Renal stones

Introduction

• 2-5% of population, M:F = 3:1
• In males first episode usually 20-50yo and first occurrence is rare over 60
• In women, bimodal at 35 and 55yo
• Pathogenesis
  • Urinary supersaturation with solutes
    • Increasing solvent (urine) and decreasing solute (calcium, uric acid) can help with prevention
  • Lack of inhibitors
    • Citrate, magnesium, Tamm horsfall mucoproteins can all prevent stone formation
  • Urinary stasis
    • Neurogenic bladder, anatomic abnormality, foreign bodies or Randall’s plaque (interstitial subendothelial calcium phosphate particles on surface of renal papillae)

Types of Stones

• 80% calcium (oxalate, phosphate or both)
  • Calcium excretion is increased in hyperparathyroidism, absorptive and renal hypercalciuria and immobilisation syndrome
  • Oxalate excretion is enhanced in IBD and following small bowel resection or jejunoileal bypass
• 15% struvite stones (magnesium-ammonium-phosphate)
  • Associated with urea-splitting bacteria and are the most common type of staghorn calculi
  • Proteus, Klebsiella, Staph, Providencia and Corynebacterium
  • Also raise urine pH (pH >7.5 suggests this)
  • Antibiotic penetration into staghorns is low and potential for urosepsis exists as long as stone remains
• 10% uric acid stones
  • Urate stones are radiolucent and urine is typically acidic (pH <5)
• 1% cystine stones
  • Found in patients with cystinuria, autosomal recessive genetic disorder)

Introduction

• Medications
  • Indinavir has 4-10% incidence of stones
  • Pure indinavir stones can form 
  • Carbonic anhydrase inhibitors and laxative abuse increase risk of stones
• 85% of calcium oxalate stone recurrences can be prevented

Pathophysiology

• Pain
  • Due to obstruction of hollow viscous (ureter)
  • Small renal pelvis stones usually painless unless entrance to ureter obstructed
  • Migrating, but non-obstructive stones are usually painful also
• Renal dysfunction
  • In acute ureteral obstruction, renal blood flow and renal pelvic pressure increase initially
  • Over 4 hours, renal blood flow normalises,  but renal pelvic pressure remains elevated
  • Over time, renal blood flow will fall below normal while renal pelvic pressure remains above baseline and if not relieved, irreversible renal damage occurs within 3 weeks
  • Most patients have no rise in serum creatinine as unobstructed kidney can increase function to 185% above baseline
  • Rise in creatinine suggests pre-existing renal disease or solitary kidney

• Factors that determine spontaneous passage
  • Size
    • 98% of stones <5mm will pass within 4 weeks
    • 60% of stones 5-7mm will pass within 4 weeks (Tintinalli); 4-6mm pass 50% of time (Cameron)
    • 39% of stones >7mm will pass within 4 weeks (5% in Cameron)
  • Shape
  • Location – Ureteropelvic junction > pelvic brim, ureterovesical junction
    • Proximal ureteral stones pass 25% of time time
    • Midureteral stones pass 45% of the time
    • Distal ureteral stones pass 70% of the time
  • Degree of ureteral obstruction – If complete, less likely to pass spontaneously

Clinical features

• Visceral loin to groin pain without peritoneal irritation
• Write and cannot find position of comfort
• Rebound tenderness (29%), guarding (61%), rigidity (8%)
• Nausea and vomiting in 50%
• Haematuria in 85% (30% have gross haematuria)
• Upper ureter refers to high flank
• Mid-ureter refers to lower anterior quadrants of abdomen
• Distal ureter refers to groin (75% of cases)
• Stones at ureterovesical junction can mimic UTI with frequency, urgency, dysuria in 3-24% of patients

Important history

• Risk factors for stone
  • HTN, dehydration, low fluid intake, prolonged immobilisation, FHx, hyperparathyroidism, previous nephrolithiasis, peptic ulcer disease (hypercalciuria), IBD (hyperoxaluria) , gout (hyperuricaemia)
  • Myeloproliferative disorders, malignancy, glycogen storage disorders, RTA, calcium supplements, acetazolamide, Vit C, Vit D, antacids
• Risk factors for poor stone outcomes
  • Renal function at risk (DM, HTN, pre-existing renal disease, single kidney or transplant)
  • Hx of difficulty with stones (extractions, stents, ureterostomy tubes)
  • Risk factors for infection (fever, systemic illness, UTI symptoms)

Important history

• Risk factors for stone mimics
  • AAA (nephrolithiasis is the most common misdiagnosis in rupturing or expanding AAA)
    • Stones do NOT cause hypotension and are exceedingly rare as first presentation in men >60yo
  • Renal artery infarction
    • Easily missed even with CT as no contrast used and early in course may not see inflammation around the kidney

Diagnosis

• Rule out infection
• Urinalysis to rule out infection
• Haematuria (>=5 RBC/HPF) or absence can mislead
  • 10-15% of patients with nephrolithiasis will have no haematuria
  • 24% of patients with flank pain and haematuria have no radiographic evidence of nephrolithiasis
  • Therefore, should not be used alone to rule in/out nephrolithiasis
• Check renal function
• WCC > 15 suggestive of infection

Imaging

• Stone size is magnified 20% by plain film
• Stone size measured on CT is 88% of actual stone size
• Stones >1000 HFU are less likely to be amenable to lithotripsy

Imaging (WA GUIDELINES)

• First-time presenters
  • Alternative diagnosis found in 33% of highly suspicious cases based on clinical grounds
  • If <50
    • USS first:
      • If positive, XR KUB +- CT KUB if intervention contemplated
      • If negative and stone passed or symptoms resolve – No further imaging
      • If negative and persistent symptoms – low-radiation CT KUB
  • If >50
    • If typical symptoms and signs can follow path above
    • If atypical, older or alternative diagnosis likely low-radiation CT KUB first line

• Repeat presenters
  • Only image if previous complications from stones, >50yo, persistent pain or evidence of complication i.e. AKI, fever, solitary kidney
• This pathway avoids CT in 70% of patients

Imaging

• CT
  • Non-contrast helical CT KUB is sensitive and specific
    • Not as sensitive for AAA, appendicitis, renal infarct or perinephric abscess and renal function is not assessed
  • Secondary signs of ureteral obstruction (ureteral dilatation, perinephric fat stranding, dilatation of collecting system and renal enlargement) all helpful
  • Unilateral ureteral dilatation and perinephric stranding PPV 96% for stone disease; If both absent NPV 97%
  • Low-dose CT is as sensitive for stones >3mm in BMI <30
    • Suitable for pregnant women in 2^nd/3^rd trimester (luckily when most cases occur)
  • Nearly all stones are opaque on CT
  • Phleboliths do not have a soft tissue rim sign of ureteral wall

• Plain X-ray
  • 90% are radioopaque. Struvite slightly less radiodense than calcium
  • Cystine is only partly radioopaque
  • Uric acid stones radiolucent
  • Not sensitive or specific enough to rule in/out stones but can be used to monitor progress once diagnosed on CT
  • Only 60% sensitive
  • Phlebitis in pelvic veins and calcified mesenteric lymph nodes can be false positive

• USS
  • Misses 30% of stones (70% sensitive) but highly sensitive for hydronephrosis
    • Useful for detecting larger distal stones mainly but cannot determine size of stone accurately
    • May miss <5mm ureteral stones
    • Most useful in positively identifyinf proximal and distal ureter but insensitive for mid-ureteral stones
  • 98% sensitive for hydronephrosis, however, 22% of these are actually normal anatomic variation, full bladder or renal cysts (physiological hydronephrosis of pregnancy can be difficult to differentiate)
  • Can also assess renal blood flow and urine flow + renal size
  • Limited other information on alternative diagnoses
  • Operator dependent

Differential diagnosis

• Vascular – AAA, renal artery thrombosis, aortic dissection, renal vein thrombosis, mesenteric ischaemia
• Renal – Pyelonephritis, papillary necrosis, renal cell carcinoma, renal infarct, renal haemorrhage
• Ureter – Blood clot, stricture, tumor
• Bladder – Tumor, varicose vein, cystitis
• GI – Biliary colic, pancreatitis, appendicitis, diverticulitis, perforated PU, inguinal hernia, cancer, bowel obstruction, ischaemia
• Gynaecological – Ectopic, PID, ovarian cyst rupture, ovarian torsion, endometriosis
• GU – Testicular torsion, epididymitis
• Other – Drug-seeking, shingles, retroperitoneal haematoma/abscess/tumor

Treatment

• Analgesia, antiemetics, antibiotics if evidence of infection and medical expulsion therapy
• Forced IV hydration makes no difference to stone passage compared to usual IV hydration
• NSAIDs = Opioids in renal colic
• PR indomethacin 100mg highly effective for analgesia (esp. if vomiting)
• PO ibuprofen 800mg PO stat then 400mg TDS
• Fentanyl/morphine/oxycodone
• Metoclopramide provides both antiemetic AND ANALGESIC effect = opioids
• 4-6mm stones have a 50% intervention rate vs. >6mm having a 99% intervention rate
• Proximal stones have a 50% passage rate vs. 80% for distal stones

Treatment

• Medical expulsion therapy
  • Alpha-blockers are associated with increased rates of expulsion, decreased time to expulsion, decreased pain (NNT = 3.3) with average 2-6 day improvement in time to expulsion
  • Cochrane review 2018 showed low to moderate level evidence of increased rate of expulsion, less diclofenac use, less likely to be admitted and similar rates of surgery. More benefit if stones >5mm
  • 4% of patients have adverse effects
  • Benefit limited to distal third of ureter stones (supposedly higher alpha-receptor density)
  • Tamsulosin 400mcg PO daily for 4 weeks

Disposition and follow-up

• Most outpatient management
• Discuss with urologist and arrange early follow-up within 1 week if:
  • Renal insufficiency/solitary kidney/transplanted kidney
  • Severe underlying disease
  • Multiple ED visits
  • Stone >5mm
  • Sloughed renal papillae
  • Associated UTI without sepsis
• Admission
  • Stones >5mm, irregular or proximal stones and infected stones should all be considered for admission
  • If severe comorbidities, may not tolerate experience and warrant admission also
  • Intractable pain or vomiting
• Urgent decompression
  • Solitary kidney and complete obstruction
  • Ureterolithiasis with hydronephrosis and fever
  • Urosepsis with obstruction
• Instructions
  • Pee through strainer to save stone for pathology
  • Stone passage can occur in 7-20 days for 5-6mm stones
  • Promptly return if increased pain, fever, or vomiting

Re-presenters

• If re-present with continued pain need to evalute for:
  • Worsening renal function
  • Evidence of obstruction (USS to limit radiation)
  • Evidence of infection
  • Movement of stone (repeat X-ray KUB if radio-opaque)
  • Clear evidence that stone is the cause of pain

Pregnancy

• Stones occur in 1/1500 pregnancies
• 80-90% in second or third trimester
• USS is preferred, however, 90% of pregnant women show physiological hydronephrosis (more common and more severe on right side)
• CT KUB is <5Cgy cut-off for causing a congenital abnormality and benefit likely outweighs risk
  • Useful in 2^nd/3^rd trimester when most cases occur
  • If first trimester, consider MRI if not responding to symptomatic treatment and lying away from affected side (reduces pressure on ureter from gravid uterus

Infected stones

• If unwell – Gent 5mg/kg IV load + Ampicillin 1-2g q4h IV
  • Need urgent decompression and urological consult
• If has stone and UTI but no evidence of obstruction can manage as an outpatient after discussion with urologist with oral antibiotics as per usual

Last Updated on March 27, 2024 by Andrew Crofton