Renal and Ureteral Stones: Pathophysiology and Risk Factors

Renal and ureteral stones are calculi that form in the kidney and may pass into or lodge within the ureter, producing the classic syndrome of acute renal colic. Their formation reflects an imbalance between urinary supersaturation with stone-forming salts and the inhibitory capacity of the urine, shaped by metabolic, dietary, and environmental risk factors.

Definition

Renal and ureteral stones (upper urinary tract urolithiasis) are crystalline concretions that form within the kidney from supersaturated urine and may migrate into the ureter, where they can obstruct flow and cause colic.

Scope

This topic covers how upper urinary tract stones form (supersaturation, nucleation, growth, aggregation, and retention at the papilla), the metabolic and lifestyle factors that promote them, and the typical clinical presentation of obstruction. It treats the disease as a reference subject and does not prescribe individual diagnostic or therapeutic plans.

Core questions

• What makes urine supersaturated enough for crystals to nucleate and persist?
• Why do calcium stones tend to anchor and grow at the renal papilla?
• Which metabolic abnormalities (hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria) drive stone formation?
• What determines whether a ureteral stone passes spontaneously?

Key concepts

• Urinary supersaturation
• Nucleation, crystal growth, and aggregation
• Randall's plaque and papillary anchoring
• Hypercalciuria
• Hyperoxaluria
• Hypocitraturia
• Renal colic and ureteral obstruction

Mechanisms

Stone formation begins when urine becomes supersaturated with a stone-forming salt, most often calcium oxalate or calcium phosphate, so that crystals nucleate and grow faster than inhibitors such as citrate can prevent. For idiopathic calcium oxalate stones, growth is thought to be anchored to Randall's plaques, which are deposits of calcium phosphate that begin in the renal interstitium and become exposed at the papillary surface, providing a substrate for overgrowth. Metabolic risk factors raise supersaturation by increasing urinary calcium, oxalate, or uric acid or by lowering inhibitors and urine volume; low fluid intake, certain diets, and systemic conditions all contribute. When a stone enters the ureter it may obstruct urine flow and trigger renal colic, with spontaneous passage depending largely on stone size and location (Khan 2016; Moe 2006).

Clinical relevance

Upper tract stones are a leading cause of acute flank pain and a common reason for emergency urological care, and understanding their drivers underpins recurrence prevention. This entry describes the pathophysiology and risk factors as background knowledge and is not a guide to managing an individual patient.

Epidemiology

Kidney stones are common and increasingly prevalent; United States data indicate roughly one in eleven adults reported a history of stones by the late 2000s, with higher prevalence in men, in people with obesity or diabetes, and with rising temperatures (Scales 2012). Recurrence is frequent, and dietary factors such as fluid, calcium, sodium, and animal-protein intake modulate risk (Borghi 2002; Khan 2016).

History

Although stones have afflicted humans since antiquity, the modern view of nephrolithiasis as a disorder of urinary crystallization emerged with quantitative urine chemistry in the twentieth century. The recognition of Randall's plaque as an anchoring site for calcium oxalate stones, and the demonstration through controlled dietary trials that intake patterns alter recurrence, reframed upper tract stone disease as a metabolic condition amenable to prevention (Borghi 2002; Moe 2006; Khan 2016).

Debates

How central is Randall's plaque to all calcium stone formation?

Papillary plaque provides a plausible anchoring mechanism for idiopathic calcium oxalate stones, but whether it accounts for the full spectrum of calcium stone formation, and how plaque itself initiates, remains an area of active investigation.

Key figures

• Saeed R. Khan
• Orson W. Moe
• Loris Borghi
• Charles D. Scales

Seminal works

• moe-2006
• khan-2016
• scales-2012

Frequently asked questions

What causes the pain of a ureteral stone?

When a stone lodges in the ureter and obstructs urine flow, pressure rises in the collecting system and the ureter spasms, producing the severe, colicky flank pain known as renal colic.

Are kidney stones usually a one-time event?

No; recurrence is common after a first stone, which is why identifying metabolic and dietary risk factors is an important part of evaluation in the literature.