60 STONES IN UROLOGY

# 61 STONES IN UROLOGY

Detailed notes

Urolithiasis is one of the most frequently examined urology topics in MRCS Part A. The lifetime risk is around 10–15%, with a male-to-female ratio of roughly 3:1, and peak incidence in the third to fifth decade. Most stones form in the kidney and become symptomatic only when they migrate into the ureter and impact at a narrowing.

Clinical presentation

The textbook story is sudden-onset, severe, colicky "loin-to-groin" pain, often with the patient writhing in pain (in contrast to peritonitis, where patients lie still). Associated features:

- Microscopic or macroscopic haematuria (>90% on urinalysis)

- Nausea and vomiting (shared coeliac plexus innervation with the gut)

- Restlessness, pallor, sweating

- Referred pain to the ipsilateral testis or labium as the stone descends

- Strangury and suprapubic discomfort if the stone reaches the VUJ

The pain is visceral. Ureteric afferents travel with sympathetic fibres through T11–L2, which explains why pain refers from the flank (T11–T12 dermatomes) down to the groin and scrotum/labium (L1–L2, ilioinguinal and genitofemoral territories) as the stone migrates distally.

Three sites of impaction

Stones lodge where the ureter is anatomically narrowest:

Site	Location	X-ray landmark
Pelviureteric junction (PUJ)	Renal pelvis meets ureter	L2 transverse process
Pelvic brim	Ureter crosses common iliac vessels	Sacroiliac joint
Vesicoureteric junction (VUJ)	Ureter enters bladder — narrowest point	Ischial spine

The VUJ is the single most common site of impaction and the favourite MRCS distractor.

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Stone composition

Knowing stone types is high-yield because each has a characteristic patient, urinary pH, radiographic appearance and underlying metabolic cause.

Stone	Frequency	Radiography	Urine pH	Key associations
Calcium oxalate	~80%	Radio-opaque	Variable	Hypercalciuria, hyperoxaluria, hypocitraturia; spinach, rhubarb, tea
Calcium phosphate	~10%	Radio-opaque	Alkaline	Hyperparathyroidism, renal tubular acidosis
Struvite (Mg-ammonium-phosphate)	~10%	Radio-opaque	Alkaline (>7)	Urease-producing organisms (Proteus, Klebsiella, Ureaplasma); women; staghorn
Uric acid	5–10%	Radiolucent	Acidic (<5.5)	Gout, high-purine diet, tumour lysis, chemotherapy
Cystine	1–2%	Semi-opaque ("ground-glass")	Acidic	Cystinuria (autosomal recessive defect in tubular reabsorption of COLA — Cystine, Ornithine, Lysine, Arginine); hexagonal crystals; young patients

👩‍⚕️ Only uric acid stones are truly radiolucent on plain film — but all stones (including uric acid) are visible on CT-KUB. This is exactly why CT replaced IVU as the gold standard.

👩‍⚕️ Struvite stones form only in alkaline urine. Urease splits urea into ammonia, which raises the pH and precipitates Mg-ammonium-phosphate. If a stone forms in a UTI, think Proteus.

Underlying metabolic causes

➡ Idiopathic hypercalciuria — by far the commonest cause of recurrent calcium oxalate stones in adults; serum calcium is normal.

➡ Primary hyperoxaluria — rare autosomal recessive enzyme defect; recurrent calcium oxalate stones in children/young adults, systemic oxalosis, renal failure.

➡ Primary hyperparathyroidism — hypercalcaemia → hypercalciuria; think "stones, bones, abdominal groans, psychiatric moans".

➡ Cystinuria — autosomal recessive; suspect in a young patient with recurrent stones and a positive family history.

➡ Gout / tumour lysis / chemotherapy — uric acid stones; prevent with allopurinol and urinary alkalinisation.

Investigations

- Urinalysis — haematuria (>90%), nitrites/leucocytes if infection, urinary pH (acid → uric acid/cystine; alkaline → struvite/Ca phosphate)

- Bloods — U&Es, calcium, urate, FBC, CRP

- CT-KUB (non-contrast) — gold standard. Sensitivity and specificity >95%. No contrast required. Identifies stone, location, size, and degree of hydronephrosis.

- Ultrasound — first-line in pregnancy and children to avoid radiation; also useful for hydronephrosis. Misses small mid-ureteric stones.

- Plain KUB X-ray — useful for follow-up of known radio-opaque stones, but not for diagnosis.

Management

Acute analgesia

- NSAIDs (PR diclofenac) — first-line. They reduce ureteric smooth muscle contraction and glomerular filtration pressure, easing pain more effectively than opioids in renal colic.

- Opioids are second-line.

- IV fluids and antiemetics as needed.

Definitive management by size and location

Scenario	Management
<5 mm, uncomplicated	Conservative — >80% pass spontaneously; hydration + analgesia
5–10 mm distal ureteric	Medical expulsive therapy with tamsulosin (α-blocker relaxes distal ureter)
<2 cm, not in lower pole	ESWL (extracorporeal shock wave lithotripsy)
<2 cm, ureteric or lower pole	Ureteroscopy + laser lithotripsy
>2 cm or staghorn	PCNL (percutaneous nephrolithotomy)

👩‍⚕️ ESWL contraindications: pregnancy, anticoagulation/coagulopathy, AAA, active infection, distal obstruction. A common SBA trap — the patient with a stone and a UTI cannot have ESWL.

Surgical emergency: obstructed infected kidney

A stone obstructing a kidney that is also infected is a urological emergency. Pus under pressure in a closed system causes rapid sepsis and irreversible renal damage. The kidney must be decompressed within hours.

- Distal stone (VUJ / lower ureter) → retrograde JJ stent via cystoscopy

- Proximal stone (PUJ / upper ureter) or failed retrograde → percutaneous nephrostomy

Definitive stone treatment is delayed until the infection has been treated.

Prevention

- Hydration: 2–3 L/day — single most effective intervention

- Low sodium diet (reduces urinary calcium excretion)

- Normal calcium intake (paradoxically — low calcium increases oxalate absorption)

- Low oxalate foods if oxalate stones

- Low animal protein (reduces acid load and urinary calcium)

- Increase citrate (lemon juice, potassium citrate — inhibits crystallisation)

- Allopurinol for recurrent uric acid stones; urinary alkalinisation with potassium citrate

[Image: MCQs banner]

Test yourself

A man has left loin colicky pain. Imaging shows a stone at the vesicoureteric junction. Where is it seen?

• ((Ischial tuberosity::Too inferior — sits at the perineum, not the VUJ.))
• ((Ischial spine::☑️ VUJ projects at the ischial spine — the narrowest point of the ureter.))
• ((Sacroiliac joint::Landmark for the pelvic brim, where ureter crosses common iliac vessels.))
• ((L2 transverse process::Landmark for the PUJ, not the VUJ.))

👩‍⚕️ Three sites, three landmarks: PUJ = L2 TP, pelvic brim = SI joint, VUJ = ischial spine.

A 16-year-old presents with sudden loin-to-groin pain and haematuria, with no history of trauma. Diagnosis?

• ((Wilms tumour::Younger children; presents as a painless abdominal mass, not colic.))
• ((Ureteric stone::☑️ Classic loin-to-groin colic with haematuria — even in adolescents.))
• ((Pyelonephritis::Fever, rigors and systemic upset rather than colic.))
• ((Bladder rupture::Requires major trauma; absent here.))

A patient has a ureteric stone with pain radiating to the groin. Which nerve roots are responsible?

• ((S2–S4::Sacral roots — pelvic floor and perineum.))
• ((L3–L4::Anterior thigh dermatomes, not the ureter.))
• ((T11, T12, L1, L2::☑️ Ureteric visceral afferents travel with sympathetics from T11–L2.))
• ((T6–T8::Upper abdominal viscera (foregut), not ureter.))

A man presents with tearing left loin-to-groin pain. CT shows a radio-dense ureteric stone. Which composition?

• ((Calcium phosphate::Radio-opaque but accounts for only ~10% of stones.))
• ((Calcium oxalate::☑️ ~80% of stones — the default answer for a radio-opaque urolith.))
• ((Cystine::Semi-opaque, "ground-glass"; hexagonal crystals in young patients.))
• ((Struvite::Radio-opaque but infection-related and typically staghorn.))
• ((Uric acid::Radiolucent on plain film; visible only on CT.))

A 32-year-old has recurrent calcium oxalate stones. Most likely underlying cause?

• ((Hyperparathyroidism::Would expect hypercalcaemia and systemic features.))
• ((Urinary tract infection::Associated with struvite, not oxalate stones.))
• ((Hypoparathyroidism::Low calcium — does not cause calcium stones.))
• ((Idiopathic hypercalciuria::☑️ Commonest metabolic cause of recurrent CaOx stones in adults; serum calcium normal.))

A 24-year-old has recurrent loin-to-groin pain since childhood; X-ray shows multiple calcium oxalate kidney stones. Diagnosis?

• ((Proteus infection::Would cause struvite stones, not oxalate.))
• ((Urinary tract infection::Causes struvite stones.))
• ((Primary hyperoxaluria::☑️ Autosomal recessive enzyme defect — recurrent CaOx stones from childhood, systemic oxalosis.))
• ((Idiopathic hypercalciuria::Typical of adults; less likely with onset in childhood.))

👩‍⚕️ Adult onset = idiopathic hypercalciuria; childhood onset / family history = primary hyperoxaluria.

A 47-year-old woman has loin pain, haematuria and a Proteus UTI. X-ray shows a staghorn calculus. Most likely composition?

• ((Calcium oxalate::Commonest stone overall but not staghorn and not infection-related.))
• ((Calcium phosphate::Can co-exist but staghorns are classically struvite.))
• ((Struvite::☑️ Mg-ammonium-phosphate; forms in alkaline urine from urease-producing bacteria (Proteus, Klebsiella).))
• ((Uric acid::Radiolucent and never staghorn-shaped.))

A patient has an 8 mm stone at the VUJ with pyrexia and upstream hydroureter. Management?

• ((Cystoscopy with retrograde JJ stent::☑️ Distal obstructed-infected kidney — drain via JJ stent.))
• ((ESWL::Contraindicated in active infection and obstruction.))
• ((Conservative management::Sepsis + obstruction demands urgent decompression.))
• ((PCNL::Definitive treatment delayed until infection controlled.))

A 45-year-old has a stone at the L2–L3 level with hydronephrosis, severe pain and fever. Management?

• ((ESWL::Contraindicated with active infection.))
• ((PCNL::Definitive treatment, not used during acute sepsis.))
• ((Percutaneous nephrostomy::☑️ Proximal (PUJ) obstructed-infected kidney — retrograde stenting is difficult; nephrostomy decompresses fastest.))
• ((Ureteroscopy::Hard to reach proximal stones safely in an infected obstructed system.))

👩‍⚕️ Distal stone = JJ stent; proximal stone = nephrostomy. Definitive treatment waits until sepsis resolves.

A 35-year-old has colicky flank pain; CT-KUB shows a 3 mm ureteric stone. He is otherwise well with no signs of infection. Initial management?

• ((Conservative — analgesia and fluids::☑️ Stones ≤5 mm pass spontaneously in >80% of cases.))
• ((Ureteroscopy::Reserved for larger or persistent stones.))
• ((ESWL::Not first-line for small, uncomplicated stones.))
• ((Percutaneous nephrostomy::Far too invasive without obstruction or infection.))

A 52-year-old man has a 4 mm ureteric stone with mild ureteric dilation. Most appropriate management?

• ((Conservative management::☑️ First-line for stones <5 mm without complications.))
• ((JJ stent::Not indicated without obstruction or infection.))
• ((Ureteroscopy::Reserved for larger or refractory stones.))
• ((ESWL::Not first-line for small stones.))

Which is the first-line analgesic for acute renal colic?

• ((Paracetamol::Insufficient for the severity of ureteric colic.))
• ((Diclofenac (NSAID)::☑️ First-line — reduces ureteric smooth muscle tone and glomerular pressure.))
• ((Morphine::Effective but second-line behind NSAIDs.))
• ((Codeine::Insufficient and pro-emetic.))

Which drug is used as medical expulsive therapy for a 7 mm distal ureteric stone?

• ((Finasteride::5α-reductase inhibitor — used in BPH, not stone expulsion.))
• ((Tamsulosin::☑️ α-blocker relaxes distal ureteric smooth muscle and aids stone passage.))
• ((Allopurinol::Prevents uric acid stones; no acute role.))
• ((Bendroflumethiazide::Reduces urinary calcium for prevention, not acute expulsion.))

Revision summary

- Loin-to-groin colic + haematuria = ureteric stone until proven otherwise.

- Ureteric afferents T11–L2 explain pain radiation.

- Three sites of impaction: PUJ (L2 TP) → pelvic brim (SI joint) → VUJ (ischial spine, narrowest).

- Calcium oxalate (~80%) — radio-opaque, commonest; idiopathic hypercalciuria in adults, primary hyperoxaluria in children.

- Struvite — staghorn, alkaline urine, urease-producing bacteria (Proteus).

- Uric acid — radiolucent on X-ray, acidic urine, gout / tumour lysis.

- Cystine — semi-opaque, hexagonal crystals, AR cystinuria.

- CT-KUB is gold standard; USS in pregnancy/children.

- <5 mm pass spontaneously; 5–10 mm distal → tamsulosin; <2 cm → ESWL or ureteroscopy; >2 cm or staghorn → PCNL.

- ESWL contraindications: pregnancy, anticoagulation, AAA, infection.

- Obstructed + infected kidney = emergency: distal stone → JJ stent; proximal stone → nephrostomy.

- NSAIDs (diclofenac) first-line for analgesia.

- Prevent with 2–3 L/day fluids, low Na, normal Ca, low oxalate, low animal protein, increase citrate.