Video summary

ESTUDIOS DE MEDICINA NUCLEAR EN UROLOGIA PEDIATRICA - CIRUPED JAVERIANA

Main summary

Key takeaways

Educational

Main ideas / lessons

  • Purpose of the talk: Teach how to rationally use nuclear medicine studies in pediatric urology, specifically:

    • When to order
    • When not to
    • How to decide which test based on the clinical question

  • Why it matters:

    • There is overuse of nuclear medicine in pediatrics, often from not knowing what information each study provides
    • There is variability/no consensus in indications
    • Children are more sensitive to ionizing radiation and have greater long-term cumulative risk
    • Key principle: request only when it will change behavior/management

Core imaging concept: anatomy vs function

  • Ultrasound (US): mainly provides anatomical information
  • Voiding cystourethrogram (mixed cystourethrography): anatomy and presence/absence of vesicoureteral reflux
  • Nuclear medicine: mainly provides functional information**
    • Example functional targets: renal function (global/differential), perfusion, drainage, and cortical integrity/scarring

Methodology / decision framework (what to request and why)

General rule

  • Nuclear medicine should be selective and risk-based
  • Central question: “Will this study change my behavior?”
  • If the result won’t alter clinical management, avoid testing (and avoid radiation)

Use nuclear medicine only when it answers a clinical question such as:

  • Is there cortical damage/scarring? → DMSA
  • Is there obstruction / impaired urinary drainage? → MAG3 (diuretic renogram)
  • Is there mainly glomerular filtration reduction / GFR concern? → DTPA / alternative contexts
  • Does reflux persist after treatment / follow-up? → Isotopic cystography

Nuclear medicine studies described (purposes and key instructions)

1) DMSA (Tc-99m labeled dimercaptosuccinic acid) — “renal cortical scintigraphy”

What it evaluates

  • Cortical integrity and scarring
  • Differential renal function
  • Does not evaluate urinary drainage/dynamics and does not diagnose reflux

Mechanism

  • Selectively binds to proximal tubular cells in the renal cortex
  • Provides cortical visualization with minimal interference from collecting system activity

How it is performed (timing & acquisition)

  • Administer IV DMSA
  • Imaging typically 2–4 hours post-injection
  • Posterior views of both kidneys (assessing size and cortical uptake)
  • Additional magnified views (posterior oblique/anterior/posterior)

Main clinical indications

  • Febrile UTI / suspected acute pyelonephritis
    • Helps detect acute inflammatory lesions; sensitivity ~87%, specificity ~100%
  • Vesicoureteral reflux (VUR)
    • Detects reflux nephropathy (scarring risk and long-term complications)
  • Monitoring existing scars and risk stratification
  • Selected congenital abnormalities (e.g., dysplastic kidneys, other malformations)

Key interpretation rules (patterns)

  • Normal pattern requires:

    • Differential function ~45–55% for each kidney
    • Rounded/smooth renal contours
    • No focal cortical uptake defects implying injury
    • Note: some contour shapes can be normal variants in young children (e.g., triangular/rotated/pear-like patterns)

  • Acute pyelonephritis pattern

    • Decreased uptake with preserved contour, or
    • Enlarged kidney with diffuse decreased uptake
    • Often poorly defined focal uptake defects (patchy distribution)

  • Renal scars pattern

    • Decreased uptake with cortical loss or decreased renal volume
    • Clearly defined cortical defects
    • Persistent for ≥6 months (cortical thinning, retracted contour)

  • Old scar classification (types 1–4) based on extent/pattern:

    • Type 1: ≤2 scar areas
    • Type 2: >2 scar areas separated by normal parenchyma
    • Type 3: widespread kidney damage (pattern similar to obstructive nephropathy)
    • Type 4: end-stage with markedly reduced uptake (total function often <10%)

When to perform DMSA (“should” situations)

  • Febrile UTI with risk factors, especially:
    • Infants <6 months
    • Atypical or severe infection
    • Poor response to treatment
    • Unusual germs
    • Significant elevation of acute-phase reactants
  • Delayed evaluation after febrile UTI (4–6 months) for scar detection and long-term risk stratification
  • VUR risk assessment (not to diagnose reflux initially, but to evaluate reflux nephropathy)
  • Congenital renal anomalies / solitary kidney / monitoring in previously scarred or recurrent infection patients

When not to use (avoid)

  • First febrile UTI without risk factors, especially if:
    • Ultrasound is normal
    • Good clinical response to treatment
  • Routine testing for all VUR patients (individualize; does not replace cystourethrogram)
  • Repeated studies that do not change clinical management

2) MAG3 diuretic renogram (Tc-99m labeled mercaptoacetyltriglycine) — “dynamic study for drainage/obstruction”

What it evaluates

  • Dynamic renal function:
    • Perfusion & tubular uptake
    • Urinary drainage/urodynamics (key for obstruction vs dilation)
  • Effective renal plasma flow/clearance (driven by tubular secretion)

Mechanism

  • MAG3 binds to plasma proteins (~90%)
  • Taken up by kidney via active proximal tubular secretion
  • Not dependent on glomerular filtration, therefore more efficient in immature/impaired kidneys than alternatives

Core purpose

  • Differentiate true obstruction from obstructive dilation
  • Support surgical decision-making (but does not define surgery alone)

How it is performed (instructions)

  • IV injection of MAG3
  • Adequate hydration beforehand (important to reduce false interpretation)
  • Dynamic acquisition initially ~20–30 minutes
  • Then administer diuretic:
    • Usually furosemide 1 mg/kg
    • Timing relative to tracer varies by protocol/institution
  • Ensure bladder management:
    • Empty bladder preferred
    • Catheterization in infants who can’t cooperate
  • Interpret using:
    • Qualitative dynamic images
    • Semi-quantitative time-activity curves
    • Quantitative parameters
    • Always correlate with clinical context and ultrasound

Interpretation (curve/phases)

  • Vascular phase (~30 seconds): perfusion
  • Cortical/tubular phase (~1–3 minutes): uptake and intrarenal transit
  • Excretory phase (~3–20 minutes): collecting system + bladder; key for obstruction diagnosis

Key quantitative/threshold concepts

  • Tmean (mean emptying time)
    • Normal: <10–15 min
    • Indeterminate: 15–20 min
    • Obstruction suggested at ~≥20 min, but must not be used alone
  • Differential renal function
    • Normal roughly 45–50%
    • <40% suggests functional impairment
    • <10–15% severe impairment
  • Trend over time more important than isolated values

Pattern recognition

  • Normal drainage

    • Rapid rise, early peak (Tmax ~3–5 min), progressive decline

  • True obstructive pattern

    • Upward/plateauing curve after diuretic
    • No decrease post-diuretic
    • Prolonged Tmean (>20 min)

  • Non-obstructive dilated pattern

    • Slow decline but improves after furosemide
    • Suggests reservoir/high compliance (dilation without obstruction)

  • Poor renal function pattern

    • Low uptake, flat curves → drainage assessment may be unreliable

Common errors/limitations

  • Relying only on mean time without considering hydration/technique
  • Ignoring renal overall function and ultrasound correlation
  • Overcalling obstruction in markedly dilated systems
  • False results possible due to:
    • Dilation severity
    • Intermittent obstruction
    • Low function

When to use MAG3

  • Prenatal or postnatal hydronephrosis follow-up with suspected obstruction
  • Suspected obstruction at ureteropelvic junction (UPJ)
  • Pre-surgical functional evaluation
  • Post-surgical follow-up of obstruction
  • Solitary kidney
  • Progressive functional deterioration

When not to use MAG3

  • Stable mild hydronephrosis without need for serial testing / no expected management change
  • No significant dilation on ultrasound and stable normal function
  • Repeated tests with no new clinical impact
  • Caution in special cases:
    • Neonates: higher risk of false positives (immature renal handling)
    • Very dilated systems: physiologic retention may mimic obstruction
    • Intermittent obstruction: may appear normal on renogram

3) DTPA diuretic renogram (Tc-99m labeled DTPA) — “glomerular filtration-focused alternative”

What it evaluates

  • Primarily glomerular filtration rate (GFR)
  • Can show urinary elimination patterns

Key attributes/limitations

  • Requires adequate kidney function:
    • Lower performance in newborns and impaired kidneys
  • Lower radiation than some alternatives
  • Less commonly used in pediatrics today

Interpretation logic (curve-based)

  • Uptake phase reflects glomerular filtration
  • Excretion/drainage via curve behavior:
    • Downward curve: adequate drainage
    • Plateau: doubtful
    • Upward: suggests obstruction
  • Timing thresholds:
    • Normal emptying time: <10–15 min
    • Indeterminate: 15–20 min
    • Obstruction: >20 min
  • Differential function:
    • Typically 45–55% as reference normal range

When to consider DTPA

  • Evaluate overall renal function / monitor CKD
  • Bilateral relative assessment where GFR is key
  • Very selected pre-surgical contexts
  • As an alternative if MAG3 is not available
  • Preferably not in newborns/young infants with impaired renal function
  • Not preferred as primary study for surgical obstruction decisions compared with MAG3

4) Isotopic cystography (isotopic “cystogram”)

What it evaluates

  • Retrograde passage of urine (reflux) detected via radiopharmaceutical in bladder
  • Highly sensitive functional detection of reflux, including intermittent cases
  • Not anatomical; does not precisely classify reflux anatomy/degree

How it is performed (direct vs indirect)

  • Radiotracer introduced to bladder:
    • Direct: radiotracer placed directly into bladder → may require catheter
    • Indirect: tracer via another route (often involving patient cooperation)
  • Reflux can be detected during bladder filling or urination

Interpretation

  • Qualitative: detects whether reflux occurs
  • Can identify low-volume reflux (high sensitivity)
  • Limitation: cannot standardize or provide precise anatomical classification/degree

Indications

  • Follow-up of known reflux
  • Evaluate resolution after reflux treatment (medical/endoscopic/surgical)
  • Bladder dysfunction contexts (e.g., neurogenic bladder, dysfunctional voiding)
  • Screening high-risk patients in serial monitoring to reduce radiation

When not to request

  • As an initial diagnosis requiring anatomy/degree/classification
  • When urethral pathology needs detailed anatomical visualization (e.g., posterior urethral valves)
  • It does not replace cystourethrography for anatomic reflux classification

Key differences vs mixed cystourethrography

  • Isotopic cystography:
    • More functional, less radiation, good for monitoring
    • Answers: Does reflux persist?
    • Does not answer: degree/anatomical classification
  • Mixed cystourethrography:
    • More anatomical, used for initial diagnosis and classification
    • Better for characterizing reflux anatomy

“Three pediatric clinical scenarios” workflow (summary algorithms)

Scenario 1: Febrile urinary tract infection (UTI)

  1. Confirm diagnosis and start treatment
    • Urinalysis, urine culture, antibiotics
  2. Initial imaging
    • Renal & urinary tract ultrasound (hydronephrosis/malformation/renal size/anatomy)
  3. When to request cystourethrogram (mixed cystourethrography)
    • Abnormal ultrasound
    • Recurrent febrile UTI
    • Clinical suspicion of VUR
    • Not indicated routinely in the first episode if ultrasound is normal
  4. When to request DMSA
    • Febrile infection with risk factors
    • Suspected acute pyelonephritis/scarring assessment
    • Monitoring kidney damage (e.g., reflux nephropathy)
  5. When NOT to request
    • Low-grade/non-febrile infection
    • First febrile episode without risk factors
    • If it won’t change management (especially with normal US and good response)

Scenario 2: Vesicoureteral reflux (VUR)

  1. Suspect clinically
    • Febrile infection, prenatal hydronephrosis, or ultrasound findings
  2. Initial imaging
    • Renal ultrasound + urinary tract assessment (pyelocaliceal dilation, asymmetry, structural issues)
  3. Confirm & classify reflux
    • Mixed cystourethrography
  4. Assess kidney damage
    • DMSA for scarring and differential function (evaluate reflux nephropathy)
  5. Follow-up
    • With DMSA and/or other studies based on progression and risk
  6. Higher risk suspicion
    • High-grade VUR, recurrent infections, ultrasound abnormalities, progressive renal function decline
  7. If low-grade and stable
    • Avoid further testing if it won’t alter behavior

Scenario 3: Hydronephrosis / urinary tract dilation

  1. Detection
    • Prenatal ultrasound or postnatal/incidental or during initial UTI evaluation
  2. Initial assessment
    • Renal + bladder ultrasound
    • Severity, cortical thickness, ureteral dilation, bladder abnormalities
  3. When to request mixed cystourethrography
    • Ureteral dilation
    • Reflux suspicion
    • Recurrent febrile infections
    • Bladder alterations
    • Not routinely indicated in mild isolated hydronephrosis
  4. Assess function
    • MAG3 renogram to differentiate obstruction vs obstructive dilation
  5. Interpret management strategy
    • Adequate drainage → conservative management
    • Altered drainage → suspect obstruction; use differential function + follow-up (US over time)
  6. Suspect significant obstruction if
    • Progressive hydronephrosis
    • Decreasing cortical thickness
    • Function deterioration
    • Ongoing clinical symptoms
  7. When NOT to request MAG3
    • Stable patient where additional testing won’t change management

Speakers / sources featured

  • Dr. Adriana Marcela Arenas Rojas — presenting resident (main speaker)
  • Dr. Alejandro Quintero Espinosa — tutor/mentor (pediatric urologist; joined online later)
  • Dr. Juan Carlos — referenced as having given an earlier presentation
  • Dr. José Echeverría — asked a question during the Q&A
  • “Edo” (as referenced in subtitles) — interjecting speaker who replied to José’s question (likely a colleague; name unclear from subtitles)

Original video