Explain the cause of urinary stone formation. [TU 63]
Physio-chemistry of stone formation?
- Urine must be supersaturated for stones to form.
- Supersaturation alone is not sufficient for crystallization to occur in urine, owing to the presence of urinary inhibitors.
- The nucleation theory suggests that urinary stones originate from crystals or foreign bodies immersed in supersaturated urine.
- The crystal inhibitor theory claims that calculi form due to the absence or low concentration of natural stone inhibitors including magnesium, citrate, pyrophosphate, and a variety of trace metals. [@PCM] Nephrocalcin, uropontin, and Tamm-Horsfall protein are also important inhibitors of crystal nucleation, growth, or aggregation. [@ NUT]
- Common calcium stones may originate from subepithelial plaques composed of calcium apatite that serve as an anchor on which calcium oxalate stones can grow.
- The noncrystalline component of stones is matrix, which is composed of a combination of mucoproteins, proteins, carbohydrates, and urinary inhibitors.
Theories of stone formation?
(1) Free particle model
- represents ‘free particle’ formation, either in the collection system of the kidney or along the nephron (asterisk). The second pathway
(2) Fixed particle model
- requires crystal nuclei to form in the lumen of a nephron at sites of cell injury, which results in crystal attachment and growth. In this illustration, crystal attachment occurred at the opening of a duct of Bellini, and a plug of crystalline material projects into a minor calyx. The third pathway
(3) Randall’s plaque hypothesis
- suggests that crystals in the urine can become attached to a site of exposed crystalline deposits of interstitial calcium phosphate following loss of the normal urothelial covering of the renal papilla
Classify stones based on etiology?
Non-infection stones - Calcium oxalate, Calcium phosphate, Uric acid
Infection stones - Magnesium ammonium phosphate (struvite), Carbonate apatite, Ammonium urate
Genetic causes - Cystine, Xanthine, 2,8-dihydroxyadenine
Drug stones - Indinavir
Mechanism of formation of uric acid stone?
- The most important determinant of uric acid stone formation is low urinary pH.
- Low urine pH seen in uric acid stone formers is likely due to impaired ammoniagenesis as a result of insulin resistance.
Pathogenesis of infection stone?
- Urealysis provides an alkaline urinary environmentand sufficient concentrations of carbonate and ammonia to inducethe formation of infection stones. Because urease is not present in sterile human urine, infection with urease-producing bacteria is a prerequisite for the formation of infection stones.
- The most common urease-producing pathogens are Proteus, Klebsiella, Pseudomonas, and Staphylococcus species, with Proteus mirabilis the most common organism associated with infection stones.
- Because infection stones occur most commonly in those prone to frequent urinary tract infections, struvite stones occur more often in women than men by a ratio of 2 : 1.
Abbreviated Evaluation of Single Stone Formers?
- Underlying predisposing conditions
- Medications (calcium, vitamin C, vitamin D, acetazolamide, steroids)
- Dietary excesses, inadequate fluid intake or excessive fluid loss
- Multichannel blood screen
- Basic metabolic panel (sodium, potassium, chloride, carbon dioxide, blood urea nitrogen, creatinine)
- Intact parathyroid hormone
- Uric acid
- pH > 7.5: infection lithiasis
- pH < 5.5: uric acid lithiasis
- Sediment for crystalluria
- Urine culture
Stone analysis -
- - Radiopaque stones: calcium oxalate, calcium phosphate, magnesium ammonium phosphate (struvite), cystine
- - Radiolucent stones: uric acid, xanthine, triamterene
- Intravenous pyelography: radiolucent stones, anatomic abnormalities
- NCCT detect uric acid and xanthine stones, but not indinavir stones
calcium, uric acid, oxalate, citrate, phosphate, sulfate, sodium
Indications for a Metabolic Stone Evaluation
- Infirm health (unable to tolerate repeat stone episodes)
- Personal history of gout
- Strong family history of stones
- History of urinary tract infection with calculi
- Recurrent stone formersPathologic skeletal fractures
- Solitary kidneyRenal insufficiency
- Anatomic abnormalities
- Stones composed of cystine, uric acid, struvite
- Intestinal disease (particularly chronic diarrhea)
Extensive metabolic evaluation?
For metabolic evaluation, in addition to abbreviated evaluation, the following investigations are to be done.
24 Hr Urinary calcium, uric acid, Oxalate, Citrate, Sodium. Urine volume, Qualitative cystine. Also adds calcium fast and load tests.
[@ SSP ko Calo OX urinates in SiSi]
Fluid Recommendations in renal stone?
- Patients should be strongly encouraged to consume enough fluids to produce 2 L of urine per day.
- Carbonated water may confer some protective benefit.
- Soda flavored with phosphoric acid may increase stone risk, whereas those with citric acid may decrease risk.
- Citrus juices (particularly lemon and orange juices) may be a useful adjunct to stone prevention.
Diagnostic evaluation of renal stones?
- Ultrasound (US) should be used as the primary diagnostic imaging tool.
- Following initial US assessment, use NCCT to confirm stone diagnosis in patients with acute flank pain, because it is superior to IVU.
- In pregnant women, use MRI as a second line imaging modality.
- In children, use KUB radiography as second line imaging modality (or low-dose NCCT).
Advantages NCCT KUB?
Determine stone density, inner structure of the stone and skin-to-stone distance and surrounding anatomy; all of which affect selection of treatment modality.
Radiation exposure in radiation modality (in millisievert (mSv))?
- KUB radiography - 0.5-1
- IVU - 1.3-3.5
- Regular-dose NCCT - 4.5-5
- Low-dose NCCT - 0.97-1.9
- Enhanced CT - 25-35
Pain management for renal colic?
Whenever possible, offer an NSAID as the first drug of choice.
Offer hydromorphine, pentazocine or tramadol as a second choice.
Use α-blockers to reduce recurrent colic in informed patients.
Stone density and management?
- Stones with density > 1,000 HU on NCCT are less likely to be disintegrated by SWL.
- Attempt to dissolve radiolucent stones.
Flow chart for management of urinary stones. [TU 2064/12]
Mention various techniques of management of nephrolithiasis. Enlist their advantages and disadvantages. [TU 2062, 69]
Different modalities available for management of renal stones. [TU 2062/5]
Outline the management of urinary stone. [TU 2059,63]
Describe advantage and disadvantage of each treatment modality. [TU 2070]
From surgical Perspective, renal stone can be classified as:
- Non-Staghorn Calculi
- - Non-Lower pole
- - Lower Pole
- Staghorn calculi
Selection of procedure for active removal of non-staghorn stones?
Stones ≤5 mm - pass spontaneously.
Stone <10 mm and whose symptoms are controlled - MET therapy (controversial)
Stone <10 mm with symptoms - ESWL, RIRS
Stones ≥10 mm - unlikely to pass spontaneously
Stones < 2 cm within the renal pelvis and upper or middle calices - RIRS (preferred), SWL, PNL
Stones > 2 cm - PNL
Lower pole stone - PNL (preferred) or RIRS, even for stones > 1 cm, as the efficacy of SWL is limited
Skin stone distance (SSD) - RIRS, PCNL
HU >1000 - RIRS, PCNL
Management of staghorn calculus?
- Multimodal Treatment needed
- PCNL- Staged
- Sandwich therapy
- Open- Anatrophic Nephrolithotomy
Open surgery for renal calculi?
Pyelolithotomy - for stones in the renal pelvis, Suitable for stones in extrarenal pelvis
Extended pyelolithotomy – for large stag-horn stones, In case of intrarenal pelvis
Nephrolithotomy - If there is a complex calculus branching into the most peripheral calyces, it may be necessary to make incisions into the renal parenchyma to clear the kidney. It may also be necessary when the adhesions from previous surgery complicate access to the renal pelvis
Partial nephrectomy - a stone in the lowermost calyx with infective damage to the adjacent parenchyma.
Total Nephrectomy – for non functioning kidney
Oral chemolysis of renal stones?
- Stones composed of uric acid, but not sodium or ammonium urate, can be dissolved by oral chemolysis.
- Oral chemolitholys is is based on alkalinisation of urine by application of alkaline citrate or sodium bicarbonate.
- The pH should be adjusted to 7.0-7.2.
- Chemolysis is more effective at a higher pH, which might lead to calcium phosphate stone formation.
- Inform the patient how to monitor urine pH by dipstick three times a day (at regular intervals).
- Morning urine must be included.
What is PCNL? Discuss its indications and complications. [TU 2070]
Indications of PCNL?
Removal of renal and proximal ureteral calculi
- - large (>2.0 cm) calculi;
- - Resistant to SWL
- - Select lower pole calyceal stones with a narrow, long infundibulum and an acute infundibulopelvic angle
- - evidence of obstruction
Types of PCNL?
Based on the size of Amplaz -
- Standard PCNL - 24-30 Fr
- Mini PCNL - 14-20 Fr
- Ultramini PCNL - 11-13 Fr
- Micro PCNL - 4.8 Fr
Contraindications of PCNL?
- Patients receiving anticoagulant therapy
- Other important contraindications include:
- • untreated UTI;
- • tumour in the presumptive access tract area;
- • potential malignant kidney tumour;
- • pregnancy
Types of lithotripsers?
- LASER - Ho:YAG devices
Anatomy of kidney for PCNL?
It is important to determine anterior-posterior orientation of the calyces because access (from the typical posterior or posterolateral approach) into a posterior calyx allows relatively straight entry into the rest of the kidney, whereas percutaneous puncture of an anterior calyx requires an acute angulation to enter the renal pelvis, which may not be possible with rigid instrumentation.
Arterial supply to the kidney?
- Anterior and posterior branches of the main renal artery.
- The anterior branch supplies both the anterior half of the kidney and the polar regions via four segmental branches.
- The posterior branch supplies the posterior aspect of the kidney (represented by the shaded region).
- An avascular plane, known as Brödel line, separates the anterior and posterior circulations.
- Additionally, the safest place to percutaneously access the collecting system is directly into the calyceal fornix because this will avoidthe interlobar (infundibular) arteries adjacent to the calyceal infundibula and the arcuate arteries that skirt the renal pyramid
Steps of PCNL?
- supine and prone positions are equally safe. Prone position offers more options for puncture and is therefore preferred for upper pole or multiple access.
- - If stone in PUJ - from Upper and middle calyx
- - If in middle calyx - Puncture middle calyx
- - In in lower calyx - puncture lower calyx
- - Percutaneous access should never be directly into an infundibulum or the renal pelvis, which greatly increases the risk of vascular injury.
- - Two methods of fluoroscopic guidance for antegrade percutaneous access - the “eye-of-the needle” technique and the “triangulation” technique
- Dilatation -
- - sequential Plastic dilators (AmPlatz system), telescoping metal dilators (Alken), or balloon dilation.
Access in horseshoe kidney?
Upper pole access is useful in horseshoe kidneys because this is the easiest calyx to enter, the puncture rarely needs to be supra-costal, and it provides excellent access to most of the kidney and the ureter owing to the alignment of long axis of the moiety.
Types of dilatation in PCNL?
- Metalic dilator
- - Advantages - it is the most effective dilator, able to dilate even when there is dense perirenal scarring from prior procedures, and that is it inexpensive on a per-case basis because it is reusable. SInce there is temponade effect, there is less bleeding.
- - Disadvantage - can do considerable damage.
- Semirigid plastic dilation system
- - Advantages - are that trauma to the collecting system is theoretically less likely than with the rigid metal dilators
- - Disadvantage - hemorrhage can occur each time a dilator is withdrawn.
- Balloon dilators- are expensive one-time use devices
- - less effective than rigid metal and semirigid plastic dilation systems in densely scarred tissue but are more effective when the kidney is hypermobile
The lumbar notch?
Anatomic landmark for blind percutaneous access to the renal collecting system.
- Boundaries -
- - Superiorly by the latissimus dorsi muscle and the 12th rib,
- - Medially by the sacrospinalis and quadratus lumborum muscles
- - Laterally by the transversus abdominis and external oblique muscles
- - Inferiorly by the internal oblique muscle.
Indication of nephrostomy tube after PCNL?
- • presence of residual stones;
- • likelihood of a second-look procedure;
- • significant intraoperative blood loss;
- • urine extravasation;
- • ureteral obstruction;
- • potential persistent bacteriuria due to infected stones;
- • solitary kidney;
- • bleeding diathesis;
- • planned percutaneous chemolitholysis
Nephrostomy tubes, if used, are clamped for 4-24 hours for tamponade effect, then released.
Tubeless and totally tubeless PCNL?
- Tubeless PNL - without a nephrostomy tube.
- Totally tubeless PNL - neither a nephrostomy tube nor a ureteral stent is introduced.
- In uncomplicated cases, totally tubeless procedure results in a shorter hospital stay, with no disadvantages.
Short note on Retrograde intrarenal surgery (RIRS). [TU 2068/2]
What is RIRS?
- Also called as flexible ureterorenoscopy (FURS).
- The ureteroscope can be bend upto 2700
- It is the procedure to remove stone from kidney by using fibreoptic endoscope.
- The Holmium:YAG laser is the lithotripter of choice for RIRS nowadays
- The laser energy is delivered via quartz fibres to the stone surface, where it is absorbed and turned into heat energy that pulverises the stone into dust by a "photothermal" effect. Thus, stone fragment retrieval with basket / grasping forceps would not be necessary.
- Laser lithotripsy can be carried out safely in patients on anticoagulants
Indications of RIRS?
- 1. Failed Extracorporeal shockwave lithotripsy
- 2. Radiolucent stones
- 3. Concomitant ureteric and renal stones
- 4. Anatomical problems e.g. infundibular stenosis
- 5. Nephrocalcinosis
- 6. Bleeding disorders
- 7. Need for complete stone removal e.g. pilot
Advantages of RIRS?
- No skin incision is required
- Stone clearence rate is very high
- Low risk procedure
- Low operative time
- No damage to renal tissue
- Fast recovery
- Minimal hospitalization
Disadvantages of RIRS?
- Need to do stages procedure if ureter could not be dilated
- Higher cost
- Multiple sessions to do stone clearence
- Risk of ureteric damage
Complications of RIRS is mainly due to ureteroscopy that include sepsis, steinstrasse, stricture, ureteric injury and urinary tract infection
Factors that make SWL less likely?
- Shockwave-resistant stones (calcium oxalate monohydrate, brushite, or cystine).
- Steep infundibular-pelvic angle.
- Long lower pole calyx (> 10 mm).
- Narrow infundibulum (< 5 mm).
Advantages of ESWL?
- • No anaesthesia is required
- • Can be done as an OPD procedure
- • Less than 2.0 cm sized stones are well fragmented
- • ESWL can be done repeatedly in different sittings
- • If it is not successful one can switch over to PCNL
Contraindications of ESWL?
- • Stone attenuation >1000 HU
- • Skin to stone distance >10cm
- • pregnancy, due to the potential effects on the foetus
- • Renal anatomic anomalies - Horseshoe kidney, calyceal diverticulum
- • bleeding diatheses, which should be compensated for at least 24 h before and 48 h after treatment
- • uncontrolled UTIs;
- • severe skeletal malformations and severe obesity, which prevent targeting of the stone;
- • arterial aneurysm in the vicinity of the stone;
- • anatomical obstruction distal to the stone.
Use a shock wave frequency of 1.0-1.5 Hz.
Complications of ESWL?
- Related to stone fragments
- Regrowth of residual fragments
- Renal Colic
- Tissue effect
- Renal - Hematoma
- Cardiovascular - Dysrrhythmia, Morbid cardiac events
- Gastrointestinal - Bowel perforation, Liver and spleen hematoma
Medical expulsion therapy?
There is evidence in a large number of small single centre trials that MET accelerates spontaneous passage of ureteral stones and fragments generated with SWL, and limits pain
Management of residual renal stones?
Identify biochemical risk factors and appropriate stone prevention in patients with residual fragments or stones. Follow-up patients with residual fragments or stones regularly to monitor disease course.
- < 4-5 mm
- - For symptomatic residuals- Stone removal
- - For asymptomatic cases - Reasonable follow-up (dependent on risk factors)
> 5 mm - Removal of stone
Agents for urine acidification?
- Ammonium Chloride - 1 g bid or tid
- Methionine - 200-500 mg 1-3 times/d
Opacities on a plain abdominal radiograph that may be confused with renal calculus?
- Calcified mesenteric lymph node
- Gallstones or concretion in the appendix
- Tablets or foreign bodies in the alimentary canal (e.g.cyclopenthiazide (Navidrex-K))
- Phleboliths – calcification in the walls of veins, especially inthe pelvis
- Ossified tip of the 12th rib
- Calcified tuberculous lesion in the kidney
- Calcified adrenal gland
Short notes on Bladder stones?
PRIMARY - Develops in sterile urine, not in presence of anatomical or functional abnormality.
SECONDARY - Occurs in presence of infection ,outflow obstruction, impaired bladder emptying or a foreign body.
Clinical features -
- 1. Frequency : sensation of incomplete bladder emptying.
- 2. Pain (strangury) occurs at the end of micturition refered to tip of penis. Pain is worsened by movement
- 3. Haematuria drops of bright-red blood at the end of micturition.
- 4.Interruption of the urinary stream stone blocking the internal meatus.
- 5. UTI
- Treatment -
- - Cystolitholapaxy - removal of stone, for <1cm stone
- - Cystolithotriety - crush the stone and remove, for <2cm
- - Percutaneous cystolithotomy (PCCL)
Normal urethral narrowing?
Short note on Cystolithotomy. [TU 2072/6]
Cystolithotomy is the surgical removal of bladder stones via a lower abdominal incision.
- Bladder stones (Cystolithotomy)
- Removal of foreign bodies in the urinary bladder
- Treatment of bladder tamponade and severe bladder bleeding, which cannot be managed via transurethral surgery
- Coagulation disorders
- Untreated urinary tract infection
- Bladder cancer.
- Drains and Catheters:
- - Wound drainage 1–2 days
- - Foley catheter for 5 days, do cystography before catheter removal
Various laser used in Urosurgery
For soft-tissue incisions (eg, urethral strictures, posterior urethral valves, endopyelotomy, bladder neck contractures), use Ho:YAG, Nd:YAG, or KTP.
For resection and ablation (eg, benign prostatic hyperplasia [BPH], TCC, condylomata, penile carcinoma, bladder and skin hemangiomata), use Nd:YAG, Ho:YAG, KTP:YAG, semiconductor diode, or CO 2.
For lithotripsy (renal pelvis, ureter, and bladder stones), use Ho:YAG, FREDDY, pulsed dye, or alexandrite.
For tissue welding (eg, vasovasotomy; urethral reconstruction for hypospadias, strictures, diverticula, or fistulas; pyeloplasty, bladder augmentation, and continent urinary diversion), use diode, KTP, Nd:YAG, or CO 2.
For autofluorescence (eg, for diagnosis of bladder malignancies), use a nitrogen laser.
For laser hair removal (eg, perineal skin used for local urethral grafts), use ruby, alexandrite, diode, or Nd:YAG.
Short note on DJ stent.
Material - Polyurethane or Silicon
Diameter - Usually 6F
DJ stent removal in 3 months. In pregnancy, within 6 weeks. Silicon can be removed in 6-12 months.
2/3rd urine is drained from outside, and 1/3 is drained from inside the DJ stent.
Short note on Ureteric stent.
- Material - Polyurethane
- Length - 70cm
- Diameter - 6F, 4F