Can endometriosis cause flank pain?

Can Endometriosis Cause Flank Pain?

Yes, endometriosis can cause flank pain when deep infiltrating endometriosis involves the ureter or other retroperitoneal structures, though this represents a less common presentation than typical pelvic pain symptoms.

Mechanism of Flank Pain in Endometriosis

The World Endometriosis Society classification system specifically recognizes ureter involvement (designated as "FU: Ureter intravx") as a distinct compartment of deep infiltrating endometriosis 1. When endometriotic lesions infiltrate or compress the ureter, this can produce flank pain through:

• Ureteral obstruction causing hydronephrosis and stretching of the renal capsule 1
• Direct neural infiltration of retroperitoneal structures, which can activate nociceptors up to 2.7 cm from the lesion itself 2
• Inflammatory reaction in the retroperitoneal space from deep infiltrating disease 2

Clinical Presentation Patterns

Endometriosis pain typically manifests in three primary patterns: secondary dysmenorrhea, deep dyspareunia, and sacral backache with menses 3. However, when deep infiltrating disease extends beyond the pelvis:

• Flank pain may be cyclical (worsening with menses) or constant depending on the degree of ureteral involvement 4, 5
• The severity of pain correlates with the depth of endometriotic lesions rather than the type of lesions visible on laparoscopy 3, 6
• Up to 90% of patients with endometriosis report pelvic pain, but extragenital manifestations including urinary tract involvement occur in a subset 4

Diagnostic Approach

When evaluating flank pain in a woman of reproductive age with suspected endometriosis:

• Do not rely on imaging alone to exclude endometriosis, as normal physical examination and imaging do not rule out the diagnosis 4
• Consider noncontrast CT abdomen/pelvis as the reference standard if urolithiasis needs to be excluded (sensitivity 97% for stones) 1
• Transvaginal ultrasound or pelvic MRI can support the clinical diagnosis of endometriosis, though surgical visualization remains the gold standard 4, 5
• Laparoscopy with direct visualization is required for definitive diagnosis and allows assessment of ureteral involvement 1

Important Clinical Pitfall

The average diagnostic delay for endometriosis is 5-12 years after symptom onset, with most women consulting 3 or more clinicians before diagnosis 4. When flank pain is the presenting symptom rather than typical pelvic pain, this delay may be even longer as clinicians focus on more common causes of flank pain such as urolithiasis 1. Always consider endometriosis in reproductive-age women with unexplained flank pain, particularly if cyclical or associated with other gynecologic symptoms 4, 5.

Management Implications

If deep infiltrating endometriosis with ureteral involvement is suspected:

• Start first-line hormonal therapy (combined oral contraceptives or progestin-only options) for symptomatic relief while arranging definitive diagnosis 3, 6, 4
• Refer to gynecology for surgical evaluation if empiric medical therapy is ineffective, as ureteral endometriosis may require excisional surgery involving ureter dissection 6, 2
• Recognize that medical therapy alone may be insufficient for severe deep infiltrating disease with ureteral involvement 6, 2
• Monitor for hydronephrosis with renal ultrasound if ureteral obstruction is suspected, as this can lead to permanent renal damage if untreated 1