Which segment of the ureter is most commonly involved in ureteral endometriosis?

Ureteric Endometriosis: Most Commonly Affected Segment

The distal third of the ureter is most commonly involved in ureteric endometriosis, with a strong predilection for the left side. 1, 2

Anatomic Distribution Pattern

Location specificity:

• The distal one-third of the ureter (lower segment) is affected in approximately 85-90% of cases 1, 2
• The middle third is involved in only 10-15% of cases 1, 2
• The proximal ureter is rarely affected 2

Laterality preference:

• The left ureter is involved in approximately 85% of cases 1
• Right-sided involvement occurs but is distinctly less common 3
• Bilateral ureteric involvement is rare, occurring in only 9% of cases 4

Pathophysiologic Basis for Distal Involvement

The distal ureter's vulnerability relates to its anatomic proximity to the posterior cul-de-sac and uterosacral ligaments, which are common sites of deep infiltrating endometriosis 5, 6. The rectosigmoid colon is involved in approximately 90% of bowel endometriosis cases, and the distal ureter lies in close proximity to these structures 6.

Clinical Implications of Segment Involvement

Surgical approach varies by location:

• Distal ureteric lesions (most common) are typically managed with distal ureterectomy and ureteroneocystostomy, which has lower recurrence rates (0-18%) compared to endourological approaches 7
• Middle third lesions may require segmental ureterectomy with ureteroureterostomy, though this location is associated with higher failure rates than distal ureter surgery 7
• The distal location typically allows for more straightforward surgical reconstruction with better functional outcomes 1, 2

Critical Diagnostic Considerations

Imaging performance by location:

• MRI demonstrates 88% sensitivity and 83.3% specificity for detecting deep infiltrating endometriosis in posterior locations (including the distal ureter) 5
• The distal ureter can be evaluated with expanded protocol transvaginal ultrasound, which requires assessment of uterosacral ligaments where distal ureteric involvement typically occurs 5

Common Clinical Pitfall

Silent obstruction risk: Ureteric endometriosis is usually asymptomatic and can lead to silent loss of renal function, particularly because the distal location may cause gradual rather than acute obstruction 3, 1, 2. The disease most commonly affects women of reproductive age, though it can present in postmenopausal patients, especially those with prior hysterectomy and bilateral salpingo-oophorectomy 1.