Renal calculi

Question 1

Types of stones

Answer 1

• 80% of urinary tract stones are made of calcium, as either calcium oxalate (35%), calcium phosphate (10%), or mixed oxalate and phosphate (35%)
• struvite stones* (magnesium ammonium phosphate),
• urate stones (the only radiolucent stones)
• cystine stones (typically associated with familial disorders affecting cystine metabolism- hypocystinuria).

Question 2

Symptoms on hx + exam

Answer 2

• one sided ureteric colic: sudden onset, severe, and radiating from flank to pelvis (termed “loin to groin”),
• nausea and vomiting
• Haematuria occurs in around 90% cases; this is typically non-visible.
• Concurrent infection should be assessed for, with symptoms such as rigors, fevers, or lethargy.

-Examination is typically unremarkable, only demonstrating some tenderness in the affected flank.

• bilateral/unilateral?
• associated hydronephrosis?
• signa of obstructed kidney (speric febrile)
• renal function

Question 3

DDx

Answer 3

pyelonephritis, ruptured AAA, biliary pathology, bowel obstruction, lower lobe pneumonia, or musculoskeletal related pain.

Question 4

Inv

Answer 4

-A urine dip: microscopic haematuria, as well as evidence of infection (always ensure to send a urine culture as well in such cases).

• Routine bloods should be performed, include FBC & CRP (for evidence of infection) and U&Es (to assess renal function).
• Urate and calcium levels can also aid in the assessment of stone analysis; if the patient notices they have passed the stone during micturition, retrieval of the stone and sending for analysis can also be of use.

Imaging
-Gold standard non-contrast CT scan of the renal tract (KUB).
high sensitivity and specificity in identifying stone disease, as well as concurrent assessment of any alternative pathology.

-Plain film abdominal radiographs* (not all stones are radio-opaque so limits their use, alongside their associated high radiation exposure)

-Ultrasound scans of the renal tract can often be used concurrently in cases of known stone disease, to assess for any hydronephrosis (they can also often detect renal stones, however not ureteric stones).
(Its benefits are in no radiation risk, however are often operator dependent)

*Intravenous Urograms involve taking a series of abdominal radiographs following injection of contrast, to demonstrate any filling defect; however these are rarely used due high radiation exposure and superiority of CT imaging

Question 5

Mx

Answer 5

Initial Management
-Patients with renal stones will often be dehydrated, secondary to reduced oral fluid intake +/- vomiting, so ensure adequate fluid resuscitation if required.

Most stones will pass naturally with analgesia and hydration, especially if in the lower ureter or <5mm in diameter.

• Ensuring patients have sufficient analgesia is paramount, specifically opiate analgesia and NSAIDs per rectum typically being the most effective. (diclofenac suppository)
• Any evidence of significant infection or sepsis present warrants intravenous antibiotic therapy and urgent referral to the urology team.
• Meds: Tamsulosin *Use of alpha receptor antagonists, Improves Passage of Large Ureteric Stones

-Temporary mx:
Stent Insertion or Nephrostomy
obstructive nephropathy or significant infection may warrant stent insertion or a nephrostomy. obstruction must be immediately relieved to avoid renal damage; neither options are definitive

-follow up outpatient RAC clinic

Question 6

Criteria for admission

Answer 6

Post-obstructive acute kidney injury
Uncontrollable pain from simple analgesics
Evidence of an infected stone(s)
Large stones (>5mm)
Bilateral stones

Question 7

Definitive Mx

Answer 7

If not passed spontaneously

• Extracorporeal Shock Wave Lithotripsy (ESWL) involves targeted sonic waves to break up the stone, to then be passes spontaneously. This is typically reserved for small stones (<2cm), performed via radiological guidance (either X-ray or ultrasound imaging). Contra-indications include pregnancy or stone positioned over a bony landmark (e.g. pelvis).
• Percutaneous nephrolithotomy (PCNL) is used for renal stones only, being the preferred method for large renal stones (including staghorn calculi). Percutaneous access to the kidney is performed, with a nephroscope passed into the renal pelvis. The stones can then be fragmented using various forms of lithotripsy.
• Flexible uretero-renoscopy (URS) involves passing a scope retrograde up into the ureter, allowing stones to be fragmented through laser lithotripsy and the fragments subsequently removed.

Question 8

Complications

Answer 8

infection and post-renal acute kidney injury

Recurrent renal stones can lead to renal scarring and loss of kidney function

Question 9

Management of Recurrent Stone Formers

Answer 9

• Hydrated.
• Analyse stone

Specific management options depend on the underlying stone composition:

• Oxalate stone formers should be advised to avoid high purine foods and high oxalate foods (such as nuts, rhubarb, and sesame)
• Calcium stone formers should have PTH levels checked to exclude any primary hyperparathyroidism and avoid excess salt in their diet
• Urate stone formers should be advised to avoid high purine foods (such as red meat and shellfish) and may need to be considered for urate-lowering medication (e.g. allopurinol)
• Cystine stone formers may warrant genetic testing for underlying familial disease

Question 10

Bladder stones

Answer 10

typically form from urine stasis within the bladder, hence are commonly seen in cases of chronic urinary retention. They may also occur secondary to infections (classically schistosomiasis) or as passed ureteric stones.

They will most often present with lower urinary tract symptoms and require investigation the same as for renal and ureteric stones.

Definitive management is through cystoscopy, allowing the stones to drain or fragmenting them through lithotripsy if required.

Bladder stones often occur, especially if the underlying cause is not addressed. The chronic irritation of the bladder epithelium can also predispose to the development of TCC bladder cancer.