Renal Calculus

Question 1

What are the common sites for kidney stones to form?

Answer 1

Stones can form anywhere in the urinary tract, but common sites include- vesicoureteric junction (60%), ureteropelvic junction in kidney and sacroiliac joint (where ureter crosses iliac vessels).

Question 2

What are kidney stones made of?

Answer 2

80% are calcium stones, which also contain oxalate (commonest), phosphate or both.

Other stone types include struvite (magnesium ammonium phosphate)- forming stag horn stones- and urate.

Question 3

What are the signs and symptoms of kidney stones?

Answer 3

RENAL COLIC-

• sudden onset of severe, intermittent pain, due to peristalsis against the obstruction.
• ureteric stone pain radiates from loin to groin.
• midureteric stones can mimic appendicitis or diverticulitis.
• patient writhing, trying to get comfortable, unlike peritonitis where they lie still.
• generally unwell- sweaty, nausea and vomiting.

Question 4

What are the risk factors for kidney stones?

Answer 4

• dehydration
• hypercalciuria (and hence hypercalcaemia)
• family history
• kidney disease- renal tubular acidosis, medullary sponge kidney, polycystic kidney disease.
• gout (urate stones)
• proteus infection (struvite stones)
• drugs- furosemide, steroids, acetazolamide, theophylline. thiazides reduce the risk via tubular reabsorption of calcium.

Question 5

How are kidney stones investigated?

Answer 5

Diagnosis-

• urine dip- 90% will have haematuria- confirm via microscopy.
• CT KUB (non-contrast) is the definitive test- will identify stones as well as other causes of renal colic- eg. transitional cell carcinoma, retroperitoneal lymph nodes- and other differentials such as appendicitis. shows 99% of stones vs. 60% on an XR KUB.
• XR KUB can be used to monitor passage of a stone.

OTHER TESTS-

• FBC and CRP (looking for infection markers)
• U&Es
• Check calcium, phosphate and urate if recurrent.

Question 6

How are kidney stones managed?

Answer 6

INITIAL MANAGEMENT

• analgesia- NSAIDs are first line, commonly diclofenac IM or PR.
• antiemetics and fluids may also be needed.
• if pain resolves and no obstruction, patients can be discharged with outpatient follow up if needed
• if pain continues or there is obstruction- ureteric stent via cystoscopy, done under general anaesthesia (temporary measure until definitive stone removal)
• if there is sepsis- IV antibiotics and urgent nephrostomy.

Most stones are <5mm and pass spontaneously-

• encourage good fluid intake
• offer regular analgesia eg. paracetamol or codeine
• try and urinate into container to catch stone
• usually takes 1-3 weeks to pass-review if not passed after 3 weeks.

Stones >1cm usually require removal-

• extracorporeal shock wave lithotripsy is the commonest method- uses electromagnetic energy to destroy the stone- targeted using XR and US- with the fragments then passed into urine.
• in rarer cases, ureteroscopy is used and the stone broken up with a laser, or percutaneous removal is used for large stones (>2cm) in the renal pelvis.

Stones 5-10mm are intermediate-

• 50% pass spontaneously, though this is rare if >7mm.
• passage of distal ureteric stones can be aided by alpha blockers, calcium channel blockers, or (for men) regular sexual intercourse (3-4 times/week).

Question 7

What are the complications of kidney stones?

Answer 7

• obstructive nephropathy
• infection
• renal failure in delayed presentation