Renal Calculi (Kidney Stones)

Definition

Renal calculi (kidney stones) are solid deposits of minerals and salts that form in the urinary tract. They can cause obstruction, pain, and infection depending on their size and location.

Aetiology

Kidney stones form due to an imbalance between stone-forming substances and inhibitors in the urine.

Types of Kidney Stones:

Calcium stones (80%): composed of calcium oxalate or calcium phosphate, often due to high urinary calcium.
Struvite stones: composed of magnesium ammonium phosphate, typically associated with urinary tract infections.
Uric acid stones: form in acidic urine, often in patients with gout or high purine intake.
Cystine stones: rare, occurring in individuals with cystinuria (a genetic disorder affecting amino acid transport).

Pathophysiology

Supersaturation of urine with stone-forming substances (e.g., calcium, oxalate, uric acid).
Reduced urinary citrate levels (a natural inhibitor of stone formation).
Urinary stasis or infection increases the risk of stone development.
Crystal aggregation leads to the formation of calculi, which can cause obstruction and pain.

Risk Factors

Dehydration (low urine output increases stone formation).
High dietary intake of oxalate (e.g., spinach, nuts, chocolate).
Hypercalciuria (high urinary calcium levels).
Metabolic disorders (e.g., hyperparathyroidism, gout).
Recurrent urinary tract infections (increases struvite stones).
Family history of kidney stones.
Obesity and sedentary lifestyle.
High salt and protein diet (increases urinary calcium excretion).

Signs and Symptoms

Renal colic: sudden, severe loin-to-groin pain, often intermittent.
Haematuria: blood in urine (microscopic or visible).
Dysuria: painful urination, often with small stones.
Urinary urgency and frequency: if the stone is near the bladder.
Nausea and vomiting: due to severe pain.
Fever and chills: suggests secondary infection (pyelonephritis).

Investigations

Non contrast CT KUB (kidney, ureter, bladder): gold standard for detecting stones.
Ultrasound scan: preferred in pregnancy; detects hydronephrosis and larger stones.
Urinalysis: identifies haematuria, infection, and urine pH.
24-hour urine collection: assesses stone-forming substances (e.g., calcium, oxalate, citrate).
Serum biochemistry: U&Es, calcium, phosphate, uric acid to assess metabolic causes.
Stone analysis: identifies composition to guide prevention strategies.

Management

1. Acute Pain Management:

NSAIDs (e.g., Diclofenac 75 mg IM): first line for renal colic.
Opioids (e.g., Morphine): consider if pain persists despite NSAIDs.
Anti-emetics (e.g., Metoclopramide): for nausea and vomiting.

2. Conservative Management (Stones <5mm):

Encourage high fluid intake (≥2.5L/day) to promote passage.
Alpha-blockers (e.g., Tamsulosin) can aid stone passage.
Monitor with repeat imaging if pain persists.

3. Medical Expulsive Therapy:

Alpha-blockers (e.g., Tamsulosin) relax the ureter and facilitate stone passage.
Consider in patients with distal ureteric stones.

4. Surgical Management (Indications: Stones >10mm, Obstruction, Infection, Refractory Pain):

Extracorporeal Shock Wave Lithotripsy (ESWL): non invasive, uses sound waves to break stones (best for stones <2cm).
Ureteroscopy with laser lithotripsy: used for ureteric stones or failed ESWL.
Percutaneous Nephrolithotomy (PCNL): indicated for large or complex renal stones (>2cm).
Ureteric stenting: considered if obstruction with infection.

5. Prevention and Long-Term Management:

Increase fluid intake: aim for at least 2.5L of urine output daily.
Dietary modifications:

Reduce oxalate-rich foods (e.g., spinach, nuts).
Limit salt intake (reduces urinary calcium excretion).
Moderate protein intake (prevents uric acid stones).

Thiazide diuretics: reduce calcium excretion in recurrent calcium stone formers.
Allopurinol: used in uric acid stones to lower serum uric acid levels.

Renalmypanotes18 February 2025Renal Calculi (Kidney Stones)