Urinary Stones

Exam Cram

• Urinary stones form when urinary compounds crystallize, within the urinary system

• Presentation: unilateral loin to groin pain with blood on urine dip

• Diagnosis: CT KUB

• Management: NSAIDS, morphine + intervention based upon size

Outline

Background

• The burden of disease from urinary stones is greater than bladder cancer, in part due to their increasing prevalence from poor diet

• Urinary stones are also renal calculi or renal/ bladder stones

Assessment

History

• Renal colic: 

  • Severe sudden onset sharp loin-groin pain

  • Lasts c. 40 mins

• Patients pace during pain

Examination

• Tachycardic, hypertensive

• Febrile if infected stone

Investigations

• CTKUB: 95% sensitivity & specificity

• Urea and creatinie- ?obstructive stone

• Septic screen ?infected stone- urine & blood cultures, FBC, CRP

• Stone analysis ?type

Diagnosis and Classification

Diagnosis: usually image finding on CTKUB (also if passed can be on stone retrieval or if missed, clinically)

Differentials: AAA, pyelonephritis, pancreatitis, ectopic pregnancy

Classification

• Aetiology: stone type, first or recurring

• Severity: stone size + complications (infection, obstructive AKI)

• Site: bladder, ureteric, renal

Acute Management

1. Stone Management: PCNL, ureteroscopy, lithotripsy or watch and wait

2. Analgesia: PR diclofenac, regular paracetamol, opioids (e.g. morphine PO 5mg)

3. Urinary Stones MDT

4. Further investigations: stone analysis, AXR- ?stone radio-opaque

Types of Urinary Stones

Calcium Oxalate

• Most common urinary stone

• Associations: metabolic syndrome, short gut syndrome, thiazide diuretics, high protein diet

• Radio-opaque

• Secondary prevention

  1. Low oxalate diet & measure 24hr urinary calcium

  2. Calcium citrate (potassium citrate comparable)

  3. Thiazide diuretic

Ammonia

• Staghorn calculus

• Associated with proteus infection

• Also called magnesium phosphate

Cystine

• Radiolucent

• 2% of urinary stons

• Prophylaxis: penicillamine, low methionine diet

Urate

• Associated with hyperuricemia in gout & treatment for hematologic malignancies

• Prophylaxis

  1. Low purine diet

  2. Allopurinol + potassium citrate

Calcium phosphate

• Associated with Renal tubular acidosis I

Admission Cycle

Renal Colic Assessment

1. Urine dip: sensitivity 90%, poorly specific

2. CTKUB

3. Septic screen: urine & blood cultures, consider CXR & covid PCR

4. Baseline bloods- FBC, UEs, LFTs, CRP; 

5. Differentials: Lactate, bHCG, amylase,

6. Analgesia: PR diclofenac, regular paracetamol, opioids (e.g. morphine PO 5mg)

7. Antibiotics if infected, slow IVF if AKI

A negative urine dip makes a urinary stone significantly less likely but not impossible. 

CT-Angio, CTAP with contrast and Renal USS can be considered, see Surgical Registrar secton below. 

Disposition

Key factors determining disposition:

1. Stone characteristics: size, type, number

2. Symptom burden

3. Complications: 

   • Urosepsis/ infected stone

   • Obstruction / AKI

4. Baseline / PMH 

   • Single vs two kidneys

   • Social setting

Likely requires admission 

• Stone > 6mm

• Evidence of infection or obstruction (hydronephrosis)

• Highly symptomatic

• Single kidney, immunocompromised, frailty

Acute Surgical Management

By size: 

0-6 mm     Watch and wait Note tamsulosin has been shown to be ineffective and is no longer prescribed. 

<10 mm Lithotripsy

0-8-12 mm Ureteroscopy

12mm+ Percutaneous nephrolithotomy (PCNL)

Complications

1. Sepsis

An infected stone requires urine culture and IV antibiotics (Gentamicin). It can be difficult to differentiate an inflammatory from an infective response. 

2. AKI

If AKI is present, this requires admission and prompt surgical intervention, usually ureteroscopy. 

3. Hydronephrosis

This often requires a repeat ultrasound scan at 6 weeks to ensure resolution. 

Discharge planning

1.  Blood serum urate and calcium levels ?cause

2.  AXR

3. Referral to stone MDT for follow up

4. Urine sieve + stone analysis

The Urology Stone MDT varies per department but usually includes the urology stone specialist +/- radiologist and metabolic expert. Function:

• Follow up requirement: urology vs metabolic/ biochemist

• Future management planning in complex cases

Long Term Management

Outcomes

• Reduce recurrence of urinary stone

• Prevent Chronic Kidney Disease: renal parenchymal scarring, nephrectomy

Lifestyle:

• Water intake:  2-3 litres/ day

• Reduce fizzy drinks

• Balanced diet

Medical management (as per stone type)

mED rEG Notes

Why use AXR in urinary stones?

If the stone is observed on abdo XR, this in the future AXR can be used rather than CTKUB to track the stone. 

What is Renal colic

Colicky pain occurs when there is a blockage to a tube and the tube contracts to dislodge the blockage. The pain is usually in waves and spasmodic as the tube contracts. The GI tract or biliary tract can produce colicky pain if obstructed in constipation or cholecystitis. 

Bilateral Renal Stones 

These are possible and a surgical emergency due to the risk of kidney failure. These require immediate surgical decompression. 

It is much more common to have bilateral nephrolithiasis. 

Myth busting: 10%

• 10% stones are painless

• 10% stones don't produce blood on urine dip

CTKUB vs CT-Angio, CTAP with contrast or Renal USS

Some consultants I've worked with, use contrast for all renal colic presentations to look for pyelonephritis. I heard of one who'd use a CT angio to rule out a AAA for all renal colic patients. Some departments insist on a renal ultrasound prior to look for a stone and negate the requirement for a CTKUB. 

The UK royal college of radiology recommends CTKUB firstly for renal colic presentations and these should be done within 24hrs. 

CTKUB vs CTAP 

CTKUB is a CTAP non contrast, a CTAP is usually with contrast. 

Pregnancy

CT's have significant radiation burden causing cancer to neonate and mother. Therefore in those pregnant and under 40 years a renal ultrasound is usually first line. 

Further Reading

Stones

The common phrase I have heard is renal stones because they do usually form in the kidney. I have called this page urinary stones because they can rarely form in the bladder and I enjoy being pedantic :p

Urinary stones Stones formed in the urinary tract

Renal stones Stones located in the kidney 

Bladder stones Stones located in the kidney (usually a stone formed in the kidney that moves into the bladder would be referred to as a bladder stone so current location denotes name > location of formation)

Calculi Synonymous with stone

Staghorn calculi Type of stone that forms in the renal pelvis, that fills the whole renal pelvis taking the form of a staghorn; these require PCNL

Procedures

Knowing the anatomy of the urinary system can be helpful. 

PCNL Percutaneous nephrolithotomy:  cutting through the skin (usually in the back) and sticking a tube into the kidney to remove the stone

Percutaneous = through the skin

Nephro = kidney

Lith = stone

-otomy = removal

Retrograde Direction of travel of instrument with respect to the flow of urine. Retrograde is swimming upstream (like a salmon). All ureteroscopy is upstream through the urethra, bladder and then ureter. 

Anterograde Moving from the kidney down the ureters. A stent could be inserted anterogradely from the renal pelvis into the ureter. 

Nephrostomy Tube into kidney that drains urine into a catheter bag. It is like a stoma for urine but it drains urine straight from the kidney

Urostomy Is a bag with urine, (like a colostomy is a bag with colon contents). Urostomies is the umbrella term for any bag connected to the urinary tract/ hence containing urine .

Foley catheter Foley catheter is a standard catheter that is an artificial urethra. It is a tube that is inserted into the bladder via the urethra and drains urine. 

IDC In dwelling catheter

TWOC Trial without catheter (clinic for individuals with urinary retention and catheters in situ to attend, remove the catheter and see if they can urinate 

Ureteroscopy Ureter + scopy, scopy = scope or camera, therefore this is putting a camera into your ureter

Cystoscopy Cyst = bladder, scopy = camera. Camera into bladder, this can be rigid or flexible. 

Comparison with Biliary Stones

The other place stones form are in the biliary tree and are an obvious comparison. The management is relatively different, renal stones largely use a wire to fish out the stone (ureteroscopy). Biliary stones can use an ERCP to fish out the stone if it accessible but largely rely on a cholecystectomy (removal of the gallbladder).  Why is this? ERCP can release stones from the common bile duct but it cannot reach into the cystic duct because it is too small. The majority of gallstones stay in the gallbladder and removal of the gallbladder is safe,  in contrast a removal of the kidney for urinary stones (nephrectomy) is rare. 

Stones form in fluids: urine, bile and in the lymph within the inner ear, causing BPPV. They do not appear to form in CSF or in the lymphatic system (to the best of my knowledge and I do not know why, perhaps it would be quickly fatal. Blockages form in blood (thrombus, fat/ air embolus) and bowel (tumor, fecalith). 

Recently renal stones were found to have a higher population morbidity than renal cancer or bladder cancer. Rates of urinary stones are increasing (in part due to the obesity/ metabolic syndrome epidemic) and have a reportedly lifetime prevalence of 10% (which is incredible) [2]. Urinary stones are well defined structural that are generally well managed with most individuals making a full recovery.  They usually produce severe pain- distressing enough for patients report to hospital promptly, the pain is usually recognisable for clinicans, CTKUB is an available excellent test and the management is highly effective in removing the stones. 

References and Resources

1. Baus.org.uk. 2022. Kidney stones. [online] Available at: <https://www.baus.org.uk/patients/conditions/6/kidney_stones/> [Accessed 3 October 2022]. 

2. Whitehurst, L., Jones, P. and Somani, B., 2018. Mortality from kidney stone disease (KSD) as reported in the literature over the last two decades: a systematic review. World Journal of Urology, 37(5), pp.759-776. Available at: <https://pubmed.ncbi.nlm.nih.gov/30151599/> [Accessed 3 October 2022]. 

3. https://www.rcr.ac.uk/career-development/audit-quality-improvement/auditlive-radiology/radiological-investigation-in-acute-renal-colic/#:~:text=CT%20KUB%20is%20the%20most,dose%20CT%20KUB%20Ref%2010).

Written 2022.