What is the initial workup for a patient with suspected renal agenesis (absence of one kidney)?

Workup for Renal Agenesis

Initial Imaging Confirmation

Renal ultrasound is the first-line imaging modality to confirm suspected renal agenesis, followed by confirmatory imaging with either CT urography, MR urography, or nuclear medicine renal scan (DTPA or MAG3) to definitively establish absence of renal tissue and document function of the solitary kidney. 1, 2

• Ultrasound alone may miss small dysplastic remnants or ectopic kidney tissue, requiring confirmatory cross-sectional imaging or functional nuclear medicine studies 2, 3
• DMSA renal scan provides excellent documentation of functional renal tissue and can definitively confirm true agenesis versus severe dysplasia 2

Mandatory Evaluation for Associated Urological Anomalies

All patients with confirmed renal agenesis must undergo voiding cystourethrography (VCUG) to screen for vesicoureteral reflux and other collecting system abnormalities, regardless of whether hydronephrosis is present or urinary tract infections have occurred. 2, 4, 3

• Associated congenital anomalies of the kidney and urinary tract (CAKUT) occur in 32-48% of patients with unilateral renal agenesis 2, 4, 3
• Vesicoureteral reflux is the most common associated anomaly, present in 24-28% of cases and typically high-grade requiring surgical intervention 2, 4, 3
• Ureteropelvic junction obstruction occurs in 7% and ureterovesical junction obstruction in 11% of cases 2
• The absence of symptoms or normal ultrasound appearance of the solitary kidney does NOT exclude these anomalies—screening VCUG is mandatory even in asymptomatic patients 3

Evaluation for Vasal Agenesis and Renal Abnormalities

In male patients with renal agenesis, careful physical examination for presence of the vas deferens is essential, and if vasal agenesis is detected, renal ultrasonography of the contralateral side must be performed to evaluate for additional renal abnormalities. 1

• Unilateral absence of the vas deferens is associated with ipsilateral renal anomalies including agenesis in 26-75% of cases 1
• Bilateral vasal agenesis has a lower but still significant 10% prevalence of renal anomalies 1
• This evaluation should be performed regardless of CFTR mutation status 1

Assessment of Solitary Kidney Function and Long-Term Risk

Baseline assessment must include serum creatinine, estimated GFR, urinalysis for proteinuria/microalbuminuria, and blood pressure measurement, as patients with solitary kidneys face increased risk of hypertension (16%), microalbuminuria (21%), and reduced GFR <60 mL/min/1.73m² (10%). 4

• These complications can develop even in the absence of associated urological anomalies 4
• Focal segmental glomerulosclerosis may develop in solitary kidneys, potentially related to hyperfiltration injury 5

Family Screening Protocol

First-degree relatives of patients with renal agenesis should undergo renal ultrasound screening, as 20-36% of cases demonstrate familial recurrence with autosomal dominant inheritance pattern showing incomplete penetrance and variable expression. 6, 5, 4

• Silent genitourinary malformations occur in first-degree relatives even when asymptomatic 6
• Family history should specifically query for renal anomalies, unexplained neonatal deaths, and genitourinary malformations 6
• Female relatives should also undergo pelvic ultrasound to evaluate for uterine anomalies (bicornuate uterus) which can be associated 6

Critical Pitfalls to Avoid

• Do not assume a normal-appearing solitary kidney on ultrasound excludes associated CAKUT—VCUG is mandatory regardless of ultrasound findings 3
• Do not delay VCUG until after a urinary tract infection occurs—early detection and treatment of VUR is imperative to prevent renal damage in a solitary kidney 2, 3
• Do not overlook the 2.5:1 male predominance in bilateral renal agenesis when counseling families about recurrence risk 6
• Do not assume unilateral renal agenesis is a benign isolated finding—systematic evaluation for associated anomalies and long-term follow-up for renal injury is essential 4

Surgical Intervention Threshold

Surgical correction should be performed for identified anomalies in 64-87% of cases, with lower threshold for intervention given the absence of contralateral renal reserve. 2, 3

• High-grade VUR in a solitary kidney warrants surgical intervention rather than observation 2
• Obstructive lesions (UPJ or UVJ obstruction) require prompt surgical correction to preserve function 2, 3
• Mean age at surgery is approximately 4.8 years with excellent outcomes when treated appropriately 3