Nephrolithiasis: Kidney Stone Formation and Risk Factors

Definition and Overview

• Nephrolithiasis is the formation of urinary calculi in the kidney that can deposit along the entire urogenital tract.
• Risk factors include low fluid intake, high-sodium, high-purine, and low-potassium diets.
• These diets can raise calcium, uric acid, and oxalate levels in urine, promoting stone formation.

Classification and Etiology

Calcium-Based Stones

• Risk factors: Hypercalcemia and low urinary output.
• Types: Calcium oxalate and calcium phosphate.

Magnesium Ammonium Stones

• Risk factors: Ammonium urate.
• Types: Ammonium urate.

Associated Factors

• Early onset of urolithiasis, especially in children and adolescents.
• Familial stone formation.
• Recurrent stone formers.
• Short time since the last episode.
• Brushite-containing stones.
• Uric acid and urate-containing stones.
• Infection stones.

Diseases Associated with Stone Formation

• Hyperparathyroidism.
• Metabolic syndrome.
• Nephrocalcinosis.
• Polycystic kidney disease (PKD).
• Gastrointestinal diseases (e.g., Crohn's disease, malabsorption).
• Increased levels of vitamin D.
• Sarcoidosis.
• Spinal cord injury, neurogenic bladder.

Classification by Location

• Upper, middle, or lower calyx.
• Renal pelvis.
• Upper, middle, or distal ureter.
• Urinary bladder.

Classification by Size

• Up to 5 mm in largest diameter.
• 5-10 mm in largest diameter.
• 10-20 mm in largest diameter.
• > 20 mm in largest diameter.

Nephrolithiasis Definition

• Nephrolithiasis is the formation of urinary calculi in the kidney, which can be deposited along the entire urogenital tract, from the renal pelvis to the urethra and bladder.

Risk Factors

• Low fluid intake is a risk factor for nephrolithiasis.
• High-sodium, high-purine, and low-potassium diets can raise calcium, uric acid, and oxalate levels in the urine, promoting stone formation.

Classification & Etiology

• Calcium-based stones (non-infectious stones) are associated with risk factors such as hypercalcemia and low urinary output.
• Types of calcium-based stones include calcium oxalate and calcium phosphate.
• Magnesium ammonium stones (infectious stones) are associated with risk factors such as ammonium urate.
• Types of magnesium ammonium stones include ammonium urate.

Associated Factors

• Early onset of urolithiasis, especially in children and adolescents, is an associated factor.
• Familial stone formation is an associated factor.
• Recurrent stone formers are at increased risk.
• Short time since the last episode is an associated factor.
• Brushite-containing stones, uric acid, and urate-containing stones are associated with nephrolithiasis.
• Infection stones are also an associated factor.

Diseases Associated with Stone Formation

• Hyperparathyroidism is a disease associated with stone formation.
• Metabolic syndrome is associated with stone formation.
• Nephrocalcinosis is a disease associated with stone formation.
• Polycystic kidney disease (PKD) is associated with stone formation.
• Gastrointestinal diseases, such as Crohn's disease and malabsorption, are associated with stone formation.
• Increased levels of vitamin D are associated with stone formation.
• Sarcoidosis is a disease associated with stone formation.
• Spinal cord injury and neurogenic bladder are associated with stone formation.

Classification of Stones

• Stones can be classified according to their anatomical position, including upper, middle, or lower calyx; renal pelvis; upper, middle, or distal ureter; and urinary bladder.
• Stones can be classified by size, including up to 5, 5-10, 10-20, and > 20 mm in largest diameter.

Indications for Hospitalization

• Significant renal stone in a solitary kidney is an indication for hospitalization.
• Severe kidney injury or an infected renal stone is an indication for hospitalization.
• Intractable pain or nausea, urinary extravasation, or hypercalcemic crisis are indications for hospitalization.

Differential Diagnosis

• Upper UTI's may be a differential diagnosis.
• Ectopic pregnancies may be a differential diagnosis.
• Ovarian torsion may be a differential diagnosis.
• Adnexal masses may be a differential diagnosis.
• Testicular torsion may be a differential diagnosis.
• Acute aortic syndromes may be a differential diagnosis.
• Renal artery aneurysms may be a differential diagnosis.
• Renal infarction, splenic infarction, bowel obstruction, diverticulitis, and appendicitis may be differential diagnoses.

Diagnostic Tools

• Ultrasound has a sensitivity of 45% and specificity of 94% for ureteral stones and a sensitivity of 45% and specificity of 88% for renal stones.
• Non-contrast CT-scan is the gold standard for diagnosis.
• Non-contrast CT-scan can detect uric acid and xanthine stones.
• Non-contrast CT-scan can determine stone density, inner structure of the stone, skin-to-stone distance, and surrounding anatomy.
• Non-contrast CT-scan can also diagnose other causes of abdominal pain.
• Non-contrast CT-scan has limitations, including loss of information on renal function and urinary collecting system anatomy.