL/hr for 2 consecutive hours, or > 3 L over 24 hours, following relief of urinary tract obstruction.

• Main driver after relief of bilateral ureteral obstruction → ANP —
  • Retained salt and water expand the extracellular volume → atrial stretch → ANP release → ↑ GFR and Na excretion.
• Physiologic POD is self-limiting — it stops once homeostasis is restored.
• Pathologic POD is an inappropriate diuresis → risk of hypernatremia and hypovolemia.
  • Its nephrogenic DI-like form (concentrating defect — below) is a water diuresis — urine osmolality usually < 150 mOsm/kg.

Pathologic POD — three mechanisms

• Loss of active Na reabsorption in the thin ascending limb ("salt-wasting nephropathy") — mediated by ANP and downregulated Na transporters (ENaC, Na/K/ATPase, Na/K/2Cl).
  • The massive natriuresis also ↑ excretion of phosphate, K and Mg.
• Loss of urea backflux from the inner medullary collecting duct ("medullary washout") — the medullary counter-current gradient is lost.
• Decreased water reabsorption in the PCT, thick ascending limb and collecting duct — a poor response to ADH (nephrogenic DI) from downregulation of AQP-2 channels.
  • After BUO, AQP-1, -2 and -3 are all downregulated → the persistent concentrating defect (persistent polyuria) after relief; reduced AQP-1 can persist > 30 days.
  • ↑ COX-2 activity adds to the polyuria and impaired urine concentration.

Pathologic POD occurs almost only in patients with:

• Signs of fluid overload — edema, CHF, hypertension
• Abnormal renal function
• Abnormal electrolytes

Management

• Monitor vitals and mental status.
• Hourly urine output on a strict input/output chart.
• Replace approximately 50–75% of the urine output with 0.45% NS.
  • Replace orally if mental status is stable and the patient can tolerate it.
  • Over-replacement perpetuates the diuresis.
• Serum Na, K, Mg, urea, creatinine, PO4 — frequently at first, then widen the interval.
• Urine Na, K and osmolality to separate a urea from a salt diuresis.
• Renal ultrasound.
• Daily weight.

Urea diuresis is usually self-limiting; a salt diuresis can convert to a pathologic POD.

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Infundibular Stricture

Causes

• Congenital
• Acquired — post-PCNL (~2%)
• Inflammation
• Crossing vessel — Fraley syndrome

Indications for management

• Preserve renal function — progressive deterioration
• Relieve symptoms — pain, infections, stones

Treatment options

• Nephrostomy or DJ stent
• Balloon dilatation
• Endoscopic incision → incise lateral
  • Avoid incising the anterior or posterior wall — blood vessels run there
  • Depth of cut 2–3 mm
  • Success 60–80%
• Partial nephrectomy → if other methods fail
• Nephrectomy → if non-functioning kidney

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Ureteropelvic Junction Obstruction (UPJO)

Causes

Presentation

• Hydronephrosis on perinatal imaging — the commonest modern presentation
• Flank mass in a neonate
• Found during work-up for azotemia
• Intermittent abdominal or flank pain — Dietl's crisis
• Hematuria
• Recurrent UTI / pyelonephritis
• Hypertension

Investigation

• Goal: determine the anatomy and the functional significance of the obstruction
• Labs, urinalysis & culture
• Imaging:
  • Pediatric → US — ballooning of the renal pelvis
  • Adult → CT urography
• MAG3 — the preferred functional modality (function / drainage)
• RGP (retrograde pyelogram)
• Whitaker test — if RGP cannot be done, place a nephrostomy and perform it through that.
  • The renal pelvis is perfused continuously at 10 mL/min with saline or dilute contrast while the bladder is drained by an indwelling catheter (so intravesical pressure is not transmitted).

Laparoscopic and robotic pyeloplasty have reduced the need for preoperative assessment of crossing vessels — they can be dealt with at the time of pyeloplasty.

Indications for intervention — Pediatric

• Symptoms / infection
  • e.g. severe flank pain; in infants, feeding difficulty or failure to thrive
• Progressive hydronephrosis
• Split function < 40%
  • or decreasing function on serial scans
• Stones
• Consider nephrectomy in pediatrics if function < 10%
• No indication met → observe:
  • e.g. an infant with antenatal hydronephrosis, retained differential function (48%) and only mildly prolonged T1/2 (27 min; > 20 min is abnormal) → repeat US in 3 months (± repeat renal scan) —
    • Most resolve without surgery

Indications for intervention — Adult

• Symptoms & impaired renal function, or progressive impairment, or stones, or infection
• Nephrectomy if function < 20% and symptomatic
• If in doubt → place a DJ stent or nephrostomy, then repeat assessment.
  • In kidneys functioning at only 15–20%, temporize this way and repeat functional imaging later rather than proceeding straight to nephrectomy

All-comers checklist — BRUSSSHH:

• Bilateral disease
• Renal function impairment — overall < 40% with poor washout, or declining on serial studies
• UTIs
• Solitary kidney
• Symptoms
• Stones
• Hydronephrosis increasing on serial studies
• Hypertension (causal)

Treatment options — success rates

Cautions / contraindications to dismembered pyeloplasty

• (1) Small, inaccessible intrarenal pelvis
• (2) Lengthy or multiple proximal ureteric strictures (a diseased segment > 2 cm)

Flap procedures — when to choose which

Flap procedures as a group are not appropriate with a crossing vessel.

Indications for ureterocalicostomy

• UPJO with a small intrarenal pelvis
• Long proximal ureteric defect
  • Exam answer: the ideal candidate has a shorter upper ureteral stricture with thin lower-pole renal parenchyma (a long 4 cm proximal-to-mid stricture → ileal ureter instead)
• Associated rotational anomalies (e.g. horseshoe kidney) — provides completely dependent drainage
• Salvage after a failed dismembered pyeloplasty
  • e.g. failed pyeloplasty + small intrarenal pelvis with a 3 cm proximal stricture, or a later failed endopyelotomy as well

Technique: the lower-pole parenchyma is amputated and the spatulated ureter is joined to the exposed lower-pole calyx — bypasses the pelvis.

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Pyeloplasty

Goals of the repair:

• Widely patent, tension-free, watertight anastomosis
• Funnel-shaped transition between pelvis and ureter
• Ureter in a position of dependent drainage

Indications for pre-operative decompression of UPJO:

• Infection with UPJO
• Renal failure from bilateral UPJO, or UPJO in a solitary kidney
• Severe, unrelenting pain

Advantages of dismembered (Anderson-Hynes) pyeloplasty:

• Allows reduction of a redundant pelvis
  • Markedly redundant pelvis + high insertion → still dismembered — flaps are not appropriate when pelvic reduction is desired
    • The high insertion is corrected by re-anastomosing the spatulated ureter to the most dependent point of the pelvis
• Allows straightening of a tortuous proximal ureter
• Usable regardless of whether the ureter inserts high or low
• The only technique that completely excises an anatomically/functionally abnormal UPJ
• Allows transposition of the UPJ to relieve crossing-vessel compression
  • The only option for transposition relative to aberrant lower-pole vessels

Post-operative care:

• Pre-operative antibiotic coverage maintained
• Foley removed at 24–36 h
• Surgical drain removed before discharge if output is negligible.
  • If drainage increases after the Foley comes out, re-insert the Foley for 7 days — this eliminates reflux along the stent and reduces extravasation
  • External drainage is mandatory whichever repair is chosen (flap or dismembered) — avoids urinoma → suture-line disruption, scarring or sepsis
• Stent removed at 4–6 weeks; ultrasound at 6 weeks
• Renal scan at 6 months to 1 year
• Imaging again at 3 years
• After an open repair specifically:
  • Penrose drain out at 24–48 h (a suction drain prolongs a leak)
  • Antegrade nephrostogram at 7–10 days if a nephrostomy was left in situ
  • Percutaneous drain if a urinoma forms
  • Imaging 4 weeks after the stent or nephrostomy is removed.

Complications of laparoscopic pyeloplasty:

• Colon injury
• Renal vessel injury
• Hemorrhage
• Urinoma
• Pancreatic injury
• Ileus
• Pneumonia
• Thrombophlebitis
• Recurrent obstruction (~5%)

30% of failures occur beyond 2 years — hence follow-up to 3 years post-op.

Options after a failed pyeloplasty:

• Endopyelotomy
• Salvage open pyeloplasty
• A flap or dismembered technique not used at the first attempt
• Ureterocalicostomy
• Ileal ureter transposition
• Autotransplantation + Boari flap pyelovesicostomy
• Nephrectomy

Endopyelotomy — contraindications by approach

Hot-wire balloon endopyelotomy:

• Long segment of obstruction > 2 cm
• Presence of stones
• Crossing vessel
• Relative: significant hydronephrosis → an antegrade approach is better

Percutaneous endopyelotomy:

• Long segment of obstruction > 2 cm
• Active infection
• Untreated coagulopathy
• Crossing vessel — relative only

Percutaneous endopyelotomy is indicated mainly when UPJO coexists with stones. When both are present:

• Treat upper tract stones before the endopyelotomy, to avoid migration or extrusion of fragments.
• Make sure the UPJO is not simply edema from the stone disease — if in doubt, treat the stones first, leave a nephrostomy, and radiographically reassess the UPJ.
• Lower-pole stones with UPJO can be treated concurrently — the obstruction is not from edema in that case.

The advantage of the ureteroscopic approach is direct visualization of the UPJ and assurance of a properly situated, full-thickness incision, with no need for percutaneous access.

Endopyelotomy — technique & failure

• Full-thickness lateral incision from the lateral ureteral lumen out to the periureteric fat
  • Lateral because that is where crossing vessels are absent → avoids bleeding but leaves their compression untreated → failure is late (mostly within the first year)
• Most likely to fail if:
  • Stenosis > 2 cm
  • Crossing vessels
    • The best-known predictor of failure — success 42% with vs 86% without (prospective series)
    • With a crossing vessel → laparoscopic or robotic dismembered pyeloplasty is preferred
  • Ipsilateral kidney function loss (< 25% function)
  • Massive hydronephrosis
  • High-grade obstruction — success 60% vs 81% for low-grade
• Avoid strenuous activity for 8–10 days afterwards.
• Ideal stent size, stent duration and radiographic follow-up after endopyelotomy remain unclear.
• The fluoroscopically guided cautery wire balloon has a high complication rate; if used, keep the JJ stent 4–6 weeks post-operatively.

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Ureteric Stricture

Etiology

• Idiopathic
• Acquired:
  • Malignancy
  • Radiation
  • Endometriosis / retroperitoneal fibrosis
  • Renal ablation injury
  • Impacted ureteral stone
  • Ischemia or trauma from surgical dissection
    • Radical hysterectomy → ureter most often injured at the level of the uterine vessels; more common with large cancers, prior radiation or prior surgery
  • Endoscopic instrumentation
  • Infection — e.g. TB, schistosomiasis

Work-up

• Goal: determine whether the stricture impairs renal function, produces symptoms, or arises from malignancy
• History and physical — assess risk factors
• Imaging — assess location, nature and length: IVP · retrograde pyelogram · CT urography
• Renal scan — endourologic therapy needs ≥ 25% function to have a reasonable chance of success
• Bloodwork — routine, plus renal function
• Ureteroscopy ± biopsy ± barbotage — perform if the etiology of the stricture is uncertain

Management

• Stent or nephrostomy
• Balloon dilatation
• Endoureterotomy
• Surgical repair
• Nephrectomy → symptomatic, non-functioning

Endourologic management

Contraindicated if there is active infection, or the stricture is > 2 cm (stent length excluded).

• Stent — for acute decompression. A chronic stent is for a patient with poor prognosis who is not a repair candidate; it is not a good chronic option for extrinsic causes.
• Balloon dilatation
• Endoureterotomy — follow for up to 2 years with diuretic renography.
  • < 2 cm, no previous intervention → ureteroscopic laser endoureterotomy first — more durable than balloon dilatation, which gives short-term success only
  • Proximal stricture → lateral incision
  • Reconstruction remains more durable — ureteroureterostomy is reserved for recurrent strictures or those > 2 cm at presentation

Optimal therapy for a benign ureteral stricture — assess length and renal function:

Consider balloon dilatation if the kidney is a transplant on immunosuppression. Pediatric patients and selected patients with renal insufficiency may warrant repair rather than nephrectomy.

Balloon dilatation

• Diameter 12F–30F, time 30 s to 10 min
• Place a stent afterwards
• Failure rate increases if:
  • Ischemic etiology of the stricture
  • Length > 2 cm
  • Located in the mid ureter
  • Kidney function < 25%

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Open Surgical Repair

• Ureteroureterostomy → short upper or mid ureteric strictures
  • Highest success rate — > 90% → excising the scar with a spatulated anastomosis outperforms endoscopic incision or balloon dilatation
  • There is no role for ureteroureterostomy in the distal ureter.
• Ureteroneocystostomy → distal ureteric strictures (3–4 cm), ± psoas hitch ± Boari flap
• Transureteroureterostomy (TUU)
• Ileal ureter
• Renal descensus
• Autotransplantation

Ureter ligated in an irradiated field, suture removed, ureter intact → place a ureteral stent — delayed sloughing can cause obstruction or fistula, so observation carries more risk.

Psoas hitch

• For a defect in the distal one-third of the ureter — > 85% success
• Contraindications:
  • Small contracted bladder with limited mobility
  • Neurogenic bladder
  • Injury above the pelvic brim
  • Bladder outlet obstruction
• Evaluate the bladder pre-operatively — treat BOO and neurogenic bladder first, consider urodynamics
• Free the peritoneal attachments and divide the vas deferens / round ligament; for more mobility, divide the contralateral superior vesical artery
• Secure the ipsilateral bladder dome to the psoas minor tendon / psoas major muscle — watch for the genitofemoral and femoral nerves
  • Genitofemoral nerve → the nerve most likely injured; easily identified during exposure and readily mobilized away from the operative field
• Insert the ureter in a superolateral position on the bladder
• Advantages: technically simpler, lower risk of vascular compromise and of voiding difficulty

Boari flap

• For distal, mid and some proximal ureteric defects — bridges a 10–15 cm defect, and can sometimes reach the renal pelvis, especially on the right
• Contraindications:
  • Small contracted bladder with limited mobility
  • Neurogenic bladder
  • Bladder outlet obstruction
  • Prior pelvic radiation → Boari flap not indicated
• Evaluate the bladder pre-operatively — treat BOO and neurogenic bladder first, consider urodynamics
• Free the peritoneal attachments, divide the umbilical ligaments, ligate the contralateral superior vesical artery
• Raise a posterolateral bladder flap based on the ipsilateral superior vesical artery, continuing onto the anterior bladder wall
  • Superior vesical artery → first branch of the internal iliac anterior division after the umbilical artery
    • Then obturator → inferior vesical → middle rectal → internal pudendal → inferior gluteal
  • It arises from the patent segment of the umbilical artery; the obliterated umbilical artery lies lateral to the ureter at the pelvic brim
• Base ≥ 4 cm, tip ≥ 3 cm; length sufficient to cover the defect; length-to-base ratio must never exceed 3:1
  • Longer flaps need a wider base — both rules apply: for a 9 cm defect, 3:1 alone would allow a 3 cm base, but the 4 cm minimum governs
  • Measure with the bladder non-distended; add ~3 cm to the flap length if a tunneled non-refluxing anastomosis is planned

Transureteroureterostomy (TUU)

• For mid to lower ureteric defects where the length is insufficient to reach the bladder
• Absolute contraindications:
  • Donor ureter too short to reach the contralateral side
  • Diseased recipient ureter
  • Aortoiliac prosthetic graft — the donor ureter is tunneled across the retroperitoneum directly over the great vessels
• Relative contraindications:
  • Stone disease
  • Retroperitoneal fibrosis
  • Urothelial carcinoma
  • Chronic pyelonephritis
  • Abdomino-pelvic radiation
    • Exam answer: long gap after pelvic radiation → best bridged by TUU — reconstruction in an irradiated field must re-establish drainage in a non-irradiated area
  • Any disease that may affect both ureters — operating on the healthy contralateral ureter risks turning a unilateral injury into a bilateral one
• VUR must be corrected at the time of TUU — get a VCUG before proceeding
• Mobilize the colon medially on both sides, expose the recipient ureter ~5 cm proximal to the level of the divided ureter, and tunnel under the sigmoid mesentery, proximal to the IMA

Ileal ureteral substitution

• For ureteral defects too long for any other method, with a bladder unsuitable for reconstruction
  • Exam answer: irradiated child with a solitary kidney, 2.5 cm midureteral stricture, poorly compliant bladder → ileal ureter —
    • Psoas hitch or Boari flap unlikely to be feasible, and cutaneous ureterostomy tends to stenose
    • Pelvic radiation can cause poor bladder compliance — pressure rises below expected capacity (detrusor 20 cm H2O at 150 mL) → monitor bladder pressure long term
• The appendix and fallopian tube are unreliable substitutes
• Contraindications:
  • Renal insufficiency (creatinine > 2 mg/dL)
  • Bladder dysfunction
  • Bladder outlet obstruction
  • Inflammatory bowel disease
  • Radiation enteritis
    • After pelvic radiation → reserve ileal ureter for when TUU is not technically feasible — potential radiation injury to the bowel

Options for a long proximal ureteric stricture or defect

1. Culp-DeWeerd spiral flap pyeloplasty
2. Scardino-Prince vertical flap pyeloplasty
3. Davis intubated ureterotomy
4. Ureterocalicostomy
5. Boari flap + psoas hitch
6. Ileal interposition
   • Choice for a 4-cm proximal-to-mid stricture in a stone former with creatinine < 2.0 mg/dL — TUU is contraindicated in nephrolithiasis
7. Renal descensus + ureteroureterostomy
8. Renal autotransplantation
   • Choice for a 5-cm proximal defect when every other reconstruction is ruled out —
     • Ureteroureterostomy: 5 cm too long for an upper defect
     • Boari flap: small bladder < 300 mL
     • TUU: recurrent nephrolithiasis
     • Ileal ureter: creatinine > 2 mg/dL
9. Chronic stent changes
10. Nephrectomy

Principles of ureteric anastomosis

• Excise devitalized tissue — especially in gunshot wounds, where the tissue margins are burned
• Limit handling of ureteric tissue
• Preserve the adventitia to maximize ureteral blood supply
• Spatulate widely — if the ureter is dilated, transect obliquely to match the caliber of the lumen
• Watertight, tension-free anastomosis
• Stent the ureter
• Cover with retroperitoneal fat or omentum where possible
• Place a surgical drain

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Endoureterotomy & Endopyelotomy — Where to Cut

• Principle: cut away from the ureteral blood supply — the proximal ureter is supplied medially by branches of the main renal arteries.
  • Exam answer: UPJ endopyelotomy → posterolateral
    • Proximal ureter → lateral (like the UPJ)
    • Mid-ureter → anterior to anteromedial
    • Stricture overlying the iliac vessels → anteromedial, away from the vessels.
  • Posterior incision → offered for UPJ obstruction after failed open pyeloplasty.

Special situations

• Transplant kidney ureteral stricture: do NOT excise the stenosis — ischemia will develop. Initial management is endoscopic.
• Uretero-intestinal anastomosis (ileal conduit): stricture is more common on the left ureter due to extensive mobilization — kinking occurs as the left ureter courses under the IMA.
  • Endoscopic incision of a LEFT ureteroenteric stricture in an ileal conduit risks hemorrhage — the sigmoid mesentery can lie in close proximity.
    • Combined with the low endoscopic success rates on that side, these patients may be best treated with definitive repair from the outset.

Uretero-intestinal stricture — management algorithm

Long-term patency after a minimally invasive procedure for a ureteroenteric stricture is only about 50%, but these approaches are still used as the initial intervention, with operative management reserved for endourologic failure.

Consider balloon dilatation instead if the kidney is a transplant on immunosuppression.

• Within the < 2 cm group, a length > 1 cm (success 6% vs 50%) and a left-sided stricture (19% vs 41%) each predict endourologic failure —
  • Favor primary formal repair on the left.

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Retrocaval (Circumcaval) Ureter

• Embryology: persistence of the posterior cardinal as the IVC — ureter passes behind the IVC.
  • Almost always right-sided.
  • (preureteral vena cava > persistence of the subcardinal vein)
  • Retrocaval ureter = persistence of the posterior cardinal veins — not the anterior cardinal veins.
• Classic imaging: ureter loops medially behind the IVC — "reverse-J" / fish-hook appearance on IVU / CT urography.
• A retrocaval ureter is not always associated with ureteral obstruction. Diagnosis is usually confirmed by CT.
• Type 1 (more common) — the S-shaped "fish-hook" ureter
  • Associated with a greater degree of hydronephrosis, with the point of obstruction lateral to the lateral border of the IVC.
• Type 2 — the sickle-shaped ureter, with less obstruction.
• Treat only if there is functionally significant obstruction causing pain or renal function deterioration.
  • The standard repair is an open pyelopyelostomy:
    1. Place a JJ stent
    2. Identify and dissect the ureter, dilated renal pelvis and IVC
    3. Transect the dilated pelvis
    4. Transpose the ureter anterior to the IVC
    5. Then re-anastomose circumferentially with absorbable sutures, tension-free and watertight.
  • A surgical drain and internal ureteral stent are typically used.
  • Open, laparoscopic and robotic approaches are all described.

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Obstructed (Primary) Megaureter

• Definition: ureter > 7 mm distal diameter. Primary obstructive megaureter = aperistaltic juxtavesical segment (no reflux, no distal obstruction by stone/valve).
• More common in males, more often left-sided; up to ~25% bilateral.
• Work-up: US, VCUG (exclude reflux), MAG3 (function & drainage).
• Management:
  • Most resolve spontaneously → observe with serial US / renography.
  • Surgery if: declining function, breakthrough infections, worsening obstruction, or symptoms.
  • Repair = excision of aperistaltic segment + ureteral tapering / plication + reimplantation. In infants too small to reimplant, temporize with a stent or cutaneous ureterostomy.

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Retroperitoneal Fibrosis (RPF / Ormond Disease)

• Fibro-inflammatory plaque centered on the distal aorta at L4–L5, encasing the aorta, IVC, and ureters → medial deviation + ureteric obstruction (classically the mid-ureter).
• Symptoms and signs are nonspecific. Labs may show elevated ESR and CRP, moderate leukocytosis, anemia, and variable renal insufficiency with electrolyte abnormalities.
• Idiopathic (70%) — associated with chronic aortitis.
  • Idiopathic RPF sits on the chronic periaortitis spectrum — immune-mediated aortitis is the most common cause of RPF
    • Methysergide, infection, lymphoma and breast cancer are relatively rare causes overall.
• Identifiable cause (30%) — most commonly drugs: methysergide and other ergot alkaloids, also beta-blockers and phenacetin (the mechanism of drug-induced RPF is unknown)
  • Plus malignancy, radiation, infection, and IgG4-related disease.
  • Beta-blockers implicated → e.g. propranolol, metoprolol. Not linked: thiazides, metformin, amlodipine.
  • Lymphoma is the most common malignancy associated with RPF.
• Imaging: CT/MRI shows a confluent peri-aortic plaque; the aorta is NOT lifted off the spine (vs. lymphoma). Rule out malignancy by biopsy before starting medical therapy.
  • IVP: medial ureteral deviation + smooth, tapered mid-ureteral narrowing → suspect RPF.
    • With normal renal function, next step = CT urography — shows the mass and helps exclude malignancy.
  • Disease activity: PET is the most sensitive study (100% negative predictive value in one series — possibly obviating biopsy)
    • MRI assesses activity by T2 signal and gadolinium enhancement.
• Management:
  • Relieve obstruction first → DJ stent or nephrostomy. After decompression, monitor closely for post-obstructive diuresis.
  • Idiopathic → first-line is corticosteroids or tamoxifen (a nonsteroidal antiestrogen).
    • Mycophenolate mofetil, azathioprine or cyclophosphamide can be used as primary or salvage therapy but are given in combination with steroids — their stand-alone efficacy is unknown.
    • IgG4-related disease responds to steroids.
    • Stented but steroids not tolerated → tamoxifen is the next step. Medical therapy comes first — ureterolysis is reserved for failure of medical therapy.
  • Refractory / persistent obstruction → ureterolysis with intraperitoneal transposition or omental wrap. If ureterolysis fails → renal autotransplantation.
    • The process is generally bilateral, even when hydronephrosis looks unilateral → bilateral ureterolysis; the transposition or wrap protects the ureters and prevents re-entrapment.
    • Ureterolysis impossible because of extensive periureteral fibrosis → renal autotransplantation, provided differential renography after decompression shows satisfactory ipsilateral renal function.
  • Stop the offending drug in secondary cases; treat the underlying cause.
  • After aortic/iliac graft surgery: grafts should be placed posterior to the ureter.
    • Early ureteral obstruction from secondary RPF arising within six months of surgery can resolve with a four-week course of oral steroids.