Urinary tract calculi

Question 1

Define urinary tract calculi. What is another name for it?

Answer 1

Crystal deposition within the urinary tract.

Also known as nephrolithiasis.

Question 2

Where along the renal tract are stones most likely to cause obstruction?

Answer 2

Stones are most likely to obstruct in the narrowest parts of the collecting system. These are:

• Pelvouretic junction (PUJ)
• the ureteral crossing of the iliac vessels (pelvic brim)
• vesico-ureteric junction (VUJ).

Question 3

State the 5 different types of renal calculi in order of fequency

Answer 3

• Calcium - (75–85%)- calcium oxalate, calcium phosphate, or mixed
• Struvite - (10–20%)- ammonium magnesium phosphate.
• Urate - (5–10%)
• Cystine - 1%

Question 4

List the metabolic conditions that predispose to calculi formation

Answer 4

• Hypercalciuria
• Hyperuricosuria
• Hypocitraturia
• Hyperoxaluria
• Gout and other hyperuricaemic states e.g. malignancy, glucose-6-phosphate dehydrogenase
• (G6PDH) deficiency (urate stones)
• Cystinuria

Question 5

List other medical conditions that predispose to calculi formation

Answer 5

• Primary hyperparathyroidism
• Crohn’s disease (often oxalate stones, exact mechanism remains unclear)
• Chronic UTI due to urease-producing bacteria (struvite stones)
• Medullary sponge or polycystic kidneys (resulting in static collections in which stones form)
• Renal tubular acidosis (stones result from hypercalciuria, alkalinization of the urine causing precipitation of calcium phosphate, and low urinary citrate)
• Sarcoidosis (causes a hypercalcaemia that can lead to stone formation)

Question 6

What drugs may increase risk of renal calculi formation?

Answer 6

• Loop diuretics, such as furosemide and acetazolamide.
• Some antacids.
• Glucocorticoids, such as dexamethasone.
• Carbonic anhydrase inhibitors- (calcium phosphate stones)
• Indinavir (crystallises and become primary component of stone)

Question 7

Other than drugs and conditions, what physical abnormalties may increase risk of kidney stones?

Answer 7

Urinary tract abnormalities

• Pelviureteric junction obstruction
• Hydronephrosis
• Ureteral stricture
• Horseshoe kidney

Foreign bodies

• Stents
• Catheters

Question 8

State some environmental risk factors for kidney stones

Answer 8

• Low fluid intake
• Diet: chocolate, tea, rhubarb, strawberries, nuts, spinach – all increase oxalate levels
• Season: vitamin D synthesis via sunlight

Question 9

Summarise the epidemiology of urinary tract calculi

Answer 9

• COMMON
• 2-3% of general population
• 3 x more common in MALES
• Age group affected: 20-50 yrs
• Bladder stones more common in developing countries
• Upper urinary tract stones more common in industrialised countries

Question 10

State the presenting symptoms of renal calculi

Answer 10

• Often ASYMPTOMATIC
• SEVERE loin to groin pain –
  
  • Ureteric stones give a colicky (waxing and waning) pain because of periodic spasms of the ureteric smooth muscle walls trying to dislodge the blockage.
  • A constant pain is more consistent with a stone lodged in the kidney, which does not periodically contract like the ureters, or an inflammatory cause.
• Nausea and vomiting- typical of visceral organ pathology (e.g. ureteric stones, biliary colic, appendicitis)
• Restlessness- those with ureteric colic are unable to sit still and thus tend to writhe in pain
• Urinary hesitancy, reduced flow, dribbling, and incomplete voiding- ureteric obstruction
• Haematuria- 70–90% of patients with kidney/ureteric stones have haematuria (usually microscopic)

Question 11

State the signs of urinary tract calculi on physical examination and the main differential

Answer 11

• Individuals with renal or ureteric stones may have flank or loin tenderness (particularly in the costovertebral angles), but tend not to have any other abdominal signs.
• NO signs of peritonism (tenderness with guarding, eased by lying still- ie signs of peritonitis)
• Signs of systemic sepsis if there is an obstruction and infection above the stone

Leaking AAA is the main differential to consider in older men- it is possible for the pain from an AAA to be misdiagnosed as ureteric colic.

Question 12

What 6 investigations would be appropriate for a suspected renal calculi?

Answer 12

1. Urinalysis: note the presence of haematuria, white blood cells (pyuria), leucocyte esterase, and nitrites. You may also want to note the urine pH
2. Urine microscopy, culture, and sensitivity (MC&S): look for blood, evidence of infection (white cells, bacteria), and crystals
3. Urine pregmancy (exclude ectopic)- if pregnanct to USS instead of CT
4. Bloods- FBC; CRP; U+Es; serum Ca²⁺, phoshate, urate
5. CT-KUB (kidneys, ureters, and bladder)
6. Stone analysis - when removed via surgery or expelled by patient

Question 13

For each blood test performed, state why it is necessary

Answer 13

Full blood count (FBC) and C-reactive protein (CRP):

• look for a raised WCC and CRP
• indicates infection or sepsis.

Urea, creatinine, and electrolytes:

• assess renal function
• obstruction by a renal stone can precipitate renal damage.
• renal failure=medical emergency

Serum calcium, phosphate, and urate:

• valuable clues as to the aetiology of kidney stones.

Question 14

What things must you assess for on CT-KUB?

Answer 14

• Presence, size, and location of stone
• Hydronephrosis
• Perinephric stranding (indicative of inflammation or infection- appearance of edema within the fat of the perirenal space )
• Differentials- retroperitoneal tumour, AAA

Question 15

What are KUB radiographs useful for?

Answer 15

CT has a greater sensitivity and specificity than plain KUB radiographs for kidney stones, but KUB radiographs are still useful for following the progression of known stones in a way that involves less exposure to ionizing radiation

Question 16

What imaging for nephrolithiasis is used in pregnancy?

Answer 16

A magnetic resonance urogram (MRU) can be used if the patient is pregnant and therefore unsuitable for any form of ionizing radiation.

Question 17

State some differentials for urinary tract calculi

Answer 17

• Acute appendicitis
• Ectopic pregnancy
• Ovarian cyst
• Diverticular disease
• Bowel obstruction
• Acute pancreatitis- check serum AMYLASE if suspected
• Peptic ulcer disease
• Gastroenteritis
• Abdominal aortic aneurysm
• Pyelonephritis

Question 18

How should an acute presentation of renal/ureteric calculi (nephrothialisis) by managed?

Answer 18

The main goal of initial treatment for an acute stone event is symptomatic relief with hydration and analgesia/anti-emetics as needed.

1. Assess need for rescutation- Airway, Breathing, Circulation, ABC) and decide whether to admit (see next card)
2. Analgesia (e.g. paracetamol + NSAIDs)- diclofenac 75mg IV/IM or 100mg PR (IN OSCE SAY PR DICLOFENAC). If contraindicated: opioids
3. Bed rest
4. Fluid replacement – IV if unable to withstand PO
5. Urine collection to try and retrieve any stone that has passed

RULE OUT emergencies- patients with urinary calculi along with fever and other signs or symptoms of infection need emergency urological consultation for drainage and intravenous antibiotics. Failure to perform rapid renal decompression can perpetuate urosepsis and result in death.

Question 19

State the management plan for a renal calculus <5mm with no complications

Answer 19

1. Conservative management (analgesia, anti-emetics and encourage oral fluid intake).
   
   1. Ninety per cent of stones <0.5 cm pass spontaneously
   2. only 10% of larger stones do.
2. Patients should be asked to strain their urine to recover the stone for analysis.
3. You may consider adding medication to relax the smooth muscle of the ureter:
   
   • α-blocker (e.g. tamsulosin)
   • calcium-channel blocker (e.g. nifedipine).
4. ​Follow up patients after 2–3 weeks and request a plain KUB radiograph to minimize the radiation exposure of repeat CT-KUB.

Question 20

State possible management plans for a renal calculus >5mm or <5mm which has not passed in 4-6 weeks and has continuing discomfort

Answer 20

1. Lithotripsy, otherwise known as extracorporeal shock wave lithotripsy (ESWL) if small enough (renal stones <2 cm, ureteric stones <1 cm).
2. Ureterorenoscopic removal (using a fine telescope inserted via the urethra) with a dormia basket, holmium laser, mechanical lithotripsy etc., if too large for ESWL.
   
   • Note that this commonly requires a post-operative ureteric stent as it can cause ureteric stricture.
3. Percutaneous nephrolithotomy (PCNL) is rarely used nowadays as it is invasive and thus there are risks of bleeding and damage to the collecting system and neighbouring structures- performed for large, complex stones (e.g. staghorn calculi)
4. Stenting (using a JJ stent) or percutaneous nephrostomy may be performed in order to prevent hydronephrosis, if the obstruction cannot be resolved surgically.
5. Antibiotic cover if an invasive procedure is employed.

Question 21

After stone removal/expulsion, what further management must be done?

Answer 21

All patients should be advised to increase their fluid intake-

at least 2 litres of urine output daily should be recommended to help prevent future episodes of stone formation.

In addition, it is appropriate to try to identify the underlying cause

Question 22

What risk factors encourage further testing post-calculi removal?

Answer 22

Appropriate criteria for further testing could include:

• strong family history
• multiple stones at first diagnosis
• recurrent stone formation/passage

Where specific metabolic abnormalities exist and are not responsive to dietary modification, specific preventative therapies may be required

Question 23

Identify possible complications of urinary tract calculi

Answer 23

1. Ureteric stricture from the passage of the stone (or ureteroscopic removal of a stone)
2. Acute or chronic pyelonephritis, potentially leading to sepsis.
3. Renal failure, due to obstruction and back-pressure causing hydronephrosis and kidney damage.
4. Intrarenal or perinephric abscess. Abscesses may occur as a complication of pyelonephritis, particularly if there are large ‘staghorn’ stones present blocking the ureters. Pus discharges through the renal capsule into the perinephric fat. Patients present with systemic features and pyuria.
5. Xanthogranulomatous pyelonephritis. This is a type of chronic bacterial pyelonephritis characterized by the destruction of renal parenchyma and the presence of granulomas and abscesses.
6. Urine extravasation into the pelvic cavity. Although uncommon, this has severe consequences, as the combination of urine and the subsequent infection produces severe oedema, high fever, and dehydration.

Question 24

Summarise the prognosis for patients with urinary tract calculi

Answer 24

• GOOD
• However, infection of the calculus could lead to irreversible renal scarring
• Recurrence of about 50% over 5 yrs

Question 25

What radiographical findings would you look for in a patient with suspected kidney stones?

Answer 25

1. The stones themselves
2. Hydronephrosis and/or hydroureter (dilated ureters) due to obstruction
3. Perinephric fluid (stranding)

Question 26

How would patients with calcium stones be treated?

Answer 26

These may be treated in different ways depending on the presence of an underlying metabolic imbalance:

Patients with:

• hypercalciuria
  
  • investigated to exclude hyperparathyroidism.
  • treated with thiazides (which decrease renal excretion of Ca2+) and a low-calcium diet.
• hyperuricosuria
  
  • allopurinol
  • inhibits the production of uric acid during the breakdown of nucleic acids
• hypocitraturia
  
  • potassium citrate
  • citrate alkalinizes the urine and inhibits the formation of crystals

Question 27

How would patients with struvite (ammonium magnesium phosphate) stones be treated?

Answer 27

These are most common in women and are secondary to infection with a urease-producing bacteria (e.g. Proteus, Pseudomonas, Klebsiella) which can break down urea into ammonium.

Treatment of the underlying infection is indicated.

Question 28

How are urate stones treated pharmacologically?

Answer 28

Potassium urate- alkalinizes the urine- urate crystals form in the presence of acid urine,

Allopurinol- lowers urate production and subsequent excretion.

Question 29

How are cysteine stones treated pharmacologically?

Answer 29

These stones form secondary to cystinuria, a rare autosomal recessive disorder with increased cystine excretion.

• Patients should be advised to increase fluid intake as a means to diluting the urinary cystine concentration.
• As with urate stones, the solubility of cystine is pH dependent and so potassium citrate can also be given.
• Cystine-binding drugs may be given if all else fails, e.g. tiopronin.

Question 31

When should a patient with nephrothialisis be admitted as inpatient?

Answer 31

1. there is evidence of upper urinary tract infection (cloudy urine ± white cell casts, high WCC in blood, high CRP, fever) … infection proximal to an obstruction is a surgical emergency, requiring drainage;
2. there is evidence of renal failure (high creatinine, high urea, high K+);
3. there is refractory pain (despite analgesia)
4. there are bilateral obstructing stones (or a single obstructing stone if only one kidney present)
5. the patient is elderly, a child, or otherwise unwell (e.g. unable to tolerate oral fluids), for closer monitoring.