Renal stones

Question 1

Lifetime prevalence of nephrolithiasis

Answer 1

5-12%

• Most common in 30-50 y/o
• Prevalence and incidence directly correlates to weight and BMI

Question 2

Aetiology of renal stones

Answer 2

Renal stones = crystalline mineral deposits that form microscopic crystals in the nephrons

• Usually due to high levels of urinary solutes such as calcium ,uric acid, oxalate and sodium
• Causes urine supersaturation with stone forming salts and stones form

Question 3

Pathophysiology of nephrolithiasis

Answer 3

• Too many solutes = supersaturation, solutes precipitate out of solution and form crystals upon which more solutes aggregate and form a stone

Question 4

Most common form of nephrolithiasis

Answer 4

Calcium oxalate stones

Black/ dark brown stone which is radiopaque on x-ray

Calcium phosphate stones can also form which are white and radiopaque on x-ray

Risk factors: hypercalcaemia, hyperparathyroidism, diet rich in oxalate e.g. rhubabrd, spinach, chocolate, nuts, beer

Question 5

Discuss uric acid stones

Answer 5

Yellow/ red-brown in colour, radiolucent

Caused by high levels of uric acid due to consumption of food high in purines e.g. shellfish, red meat, anchovies, organ meat

Question 6

What are struvite stones?

Answer 6

Infection stones

Magnesium + ammonium + phosphate

Form when bacteria split urea into co2 and ammonia

Ammonia makes urine more alkaline which promotes precipitation of magnesium, ammonium and phosphate into jagged crystals

Radiopaque and dirty white

Risk factors: UTIs, vesicoureteral reflux, obstructive uropathies

Question 7

Cystine stones

Answer 7

Small minority

Amino acid cystine leaks into urine and crystalises to form yello/ light pink stones which are radiopaque

Question 8

Xanthine stones

Answer 8

Rare

Xanthine = product of purine breakdown

Red/brown

Radiolucent

Question 9

Clinical presentation - nephrolithiasis

Answer 9

• Obstructed renal and ureteric stones can cause renal colic, severe acute flank pain that may radiate to ipsilateral groin
• Nausea and vomiting
• Urinary frequency and urgency
• Obesity
• Examination: costovertebral angle and ipsilateral flank tenderness, signs of sepsis if infection associated with stone

Question 10

Investigation for nephrolithiasis

Answer 10

FBC

U&E

Calcium

Uric acid

Urinalysis: majoirty will have microscopic haematuria

**Prior to imaging using ionising radiation, pregnancy test

Question 11

Preferred imaging modality for renal stones

Answer 11

Non-contrast helical computed tomography (NCCT)

Question 12

Which type of renal stones may form in patients with HIV?

Answer 12

Indinavir and ritonavir (proteases) - due to antiviral medication

Radiolucent

*the above drugs are the most common causes of drug-induced renal stones

Question 13

Management of renal stones

Answer 13

NSAIDs either oral or IV

Paracetamol if NSAIDs contraindicated

Antispasmodics if NSAIDs not effective