Interventional Radiology in the Urinary Tract

Introduction

I. ANATOMICAL BASIS FOR RENAL ACCESS (Essential Foundation)

Renal Position

• Kidneys lie in the perinephric space at T12-L2/L3 level
• Upper pole is more medial and more posterior than the lower pole (coronal axis tilt ~15 degrees)
• Renal pelvis points anteromedially in the short axis

Pelvicalyceal Anatomy

• Adult kidney has ~8-9 calyces; upper and lower pole calyces are often fused (larger, easier to access)
• Posterior calyces are ideal for access - closer to the skin surface, allow straight-line navigation to adjacent calyces or renal pelvis
• Access to the pelviureteric junction (PUJ) and ureter is easier from an interpolar or upper pole calyx

Vascular Anatomy (Brodel's Line)

• Main renal artery divides into anterior (larger) and posterior (smaller) divisions, then segmental and lobar divisions
• Peripheral lobar and arcuate arteries skirt around the calyx in the columns of Bertin - termed the "vascular ring"
• Brodel's bloodless line (posterior avascular plane) runs along the lateral border of the kidney - the safest approach for renal puncture
• A posterior calyx is approached from slightly lateral to posteromedial, thus traversing the relatively avascular zone between anterior and posterior arterial divisions

Safest Puncture Site

• Lower pole, posterolateral puncture of the centre of the calyx is theoretically safest
• Upper pole is more posterior (easier navigation) but must be approached with care to avoid pleural transgression

II. GENERAL EQUIPMENT FOR RENAL ACCESS

III. PERCUTANEOUS NEPHROSTOMY (PCN)

Indications (Table 85.2 - Key ones)

• Relief of renal obstruction with or without associated infection
• Pyonephrosis / infected hydronephrosis (most urgent)
• Pre-operative or palliative decompression
• Access for subsequent antegrade stenting, PCNL, or nephrolithotripsy
• Treatment of urinary leaks and fistulas
• Urinary diversion in ureteric injury or leak

Timing

• Should ideally be performed within working hours on a stable, well-resuscitated patient
• Must NOT be delayed in suspected pyonephrosis or infected hydronephrosis - urgent decompression is required

Technique

1. US guidance is used to identify the collecting system
2. Fluoroscopy confirms wire and catheter placement
3. Two-part system (21-G initial needle, 0.018-inch platinum-tipped wire, 4-F dilator, then 0.035-inch working wire) OR one-part 18-G diamond point needle
4. Ideally puncture the centre of a calyx to stay within the vascular ring
5. Navigate wire from calyx into renal pelvis, then down the ureter
6. Dilate tract and insert pigtail drainage catheter (>6F); locking pigtail preferred for anchorage

Guidance Modalities

Special Situations

• Under general anaesthesia
• System can rapidly decompress on needle entry - catheter must be inserted swiftly
• Stiff 0.035-inch wire inserted directly; no pre-dilatation needed for dilated systems
• Neonatal 5-F catheters available; standard 6-F pigtail also works
• Minimize radiation: low-dose techniques, good collimation

• Urolithiasis is the commonest cause of ureteric obstruction
• US-guided procedure preferred; fluoroscopy only if necessary
• Lateral or supine/oblique approach; IV opiates to minimize fetal respiratory depression
• Lead shielding when fluoroscopy is used

Complications of PCN and Management (Table 85.3)

IV. PERCUTANEOUS NEPHROLITHOTOMY (PCNL)

• Gold standard for renal stones >2 cm or those not amenable to ESWL/ureteroscopy
• Requires stiff Amplatz-type guidewire and larger tract dilatation
• Upper or interpolar calyx access preferred for better instrument angulation
• Performed under GA; ultrasonic, pneumatic, or laser lithotripsy used intracorporeally
• Post-procedure nephrostomy left for drainage and tamponade

V. ANTEGRADE URETERIC STENTING

Indications

• Ureteric obstruction (benign or malignant stricture)
• Primary stenting or second procedure after several days of external PCN drainage

Ureteric Stents - Versus PCN

Types of Ureteric Stents

• Hollow tube with pigtail in renal pelvis and bladder
• Made of modern polymers (better biocompatibility than early polyethylene/polyurethane)
• High encrustation rate - require regular exchange
• Dysuria/urinary frequency in up to 50% of patients

• Wallstent (conventional) - becomes permanently incorporated via urothelial epithelialisation; NOT ideal for ureter
• Uventa / Allium stents - NiTiNol mesh with PTFE or polymer covering
• Memokath stent - uncovered NiTiNol wire spiral
• Modern metallic stents do not become incorporated; some are removable even after several years

Pathological Changes After Stenting

• All stents cause reactive urothelial hyperplasia, thickened mucosa, periureteral inflammation
• Reduced and ineffective peristalsis - early drainage is passive, dependent on renal-bladder pressure gradient
• Peristalsis rarely seen before 2 months post-stenting
• Plastic stents develop biofilm and become encrusted/blocked
• Technical success for antegrade stenting: 77-95%; 30% blocked at 3 months in one study

Technique of Antegrade Stenting

• Interpolar or upper pole access preferred
• Nephrostogram confirms level and completeness of stricture
• Curved tip hydrophilic wire + angled high-torque catheter used to cannulate stricture
• Stent deployed across stricture with proximal pigtail in renal pelvis and distal pigtail in bladder

Balloon Dilatation of Ureteric Strictures

• Used for benign ureteric strictures (post-surgical, post-inflammatory)
• High-pressure balloon catheters used
• Best results in short, recent, benign strictures
• Results are inferior for longer, chronic, or malignant strictures

VI. TREATMENT OF URINARY LEAKS AND FISTULAS

• PCN drainage alone often sufficient to allow healing of urinary leaks
• Bypassing the leak site with an internal stent diverts urine away from the fistula
• Combined approach (PCN + stent) used for persistent leaks
• Role of interventional radiology well-established in managing leakage after continent urinary diversion

VII. SUPRAPUBIC BLADDER CATHETERISATION

Indications

• Urethral obstruction not amenable to urethral catheterisation
• Complex urethral trauma
• Neurogenic bladder management

Technique

• Bladder must be adequately distended before puncture
• Catheter should pass through the rectus sheath in the midline, not more than 2 cm above the pubic symphysis
• Seldinger technique: US-guided puncture, wire inserted, serial dilatation, peel-away sheath, catheter placed, balloon inflated; fluoroscopic confirmation
• Trocar technique: After urine aspiration, catheter advanced directly into bladder
• CT-guided insertion for complex pelvic anatomy (previous surgery/congenital abnormalities)
• Image-guided bowel perforation rate: 0.3% vs. 2.4-2.7% for cystoscopically-assisted insertion

VIII. MANAGING A NON-DEFLATABLE URINARY CATHETER BALLOON

• Overinflation (balloon rupture) - risk of bladder rupture + retained fragments: not recommended
• Liquid dissolution agents - risk of chemical cystitis
• Best method: Reopen balloon channel with a hydrophilic or 0.018-inch stiff guidewire
• Alternatively: sharp end of guidewire ruptures the balloon
• If fails: transabdominal US-guided puncture of balloon with a 22-G needle (balloon fixed by gentle urethral traction) OR transrectal US-guided puncture (under antibiotic prophylaxis)

IX. PERCUTANEOUS CYSTOLITHOTRIPSY (PCCL)

• Used for large bladder stones not amenable to endoscopic fragmentation
• Suprapubic access using similar Seldinger technique as SPC
• Lithotripsy performed via percutaneous access
• Particularly useful in patients with urethral stricture or small urethra

X. EMBOLISATION IN THE URINARY TRACT

Renal Artery Embolisation

• Indications: Renal AVM, post-traumatic haemorrhage, AML (angiomyolipoma) bleeding, pre-operative tumour devascularisation, post-PCN arterial haemorrhage
• Endovascular approach has largely replaced open surgery
• Embolic agents: coils, particles (PVA), liquid agents (NBCA, Onyx)

Prostatic Artery Embolisation (PAE)

• Approved by NICE (2018) for benign prostatic hypertrophy (BPH)
• Reduces prostate volume and improves urinary symptoms
• Steep learning curve; refinements in technique ongoing

Varicocele Embolisation

• Via percutaneous sclerotherapy or coil embolisation of the spermatic vein
• Approach: transvenous (left renal vein → left spermatic vein OR right femoral → ovarian vein for females)
• Technical success ~100%; clinical success ~85%
• Complications: venous spasm, perforation, non-target embolisation, thrombophlebitis
• Gonadal shield to minimize radiation to testes

Pelvic Congestion Syndrome (PCS)

• Ovarian vein embolisation (left-sided more common)
• Left renal venogram shows reflux into left ovarian vein
• Tortuous pelvic veins crossing midline
• Amplatzer vascular plug or coils used

XI. RENAL DENERVATION (RDN)

• Used for resistant hypertension (uncontrolled despite 3+ antihypertensive drugs)
• Renal sympathetic nerves run in the adventitia of the renal arteries
• Mechanism: Ablation reduces afferent (chemoreceptor/mechanoreceptor) and efferent sympathetic activity, lowering RAAS activation, reducing noradrenaline spillover
• Technique: Spyral catheter (multiple electrodes) via transfemoral approach into renal artery; radiofrequency energy pulses applied to destroy nerves
• Performed bilaterally, usually as a day case under local anaesthesia and sedation
• Evidence: HTN-3 trial was negative; more recent sham-controlled trials (SPYRAL HTN-ON MED, SYMPLICITY HTN-3) have shown modest but significant BP reduction
• Non-atheromatous disease responds well to PTA alone; stents perform better than PTA for atheromatous disease

XII. ABLATION OF RENAL CYSTS / LYMPHOCELES

• Percutaneous aspiration and injection of sclerosant (e.g., ethanol) for symptomatic simple renal cysts
• Lymphoceles post-renal transplant: percutaneous drainage +/- sclerotherapy
• US-guided approach; fluoroscopic confirmation

SUMMARY TABLE: Key Points for PG Exam

Medullary Sponge Kidney (MSK)

Definition

Epidemiology

• Frequency: approximately 1 in 5000 in the general population (many cases are asymptomatic and underestimated)
• Found in up to 20% of patients presenting with nephrolithiasis
• Incidence of MSK in calcium stone formers: ~13% (vs ~2% in otherwise normal patients)
• Associated with a 60% lifetime risk for renal stones
• Women have a greater incidence of MSK than men among calcium stone formers
• Symptoms typically begin between the 4th and 5th decade of life; adolescent presentations are reported

Genetics / Pathogenesis

• Usually regarded as sporadic, but familial clustering with autosomal dominant inheritance (reduced penetrance, variable expressivity) is well-documented
• GDNF (Glial cell-derived neurotrophic factor) gene variants cosegregate with MSK in familial cases
• Mutations in the RET proto-oncogene and GDNF suggest a developmental defect in ureteric bud-metanephric mesenchyme interaction
• Mutations in hydrogen proton pump genes ATP6V1B1 and ATP6V0A4 link MSK to distal RTA
• Associated conditions:
  • Congenital hemihypertrophy
  • Beckwith-Wiedemann syndrome
  • CAKUT syndrome, Wilms tumor
  • Ehlers-Danlos syndrome
  • Primary hyperparathyroidism
  • ADPKD (precalyceal canalicular ectasia commonly seen)

Pathology

• Bilateral in 70% of cases; may involve one or more papillae
• Dilated ducts communicate proximally with normal-sized collecting tubules and show relative constriction at their junction with the calyx
• Duct diameter: usually 1-3 mm, occasionally 5 mm, rarely up to 7.5 mm
• Cysts measure 1-8 mm - spherical or oval, may be isolated or communicate with the collecting system
• Cysts frequently contain spherical concretions composed of apatite (calcium phosphate)
• Affected pyramids and calyces are enlarged; nephromegaly can result when many pyramids are involved
• Renal cortex, medullary rays, calyces, and renal pelvis appear grossly normal
• Histology: dilated ducts may show inflammatory cell infiltration or interstitial fibrosis in prominent cases

Clinical Features

Metabolic Abnormalities (Stone Risk Factors)

• Hypercalciuria - most commonly absorptive (59%); renal calcium leak in 18%
• Hypocitraturia - most common metabolic abnormality in some series (77%); marker of distal RTA
• Urinary stasis within ectatic tubules
• Hyperparathyroidism (primary) association
• The combination of stasis + hypercalciuria + hypocitraturia drives stone formation

Diagnosis / Imaging

Plain X-ray (KUB)

• Small, round calculi in the pyramidal regions just beyond the calyces
• Calculi arranged in clusters fanning away from the calyx - characteristic distribution

IVU / Excretory Urography (Gold standard - traditional)

• Definitive diagnosis made on excretory urography
• Dilated collecting ducts visualised on early and later radiographs without compression and without ureteral obstruction
• "Bouquet of flowers" or "paintbrush" appearance - dilated (streaked) tubules seen just lateral to calyces; many contain round masses of radiopaque material
• Calyces are large; stones are located in dilated collecting tubules
• Renal pelvis and calyces are normal in configuration

Fig: Medullary sponge kidneys. Left: Plain film showing multiple small stones in the middle portion of the right kidney. Right: Excretory urogram showing calculi located in dilated collecting tubules; calyces are characteristically large.

CT (Now the primary investigation)

• Non-contrast CT: Medullary nephrocalcinosis (bilateral medullary calcification) - arrows pointing to medullary calcific foci
• CT Urography (CTU): Using multidetector-row CT with high-resolution 3D reconstruction and late urographic phase:
  • Medullary cysts visible
  • Dilated collecting tubules showing "papillary brush pattern" bilaterally
  • Coronal MIP (maximum intensity projection) during excretory phase best demonstrates the ectatic tubules

Fig: CT urography for MSK diagnosis - (A) bilateral medullary calcinosis on non-contrast CT; (B) papillary brush pattern on coronal MIP excretory phase.

Ultrasound

• Medullary hyperechogenicity - suggestive but NOT diagnostic
• Cannot differentiate from other causes of medullary nephrocalcinosis

Differential Diagnosis

Treatment

Stone Prevention

• High fluid intake: target urine output >2.5 L/day
• Potassium citrate (first-line): 20 mEq/day in two divided doses, titrated to urinary citrate >450 mg/24 h; monitor urine pH (keep <7.5 to prevent calcium phosphate stone formation in ectatic tubules)
  • Achieves significant reduction in stone event rate: 0.58 to 0.10 stones/year/patient
  • Also improves bone densitometry (vertebral T-score: -2.82 to -1.98; hip T-score: -2.03 to -1.86)
• Thiazide diuretics: added for persistent hypercalciuria or ongoing stone passage despite citrate
• Stone composition directs specific metabolic treatment (restrict oxalate for calcium oxalate stones, etc.)

UTI Management

• Standard antibiotic treatment for episodes
• Surveillance urine cultures in recurrent cases

Stone Clearance

• ESWL / ureteroscopy / PCNL as per stone size and location

Prognosis

• Generally excellent - benign disorder that rarely progresses to ESKD
• Most patients remain asymptomatic throughout life
• A small minority suffer from recurrent urolithiasis, bacteriuria, and pyelonephritis leading to reduced GFR
• Does not transform into malignancy
• Bone mineral density can improve with potassium citrate therapy

Summary Box for PG Exam