Intravenous Urography & Renal Radiology

Intravenous urography (IVU), also called intravenous pyelography (IVP) or excretory urography, is a contrast-based functional and anatomical study of the urinary tract. Though CT urography has largely replaced it clinically, IVU remains a perennial NEET PG favourite because its phases, classic eponymous signs, and pattern-recognition images are perfect single-best-answer material.

Definition & basic principle

IVU is a radiographic examination in which a water-soluble iodinated contrast medium is injected intravenously, freely filtered at the glomerulus (it is not significantly secreted or reabsorbed), and then concentrated and excreted by the kidney, opacifying the pelvicalyceal system, ureters and bladder on a timed series of plain radiographs.

The key concept tested: IVU assesses both function (how fast and how well each kidney excretes) and anatomy (calyces, pelvis, ureter, bladder outline) — a feature plain films and ultrasound cannot combine.

High-yield: Contrast in IVU is filtered by the glomerulus and concentrated by tubular water reabsorption; it is essentially neither secreted nor reabsorbed. Good opacification therefore requires adequate GFR and a concentrating tubule.

Contrast agents

• Non-ionic, low-osmolar iodinated agents (iohexol, iopamidol) are preferred today — fewer reactions, less nephrotoxicity than older ionic high-osmolar agents (diatrizoate).
• Iodine concentration ≈ 300–370 mg I/mL.

Technique & patient preparation

1. Bowel preparation — overnight fasting + mild laxative to clear overlying faecal/gas shadows (faecal loading mimics or obscures calculi).
2. Plain control film (KUB) → taken before contrast — to detect radio-opaque calculi, calcification, bony lesions and to set exposure factors.
3. IV contrast bolus (≈ 1 mL/kg).
4. Timed sequence of films through the excretory phases.
5. Compression band over the lower abdomen (over the ureters at the pelvic brim) → distends the pelvicalyceal system for better calyceal detail; released to opacify ureters.
6. Post-micturition film → assesses bladder emptying and residual volume; useful in BPH and reflux.

High-yield: The plain control (scout) KUB film is the single most important film — most urinary calculi are radio-opaque and may be invisible once contrast fills the system.

Phases of IVU (most tested concept)

The excretion of contrast produces a predictable, time-ordered sequence. Memorise the order and timing.

Phase	Timing after injection	What opacifies	Clinical use
Nephrogram phase	~30 seconds – 1 min (immediate)	Renal parenchyma (cortex + medulla)	Renal size, contour, scars, masses
Pyelogram (calyceal) phase	~3–5 min	Calyces & renal pelvis	Calyceal architecture, blunting
Ureterogram phase	~5–15 min (after compression release)	Ureters	Strictures, deviation, obstruction
Cystogram phase	~15–30 min	Urinary bladder	Filling defects, outline, emptying

Flow of a normal study: Plain KUB → nephrogram (30 s) → pyelogram (5 min) → release compression → ureterogram → cystogram → post-void film.

High-yield: The nephrogram is produced by contrast within the tubules/parenchyma (immediate, ~30 s), while the pyelogram is contrast within the collecting system (~5 min). Examiners love this distinction.

Abnormal nephrograms (classic pattern questions)

Nephrogram pattern	Cause
Immediate, persistent, dense (obstructive) nephrogram	Acute ureteric obstruction (e.g. stone)
Immediate, faint, persistent	Acute tubular necrosis, hypotension
Delayed, increasingly dense	Renal artery stenosis, acute glomerular disease
Striated nephrogram	Acute pyelonephritis, obstruction, medullary sponge kidney
Absent nephrogram	Non-functioning kidney, complete arterial occlusion

Normal anatomy on IVU

• Calyces: sharp, cupped (concave) fornices with delicate sharp angles.
• 2–3 major calyces, draining into the renal pelvis.
• Ureters: pass anterior to transverse processes, cross the sacroiliac joint, swing laterally near ischial spine, then medially to insert into bladder trigone.
• Three normal ureteric constrictions = pelviureteric junction (PUJ) → crossing of iliac vessels (pelvic brim) → vesicoureteric junction (VUJ). These are the commonest sites a stone impacts.

High-yield: Commonest sites of ureteric calculus impaction = the three physiological narrowings, with the VUJ (vesicoureteric junction) being the narrowest and most common site of impaction.

Classic IVU findings (image-based MCQ goldmine)

1. Renal calculi & staghorn calculus

• Most renal stones are radio-opaque on plain film: calcium oxalate (most common, dense), calcium phosphate, struvite.
• Radiolucent stones = uric acid, xanthine, 2,8-dihydroxyadenine, pure matrix, indinavir — invisible on plain KUB, seen as filling defects in the contrast-filled system on IVU.
• Staghorn (coraliform) calculus: fills and takes the shape of the pelvicalyceal system (like a stag's antlers). Composed of struvite (magnesium ammonium phosphate) + carbonate apatite — a triple-phosphate "infection stone" associated with urease-producing organisms (Proteus, Klebsiella) and alkaline urine.

High-yield: Radio-opacity order (most → least opaque): Calcium phosphate ≈ calcium oxalate > struvite > cystine > uric acid (radiolucent). Mnemonic for radiolucent stones — "I X-ray UnXploitable": Uric acid, Xanthine, Indinavir, 2,8-DHA.

2. Hydronephrosis & obstruction

• Dilated, blunted/clubbed calyces (loss of the normal cupped concavity) → the fornices become convex.
• Delayed dense nephrogram + delayed excretion on the obstructed side.
• Standing column of contrast in a dilated ureter; abrupt cut-off at the level of obstruction.
• PUJ obstruction: dilated pelvis and calyces with a normal-calibre ureter below.

3. Renal cell carcinoma (RCC)

• A space-occupying mass causes stretching, splaying, distortion and displacement of calyces — the classic "spider-leg" / "spider-legging" deformity of the pelvicalyceal system.
• May show calcification, bulge of the renal contour.

High-yield: The "spider-leg deformity" of stretched, splayed calyces is the IVU hallmark of a renal cell carcinoma (or any expanding renal mass).

4. Transitional cell carcinoma (TCC / urothelial carcinoma)

• Arises from urothelium of calyces, pelvis, ureter or bladder.
• Appears as an irregular filling defect within the contrast-filled collecting system or ureter.
• "Goblet sign" / champagne-glass sign — a ureteric TCC produces a cup-shaped dilatation of the ureter just below the lesion (because the slow-growing intraluminal tumour allows the ureter to dilate around it), pointing to a transitional cell carcinoma rather than a stone (which gives proximal dilatation only).
• TCC is multifocal ("field change") — examine the whole urothelium.

Filling defect	Classic clue
Radiolucent calculus	Mobile, smooth, no wall infiltration
TCC / urothelial tumour	Irregular, fixed, goblet sign, multifocal
Blood clot	Changes/disappears on follow-up films
Sloughed papilla	Triangular, "ring shadow" in papillary necrosis
Air bubble	Smooth, round, moves to non-dependent part

5. Other named signs

• Bear-paw / striated nephrogram → xanthogranulomatous pyelonephritis (with staghorn stone, non-functioning kidney).
• Ring shadow / "ball-on-tee" / "lobster-claw" → renal papillary necrosis (sloughed papilla outlined by contrast). Mnemonic "POSTCARDS" for papillary necrosis causes: Pyelonephritis, Obstruction, Sickle cell, Tuberculosis, Cirrhosis/Chronic alcoholism, Analgesic nephropathy, Renal vein thrombosis, Diabetes mellitus, Systemic vasculitis/Sarcoidosis.
• "Drooping lily" / drooping flower sign → duplex kidney — the obstructed upper-moiety hydronephrosis pushes the functioning lower-moiety calyces downward and laterally.
• "Flower-vase" / "fish-hook" / J-shaped ureter → retrocaval ureter (right ureter loops medially behind the IVC) or bladder outlet obstruction (fish-hook from BPH).
• Medullary sponge kidney → "paint-brush" / "bouquet of flowers" appearance from contrast in dilated collecting ducts, with medullary nephrocalcinosis.
• Cobra-head / adder-head sign → ureterocele (lucent halo around the contrast-filled distal ureter in the bladder).
• "Soap-bubble"/ phantom calyces, moth-eaten calyces → renal tuberculosis (irregular calyceal erosion, infundibular stricture, autonephrectomy/putty kidney with calcification).

High-yield: Match the sign — Spider-leg = RCC, Goblet sign = ureteric TCC, Drooping lily = duplex system, Cobra-head = ureterocele, Bear-paw = XGPN, Ball-on-tee = papillary necrosis.

Investigation of choice (modern context)

While IVU details the collecting system beautifully, current first-line imaging differs by indication:

Clinical question	Investigation of choice
Suspected renal/ureteric colic (stone)	Non-contrast helical CT KUB (NCCT) — gold standard; detects radiolucent stones
Renal mass characterisation	Contrast-enhanced CT (CECT) abdomen
Haematuria / urothelial tumour workup	CT Urography + cystoscopy
First-line, radiation-free screening, children, pregnancy	Ultrasound
Vesicoureteric reflux	Micturating cystourethrogram (MCUG)
Renovascular / split function	DTPA / MAG3 radionuclide renography
Suspected renal artery stenosis	CT/MR angiography

High-yield: NCCT KUB is the investigation of choice for acute renal colic and has superseded IVU. IVU's chief surviving role is detailed pelvicalyceal/ureteric anatomy (e.g. PUJ obstruction, suspected papillary necrosis, congenital anomalies) where CT urography is unavailable.

Contraindications & complications

Contraindications

• Known severe contrast (iodine) allergy / anaphylaxis to previous contrast.
• Renal impairment (raised creatinine, eGFR < 30–45) — risk of contrast-induced nephropathy (CIN).
• Metformin therapy with renal impairment — risk of lactic acidosis; withhold metformin around contrast administration.
• Pregnancy (radiation), severe untreated hyperthyroidism, multiple myeloma with dehydration, severe cardiac failure.

Complications

• Acute contrast reactions: urticaria, bronchospasm, anaphylactoid reaction (treat with adrenaline, oxygen, antihistamine, steroids, fluids).
• Contrast-induced nephropathy — rise in creatinine 48–72 h post-contrast; prevent with hydration.
• Extravasation at injection site.

High-yield: First-line drug for a severe anaphylactoid contrast reaction is intramuscular adrenaline (0.5 mg of 1:1000). Ensure adequate hydration and stop nephrotoxic/metformin drugs to prevent CIN.

Key differentials of a collecting-system filling defect

Use the mnemonic "BLT-CC" for radiolucent filling defects in the pelvicalyceal system/ureter:

• Blood clot
• Lucent (radiolucent) calculus — uric acid
• Tumour — transitional cell carcinoma
• Congenital — ureterocele/blood vessel impression
• Caseous material / sloughed papilla / fungal ball / air

Differentiating features were tabled above — chiefly mobility, change on serial films, and the goblet sign of TCC.

Renal radiology — quick allied facts

• Plain KUB: ~90% of renal calculi radio-opaque; "soft-tissue technique."
• Ultrasound: posterior acoustic shadowing behind a stone; detects hydronephrosis & is the screening test in pregnancy/children. Cannot reliably see mid-ureteric stones.
• NCCT KUB: every stone except indinavir (protease-inhibitor) stones and pure matrix stones is dense; stone density measured in Hounsfield units (HU) predicts composition (uric acid ~200–400 HU, calcium oxalate >1000 HU).
• Spiral CT signs of obstruction: perinephric/periureteric stranding, "rim/tissue-rim sign" around a ureteric stone (distinguishes a stone from a phlebolith, which shows a "comet-tail sign").
• DMSA scan = cortical scarring & differential function; MAG3/DTPA = drainage & obstruction.

Recently asked / exam angle

• Phase identification: "Nephrogram appears at ___ after injection" → ~30 seconds. "Pyelogram phase" → ~5 minutes.
• Eponym matching is heavily tested: spider-leg (RCC), goblet sign (ureteric TCC), drooping lily (duplex/upper-moiety obstruction), cobra-head (ureterocele), bear-paw (XGPN), ball-on-tee/ring shadow (papillary necrosis), paint-brush (medullary sponge kidney).
• Staghorn calculus composition → struvite/triple phosphate, urease organisms (Proteus), alkaline urine.
• Radiolucent stone → uric acid; seen as filling defect on IVU, may be missed on KUB but seen on NCCT.
• Investigation of choice for renal colic → NCCT KUB, not IVU.
• Importance of the plain control film before contrast.
• Sites of ureteric narrowing/impaction → PUJ, pelvic brim (iliac vessels), VUJ.
• Contrast nephropathy & metformin — a recurrent pharmacology-radiology cross-link.
• Comet-tail sign (phlebolith) vs rim sign (ureteric stone) on CT.

Rapid revision

1. IVU contrast is glomerular-filtered, tubular-concentrated, neither secreted nor reabsorbed — needs functioning nephrons.
2. Order of films: plain KUB → nephrogram (30 s) → pyelogram (5 min) → ureterogram → cystogram → post-void.
3. The scout/control KUB film is the most important — taken before contrast.
4. Compression distends the pelvicalyceal system; released to fill ureters.
5. Spider-leg deformity of calyces = renal cell carcinoma.
6. Goblet (champagne-glass) sign of the ureter = ureteric transitional cell carcinoma; TCC is multifocal.
7. Drooping lily sign = obstructed upper moiety of a duplex kidney; cobra-head sign = ureterocele.
8. Staghorn calculus = struvite/triple phosphate, urease-producing Proteus, alkaline urine; "bear-paw" nephrogram = XGPN.
9. Radiolucent stones (uric acid, xanthine, indinavir, 2,8-DHA) appear as filling defects on IVU.
10. Ball-on-tee / ring shadow = papillary necrosis (POSTCARDS causes); paint-brush calyces = medullary sponge kidney.
11. Investigation of choice for acute renal colic = NCCT KUB; ultrasound for pregnancy/children; CT urography for haematuria/TCC.
12. Withhold contrast in renal failure & metformin; treat severe contrast anaphylaxis with IM adrenaline.