UTD Classification System

The UTD (urinary tract dilation) classification system uses six ultrasound findings to describe the urinary tracts:

• anterior-posterior renal pelvic diameter (APRPD)
• calyceal dilation with distinction between central and peripheral calyces postnatally
• renal parenchymal thickness 
• renal parenchymal appearance
• bladder abnormalities 
• ureteral abnormalities

AP RPD = anterior-posterior renal pelvis diameter; transverse view measurement of max diameter of intrarenal pelvis

GU embryology

Differential diagnosis

• 40-80% transient
• Gr 1 - most resolves by 2 years
• Gr 2 - most resolves by 4 years
• 10-30% UPJ obstruction
• Diagnosis probability increases with severity of hydronephrosis
• Etiology
• Crossing vessel
• Aperistaltic/scar tissue at that site
• High insertion
• AP diameter > ~ 15 mm (3rd trimester) as predictor for needing surgery
• Usually don't need early surgery
• Indications for surgery: failure to improve severe dilation on multiple early studies, or function < 40%/drops > 5%
• SFU4/UTD P3 has 25-50% chance of needing pyeloplasty; SFU3/UTD P2 are 15%, and low grade is ~0%
• Only SFU gr IV tend to have decreased renal function
• If Gr III and worsening, 50% will need surgery
• If Gr III and stable hydro, renal function also stable
• Dilation != obstruction - get Mag3 to prove obstructed (most times)
• 90-95% success rate
• Cutoff for nephrectomy: adult < 20%, peds < 10%
• 10-40% VUR
• Posterior urethral valves
• Congenital flaps of tissue obstructing urine outflow
• Type 1 - Bicuspid valve (95%)
• Type 2 - hypertrophy of membranous urethra
• Type 3 - thin membrane
• Anterior valves (eg in anterior urethra) are 25-30 times less common than PUVs
• a/w anterior urethral diverticulum - unclear which causes the other
• > 50% with associated VUR
• Variable presentation
• 2/3 diagnosed prenatally
• Can have life-threatening renal/pulmonary conditions at birth (pulmonary hypoplasia from oligohydramnios, renal insufficiency)
• Presents as voiding dysfunction in older children
• Diagnosis - VCUG and cystoscopy
• Imaging - "keyhole bladder" with dilated prostatic urethra, bladder thickening. Can see reflux into ejaculatory ducts, trabeculations in bladder, bladder neck hypertrophy, then valve in urethra on VCUG
• Tx
• Neonatal management - respiratory stabilization, bladder drainage with urethral catheter (can be difficult do to high bladder neck) vs SPT, RBUS/VCUG when stable, and trend Cr
• Cystoscopy and ablation/resection of valves
• Laser vs cold knife?
• Shouldn't leave catheter; urine flow across it will promote healing/avoid stricture
• Cutaneous vesicostomy if poor renal function, or too premature/small to insert a cystoscope (or can do an SP tube)
• VCUG 3 mo after valve resection to make sure valves are gone (vs second look cystoscopy)
• Most (>60%) of VUR resolves after valve resection
• Poor outcome predicted by nadir Cr > 1
• Valve bladder: stretch -> collagen changes, increased bladder pressures, renal tubulular damage -> concentrating defect and polyuria
• Leads to delayed myogenic failure of detrusor around teenage years requiring CIC
• Or - detrusor overactivity
• Decreased compliance with small bladder
• VURD: VUR and dysplasia syndrome; high grade unilateral reflux into poorly functioning kidney, as 'pop-off' mechanism while contralateral kidney appears normal, but overall long-term renal function still poor
• Multicystic dysplastic kidney
• ***
• About 25% will have VUR in the contralateral kidney
• Ureterocele, ectopic insertion

Megaureter (ureter > 7 mm)

• Non-refluxing, non-obstructive
• Refluxing, non-obstructive
• Primary obstructive megaureter (Non-refluxing, obstructive)
•  > 17 mm predictive of needing surgery
• Ureteral reimplant - taper if dilation > 1 cm
• If pt too small - temporary drainage with PCN, cutaneous ureterostomy, etc
• Obstructing and refluxing (eg ectopic insertion into sphincter

Antenatal measurement of AP diameter of renal pelvis

• most predictive outcome measure
• < 33wks and AP > 4 mm or > 33wks and AP > 7mm -> diagnosis/eval after birth with RBUS
• SFU Gr 4 starts to show decreased function

Postnatal radiologic evaluation - follow most with serial ultrasounds

• Get 1st ultrasound after 48 hours (lots of fluid shift/3rd spacing during first 48 hrs of life)
• Even still tend to be dehydrated
• 1 month ultrasound is usually more accurate

Ultrasound

• Ureterocele - thin walled, cystic dilation, intravesical, acute angle
• Ectopic ureter - thick walled, extravesical component, obtuse angle, dysplastic parenchyma

VCUG

• Recommended for high risk postnatal UTD, hydroureter

Diuretic renography

• Renal scan
• Perform after 1 mo because renal prematurity affects diuretic efficacy and processing of tracer
• Use to determine if upper tract obstruction
• Ureteral dilation > 10 mm -> probably need MAG3 study
• Can use as provocative testing for intermittent UPJ

MR urogram

• Can delineate complex anatomy eg nondilated ectopic ureter (but requires sedation for kids)

 Postnatal management

• Surgical treatment of hydronephrosis will stabilize kidney function but not improve it

• Antibiotics
• Recommended for high risk UTD
• Risk factors for UTI - distal ureteral dilation, < 6 mo age, girls, uncircumcised boys
• Begin prophylaxis before VCUG
• Ppx decreases incidence of UTI 60-80% (without abx, incidence 1x/year on average)