The kidneys and urinary tract are affected by a broad spectrum of conditions — from the common (kidney stones and urinary tract infections) to the complex (chronic kidney disease, hydronephrosis, and ureteral strictures). Effective management increasingly relies on minimally invasive endourological procedures including flexible ureteroscopy (fURS/RIRS), percutaneous nephrolithotomy (PCNL), and balloon dilation. This guide covers the anatomy, conditions, and procedures most relevant to urological practice — and links to the single-use instruments used at each step.
Anatomy of the Kidney & Urinary Tract
Adrenal Glands
Sit atop the kidneys. Produce hormones including cortisol and aldosterone, which influence kidney function and blood pressure.
Kidneys
Bean-shaped organs (~11 cm long) located in the retroperitoneum. Each contains ~1 million nephrons — the functional filtration units.
Renal Pelvis & Ureters
The renal pelvis collects urine from the calyces; the ureters (25–30 cm) transport it by peristalsis to the bladder.
Bladder & Urethra
The bladder stores up to ~500 mL of urine. The urethra carries it to the exterior; length varies (female ~4 cm, male ~20 cm).
Clinically Relevant Microanatomy
- • Nephron: Composed of the glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting duct. Proximal tubule responsible for ~67% of solute/water reabsorption; primary target of ischaemic AKI.
- • Juxtaglomerular apparatus (JGA): Macula densa senses tubular sodium and regulates renin secretion — central to blood pressure homeostasis and the RAAS axis.
- • Uretero-vesical junction (UVJ): Acts as a physiological valve preventing reflux; most common site for stone impaction. Ureteroscopy access through the UVJ may require balloon or active dilation.
- • Pelvi-ureteric junction (PUJ): Second most frequent stone impaction site; PUJ obstruction often requires endopyelotomy or pyeloplasty.
Kidney Function
The kidneys are remarkable multi-functional organs. Far more than simple filters, they regulate the entire fluid balance of the body and produce vital hormones.
Filtration
Remove urea, creatinine, drugs, and waste from blood — approximately 125 mL filtered per minute (GFR)
Fluid & Electrolyte Balance
Regulate sodium, potassium, calcium, phosphate, and water balance through precise tubular reabsorption
Hormonal
Produce erythropoietin (EPO), activate vitamin D, and release renin — critical for blood pressure and red cell production
GFR-Based CKD Staging (KDIGO 2024)
* Albuminuria category (A1–A3) must always be combined with GFR staging for prognosis. KDIGO 2024 emphasises heat map risk stratification.
Kidney Stones (Nephrolithiasis)
Kidney stones are hard mineral deposits that form inside the kidneys when urine becomes concentrated. They vary in size from a grain of sand to several centimetres. Small stones may pass on their own; larger ones may require medical intervention.
Types of Kidney Stones
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Calcium Oxalate
Most common (80%). Associated with low fluid intake & high oxalate diet
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Uric Acid
~10%. Linked to gout, high-protein diet, dehydration
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Struvite
~10%. Caused by urease-producing bacteria; can form large staghorn calculi
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Cystine
Rare (<1%). Genetic disorder causing excess cystine excretion
Symptoms of Kidney Stones
| Stone Size | Location | Preferred Treatment (EAU 2024) | Instrument |
|---|---|---|---|
| <4 mm | Ureter / Renal | Watchful waiting / MET (α-blockers or CCBs) | — |
| 4–10 mm | Distal ureter | SWL or semi-rigid URS | UAS (e.g. Manawa FANS), laser fibre |
| 10–20 mm | Renal pelvis / calyx | SWL or flexible URS (fURS / RIRS) | UAS with suction; single-use scope |
| >20 mm | Renal | PCNL (standard or mini) | Nephrostomy balloon dilator (e.g. Tahina); nephrostomy access sheath |
| Staghorn | Complete renal pelvis | PCNL ± staged SWL | Large bore nephrostomy sheath; suction drainage |
Metabolic Workup Indications
24-hour urine collection (calcium, oxalate, citrate, uric acid, sodium, creatinine, volume) indicated for: recurrent stone formers, bilateral or multiple stones, children, family history, solitary kidney, or first-time stone in patient with CKD. Serum workup: calcium, PTH, uric acid, bicarbonate.
Obstruction & Hydronephrosis
Hydronephrosis is a swelling of one or both kidneys caused by a build-up of urine. This usually occurs because a blockage prevents urine from draining properly. Causes include kidney stones, strictures, enlarged prostate, or tumours.
Left untreated, obstruction can lead to permanent kidney damage. Treatment depends on the cause and severity — ranging from ureteral stents to surgical correction.
| Grade | Ultrasound Finding | Clinical Significance |
|---|---|---|
| Grade I | Mild renal pelvis dilatation only | Often physiological; monitor |
| Grade II | Pelvis + major calyceal dilatation | Investigate for obstructive cause |
| Grade III | All calyces dilated; cortex preserved | Intervention likely required |
| Grade IV | Cortical thinning (<2 mm) | Urgent drainage; long-term function at risk |
⚠️ Obstructed Infected Kidney — Urological Emergency
Obstructed pyonephrosis (infection proximal to obstruction) carries mortality rates of 20–40% if drainage is delayed. Urgent decompression via percutaneous nephrostomy or retrograde ureteral stenting must precede definitive stone treatment. Antibiotic therapy alone is insufficient — drainage is mandatory. Elective ureteroscopy should not be attempted on infected, obstructed systems.
Chronic Kidney Disease (CKD)
CKD is a gradual loss of kidney function over months or years. It is often silent in early stages but can progress to kidney failure requiring dialysis or transplantation. The most common causes are diabetes and high blood pressure.
Common Causes
- • Diabetes mellitus (T1 & T2)
- • Hypertension
- • Glomerulonephritis
- • Polycystic kidney disease
- • Recurrent obstructive uropathy
- • Chronic NSAID use
Warning Signs
- • Fatigue & weakness
- • Swollen ankles/legs (oedema)
- • Shortness of breath
- • Nausea / poor appetite
- • Foamy or dark urine
- • Persistent itching (pruritis)
Management Goals
- • BP control (<130/80 mmHg)
- • Glycaemic optimisation
- • RAAS blockade (ACEi/ARB)
- • SGLT2 inhibitors (CKD + T2DM)
- • Low-protein diet (G4–G5)
- • Nephrology referral
CKD & Urological Intervention — Practical Considerations
- • Contrast-induced nephropathy risk: use iso-osmolar contrast; pre-hydration; consider CO₂ urography in eGFR <30 mL/min/1.73m².
- • Nephrotoxic antibiotics (aminoglycosides, vancomycin) require dose adjustment; use with caution in eGFR <60.
- • Stone disease accelerates CKD progression — complete clearance and metabolic prevention are priority.
- • PCNL in solitary kidneys: suction drainage sheaths are preferred to minimise pyelovenous backflow and post-operative sepsis risk.
- • JJ stent dwell time: avoid >3 months; encrustation risk dramatically elevated in hyperoxaluria, hypercalciuria, and infection.
Ureteral Strictures
A ureteral stricture is a narrowing of the ureter that can impede normal urine flow from the kidney to the bladder. It may cause pain, recurrent infections, or kidney damage if untreated.
Common Causes
- • Prior urological procedures (ureteroscopy, stone treatment)
- • Radiation therapy to the pelvis or abdomen
- • Retroperitoneal fibrosis
- • Ischaemia (post-transplant, vascular)
- • Tumour compression or invasion
- • Congenital (PUJ obstruction)
Treatment Options
- • Balloon dilation: First-line for short, non-ischaemic strictures — using high-pressure ureteral balloon dilators
- • Endoureterotomy: Laser or cold-knife incision
- • JJ stenting: Temporary or long-term urinary diversion
- • Open / laparoscopic repair: Ureteroureterostomy, Boari flap, psoas hitch, ileal interposition for complex/long strictures
- • Ureteral reimplantation: For distal strictures
Balloon Dilation — Clinical Context
High-pressure balloon dilation (up to 20 ATM) with non-compliant balloon catheters (e.g. Tahina Ureteral) allows radially uniform force delivery across a stricture. Success rates of 50–80% in short (<1 cm), non-ischaemic, non-radiation-induced strictures. Ischaemic and radiation-induced strictures have higher recurrence rates (>50%); endoscopic balloon dilation serves as temporisation or repeated palliation in these cases. Kink-resistant shaft and hydrophilic distal coating are essential properties for negotiating tortuous ureters and tight strictures.
Urological Procedures: Ureteroscopy, PCNL & Minimally Invasive Treatments
When medication and watchful waiting are not enough, various minimally invasive procedures can treat kidney and urinary tract conditions safely and effectively. Here's a plain-language overview of the most common ones.
Ureteroscopy (URS / fURS)
A thin flexible or semi-rigid scope is passed through the urethra and bladder into the ureter or kidney. Stones can be fragmented with a laser and removed, or biopsies taken.
Flexible URS (RIRS) preferred for renal calculi >10 mm. Ureteral Access Sheaths (UAS) maintain access, reduce intrarenal pressure, and improve stone clearance. Active suction UAS (Manawa FANS) further reduces pyelovenous backflow and post-procedural sepsis. Single-use flexible ureteroscopes eliminate cross-contamination risk and maintain consistent optical performance.
Percutaneous Nephrolithotomy (PCNL)
A small incision is made in the back to create a direct tract into the kidney. A nephroscope removes large or complex stones. Standard PCNL (24–30 Fr), Mini-PCNL (14–20 Fr), Micro-PCNL (<14 Fr).
Tract dilation is accomplished using nephrostomy balloon dilators (e.g. Tahina Nephrostomy, 24Ch/30Ch, 17 ATM rated burst) or sequential fascial dilators. Balloon dilation is faster and associated with less blood loss vs. sequential. Suction nephrostomy access sheaths (Manawa Nephrostomy) reduce calyceal fluid distension, stone fragment migration, and systemic absorption of irrigation fluid — particularly valuable in renal insufficiency or complex staghorn stones.
Shock Wave Lithotripsy (SWL)
Non-invasive procedure using focused sound waves to break kidney stones into small fragments. Best for stones <10–15 mm in the renal pelvis or upper ureter.
Ureteral Stenting & Nephrostomy Drainage
A JJ (double-J) stent is placed inside the ureter to maintain drainage. A nephrostomy tube provides external kidney drainage when a retrograde approach is not possible (e.g. in obstruction with infection).
Nephrostomy access is guided by fluoroscopy or ultrasound; tract established by serial dilation or balloon dilation over a guidewire. Balloon dilators with radiopaque markers (e.g. Tahina Nephrostomy) enable real-time fluoroscopic confirmation of position. Post-PCNL nephrostomy tubes maintain tract patency for potential second-look procedures.
Frequently Asked Questions: Kidney & Urinary Tract
What causes kidney stones and how are they treated?
Kidney stones (nephrolithiasis) form when urine is concentrated with calcium, oxalate, uric acid, or other minerals. The most common type is calcium oxalate (~80%). Small stones under 4 mm often pass naturally. Stones 4–20 mm are treated with shock wave lithotripsy (SWL) or flexible ureteroscopy (RIRS) using a ureteral access sheath. Stones over 20 mm typically require percutaneous nephrolithotomy (PCNL).
What is flexible ureteroscopy (RIRS) and when is it recommended?
Flexible ureteroscopy (fURS), also called Retrograde Intra-Renal Surgery (RIRS), passes a thin flexible camera through the urethra and bladder into the kidney. It is recommended for renal stones over 10 mm. A ureteral access sheath (UAS) is placed inside the ureter to maintain instrument access, reduce intrarenal pressure, and improve stone clearance.
What is PCNL (percutaneous nephrolithotomy)?
Percutaneous nephrolithotomy (PCNL) is a minimally invasive procedure for large kidney stones over 20 mm or staghorn calculi. A small incision in the back creates a tract directly into the kidney, dilated using a nephrostomy balloon dilator. A nephroscope then fragments and removes the stones under direct vision. Suction access sheaths help reduce intrarenal pressure and post-operative infection risk.
What is hydronephrosis and how is it treated?
Hydronephrosis is swelling of one or both kidneys caused by blocked urine flow. Common causes include kidney stones, ureteral strictures, or tumours. Mild cases (Grade I–II) may be monitored. Severe cases (Grade III–IV) require urgent drainage via ureteral stenting or percutaneous nephrostomy to prevent permanent kidney damage.
What is a ureteral access sheath?
A ureteral access sheath (UAS) is a thin dual-lumen tube inserted into the ureter to provide continuous access during flexible ureteroscopy. It reduces intrarenal pressure, improves irrigation outflow, and enables repeated instrument passes. Suction-enabled access sheaths (such as the Manawa FANS) actively evacuate stone fragments and irrigation fluid, reducing post-procedural infection risk and improving operative field clarity.