Where is the most likely location of a kidney stone in a patient with flank tenderness, fever, and a recent history of Urinary Tract Infection (UTI)?

Stone Location in Infected Urolithiasis

In a patient with flank tenderness, fever, and recent UTI, the stone is most likely located in the ureter (particularly the ureterovesical junction or proximal ureter), not within the renal parenchyma itself—making none of the provided anatomical options (minor calyx, major calyx, renal capsule, renal cortex) the correct answer. 1

Understanding the Clinical Scenario

This presentation suggests either an obstructive pyelonephritis (infected obstructing stone) or an infection stone (struvite calculus formed secondary to urease-producing bacteria). 2

Key Clinical Distinction

• Obstructive pyelonephritis represents a urologic emergency where a stone of any composition obstructs the urinary tract, causing upstream infection and potential sepsis 2
• Infection stones (struvite/staghorn calculi) form as a consequence of chronic UTI with urease-producing organisms and typically develop in the renal collecting system 3, 2

Most Likely Stone Locations

Ureteral Stones (Most Common at Presentation)

When patients present to the emergency department with acute symptoms:

• 60.6% of stones are at the ureterovesical junction 1
• 23.4% are in the proximal ureter (between ureteropelvic junction and iliac vessels) 1
• 10.6% are at the ureteropelvic junction 1
• Only 1.1% lodge where the ureter crosses the iliac vessels, despite traditional teaching 1

These ureteral locations cause obstruction leading to hydronephrosis and predispose to ascending infection. 4, 5

Infection Stones in the Collecting System

If this represents a primary infection stone rather than an obstructed metabolic stone:

• Infection stones typically form staghorn or branched calculi within the renal pelvis and calyces 3
• They consist of magnesium ammonium phosphate and carbonate apatite in alkaline urine 3
• Complex staghorn stones extending into multiple calyces have higher complication rates (19.5%) 6

Why the Given Options Are Incorrect

The anatomical locations provided in the question are not typical sites for symptomatic stone formation:

• Minor/major calyces: While infection stones can extend into calyces as part of staghorn calculi, isolated calyceal stones rarely cause acute flank pain and fever 6
• Renal capsule: Stones do not form in the renal capsule 4
• Renal cortex: Stones do not form in the renal cortex parenchyma 4

Stones form in the collecting system (pelvis, calyces) or lodge in the ureter, not in solid renal tissue. 4

Clinical Implications

Urgent Evaluation Required

• Fever with flank pain indicates possible pyelonephritis or infected stone requiring urgent intervention 5
• Obtain urinalysis for leukocyte esterase, nitrites, WBCs, and urine culture 5
• Check serum chemistries including creatinine to assess renal function 5

Imaging Approach

• Ultrasound is first-line to detect hydronephrosis (sensitivity up to 100% for obstruction) 5, 7
• Non-contrast CT provides definitive stone localization with 95%+ sensitivity and specificity 5
• CT can distinguish pyonephrosis from simple hydronephrosis, though collecting system density may be affected by recent contrast 4

Management Priority

Complete stone removal is the mainstay of treatment for infected stones, as bacteria persist within the stone matrix. 2, 8 Prompt drainage of an obstructed infected kidney prevents permanent renal damage and may be life-saving. 8