Obstructive Renal Conditions

Renal Stones (Nephrolithiasis)

This is the presence of a stone which can get lodged somewhere in the urinary tract, usually in the 3 natural points of constriction – Pelviureteric junction (PUJ), pelvic brim and vesicoureteric junction (VUJ).

 

Risk Factors:

– Dehydration –> This increases the specific gravity of the urine increasing ion concentration

– Recurrent UTIs and foreign bodies which stagnate flow e.g. stents/catheters

– Diet –> May give hypercalcemia and certain foods also increase oxalate levels

Types of Kidney Stones

i) Calcium oxalate/phosphate:

This is the most common type. Usually due to hypercalciuria and hypercalcemia

– Increased risk from loop diuretics, steroids, acetazolamide + theophylline

Hydrochlorothiazide (calcium-sparing diuretic) is used to prevent these stones as reduces urine [Ca2+]

 

ii) Struvite (Magnesium Ammonium Phosphate):

This occurs due to infection with a urease-positive organism

– This alkalinizes the urine leading to the formation of alkaline stones and Staghorn calculi

– Therefore, method of prevention is to acidify the urine

 

iii) Uric Acid:

This is the 3rd most common, which precipitate when the urinary pH is low

– Increased risk in gout, malignancy (uric acid release) and in ileostomy, as the loss of HCO3 makes the urine more acidic, so uric acid crystals are more likely to form. This gives radio-lucent stones

Prevention: Alkalization of urine or allopurinol

 

iv) Cysteine:

This is seen in children with genetic disorders e.g. cystinuria (autosomal recessive)

Symptoms:

Writhing (colicky) pain which travels from “loin” to groin with nausea/vomiting

– Painful haematuria + proteinuria and sterile pyuria

– If left untreated, increases the chance of a UTI which gives associated symptoms

Diagnosis:

Non-contrast CT is the investigation of choice

Management:

– Analgesia –> Intramuscular diclofenac for rapid relief of pain

– Stones <5mm usually pass spontaneously, so offer pain management

– Stones >5mm – if do not pass use shockwave lithotripsy –> Uteroscopy –> Percutaneous nephrolithotomy

Complications:

Failure to remove a kidney stone can lead to a Hydronephrosis

This is a urine-filled dilatation of the renal pelvis due to obstruction

– Leads to severe flank pain and impaired kidney function (raised U&Es) and potential kidney failure

– Acute obstruction treated with nephrostomy tube    – Chronic with ureteric stent or pyeloplasty

Lower Urinary Obstructions

Lower urinary tract obstructions can be divided into acute and chronic ones:

i) Acute Obstruction:

This is often due to prostatic obstruction, infection and urethral strictures

Symptoms – Suprapubic pain and acute confusion, with a distended palpable bladder.

Management – Urethral or suprapubic catheter

 

ii) Chronic obstruction:

This occurs over time and is due to prostatic enlargement, pelvic malignancy, diabetes, surgery

Symptoms – Gives urinary frequency, hesitancy, and then terminal dribbling + overflow incontinence

Management – Treat the underlying cause –> only insert catheter if there is pain.

Renal Artery Stenosis

This is narrowing of the renal arteries, usually due to long-term atherosclerosis

– Also due to fibromuscular dysplasia, which is a non-inflammatory condition that leads to protrusions in the artery walls interrupting blood flow, seen in young females

– Poor renal blood flow then causes activation of the renin-angiotensin system in order to reabsorb water

Symptoms:

– Treatment resistant ­BP, Acute decompensated heart failure giving pulmonary oedema

Secondary hyperaldosteronism (giving raised BP, hypokalaemia and metabolic alkalosis)

Diagnosis:

1st Auscultation gives renal bruit.

2nd Doppler ultrasound of renal arteries

3rd Renal artery Arteriogram

Management:

Modification of Cardiovascular risk factors + Aspirin + Statin