Renal Stones

Question 1

What is urolithiasis/renal calculus?

Answer 1

Formation of stones in the urinary tract.

Question 2

Where is the most common place for renal stones to form?

Answer 2

Most common place is within the renal pelvis but can form anywhere.

Question 3

Are renal stones often recurrent?

Answer 3

Often recurrent especially when untreated especially when there is a predisposing factor.

Question 4

What size are stones usually and how often are there more than one?

Answer 4

Can be single of multiple and 80% are unilateral. Can be minute like sand or staghorn calculi (gives a cast of pelvic and calyceal system) or large concretions in bladder.

Question 5

Who is more likely to get stones and do stones form in the ureters?

Answer 5

Men get more renal stones than women apart from struvite stones. When in the ureter almost always they have formed further up and been passed down.

Question 6

Can stones form in the ureter?

Answer 6

When in the ureter almost always they have formed further up and been passed down.

Question 7

What are the most common reasons for bladder stone formation and why don’t they happen very often anymore?

Answer 7

Often they are seen with a low protein diet, chronic diarrhoea, dehydration, increased oxalate consumption, vitamins A, B1, B6 deficiencies and magnesium deficiencies.

Question 8

What causes bladders stones to form?

Answer 8

• Bladder outflow obstruction – urethral stricture, neuropathic bladder and prostate obstruction.
• Presence of foreign body in the bladder – catheter, non-absorbable sutures
• Majority now days are passed down from upper urinary tract

Question 9

If the stones block outflow what can this lead to?

Answer 9

Can lead to anuria and painful bladder distension.

Question 10

What age is most common for stones?

Answer 10

30 years old

Question 11

What chemical make up do most stones have?

Answer 11

Calcium makes up 99% of stones – 65% are formed from calcium oxalate with calcium phosphate otherwise known as apatite. Calcium phosphate alone forms 15% of stones and is often seen with hyperparathyroidism and renal tubular acidosis. Uric acid crytals make up only 3-5% of renal stones.

Question 12

What are struvite stones?

Answer 12

Struvite’s are infection stones – urease stones, triple-phosphate stones (magnesium ammonium phosphate hexahydrate). These occur during or after infection by bacterial which have the urease enzyme.

Question 13

What type of stones don’t contain calcium?

Answer 13

Other types of stones that don’t contain calcium include Cysteine stones which occur in rare genetic disorders such as cystinuria (cysteines transporter not present for reabsorption), stones occurring from drugs such as Indinavir for HIV, triamterene – a diuretic – and sulphonamide antibiotic.

Question 14

Why do stones form?

Answer 14

Urine super saturation with minerals (more solute than can hold so crystallises out). Seed crystal forms by nucleation where first step formation results in a new structure that then self assembles. Physical not chemical reaction.

Question 15

What reasons cause urine to become super saturated?

Answer 15

• Decrease in water content – dehydration.
• Increase in mineral content – hypercalcaemia and hypercalciuria, hyperoxaluria, hyperuricaemia, hyperuricosuria and cysteinuria.
• Decrease in solubility of solute in urine such as change in pH of urine.

Question 16

How do changes in pH affect stone formation?

Answer 16

Acidic urine favours formation of calcium oxalate and uric acid stones, alkaline urine favours formation of calcium phosphate stones and they are dissolved by acid. Renal tubular acidosis results in persistently alkaline urine and decreased urinary citrate excretion.

Question 17

Which stones are most commonly caused due to supersaturation?

Answer 17

Supersaturation is the likely cause of uric acid and cysteine stones, calcium bases stone formation may be more complex.

Question 18

What is Randall’s Plaque and what are ducts of bellini?

Answer 18

Approximately 75% of calcium oxalate stones appear to grow like stalactites attached to exposed interstitial deposits of calcium phosphate, ‘Randall’s plaque’, on the tips of renal papillae. They are composed of a core of calcium phosphate surrounded by calcium oxalate.

Stones can form on plugs protruding from ducts of Bellini (excretory in the kidney) or free in solution.

Question 19

Why might stones form?

Answer 19

Urine stasis due to low urine flow, obstruction and infection. Drugs can precipitate out of solution by themselves and cause stone formation. Genetic/congenital factors – primary metabolic disturbances e.g. cysteinuria, kidney abnormalities e.g. polycystitc kidneys medullary sponge kidneys.

Question 20

What assoication do calcium oxalate stones have with metabolic disturbances?

Answer 20

5% are associated with hypercalcaemia and hypercalciuria such as in hyperparathyroidism, bone diseases and sarcoidosis.

55% have hypercalciuria without hypercalcaemia associated with hyperabsorption of calcium from gut or impairment in renal tubular absorption of calcium.

Finally 5% is associated with hyperoxaluria, this is hereditary or secondary to intestinal overabsorption in patients with enteric diseases.

Question 21

What may cause hypercalciuria?

Answer 21

Can be secondary to Hypercalcaemia, excessive dietary intake of calcium and excessive resorption of calcium from skeleton due to prolonged immobilisation and weightlessness.

Question 22

What causes are there for Hypercalcaemia relating to neoplasia?

Answer 22

1. Hypersecretion of PTH resulting in increased bone resorption. Primary hypercalcaemia is caused by parathyroid hyperplasia of functional tumour, can be secondary to renal failures which causes retention of phosphate and hence hypocalcaemia. Ectopic – secretion of PTH related proteins by malignant tumour e.g. squamous cells carcinoma of lung.
2. Destruction of bone tissue by primary tumours of bone marrow, skeleton metastases, Paget’s disease of bone and immobilisation (reduced bone formation whilst resorptions stays the same.

Question 23

What causes other than neoplasia are there for hyercalcaemia?

Answer 23

1. Excessive Vitamin D ingestion
2. Thiazide diuretics
3. Sarcoidosis – macrophages activate a vitamin D precursor
4. Milk alkali syndrome (excessive calcium intake).

Question 24

What clinical sings are there of hypercalcaemia?

Answer 24

Severe muscle weakness (opposite to hypocalcaemia where you get tetany), painful bones – fractures, renal stones, abdominal groans (constipation, peptic ulcers, pancreatitis and gallstones), psychic moans – (depression, lethargy and seizures).

Bones stones groans and moans.

Question 25

What causes hyperoxaluria?

Answer 25

Rare autosomal recessive genetic disorder of oxalate synthesis (primary hyperoxaluria types one and two).

Increased GI oxalate absorption secondary to GI disease such as Crohn’s disease and/or an intestinal resection leads to extra absorption of oxalate from colon.

Dietary habits such as high oxalate intake (spinach, rhubarb, tea and nuts) or low calcium intake as it increases GI absorption of oxalate.

Question 26

What are struvite stones composed of?

Answer 26

Struvite stones (mixed infective stones) composed of magnesium ammonium phosphate with variable amounts of calcium. Struvite stones are often large

Question 27

What causes struvite stones to form?

Answer 27

. Usually secondary to infection with organisms e.g Proteus mirabilis with the enzyme urease which hydrolyses urea to ammonium hydroxide. Also, production of mucoproteins from infection provides an organic matrix on which stones can form.

They can grow very quickly

Question 28

Who are susceptible to struvite stones?

Answer 28

Spinal cord injury, neurogenic bladder, vesicoureteric reflux and obstructive uropathy.

Question 29

What distinguishes uric acid stones form the others?

Answer 29

These are radiolucent so can’t be detected on x-rays.

Question 30

When are uric acid stones commonly seen?

Answer 30

Seen in hyperuricaemia, also in people who tend to have an acidic urine.

Question 31

What causes hyperuricaemia?

Answer 31

Uric acid is the end of purine metabolism. Hyperuricaemia is seen in idiopathic gout and secondarily to increased cell turnover such as in lympho- or myeloproliferative disorder, after chemotherapy. Dehydration leads to hyperuricaemia particularly in the presence of acidic urine and also in patients with ileostomies as they are dehydrated and they have loss of bicarbonate from GI secretions.

Question 32

What symptoms do people with renal stones present with?

Answer 32

Asymptomatic (most people) but can be seen on radiography, renal colic, stones in kidney – dull ache in loins, recurrent UTIs, haematuria, renal failure and urinary tract obstruction, if there is urinary tract obstruction and fluid intake is increased this results in an increase in pain.

Question 33

What is renal colic?

Answer 33

Renal colic – excruciating pain bouts lasting 20-60minutes. Caused by peristaltic contractions or spams of ureter as it attempts to expel the stone. Radiation from flank to iliac fossa and testes/labium or inner thigh. Distributes across 1st lumbar nerve root. Embryological link between urinary tract, GIT and gonads. Often accompanied by nausea, vomiting, pallor and restlessness, haematuria common and if untreated typically subsides in a few hours.

Question 34

What investigations can be done to diagnose renal stones?

Answer 34

Mid-stream urine looking for red blood cells, urinary casts and urinary crystals. Do a culture of the urine looking for infection as the cause or consequence of the stones. Serum – urea, creatinine, electrolytes and calcium levels to check renal function. Plain abdominal Xrays as most stones are radiopaque.

CT scan of the kidneys, ureter and bladder is the best form of investigation as all types of stones can be seen. Should be taken ideally during the pain and allows us to identify stones and any underlying primary renal diseases.

Finally, you can catch urine through a sieve and catch calculi for chemical analysis.

Question 35

What complications can occur with renal stones?

Answer 35

Acute pyelonephritis (kidney infection) +/- Gram negative septicaemia, Pressure necrosis of the renal parenchyma, urinary obstruction and hydronephrosis (distention and dilation of the renal pelvis and calyces due to water) and ulceration through the wall of the collecting system.

Question 36

How are stones treated?

Answer 36

• Analgesia, warmth to site of pain and bed rest.
• Ureteroscopy – usually for stones in bladder or lower ureter
• Percutaneous nephrolithotomy – small incision (usually for stones in the renal pelvis) ino the kidneys and cut out the stone.
• Extracorporeal shock wave lithotripsy – used for stones near the renal pelvis, delivery of external, focused, high intensite pulses of ultrasonic energy.

Question 37

How do we prevent stone formation?

Answer 37

Decrease urine supersaturation
•Drink more water – all stones
•Decrease secretion of calcium or oxalate such as thiazide diuretic
•Potassium citrate – alkalises the urine reducing stone formation for all types except it can induce calcium phosphate stones. Also forms soluble complexes with calcium ions.