Renal tract calculi

Question 1

Types of renal stones

Answer 1

• Calcium oxalate (35%)
• Calcium phosphate (10%)
• Mixed oxalate and phosphate (35%)
• Struvite - magnesium ammonium phosphate (PAM)
• Urate - radiolucent
• Cystine - familial disorders affecting cystine metabolism

PAM the staghorn deer, Struvite = Staghorn

Question 2

Pathophys of renal calculi

Answer 2

• Oversaturation of urine
• Calcium and oxalate precipitate at lower saturation levels so most common
• Others have specific underlying pathology

Question 3

Struvite stones - how do they form?

Answer 3

• Infection stones - form in alkaline urine in the presence of urease producing organisms
• Eg Proteus mirabilis and Klebsiella pneumoniae
• Urease catalyse urea to CO2 and ammonia which leads to magnesium ammonium phosphate crystals

Question 4

Urate stones - how do they form?

Answer 4

• High levels of purines in the blood
• Either from diet eg red meat or haematological disorders eg myeloproliferative disease
• = increased urate formation and crystallisation in urine

Question 5

Cystine stones - how do they form?

Answer 5

• Homocystinuria
• Inherited defect that affects the transport of cystine in the bowel and kidneys
• Citrate is a stone inhibitor - hypocitraturia can then predispose to stone

Question 6

3 main narrowed points where stones are likely to impact

Answer 6

• Pelviureteric junction (PUJ) - renal pelvis becomes ureter
• Crossing pelvic brim - where iliac vessels travel under ureter in pelvis
• Vesicoureteric junction (VUJ) - where ureter enters bladder

Question 7

Symptoms of renal calculi

Answer 7

• Pain - renal colic, from increased peristalsis around obstruction.
• Sudden onset pain, radiates from flank to pelvis (loin to groin)
• Nausea + vomitting
• Distal stones can cause urinary frequency
• Haematuria

Sometimes get no pain - if stone is non-obstructing

Question 8

Symptoms if renal calculi become infected

Answer 8

• Rigors
• Fevers
• Lethargy
• Features of sepsis

Question 9

Examination findings for renal calculi

Answer 9

• Unremarkable
• May be some tenderness in affected flank
• Signs of dehydration - reduced fluid secondary to vomitting

Question 10

Differentials for flank pain

Answer 10

Pyelonephritis
Ruptured AAA
Biliary pathology
Bowel obstruction
Lower lobe pneumonia
MSK pain

Question 11

Bedside and bloods for ?renal calculi

Answer 11

• Urine dip - haematuria, infection? –> send MC&S if signs
• FBC, CRP, U&E
• Urate and calcium levels
• If pass stone - retrieval and analysis

Question 12

Imaging for renal calculi

Answer 12

• Non contrast CT KUB - kidney, ureter, bladder
• High sensitivity and specificity
• USS to assess for hydronephrosis (if known stone), can detect renal but not ureteric stones
• AXR - rarely used, not all stones radiopaque but if known stone that is visible, may be used for stone surveillance

Question 13

Initial management renal calculi

Answer 13

• IV fluids
• Majority of cases - stones will pass spontaenously esp if distal ureter or less than 5mm
• Analgesia - NSAIDS PR
• IV abx if significant infection/sepsis and urgent urology referral

Question 14

When is tamsulosin used?

Answer 14

• Not routinely used
• Limited evidence that their use may be beneficial in distal ureteric stones >8mm

Question 15

Criteria for inpatient admission for renal stone

Answer 15

• Post obstructive AKI
• Uncontrollable pain from simple analgesics
• Evidence of infected stones
• Large stones - >5mm

Question 16

What is the management if evidence of infection or AKI?

Answer 16

• Urgent decompression
• Stent insertion or nephrostomy

Question 17

What is retrograde stent insertion?

Answer 17

• Placement of stent within ureter
• Approaching from distal to proximal via cystoscopy
• Allows ureter to be kept patent and temporarily relieve obstruction

Question 18

What is nephrostomy?

Answer 18

• Tube placed directly into renal pelvis and collecting system
• Relieves obstruction proximally
• If needed, anterograde stent can be passed via same tract made

Question 19

Management options if stone does not pass spontaneously

Answer 19

• Extracorporeal shock wave lithotripsy (ESWL)
• Percutaneous nephrolithotomy (PCNL)
• Flexible uretero-renoscopy (URS)

Question 20

What is extracorporeal shock wave lithotripsy?

Answer 20

• Targeted sonic waves to break up stone - then will be passed
• Reserved for smaller stones - less than 2cm
• Done via radiological guidance - x-ray or USS
• Contraindications - pregnancy, anticoagulants or coagulopathy

Question 21

What is percutaenous nephrolithotomy?

Answer 21

• Used for renal stones only
• Preferred for large renal stones - inc staghorn
• Percutaenous access to kidney with nephroscope passed into renal pelvis
• Stones can then be fragmented using lithotripsy

Question 22

What is flexible uretero-renoscopy?

Answer 22

• Passing scope retrograde up into ureter
• Allowing stones to be fragmented through laser lithotripsy and then fragments removed

Question 23

Complications of renal stones

Answer 23

• Infection
• Post renal AKI
• Recurrent renal stones –> scarring and loss of kidney function

Question 24

Management of recurrent stone formers - ALL

Answer 24

• Specialised management
• Manage underlying cause
• Hydration
• Retrieve stones - if unable to, check calcium and urate levels

Question 25

Recurrent oxalate stone formers management

Answer 25

• Avoid high purine foods and high oxalate foods
• eg nuts, rhubarb, sesame

Question 26

Recurrent calcium stone formers management

Answer 26

• PTH levels checked
• Exclude primary hyperparathyroidism
• Avoid excess salt in diet

Question 27

Recurrent urate stone formers management

Answer 27

• Avoid foods high in purine eg redmeat and shellfish
• May need urate lowering medication eg allopurinol

Question 28

Management of recurrent cystine stone formers

Answer 28

Genetic testing for underlying familial disease

Question 29

How do bladder stones form?

Answer 29

• Stasis of urine within bladder
• Commonly seen in cases of chronic urinary retention
• May also be secondary to infections eg schistosomiasis or passed as ureteric stones

Question 30

What to consider if identify bladder stones in male patient?

Answer 30

• Bladder outflow surgery should be considered (eg TURP?)

Question 31

Presentation and management of bladder stones

Answer 31

• Lower urinary tract symptoms
• Investigate for renal and ureteric stones - CT KUB
• Cystoscopy - allow stones to drain or fragment via lithotripsy

Question 32

Complication of bladder stone

Answer 32

Chronic irritation of bladder epithelium by stone can predispose to SCC bladder cancer