Renal Tract Calculi Flashcards
What is the other name given to renal tract calculi?
Renal tract stones also termed urolithiasis.
Who is commonly affected by renal tract calculi?
They are more common in males and typically affect those <65yrs.
Briefly describe the composition of renal tract calculi
Around 80% of urinary tract stones are made of calcium, as either calcium oxalate (35%), calcium phosphate (10%), or mixed oxalate and phosphate (35%)
The remaining stone compositions include struvite stones (magnesium ammonium phosphate), urate stones (the only radiolucent stones) and cystine stones (typically associated with familial disorders affecting cystine metabolism).
What composition of stone is commonly associated with staghorn calculi?
Struvite stones are often large soft stones, the most common cause of “staghorn calculi”, whereby the stone will fill the renal pelvis.
What is shown in the image?
A large staghorn calculi, as seen on plain film abdominal radiograph.
Briefly describe the pathophysiology of renal tract calculi
The basis for formation of urinary tract stones is over-saturation of urine. Certain stone types that form may also be caused by a specific underlying pathology
For urate stones, high levels of purine in the blood, either from diet (e.g. red meats) or through haematological disorders (such as myeloproliferative disease), results in increase of urate formation and subsequent crystallisation in the urine.
For cystine stones, these are typically associated with homocystinuria, an inherited defect that affects the absorption and transport of cystine in the bowel and kidneys; as citrate is a stone inhibitor, hypocitraturia from the condition can thus predispose affected individuals to recurrent stone formation.
Where is the urinary system is a stone likely to imact?
There are three natural narrowed points where stones are likely to impact:
- Pelviureteric Junction (PUJ), where the renal pelvis becomes the ureter
- Crossing the pelvic brim, where the iliac vessels travel across the ureter in the pelvis
- Vesicoureteric Junction (VUJ), where the ureter enters the bladder
What are the clinical features of renal tract calculi?
The most common presenting symptom of ureteric stone is pain, termed ureteric colic, which occurs from the increased peristalsis from around the site of obstruction. The pain is sudden onset, severe, and radiating from flank to pelvis (termed “loin to groin”), often associated with 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. There may be signs of dehydration, from reduced fluid intake secondary to associated vomiting
What investigations should be ordered for renal tract calculi?
Note: laboratory
A urine dip can show 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.
What investigations should be ordered for renal tract calculi?
Note: imaging
The gold standard for diagnosis of renal stones is a non-contrast CT scan of the renal tract (KUB). The benefit of the CT KUB as an imaging modality is the high sensitivity and specificity in identifying stone disease, as well as concurrent assessment of any alternative pathology.
Plain film abdominal radiographs (AXR) are still used in some centres for initial assessment of stone disease, however AXRs have the disadvantage that 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.
What is shown in the image?
A 3mm ureteric stone on non-contrast CT axial scan.
Briefly describe the initial management of renal tract calculi
Patients with renal stones will often be dehydrated, secondary to reduced oral fluid intake +/- vomiting, so ensure adequate fluid resuscitation if required.
For the majority of cases, renal stones will pass spontaneously without further intervention, 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.
Any evidence of significant infection or sepsis present warrants intravenous antibiotic therapy and urgent referral to the urology team.
When may patients require an inpatient stay for renal tract calculi?
The majority of renal stones can be treated in the outpatient setting. However, criteria that often warrant the need for hospital admission include:
- Post-obstructive acute kidney injury
- Uncontrollable pain from simple analgesics
- Evidence of an infected stone(s)
- Large stones (>5mm)
When is a stent insertion or nephrostomy used?
Patients with any evidence of obstructive nephropathy or significant infection may warrant stent insertion or a nephrostomy. For these patients, the obstruction must be immediately relieved to avoid renal damage; neither options are definitive, however can temporarily relieve the obstruction prior to definitive management.
What is retrograde stent insertion?
Retrograde stent insertion is the placement of a stent within the ureter, approaching from distal to proximal via cystoscopy. It allows the ureter to be kept patent and temporarily relieve the obstruction.
What is shown in the image?
AXR showing a JJ stent inserted, with associated right renal stone.
