Kidney Stones Flashcards
Describe the location of the kidneys and anatomical significance of the fascia
- between T12-L3
- contains Gerota’s fascia (incomplete inferiorly - risk for haemorrhage!)
Describe the 3 segments of the ureters
- proximal: pelviureteric junction to the pelvic brim
- mid: segment over the sacral bone
- distal: lower sacral border to urine output
What are the 4 layers of the ureters?
- urothelial mucosa
- lamina propria
- muscular layer
- adventitial layer
Where are the physiological narrowings of the ureter and the clinical significance of it?
- pelviureteric junction
- crossing of the iliac vessels at the pelvic brim
- vesicoureteric junction (where ureter joins the bladder)
- where calculi are likely to obstruct
- can limit flexi/rigid ureteroscopies
What intrinsic factors increase the likelihood of renal stones?
- sex (men)
- age (20-50)
- family history
- genetics (more prevalent in caucasian and asian)
- comorbidity factors
What extrinsic factors increase the likelihood of renal stones?
- fluid intake (<1200ml/day)
- diet (high animal protein, salt, low calcium)
- lifestyle (sedentary)
- climate (summer = increases urinary conc.)
- country (eg. USA)
What are renal stones commonly composed of?
- calcium oxalate (80-85%)
- uric acid (5-10%)
- calcium phosphate/calcium oxalate (10%)
How are calcium renal stones formed?
- excess of oxalate
- commonly found in fruit, vegetables, nuts and chocolate
How are uric acid renal stones formed?
- chronic dehydration
- increased risk in those with gout, genetic risk, or a high protein diet
What is the metastable state and what will occur at this point?
- metastable state is when the concentration of the solute in the urine increases past its solubility product level
results in:
- Crystal growth and aggregation
- inhibitors will inhibit crystallisation
- matrix may become involved
- new stones not usually formed in this state
At what point will renal stones form?
- when concentration of a solute in urine exceeded the formation product which results in nucleation and inability of the inhibitors to prevent crystallisation of stones
- nucleation is when the crystals begin to compound together and initiate stone formation which is driven by the supersaturation of the urine with solute
Describe the free-particle model of renal stone formation
- the crystals will increase in size and aggregate within the urine of the collecting tubules
- they will enlarge and a critical particle will become trapped blocking urine outflow from tubular openings promoting the formation of smaller stones
Describe the fixed-particle model of renal stone formation
- stones formed attach to damaged areas of the tubular wall allowing for initiation of stone formation
- this allows further aggregation of crystals
What are factors that promote stone formation?
- low volume
- low pH
- low citrate and magnesium
- high uric acid
- high calcium
- high oxalate
Describe the clinical presentation of renal stones
- incidental on imaging
- pain (colic, radiates from loin to groin, cannot settle)
- haematuria
- sepsis/infection
What is the gold standard initial investigation for renal stones?
CT KUB (CT of kidneys, ureters and bladder)
- allows measurement of stone diameter, skin to stone distance
- low radiation dose and no contrast required
What is the pharmacological treatment of renal stones?
- NSAIDs to reduce pain due to reduced glomerular filtration, renal pressure and ureteric peristalsis
- weak opiates?
When is admission to secondary care required for renal stones?
- uncontrollable pain
- fever or signs of sepsis
- solitary kidney with ureteric stone
- bilateral ureteric stones
- renal failure caused by a renal stone obstruction
What are the possible differentials of renal stones?
- AAA
- appendicitis
- gynae pathologies
What are the emergency surgical options for renal stones?
- nephrostomy (anterograde) percutaneously by interventional radiology
- retrograde ureteric stent, requires GA
What are elective surgical options for renal stones?
- ureteroscopy and basket
- ureteroscopy and fragmentation
- flexible ureteroscopy (FURS)
- extracorporeal shockwave lithotripsy (ESWL)
- percutaneous nephrolithotomy (PCNL) = for larger removals by creating tract into renal pelvis
Describe the process of ESWL for renal stones
- produces a shock wave to break stone by shearing, spalling or cavitation = shockwave produces a bubble which expands from surrounding gas particles, when the bubble collapses it causes pitting of the stone surface
- uses electro hydraulic, electromagnetic or piezoelectric shockwaves
- only requires mild analgesia
What is staghorn calculi?
- branched renal stones that fill part or all of the renal pelvis and branch into several or all of the calyces
- tend to be formed of struvite (magnesium ammonium phosphate)
- requires PCNL
