Renal stones and renal hypertension
Renal causes of hypertension; renal stones and urinary obstruction
Secondary hypertension in younger patients often has a renal cause such as renal artery stenosis or parenchymal disease, or an adrenal cause. Renal stones form when urine is supersaturated, cause colic and obstruction, and obstruction anywhere in the urinary tract damages the kidney through back-pressure, especially when infected.
Secondary hypertension: clues
Young age (< 30–40), severe or resistant hypertension, sudden onset or worsening, hypokalaemia, abdominal bruit, flash pulmonary oedema, AKI after ACE inhibitor, paroxysmal symptoms.
Renal causes
- Renal parenchymal disease (commonest secondary cause): glomerulonephritis, diabetic nephropathy, adult polycystic kidney disease (AD; bilateral flank masses, haematuria, berry aneurysms, liver cysts), chronic pyelonephritis/reflux nephropathy, CKD of any cause. Mechanism: sodium and water retention, renin activation.
- Renal artery stenosis (renovascular hypertension):
- Atherosclerotic (about 90%): older patients with vascular disease; ostial/proximal stenosis. - Fibromuscular dysplasia: young women; mid-to-distal renal artery; "string of beads" on angiography; responds well to angioplasty. - Mechanism: reduced renal perfusion, then renin release, then angiotensin II and aldosterone (Goldblatt kidney). Unilateral: contralateral kidney exposed to hypertension. - Clues: abdominal (renal) bruit, asymmetric kidney size (> 1.5 cm difference), rise in creatinine (> 30%) after ACE inhibitor/ARB, flash pulmonary oedema, hypokalaemia. - Investigations: duplex ultrasound, CT or MR angiography, catheter angiography (gold standard). - Treatment: medical (statin, antiplatelet, BP control) for most atherosclerotic disease; angioplasty ± stent for fibromuscular dysplasia, flash pulmonary oedema or progressive renal failure.
- Renin-secreting tumour (juxtaglomerular cell tumour), Wilms tumour, renal compression (Page kidney), coarctation of aorta (radiofemoral delay).
Adrenal and endocrine causes
- Primary hyperaldosteronism (Conn syndrome) — commonest endocrine cause: adenoma or bilateral hyperplasia; hypokalaemia, metabolic alkalosis, high aldosterone with low renin (raised aldosterone:renin ratio); adrenal CT and venous sampling; adrenalectomy for adenoma, spironolactone for hyperplasia.
- Phaeochromocytoma: episodic headache, sweating, palpitations, hypertension; plasma/urine metanephrines; CT/MIBG; α-blockade (phenoxybenzamine) then β-blockade before adrenalectomy; "rule of 10s" (historical).
- Cushing syndrome, acromegaly, thyroid disease, hyperparathyroidism, drugs (NSAIDs, steroids, combined pill, liquorice, sympathomimetics, cocaine), OSA, pregnancy (pre-eclampsia).
Renal stones (urolithiasis)
| Stone type | Frequency | Features |
|---|---|---|
| Calcium oxalate (± phosphate) | About 75–80% | Radio-opaque; hypercalciuria (idiopathic, hyperparathyroidism), hyperoxaluria (Crohn disease/ileal resection — enteric hyperoxaluria, high-oxalate diet), hypocitraturia, low fluid intake |
| Struvite (magnesium ammonium phosphate, triple phosphate) | About 10–15% | Urease-producing bacteria (*Proteus*, *Klebsiella*) give alkaline urine; staghorn calculi; women; radio-opaque; coffin-lid crystals |
| Uric acid | About 5–10% | Radiolucent on X-ray (visible on CT); acidic urine, gout, myeloproliferative disease, chemotherapy (tumour lysis), ileostomy; dissolve with urine alkalinisation (potassium citrate) and allopurinol |
| Cystine | About 1% | Cystinuria (AR; COLA transporter); hexagonal crystals; weakly radio-opaque; positive cyanide–nitroprusside; young patients, recurrent |
| Indinavir, xanthine | Rare | Radiolucent |
- Risk factors: dehydration/hot climates (Pakistan "stone belt"), family history, metabolic disorders, urinary stasis/infection, immobility, drugs (topiramate, acetazolamide, loop diuretics, vitamin C excess).
Renal colic
- Sudden severe loin-to-groin pain, colicky, patient restless (cannot lie still — unlike peritonitis), nausea, vomiting, haematuria (microscopic in most), radiation to testis/labium (genitofemoral nerve), strangury with stones at the vesicoureteric junction.
- Stones lodge at narrowings: pelviureteric junction, pelvic brim (crossing the iliac vessels), vesicoureteric junction (narrowest).
- Investigations: urinalysis, renal function, calcium, urate; non-contrast CT KUB (investigation of choice — about 99% sensitive); ultrasound in pregnancy and children; KUB X-ray for follow-up of radio-opaque stones.
- Differentials: ruptured AAA (older men — must exclude), appendicitis, ectopic pregnancy, pyelonephritis, biliary colic, testicular torsion.
- Treatment: NSAIDs (diclofenac IM/PR — first line analgesia), antiemetics; medical expulsive therapy with tamsulosin for distal ureteric stones 5–10 mm.
- Spontaneous passage likely: < 5 mm (most pass), 5–10 mm (some).
- Intervention: stones > 10 mm, failure to pass, uncontrolled pain, AKI, solitary kidney, infection — ESWL (renal and upper ureteric stones < 2 cm; avoid in pregnancy, coagulopathy, AAA), ureteroscopy with laser lithotripsy (ureteric stones, pregnancy), percutaneous nephrolithotomy (PCNL — staghorn/large renal stones > 2 cm), open surgery rarely.
- Obstructed infected kidney (fever + obstruction): urological emergency — urgent decompression by nephrostomy or ureteric (JJ) stent, IV antibiotics; definitive stone treatment later.
- Prevention: fluids > 2.5–3 L/day, reduce salt and animal protein, normal calcium diet (low-calcium diets increase oxalate absorption), thiazides for hypercalciuria, potassium citrate, allopurinol.
Urinary tract obstruction
- Causes by level:
- Intraluminal: stones, blood clot, sloughed papilla (papillary necrosis: diabetes, analgesics, sickle cell, pyelonephritis), tumours (transitional cell carcinoma). - Mural: pelviureteric junction obstruction (congenital — intermittent loin pain after drinking/alcohol), ureteric strictures (TB, schistosomiasis, post-surgery, radiation), neuropathic bladder, posterior urethral valves (boys), urethral stricture. - Extramural: benign prostatic hyperplasia (commonest in older men), prostate cancer, cervical and pelvic cancers, retroperitoneal fibrosis (methysergide, IgG4 disease — medial deviation of ureters), pregnancy, aberrant vessels, accidental ureteric ligation (hysterectomy).
- Pathology: back-pressure leads to hydronephrosis (pelvicalyceal dilatation), cortical thinning, tubular atrophy; infection in stagnant urine accelerates damage (pyonephrosis).
- Features: upper tract — loin pain, palpable kidney, AKI if bilateral or solitary kidney; lower tract — hesitancy, poor stream, retention; post-obstructive diuresis after relief (monitor fluids and electrolytes).
- Investigations: ultrasound (hydronephrosis), CT urogram, MAG3 renogram (functional obstruction, split function), cystoscopy, urodynamics.
- Treatment: relieve obstruction (catheter, nephrostomy, stent), treat cause (pyeloplasty for PUJ obstruction, TURP, stricture surgery).
- Acute urinary retention: painful, palpable bladder; BPH, drugs (anticholinergics, opioids), constipation, post-operative, spinal cord compression; catheterise, α-blocker before trial without catheter. Chronic retention: painless, high residual volume, overflow incontinence, risk of renal impairment (high-pressure).
How FCPS asks it
Recalls test: clues to secondary hypertension; commonest renal and endocrine causes; atherosclerotic versus fibromuscular RAS (age, sex, site, string of beads); creatinine rise with ACE inhibitor; Conn syndrome biochemistry; phaeochromocytoma preparation; commonest stone type; struvite and Proteus; radiolucent uric acid stones; cystine hexagonal crystals; enteric hyperoxaluria; sites where stones lodge; CT KUB; AAA as a differential; tamsulosin for distal stones; stone size and passage; ESWL versus ureteroscopy versus PCNL; obstructed infected kidney emergency; causes of obstruction by level; post-obstructive diuresis.
Exam trap Calcium oxalate is the commonest stone; uric acid stones are radiolucent.
Exam trap An obstructed, infected kidney needs urgent decompression by nephrostomy or stent.
Exam trap Fibromuscular dysplasia affects young women, producing a string-of-beads renal artery.
Test yourself on this topic
5 of the 16 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 28-year-old woman has BP 180/110 resistant to three drugs and a bruit in the right upper abdomen. Angiography shows a 'string of beads' appearance in the mid renal artery. What is the cause?
Answer: Fibromuscular dysplasia
Fibromuscular dysplasia is a non-atherosclerotic, non-inflammatory disease of medium arteries, usually affecting young women. In the renal artery it causes stenosis with a beaded appearance in the mid to distal artery, leading to renin-mediated hypertension. It responds well to balloon angioplasty, often curing the hypertension. Atherosclerotic stenosis affects older patients at the ostium.
Fibromuscular dysplasia
- Young woman
- Mid-artery string of beads
- Renin-driven hypertension
- Treat: angioplasty
Remember Young woman, resistant BP, bruit: FMD.
Exam trap ACE inhibitors can cause AKI with bilateral renal artery stenosis.
Why the other options are wrong
- Atherosclerotic renal artery stenosis Older patients; affects the origin.
- Polyarteritis nodosa Causes microaneurysms in a systemic illness.
- Takayasu arteritis Affects the aorta and its branch origins.
- Renal vein thrombosis Does not cause this appearance.
At which site does a ureteric stone most commonly lodge?
Answer: Vesicoureteric junction
The ureter has three natural narrowings: the pelviureteric junction, where it crosses the pelvic brim over the iliac vessels, and the vesicoureteric junction, which is the narrowest and the commonest place for a stone to stick. Stones under 5 mm usually pass. Pain moves from loin to groin and, at the VUJ, can cause urinary frequency and pain at the tip of the penis.
Ureteric narrowings
- 1. Pelviureteric junction
- 2. Crossing iliac vessels
- 3. Vesicoureteric junction (narrowest)
- <5 mm: usually passes
Remember The last gate, at the bladder, is the tightest.
Exam trap The VUJ is the narrowest point of the ureter.
Why the other options are wrong
- Pelviureteric junction A narrowing, but less common.
- Where the ureter crosses the iliac vessels A narrowing, but less common.
- Mid-ureter at L3 Not a natural narrowing.
- Renal calyx Stones form here but are not obstructing the ureter.
A 22-year-old woman has BP 165/100 mmHg. She had many urinary infections with fever as a child. Ultrasound shows small, irregular kidneys with cortical scars over deformed calyces at both poles. Urine shows proteinuria but no casts. What is the most likely cause of her hypertension?
Answer: Reflux nephropathy
Vesicoureteric reflux in childhood allows infected urine to reach the kidney. Compound papillae, found mainly at the poles, allow intrarenal reflux, so the scarring characteristically lies over clubbed calyces at the upper and lower poles. The scarred kidney produces excess renin and loses nephrons, causing hypertension and proteinuria in young adults and sometimes chronic kidney disease. It is an important renal cause of hypertension in the young.
Reflux nephropathy
- Childhood VUR + infection
- Scars over clubbed calyces at poles
- Compound papillae allow intrarenal reflux
- Young-onset hypertension
Remember Young hypertensive with childhood UTIs: look for scars.
Exam trap Scars from childhood reflux remain even after the reflux itself has resolved.
Why the other options are wrong
- Fibromuscular dysplasia Narrows the renal artery but does not scar the cortex over calyces.
- Primary hyperaldosteronism Gives hypokalaemia with normal kidneys on imaging.
- Polycystic kidney disease Gives large kidneys full of cysts.
- Coarctation of the aorta Gives radio-femoral delay and normal kidneys.
A 40-year-old woman has had right loin pain for 3 days and now has fever 39.5 °C, rigors, pulse 124/min and BP 85/50 mmHg. Her white cell count is 21 × 10⁹/L, and CT shows a 9 mm stone at the right pelviureteric junction with a dilated right renal pelvis. What is the most important next step after starting antibiotics?
Answer: Urgent drainage by nephrostomy or stent
An obstructed, infected kidney is a urological emergency. Pus under pressure in the collecting system cannot drain, antibiotics cannot reach adequate levels in it, and bacteria enter the bloodstream, causing septic shock and rapid loss of the kidney. Urgent decompression by percutaneous nephrostomy or retrograde ureteric stent is needed. The stone itself is treated later, once the infection has settled.
Infected obstructed kidney
- Stone + infection + obstruction
- Antibiotics alone fail
- Urgent nephrostomy or stent
- Treat stone later
Remember Pus under pressure must be drained.
Exam trap Fever with renal colic changes management from waiting to emergency drainage.
Why the other options are wrong
- Medical expulsive therapy with tamsulosin Not appropriate when the kidney is infected and obstructed.
- Shock wave lithotripsy within 24 hours Contraindicated in active infection; it can worsen sepsis.
- Repeat imaging in 48 hours Delay risks death and loss of the kidney.
- Increase oral fluid intake Does not relieve the obstruction.
Kidney stones are particularly common in labourers working outdoors in the hot summers of Sindh and Punjab. Which of the following is the main reason?
Answer: Low urine volume from sweating
Heavy sweating in a hot climate, without enough fluid replacement, lowers urine volume and concentrates the solutes in it. Urine becomes supersaturated with calcium oxalate and uric acid, and crystals form and grow into stones. This is why stone disease is so common in hot regions such as the Afro-Asian 'stone belt'. The most effective preventive measure is enough fluid to pass at least 2 to 2.5 litres of urine a day.
Stones and climate
- Sweating: low urine volume
- Urine supersaturated
- Calcium oxalate, uric acid stones
- Prevent: 2–2.5 L urine a day
Remember Concentrated urine makes stones.
Exam trap Cutting dietary calcium increases oxalate absorption and can increase stone formation.
Why the other options are wrong
- High dietary calcium intake Normal dietary calcium actually reduces oxalate absorption and stone risk.
- Excess sunlight-induced vitamin D Has only a small effect compared with dehydration.
- Frequent urinary infections Cause struvite stones in a minority.
- Inherited cystinuria Rare; it does not explain a regional excess.
Where this sits in the CPSP syllabus
- Surgery & Allied, Paper 2: Vascular and renal pathology, Renal causes of hypertension; renal stones and obstruction
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