Oral Exam - GU Flashcards
Acute pylonephritis findings
DMSA
Striated uptake appearance on Tc-99m DMSA
□ Pattern usually extends toward hilum (scar tends to
be more superficial)
WBC study
○ In-111 WBC scan: No normal uptake in kidneys; ↑ uptake
sensitive and specific for pyelonephritis
○ Tc-99m HMPAO WBC scan: Normal uptake in kidneys
and bladder; ↓ sensitivity, specificity for pyelonephritis
Ga-67
○ Normal symmetrical Ga-67 renal uptake up to 48hr post
injection
○ Bilateral renal Ga-67 uptake > 48hr post injection:
- Interstitial nephritis
- Renal failure
- Acute pylonephritis (unusual to be bilateral)
- Lymphoma
○ Focal increased Ga-67 uptake:
- Acute pyelonephritis
- Malignancy - lymphoma, leukemia, metastases
DMSA protocol
– Tc-99m DMSA: 40-65% injected dose bound to cortical
proximal convoluted tubules 2 hr post injection
Alternative:
○ Tc-99m glucoheptonate scan
○ Posterior and anterior supine planar images with low- energy, all-purpose parallel hole collimator at 2 hr post injection
– Differential renal function calculated using geometric
mean method
□ Geometric mean: Square root of product of
anterior and posterior counts
○ SPECT for best 3D cortical evaluation
– If SPECT not available, anterior, posterior, and bilateral posterior oblique images
– High-or ultra-high-resolution collimator; 300-500 K/image
– If known or suspected horseshoe kidney, image from anterior to discern connecting bridge of renal tissue between lower pole moieties ventral to spine
Ddx cortical defect DMSA
Pylenephritis
Cortical scar
Renal mass
Renal cyst
Fetal lobulation - normal indentation between lobules
Interstitial nephritis - mimics diffuse bilateral pyelo on Ga-67
Splenic impression
Renogram - normal angiographic phase
○ Flow to kidneys is seen quickly after aorta
○ Cortex should accumulate radiotracer over 1-3 min
– Should be homogeneous
– Cortical defects may indicate scar
○ If decreased renal function, uptake will be delayed
Renogram - clearance phase
○ Calyceal activity within 5 min
○ Bladder activity within 10-15 min
Renogram - protocol
□ Adults: Up to 10 mCi Tc-99m MAG3 IV
– Patient supine ,gamma camera posterior
– Angiographic sequence
□ 1-2 sec images for 1-2 min
– Dynamic sequence
□ 15-60 sec images for 20-30 min
– Diuresis sequence
□ Patient given furosemide and additional 15-60 sec images for 20-30 min
Lasix
□ Adults: 0.5mg/kg (max:40mg)
□ Pediatrics: 1mg/kg (max:20mg)
High grade obstruction findings
Relative function: Cannot predict functional potential in face of high- grade obstruction
Angiographic - Normal to delayed
Clearance phase - Calyceal activity usually normal, unless renal function is impaired secondary to obstruction; no bladder activity if obstruction is upper tract and bilateral
Renogram: Progressive rise in activity, even after furosemide; delayed time to cortical peak; washout t1/2 > 20 min
Partial obstruction
Angiographic phase - Normal
Clearance phase - Normal calyceal activity time, bladder activity may be delayed if bilateral
Renogram: Washout delayed until furosemide or postvoid procedure, then will decrease but still delayed; low-grade (questionable clinical significance): t1/2 10-15 min; partial obstruction, clinically significant: t1/2 15-20 min +
Functional obstruction
Angiographic phase: Normal
Clearance phase - Calyceal activity < 5 min; may have delayed bladder activity
Renogram: Washout delayed until furosemide or postvoid procedure; then washes out normally (t1/2 < 10 min)
Renal artery stenosis
Angiographic phase - delayed
Clearance phase: Delayed calyceal activity time
Renogram: Normal time-activity curve appearance, but peak is delayed
VUR findings:
Nuclear cystogram
○ Reflux of Tc-99m pertechnetate from bladder into
ureter &/or renal collecting system on filling or voiding
○ Dynamic images during filling and voiding increases
detection of VUR, including transient reflux
○ Difficult to grade VUR on nuclear cystogram due to lack
of anatomic resolution
– Qualitatively reported as mild, moderate, or severe
Nuclear cystogram protocol
– Tc-99m pertechnetate or SC
□ 0.25-0.5mCi for infants and toddlers
– Bladder volume goal: [Ageinyears+2]x30cc
– Normal saline, water
– Gravity instill fluid 70-100 cm above patient via
catheter
– Record volume at which VUR occurs
– Record volume of voided urine
– 64x64 matrix
– Posterior images of pelvis and abdomen, unless
calculation of residual bladder volume is planned
– Fillingandvoidingdynamicimagesat5-10sec/frame,
posterior
– Oncebladdergoalvolumeisreached,instructpatient
to void
– Prevoid and postvoid static images, 3-5 minutes each
Ddx VUR
Urine contamination
Bladder diverticulum
VUR Grading Nucs
○ Mild: Reflux in ureter
○ Moderate: Reflux to nondilated ureter and renal pelvis
○ Severe: Reflux to dilated collecting system
Renal transplant tracers
○ Tc-99m MAG3
– Renal tubular agent, preferred for renal transplant evaluation
○ Tc-99m DTPA
– Slower clearance than MAG3, limited utility in cases of
poor renal function with extraction fraction «_space;MAG3
(cleared by glomerular filtration)
Renal transplant protocol
Baseline renogram at 24-48hr to assess function and
allow better differentiation of ATN and AR
○ Patient position: Supine with camera anterior, centered
over side of pelvis containing transplant
○ Camera: Low-energy, all-purpose collimator
○ Computer: Acquire study in 2 phases, angiogram and
functional
– Angiogram: Dynamic 1-2 sec/frame for 60 sec
– Functional: 15-60 -sec frames for 20-30 min followed
by prevoid and postvoid images
○ Radiotracer
– Tc-99m MAG3: Up to 10 mCi
Renal transplant - normal findings
○ Perfusion to allograft: Normally within 4 sec of
radiotracer bolus passing through iliac artery
○ Normal peak cortical activity 3-5 min post injection
○ Normal renal transit: Tracer in collecting system, bladder
by 6 min
○ By end of exam, cortex should clear or be significantly
less than early in exam if no cortical retention
ATN findings
- Classically presents with relatively preserved perfusion and delayed uptake/excretion (tubular agents)
- Abnormal baseline renal scan at 24hr (AR typically occurs later)
- Bladder activity classically absent; background activity increases over time (e.g., gallbladder with MAG3)
Acute rejection
- Perfusion in AR generally worse than function: Often technically difficult to visualize
- ↑cortical retention compared with baseline from 1 week to < 1 year: Sensitive, fairly specific for AR
Drug toxicity
• Imaging appearance is similar to and difficult to distinguish from ATN (preserved perfusion and poor tubular function)
○ Typically presents later than ATN (time course very
important)
Renovascular HTN: high probability scan
○ High probability (> 90%)
– MAG-3: ↑ peak time (by 2-3 min or at least 40%)
– DTPA: ↓ peak and ↓ relative uptake or GFR > 10%
– MAG-3: Increase in 20-or30-min/peak ratio of ≥ 0.15
from baseline study
– Decrease in MAG-3uptake > 10%
– Marked unilateral parenchymal retention of DTPA
after ACEI compared with baseline study
Renovascular HTN protocol:
Prep:
– Stop ACEI 3-7 days prior to exam
– Hydrate p.o.; 7 mL/kg 30-60 min before study
– Position patient supine with camera posterior for
native kidneys and anterior for renal transplant
– NPO 4-6 hrs for best absorption of ACE-i
– 1-day protocol (high probability of disease): 1mCi low-dose baseline followed by 5-10 mCi high-dose ACEI scan
Captopril 25-50mg PO crushed; BP Q5-10 min x 1hr
○ Acquisition
– Camera: Low-energy, parallel hole collimator; 15-20% photopeak centered at 140 keV; large field of view
RVH - intermediate probability study
Abnormal baseline findings that are unchanged after ACEI
– Small, poorly functioning kidney (< 30%) may not
respond appropriately
– Symmetric bilateral abnormalities most often due to
factors such as dehydration
– Cortical retention, ratio counts at 20 to 3 minutes
(20/3 ratio) ~ 0.1-0.5
– Reduced uptake of DTPA of 5-9%
Homsy’s sign
High grade obstruction induced by high flow states
Initially see normal clearance, then retention
