What is the name of the congenital renal anomaly characterized by a left kidney with two separate collecting systems sharing a common renal pelvis and partially duplicated ureters?

Duplex Collecting System (or Double Collecting System)

The congenital renal anomaly you're describing is called a duplex collecting system (also known as a double collecting system or duplicated collecting system). This represents a common congenital urinary tract anomaly where a single kidney has two separate collecting systems that may share a common renal pelvis with partially duplicated ureters 1.

Anatomical Characteristics

A duplex collecting system occurs when:

• Two separate collecting systems drain different portions of the same kidney (typically upper and lower pole moieties)
• The ureters may be partially duplicated (joining before entering the bladder in a Y-shaped configuration) or completely duplicated (separate insertions into the bladder)
• When partially duplicated, the ureters converge at some point along their course, sharing a common distal segment 2

Clinical Significance

Prevalence and Demographics

• Affects approximately 0.7-4% of the population 3
• More common in females than males 3
• Often discovered incidentally on imaging studies 1

Associated Complications

While frequently asymptomatic, duplex systems can present with:

• Recurrent urinary tract infections (most common symptomatic presentation) 3, 4, 5
• Hydronephrosis affecting one or both moieties 6, 4, 5
• Vesicoureteral reflux (VUR) - particularly when completely duplicated 7
• Ureteroceles (cystic dilation of the distal ureter) 3, 5
• Urinary incontinence (when associated with ectopic ureteral insertion) 8
• Lithiasis (stone formation) in the duplicated system 6

Diagnostic Approach

Imaging Modalities

The diagnosis is typically established through:

1. Ultrasound - Initial screening tool that can identify:

   • Separate collecting systems within a single kidney
   • Hydronephrosis of one or both moieties
   • Dilated ureters 1

2. Voiding cystourethrography (VCUG) - Evaluates for:

   • VUR (which can be primary or secondary to the duplication)
   • Ureteral anatomy and insertion points 7

3. MR Urography - Provides superior anatomical detail for:

   • Complex duplicated systems
   • Atypical urinary tract anatomy
   • Surgical planning 7

Clinical Context

Important caveat: Duplex collecting systems are frequently detected during workup for other conditions, particularly in pediatric patients with febrile UTIs. Studies show that among children undergoing renal ultrasound after UTI, double collecting systems are found in approximately 1-7% of cases 1. The detection rate varies based on the clinical indication and imaging technique used.

The anatomical variation described—with two separate collecting systems sharing a common renal pelvis and partially duplicated ureters—represents an incomplete or partial duplication, which is the most common form of this anomaly 2, 3.