Overview

Definition

Nephrolithiasis (also known as kidney stones, urolithiasis, or urinary calculi) is the formation of stones anywhere along the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract.

Classification

There are 5 main types of kidney stones:

• Calcium oxalate stone: 
  • Accounts for 75% of all kidney stones (most common type)
  • Envelope or dumbbell-shaped crystals
• Uric acid stone:
  • Accounts for 10% of all kidney stones
  • Rhomboid or rosette-shaped crystals
• Struvite (ammonium magnesium phosphate) stone: 
  • Accounts for 5%–10% of all kidney stones
  • Coffin-lid–shaped crystals
• Calcium phosphate stone:
  • Accounts for 5% of all kidney stones
  • Wedge-shaped prism
• Cystine stone:
  • Accounts for < 5% of kidney stones
  • Hexagonal crystals
  • Mnemonic: Pronounce cystine stones as “sixtine” stones (six-sided stones) to remember their shape.

Epidemiology

• More common in men than women
• Most common in white, non-Hispanic men
• Peak incidence: 45–70 years old, but can occur at any age
• Prevalence increases with age.

Etiology

Normally soluble material supersaturates the urine and crystal formation begins.

Risk factors:

• Family history
• Medical conditions:
  • Urinary tract infections Urinary tract infections Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections (UTIs)
  • Cystinuria
  • Gout Gout Gout is a heterogeneous metabolic disease associated with elevated serum uric acid levels (> 6.8 mg/dL) and abnormal deposits of monosodium urate in tissues. The condition is often familial and is initially characterized by painful, recurring, and usually monoarticular acute arthritis, or "gout flare," followed later by chronic deforming arthritis. Gout (high uric acid)
  • Hyperparathyroidism Hyperparathyroidism Hyperparathyroidism is a condition associated with elevated blood levels of parathyroid hormone (PTH). Depending on the pathogenesis of this condition, hyperparathyroidism can be defined as primary, secondary or tertiary. Hyperparathyroidism (high calcium levels)
  • Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
  • Diabetes
  • Inflammatory bowel disease (IBD)
  • Short gut syndrome
• Diet:
  • High sodium: decreased sodium and calcium reabsorption in the proximal tubule → hypercalciuria
  • High calcium
• Dehydration: causes an excessive concentration of urine solutes → stone formation
• Loop diuretics Loop diuretics Loop diuretics are a group of diuretic medications primarily used to treat fluid overload in edematous conditions such as heart failure and cirrhosis. Loop diuretics also treat hypertension, but not as a 1st-line agent. Loop Diuretics: inhibits calcium reabsorption → hypercalciuria

Clinical Presentation and Diagnosis

Clinical presentation

• Depends on the size, number, and location of the stones
• Small stones may be asymptomatic.
• Stones within the renal pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis and bladder are usually asymptomatic.
• Symptoms are usually associated with acute ureteral obstruction:
  • Unilateral, colicky abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain due to intermittent ureteral peristalsis: 
    • Colicky pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain radiates to the groin, testes, or labia majora
    • Causes costovertebral angle tenderness
    • Usually associated with inability to lie still
  • Hematuria due to trauma to the ureter (frank or microscopic)
  • Nausea and/or vomiting
  • Fever suggests associated infection or pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess.

Diagnosis

Imaging:

• Noncontrast CT of the abdomen and pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis:
  • Gold-standard of imaging for kidney stones
  • Can show location and size of the stone
  • Can detect hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis
• Abdominal ultrasound: used in pregnant women and children to avoid radiation
• Abdominal X-ray: can detect large stones

Laboratory studies:

• Urinalysis and urine dipstick:
  • Useful for detecting microscopic hematuria
  • Determines urine pH and helps determine the type of stone
• Urine microscopy: evaluates the shape of the crystals

Management

Size-based approach

• < 5 mm: observation only (spontaneous passage is likely)
• 5–10 mm: alpha-blockers or dihydropyridine calcium channel blockers Calcium Channel Blockers Calcium channel blockers (CCBs) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBs: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers)
• 10–20 mm: extracorporeal shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock wave lithotripsy (ESWL) or ureterorenoscopy
• > 20 mm: percutaneous nephrolithotomy

Medical management

General supportive care:

• Hydration with IV fluid
• Analgesic medications ( pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain can be severe)
• Alpha-blockers (e.g., terazosin, tamsulosin) or dihydropyridine calcium channel blockers Calcium Channel Blockers Calcium channel blockers (CCBs) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBs: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers) (e.g., nifedipine) to dilate and relax the ureters and allow for passage of stones < 10 mm

Stone-specific management:

• Calcium oxalate and calcium phosphate stones:
  • Low-sodium diet to increase concomitant sodium and calcium reabsorption in proximal tubules
  • Citrate to dissolve calcium oxalate crystals
  • Thiazide diuretics Thiazide diuretics Thiazide and thiazide-like diuretics make up a group of highly important antihypertensive agents, with some drugs being 1st-line agents. The class includes hydrochlorothiazide, chlorothiazide, chlorthalidone, indapamide, and metolazone. Thiazide Diuretics to increase calcium reabsorption in the distal tubule
• Struvite stones: antibiotic therapy to eliminate the causative microbe
• Uric acid stones:
  • Urine alkalinization with potassium citrate to dissolve uric acid crystals
  • Allopurinol to decrease uric acid production
• Cystine stones: tiopronin or penicillamine to chelate cystine

Surgical management

• ESWL:
  • Stone fragmentation with sound waves
  • Not routinely performed in obese patients due to poor penetration of sound waves
• Ureterorenoscopy: a transurethral endoscopic procedure to visualize the entire urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract and retrieve the kidney stone
• Percutaneous nephrolithotomy: a surgical procedure with skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin incision to retrieve the kidney stone

Prevention

• Adequate hydration
• Low-sodium, low-protein diet

Differential Diagnosis

• Acute appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis: inflammation of the appendix caused by impaction of a fecalith in adults, or by lymphoid hyperplasia in children. The initial presentation is diffuse periumbilical pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, which then localizes to the RLQ. In contrast, nephrolithiasis causes flank pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain. The diagnosis of appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis is mostly clinical and treatment is an appendectomy Appendectomy Appendectomy is an invasive surgical procedure performed with the goal of resecting and extracting the vermiform appendix through either an open or a laparoscopic approach. The most common indication is acute appendicitis. Appendectomy. 
• Testicular torsion Testicular torsion Testicular torsion is the sudden rotation of the testicle, specifically the spermatic cord, around its axis in the inguinal canal or below. The acute rotation results in compromised blood flow to and from the testicle, which puts the testicle at risk for necrosis. Testicular Torsion: the twisting of the spermatic cord caused by increased testicular mobility in the scrotal sac. Presentation includes erythema, swelling, absent cremasteric reflex, and sudden-onset, severe testicular pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain. In contrast, nephrolithiasis-induced pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain originates in the flank and later radiates to the groin. Diagnosis of testicular torsion is via Doppler ultrasound. Treatment is manual, or surgical detorsion with bilateral orchiopexy. 
• Biliary colic: a colicky, RUQ pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain caused by intermittent obstruction of the cystic duct by the gallstone. Presentation is episodic pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, especially after ingestion of a fatty meal. In contrast, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain due to nephrolithiasis is not related to eating. Diagnosis is based on the combination of clinical signs and RUQ ultrasound findings. Unless the patient develops acute cholecystitis Cholecystitis Cholecystitis is the inflammation of the gallbladder (GB) usually caused by the obstruction of the cystic duct (acute cholecystitis). Mechanical irritation by gallstones can also produce chronic GB inflammation. Cholecystitis is one of the most common complications of cholelithiasis but inflammation without gallstones can occur in a minority of patients. Cholecystitis, treatment is observation.
• Diverticulitis: an inflammation of diverticula caused by the impaction of a fecalith. Presentation may include LLQ pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, moderate to high fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and bloody stools. In contrast, nephrolithiasis is not characterized by bloody stools. Diverticulitis is diagnosed with a CT scan of the abdomen and most cases are treated with IV antibiotics.