Urolithiasis Renal Calculi Stones

Slide 1 · Urolithiasis

Renal calculi and urinary tract stones

Etiology • crystal formation • morphology • clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain why urinary supersaturation favors calculus formation.

Distinguish calcium, struvite, uric acid, and cystine stones.

Connect stone composition and morphology with clinical injury.

Interpret short clinicopathologic teaching cases.

Slide 3 · Urolithiasis is stone formation in the urinary tract

Most stones arise in the kidney, although calculi can occur throughout the urinary tract.

Stone disease spans silent incidental findings, renal colic, infection, and structural damage.

Slide 4 · Sites of calculus formation

Renal calyces and pelvis are important stone-forming locations.

Calculi can also occur in the bladder and elsewhere in the urinary tract.

Slide 5 · Lifetime occurrence in the United States

5%–10%

This lifetime range for the U.S. Population; It is a textbook figure, not a new population estimate.

Slide 6 · Age and sex distribution

Sex pattern

Males are affected more often than females.

Age at onset

Peak age at onset is reported between 20 and 30 years.

Slide 7 · A familial predisposition can underlie stone disease

Familial or hereditary predisposition

Altered handling of stone-forming substances

Increased excretion and crystal risk

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 8 · Two inherited metabolic examples

Cystinuria

Abnormal renal reabsorption increases urinary cystine.

Primary hyperoxaluria

An inherited metabolic disorder increases oxalate burden.

Slide 9 · Four principal stone classes

Class

Principal constituent

Approximate share in Robbins

Calcium

Calcium oxalate ± phosphate

~70%

Struvite

Magnesium ammonium phosphate

5%–10%

Uric acid

Uric acid

5%–10%

Cystine

Cystine

1%–2%

Slide 10 · Calcium stones predominate

Calcium

~70%

Struvite

5%–10%

Uric acid

5%–10%

Cystine

1%–2%

Struvite, uric acid, and cystine shown at reported upper bounds; Bars are not parts of a normalized whole.

Slide 11 · Every calculus contains an organic matrix

A mucoprotein matrix accounting for approximately 1%–5% of stone weight.

Stones are not simply pure, freely precipitated inorganic crystals.

Slide 12 · The central process is urinary supersaturation

Urinary solute concentration rises

Solubility of constituent is exceeded

Crystal formation becomes favorable

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 13 · Supersaturation is a qualitative threshold

Below constituent solubility limit

Below solubility limit: The constituent remains in solution.

Above constituent solubility limit

Above solubility limit: Precipitation becomes thermodynamically favorable.

Slide 14 · Low urine volume can increase crystal risk

Lower urine volume

Greater urinary solute concentration

Increased tendency to supersaturation

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 15 · Several variables influence calculi

Urinary chemistry

Constituent concentration and urinary pH

Urinary environment

Urine volume, bacteria, and crystal inhibitors

Slide 16 · A coherent model of stone pathogenesis

Solute load

Ca / oxalate / urate / cystine

Solution state

Volume + pH

Biological modifiers

Bacteria + inhibitors

Outcome

Crystal formation / stone growth

Slide 17 · Calcium stones are chemically heterogeneous

Most contain calcium oxalate or a mixture of calcium oxalate and calcium phosphate.

The same broad stone class can arise through different metabolic disturbances.

Slide 18 · Calcium stone pathways: Two serum-calcium settings

Hypercalcemia with hypercalciuria

One recognized setting; Associated with conditions elevating serum calcium.

Hypercalciuria without hypercalcemia

A larger source-described group; Abnormal urinary calcium despite normal serum calcium.

Slide 19 · Hypercalcemia-associated calcium oxalate stones

About 5%

This subset with both hypercalcemia and hypercalciuria.

Slide 20 · Systemic settings of hypercalcemic stone risk

Hyperparathyroidism increases circulating calcium.

Diffuse bone disease can contribute to hypercalcemia.

Sarcoidosis and other hypercalcemic states are also named.

Slide 21 · Hypercalciuria despite normocalcemia

About 55%

This calcium oxalate stone subgroup without elevated serum calcium.

Slide 22 · Absorptive hypercalciuria

Excess intestinal calcium absorption

Increased calcium entering circulation

Greater urinary calcium excretion

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 23 · Renal hypercalciuria

Intrinsic impairment of tubular calcium reabsorption

Reduced renal conservation of calcium

Hypercalciuria despite normocalcemia

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 24 · Idiopathic fasting hypercalciuria

The calcium-stone differential includes fasting hypercalciuria with normal parathyroid function.

The label does not imply that the underlying transport mechanism has been fully established.

Slide 25 · Uric acid can nucleate calcium oxalate

Increased urinary uric acid

Uric acid crystals in collecting ducts

Calcium oxalate nucleation and growth

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 26 · Hyperuricosuric calcium nephrolithiasis

Up to 20%

Calcium oxalate stones may be associated with increased urinary uric acid, with or without hypercalciuria.

Slide 27 · Two major hyperoxaluria pathways

Primary

Hereditary oxalate overproduction or abnormal metabolism.

Enteric

Acquired intestinal overabsorption in enteric disease.

Slide 28 · Enteric disease and oxalate stones

Enteric disorder

Enhanced intestinal oxalate absorption

Hyperoxaluria

Calcium oxalate risk

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 29 · Primary hyperoxaluria is a hereditary stone risk

Primary hyperoxaluria among inborn errors associated with stones.

For a calcium stone, excess oxalate can be the key abnormal urinary constituent.

Slide 30 · Hypocitraturia removes a protective influence

Reduced urinary citrate

Fewer inhibitor-mediated restraints

Greater calcium crystal risk

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 31 · Clinical contexts of hypocitraturia

Hypocitraturia may be idiopathic.

It may accompany acidosis.

Chronic diarrhea of unknown cause is another association.

Slide 32 · Idiopathic calcium stone disease is a real category

No cause is found in a variable proportion of patients with calcium stones.

Absence of an identified abnormality should not be presented as absence of stone-forming pathophysiology.

Slide 33 · Calcium stone mechanisms: Compare the drivers

Driver

Primary disturbance

Stone-forming consequence

Calcium

Hypercalcemia or hypercalciuria

↑ urinary Ca

Urate

Hyperuricosuria

Ca oxalate nucleation

Oxalate

Primary or enteric hyperoxaluria

↑ urinary oxalate

Citrate

Hypocitraturia

Reduced inhibition

Slide 34 · Struvite is an infection-associated calculus

Struvite consists principally of magnesium ammonium phosphate.

Stone formation is strongly linked to infection by organisms able to split urea.

Slide 35 · Urea-splitting bacteria change urinary chemistry

Bacterial urea splitting

Ammonia generation

Urine alkalinization

Struvite precipitation

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 36 · Which organisms are implicated?

Common example

Proteus species are specifically cited.

Additional example

Some staphylococci can also be urea-splitting.

Slide 37 · Alkaline urine favors struvite precipitation

Ammonia produced by urea splitting raises urinary pH.

The altered pH environment permits magnesium ammonium phosphate salts to precipitate.

Slide 38 · Infection stones can form branching staghorn casts

Progressive salt accretion can occupy large portions of the renal pelvis.

The stone may extend into calyces and mold to the collecting system.

Slide 39 · Uric acid stones: Systemic associations

Hyperuricemia can be present in patients with gout.

High cell turnover, exemplified by leukemia, is another association.

Serum urate alone does not explain most uric acid stones.

Slide 40 · Normal systemic urate does not exclude uric acid calculi

More than half

More than half of patients with uric acid calculi lack hyperuricemia or increased urinary uric acid excretion.

Slide 41 · Acidic urine favors uric acid calculi

Less acidic than the stated risk setting

A tendency to urinary pH below 5.5 in this subset.

Urinary pH < 5.5

Uric acid is poorly soluble in acidic urine.

Slide 42 · Radiographic distinction: Calcium versus uric acid

Calcium stones

Radiopaque on conventional radiography.

Uric acid stones

Radiolucent on conventional radiography.

Slide 43 · Cystinuria produces cystine stones

Hereditary tubular amino-acid reabsorption defect

Increased urinary cystine

Cystine precipitation and stones

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 44 · Cystine stones also favor low urinary pH

Low pH is described in the formation of cystine stones.

The underlying defect is impaired renal reabsorption of cystine-containing amino acids.

Slide 45 · Acidic urine: Two distinct stone mechanisms

Feature

Uric acid

Cystine

Underlying basis

Poor solubility of uric acid

Cystinuria: amino-acid reabsorption defect

Urinary pH

Acidic; Robbins discusses pH < 5.5

Low urinary pH favors formation

Hereditary driver

Not necessary

Intrinsic to cystinuria

Slide 46 · Urinary constituents that inhibit crystals

Low-molecular/ionic inhibitors

Other named inhibitors

Citrate

Glycosaminoglycans

Pyrophosphate

Osteopontin

Diphosphonates

Nephrocalcin (glycoprotein)

Slide 47 · Why similar solute abnormalities need not yield stones

Stone-promoting urinary chemistry

Counteracting inhibitors and local conditions

Variable crystallization outcome

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 48 · A biochemical predisposition is not destiny

Patients with hypercalciuria, hyperoxaluria, or hyperuricosuria often do not develop stones.

This observation supports the importance of inhibitory and local urinary factors.

Slide 49 · Stone determinants must be interpreted together

Solute

Amount excreted

PH

Species solubility

Volume

Concentration

Inhibitors

Crystallization restraint

Slide 50 · Renal calculi are often unilateral

About 80%

Unilateral disease in roughly 80% of patients with stones.

Slide 51 · Typical anatomic distribution

Calyces and renal pelvis are common locations.

Bladder stones are also recognized in the same disease spectrum.

Slide 52 · Many renal-pelvis stones are small

2–3 mm

This average diameter for stones forming in the renal pelvis.

Slide 53 · Calculi differ in surface contour

Smooth contour

Jagged or spiculated contour

Schematic contours only; Not a photograph of stones

Slide 54 · A kidney may contain multiple calculi

Several stones may occupy separate areas in one kidney.

Multiplicity does not imply that both kidneys are involved.

Slide 55 · Staghorn calculi mirror collecting-system shape

Branching structures form with progressive accretion of salts.

Large calculi can cast the pelvis and calyces.

Slide 56 · Clinical course varies widely

Silent disease

A calculus may produce no symptoms.

Symptomatic disease

Renal colic, abdominal pain, hematuria, or renal damage may occur.

Slide 57 · Obstructing calculi can provoke renal colic

Stone lodged in urinary outflow path

Dilation / distention of urinary collecting system

Pain and renal colic

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 58 · A calculus can cause hematuria

Calculus in urinary tract

Local tissue trauma

Blood in urine (hematuria)

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 59 · Stones increase susceptibility to infection

Obstruction and local tissue trauma

Impaired urinary drainage / mucosal injury

Predisposition to superimposed infection

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 60 · Persistent stone obstruction injures the kidney

Outflow obstruction

Pelvicalyceal dilation

Pressure-related parenchymal injury

Progressive renal atrophy

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 61 · Hydronephrosis is dilation with progressive atrophy

Obstruction can dilate the renal pelvis and calyces.

Prolonged pressure is associated with loss of renal parenchyma.

Slide 62 · Chronic obstruction evolves beyond dilation

Sustained obstruction

Interstitial inflammation

Tubular atrophy and fibrosis

Structural renal damage

Conceptual sequence — direction indicates the causal relationship described in the source

Slide 63 · Teaching case: Recurrent calcium-type risk

A patient has calcium oxalate stones and increased urinary calcium, but normal serum calcium.

Question: Which metabolic category is supported? What mechanisms should be considered?

Slide 64 · Case interpretation: Normocalcemic hypercalciuria

The pattern is compatible with hypercalciuria without hypercalcemia.

Possible categories include increased intestinal absorption, tubular reabsorption impairment, or idiopathic fasting hypercalciuria.

Slide 65 · Teaching case: Large branching calculus

A patient has a staghorn-shaped calculus and an infection caused by a urea-splitting organism.

Question: Which stone type is most plausible, and why?

Slide 66 · Case interpretation: Infection-associated struvite

A urease-positive infection can raise urinary pH through ammonia generation.

Alkalinization favors magnesium ammonium phosphate precipitation and large branching calculi.

Slide 67 · Teaching case: Stone invisible on plain radiography

A patient with a stone has persistently acidic urine; The calculus is radiolucent on plain radiography.

Question: What composition is most strongly suggested by Robbins?

Slide 68 · Case interpretation: Uric acid stone

Acidic urine promotes uric acid precipitation.

Radiolucency supports uric acid rather than a typical calcium stone; Serum urate need not be elevated.

Slide 69 · Integrative differential at a glance

Stone class

Most discriminating source-based feature

Calcium

Common; multiple possible urinary metabolic drivers

Struvite

Urea-splitting infection → alkaline urine; may be staghorn

Uric acid

Acidic urine; radiolucent on plain radiography

Cystine

Hereditary amino-acid transport defect; acidic urine

Slide 70 · Clinicopathologic synthesis

Supersaturation is central, but urinary pH and inhibitors modulate crystal formation.

Calcium stones have heterogeneous mechanisms; Struvite, uric acid, and cystine have distinct clues.

Stone shape, location, obstruction, and infection determine clinical consequences.

Stone chemistry and renal morphology should be interpreted together.

Slide 71 · Primary source and scope

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026. Chapter 20: The Kidney, pp. 861–862.

The obstructive uropathy section in the same chapter was used for consequences of persistent obstruction.

Figures in this lecture are original editable schematics, not patient specimens or textbook reproductions.