Renal stones

Question 1

General risk factors for renal stones

Answer 1

• Typically occurs in 30-60 year olds
• Twice as common in males
• Dehydration
• Previous kidney stones

Question 2

What are the three most common sites of obstruction?

Answer 2

• Pelviureteric junction (PUJ) of the renal pelvis and ureter
• As the ureter enters the pelvis and crosses over the iliac vessels
• At the vesicoureteric junction (VUJ) as the ureter enters the bladder

Question 3

Types of renal stones

Answer 3

• Calcium oxalate (75%)
• Struvite (15%)
• Calcium phosphate (5%)
• Uric acid (5%)
• Cysteine (1%)

Question 4

Calcium oxalate risk factors and comments

Answer 4

• Hypercalaemia eg hyperparathyroidism
• Envelope shaped on microscopy
• Radio-opaque (less than calcium phosphate stones)

Question 5

Stuvite risk factors and comments

Answer 5

• UTI with urease-producing organisms (proteus and klebsiella)
• Coffin lid shaped on microscopy and may cause stag horn calculi
• Mildly radio-opaque

Question 6

Calcium phosphate risk factors and comments

Answer 6

• Hypercalcaemia and type 1 and 3 renal tubular acidosis
• Very radio-opaque

Question 7

Uric acid stone risk factors and comments

Answer 7

• Purine metabolism: gout and malignancy
• Rhomboid shaped on microscopy
• Radiolucent (can’t see on X-ray)

Question 8

Cysteine risk factors and comments

Answer 8

• Cystinuria (hereditary condition, this is why these stones can occur in patients in their twenties); may cause multiple stones
• Hexagonal-shaped
• Semi-opaque

Question 9

Why does Crohn’s disease increase risk of calcium oxalate stones?

Answer 9

Fat malabsorption in Crohn’s. The fat binds to calcium