Urinary tract calculi Flashcards
Define urinary tract calculi. What is another name for it?
Crystal deposition within the urinary tract.
Also known as nephrolithiasis.
Where along the renal tract are stones most likely to cause obstruction?
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).
State the 5 different types of renal calculi in order of fequency
- Calcium - (75–85%)- calcium oxalate, calcium phosphate, or mixed
- Struvite - (10–20%)- ammonium magnesium phosphate.
- Urate - (5–10%)
- Cystine - 1%
List the metabolic conditions that predispose to calculi formation
- Hypercalciuria
- Hyperuricosuria
- Hypocitraturia
- Hyperoxaluria
- Gout and other hyperuricaemic states e.g. malignancy, glucose-6-phosphate dehydrogenase
- (G6PDH) deficiency (urate stones)
- Cystinuria
List other medical conditions that predispose to calculi formation
- 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)
What drugs may increase risk of renal calculi formation?
- 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)
Other than drugs and conditions, what physical abnormalties may increase risk of kidney stones?
Urinary tract abnormalities
- Pelviureteric junction obstruction
- Hydronephrosis
- Ureteral stricture
- Horseshoe kidney
Foreign bodies
- Stents
- Catheters
State some environmental risk factors for kidney stones
- Low fluid intake
- Diet: chocolate, tea, rhubarb, strawberries, nuts, spinach – all increase oxalate levels
- Season: vitamin D synthesis via sunlight
Summarise the epidemiology of urinary tract calculi
- 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
State the presenting symptoms of renal calculi
- 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)
State the signs of urinary tract calculi on physical examination and the main differential
- 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.
What 6 investigations would be appropriate for a suspected renal calculi?
- Urinalysis: note the presence of haematuria, white blood cells (pyuria), leucocyte esterase, and nitrites. You may also want to note the urine pH
- Urine microscopy, culture, and sensitivity (MC&S): look for blood, evidence of infection (white cells, bacteria), and crystals
- Urine pregmancy (exclude ectopic)- if pregnanct to USS instead of CT
- Bloods- FBC; CRP; U+Es; serum Ca2+, phoshate, urate
- CT-KUB (kidneys, ureters, and bladder)
- Stone analysis - when removed via surgery or expelled by patient
For each blood test performed, state why it is necessary
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.
What things must you assess for on CT-KUB?
- 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
What are KUB radiographs useful for?
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
What imaging for nephrolithiasis is used in pregnancy?
A magnetic resonance urogram (MRU) can be used if the patient is pregnant and therefore unsuitable for any form of ionizing radiation.
State some differentials for urinary tract calculi
- 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
How should an acute presentation of renal/ureteric calculi (nephrothialisis) by managed?
The main goal of initial treatment for an acute stone event is symptomatic relief with hydration and analgesia/anti-emetics as needed.
- Assess need for rescutation- Airway, Breathing, Circulation, ABC) and decide whether to admit (see next card)
- Analgesia (e.g. paracetamol + NSAIDs)- diclofenac 75mg IV/IM or 100mg PR (IN OSCE SAY PR DICLOFENAC). If contraindicated: opioids
- Bed rest
- Fluid replacement – IV if unable to withstand PO
- 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.
State the management plan for a renal calculus <5mm with no complications
-
Conservative management (analgesia, anti-emetics and encourage oral fluid intake).
- Ninety per cent of stones <0.5 cm pass spontaneously
- only 10% of larger stones do.
- Patients should be asked to strain their urine to recover the stone for analysis.
- You may consider adding medication to relax the smooth muscle of the ureter:
- α-blocker (e.g. tamsulosin)
- calcium-channel blocker (e.g. nifedipine).
- Follow up patients after 2–3 weeks and request a plain KUB radiograph to minimize the radiation exposure of repeat CT-KUB.
State possible management plans for a renal calculus >5mm or <5mm which has not passed in 4-6 weeks and has continuing discomfort
- Lithotripsy, otherwise known as extracorporeal shock wave lithotripsy (ESWL) if small enough (renal stones <2 cm, ureteric stones <1 cm).
-
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.
- 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)
- Stenting (using a JJ stent) or percutaneous nephrostomy may be performed in order to prevent hydronephrosis, if the obstruction cannot be resolved surgically.
- Antibiotic cover if an invasive procedure is employed.
After stone removal/expulsion, what further management must be done?
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
What risk factors encourage further testing post-calculi removal?
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
Identify possible complications of urinary tract calculi
- Ureteric stricture from the passage of the stone (or ureteroscopic removal of a stone)
- Acute or chronic pyelonephritis, potentially leading to sepsis.
- Renal failure, due to obstruction and back-pressure causing hydronephrosis and kidney damage.
- 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.
- Xanthogranulomatous pyelonephritis. This is a type of chronic bacterial pyelonephritis characterized by the destruction of renal parenchyma and the presence of granulomas and abscesses.
- 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.
Summarise the prognosis for patients with urinary tract calculi
- GOOD
- However, infection of the calculus could lead to irreversible renal scarring
- Recurrence of about 50% over 5 yrs
