Endometriosis is a chronic condition defined by the presence of tissue similar to the uterine lining growing outside the uterus, most commonly within the pelvic cavity. This misplaced tissue responds to hormonal changes, leading to inflammation, pain, and the formation of scar tissue. While endometriosis is primarily known for affecting reproductive organs, its deep infiltration into neighboring structures can lead to complications in other body systems. An uncommon, yet serious, consequence involves the urinary tract, which can indirectly contribute to the development of kidney stones. This connection involves a cascade of events beginning with anatomical obstruction and leading to changes in urine flow that promote stone formation.
Understanding Endometriosis and Urinary Tract Involvement
The proximity of the reproductive and urinary systems within the pelvis makes the urinary tract vulnerable to endometriosis. While the bladder is the most frequently affected urinary organ, endometriotic implants can also involve the ureters, the tubes carrying urine from the kidneys to the bladder. Approximately 10% of people with urinary tract endometriosis have ureteral involvement, typically in the lower third of the ureter. Ureteral involvement is classified as extrinsic or intrinsic.
Extrinsic involvement occurs when endometriotic tissue and dense scar tissue (adhesions) grow around the ureter, compressing it from the outside. Intrinsic involvement, which is less common, happens when the tissue invades the ureter wall itself. In both scenarios, this growth creates a narrowing, or stricture, that impedes the normal flow of urine.
Endometriosis and Obstructive Uropathy
The narrowing of the ureter caused by endometriotic implants and surrounding fibrosis leads directly to obstructive uropathy. This mechanical blockage prevents urine from draining effectively from the kidney into the bladder. As urine output continues, the fluid backs up into the ureter, causing it to swell (hydroureter).
This pressure then causes swelling and dilation of the kidney’s internal collecting system, known as hydronephrosis. This sustained pressure can progressively damage the functional units of the kidney over time. Because ureteral endometriosis is often asymptomatic in its early stages, this damage can occur silently, potentially resulting in the loss of function in the affected kidney.
The Link to Kidney Stone Formation
Hydronephrosis creates an environment conducive to kidney stone formation. The obstruction causes urinary stasis, which is the pooling of urine in the renal pelvis and calyces. This pooling allows solutes to precipitate more easily, increasing the risk of crystal formation.
Urinary stasis also significantly increases the likelihood of a urinary tract infection (UTI) developing within the affected kidney. Certain bacteria that cause UTIs, such as Proteus species, possess the enzyme urease. This enzyme breaks down urea, increasing urinary pH and leading to the subsequent formation of struvite stones, also known as infection stones. Thus, the mechanical obstruction from endometriosis sets the stage for chemical and biological changes that promote the growth of specific types of kidney stones.
Diagnosis and Specialized Treatment Approaches
Diagnosing ureteral endometriosis and co-existing kidney stones requires a high index of suspicion due to non-specific symptoms that may mimic a typical kidney stone attack. Imaging techniques are necessary to visualize the obstruction and any stones present. Initial assessments often involve ultrasound, but detailed anatomical and functional information is gained through computed tomography (CT) scans or magnetic resonance imaging (MRI). An Intravenous Pyelogram (IVP) can also be used to evaluate the extent of the obstruction and the structure of the ureter.
Treatment must address both the kidney stone and the underlying endometriosis to prevent recurrence. The kidney stone may be treated using standard urological procedures like ureteroscopy or lithotripsy. However, the ureteral obstruction caused by the endometriosis must also be resolved. This frequently requires surgery to remove the endometriotic implants and fibrotic tissue compressing the ureter, a procedure called ureterolysis.
If the ureter is significantly damaged or scarred, a more complex procedure may be performed. These include segmental ureterectomy with re-anastomosis or ureteral reimplantation into the bladder. Addressing the deep infiltrating endometriosis surgically, sometimes combined with hormonal therapy, is paramount to maintain long-term kidney function and prevent future stone formation. The goal is always to relieve the obstruction and preserve the function of the affected kidney.