Background
Deep infiltrating endometriosis is a severe form of endometriosis in which tissue similar to the uterine lining grows deeply into surrounding pelvic structures. The posterior pelvic compartment, which includes areas such as the uterosacral ligaments, rectovaginal septum, vagina, and rectum, is commonly involved. Surgery in this region is often complex because of distorted anatomy, adhesions, and the close proximity of bowel, urinary tract, blood vessels, and nerves.
Because these operations can be technically demanding, postoperative complications are a major concern. They may range from bleeding, infection, and urinary or bowel problems to more serious events requiring reoperation, interventional procedures, or prolonged hospitalization. A key question in surgical care is whether patients fare better in hospitals that perform more of these operations each year. This study examined that issue on a national scale.
Objective
The study aimed to determine whether the annual surgical case volume of a hospital is associated with the risk of severe postoperative complications after posterior deep infiltrating endometriosis surgery, either during the initial hospital stay or after readmission within 90 days.
Study Design
This was a population-based cohort study using the French national medico-administrative database, known as the Program of Medicalization of Information Systems. This database captures hospitalizations across France and allows large-scale analysis of real-world surgical outcomes.
The study included all hospital stays for posterior deep infiltrating endometriosis surgery performed in France from January 1, 2021, to December 31, 2023. The main outcome was the occurrence of at least one severe postoperative complication during the first hospitalization or within 90 days after surgery if the patient was readmitted.
Complications were identified using ICD-10 diagnosis codes and then classified according to the Clavien-Dindo system, a widely used method for grading surgical complications. Severe complications were defined as grade III to grade V, meaning they required invasive treatment, intensive care, reoperation, or were associated with death.
Hospital annual case volume was grouped into two levels based on the best cutoff identified through statistical modeling. The researchers also adjusted for important patient and surgery-related factors, including whether the operation was radical or conservative, the surgical approach used, age, prior endometriosis surgery in the previous 3 years, associated procedures, comorbidity burden measured by the Charlson Comorbidity Index, and type of healthcare institution. A generalized estimating equation model was used to account for clustering of patients within the same hospital.
Key Findings
A total of 15,364 hospital stays for posterior deep infiltrating endometriosis surgery were identified.
Among these cases, 658 patients, or 4.3%, experienced at least one severe postoperative complication classified as Clavien-Dindo grade III to V.
The analysis identified 40 hospital stays per year as the optimal cutoff for case volume. Hospitals performing fewer than 40 such surgeries annually had a severe complication rate of 318 out of 6,005 cases, or 5.3%. In comparison, hospitals with 40 or more cases per year had a lower severe complication rate of 340 out of 9,359 cases, or 3.6%.
After adjustment for the measured clinical and surgical factors, higher surgical volume remained associated with better outcomes. Specifically, hospitals performing at least 40 posterior deep infiltrating endometriosis surgeries per year had a reduced risk of severe postoperative complications, with an adjusted odds ratio of 0.83 (95% confidence interval 0.70 to 0.99; p = 0.03). In practical terms, this suggests that patients treated in higher-volume centers had about a 17% lower odds of severe complications than those treated in lower-volume centers, after accounting for other factors.
The study also assessed how much of the variation in complications could be explained by differences between centers. This center effect supports the idea that institutional experience, multidisciplinary organization, and surgical expertise may influence outcomes.
Interpretation
These findings reinforce the concept of volume-outcome relationship in complex surgery: hospitals that perform more cases tend to achieve better results. For posterior deep infiltrating endometriosis, this may reflect several advantages of higher-volume centers, such as:
1. Greater surgical expertise in difficult pelvic anatomy
2. Better preoperative planning and imaging interpretation
3. More consistent access to multidisciplinary teams, including gynecologic surgeons, colorectal surgeons, urologists, radiologists, anesthesiologists, and pain specialists
4. More efficient perioperative protocols and postoperative monitoring
5. Earlier recognition and management of complications
This is especially important because endometriosis surgery often requires a tailored strategy. Some patients may benefit from conservative surgery that preserves tissue and function, while others need more radical excision to fully remove deeply infiltrating disease. The safest approach depends on lesion location, symptoms, fertility plans, prior surgery, and the experience of the surgical team.
Clinical Implications
The results suggest that referral to experienced centers may improve outcomes for patients undergoing posterior deep infiltrating endometriosis surgery. For patients and clinicians, this study supports the idea that complex endometriosis surgery should preferably be concentrated in hospitals with established expertise and sufficient annual case volume.
This does not mean that every lower-volume hospital provides poor care. However, for high-complexity procedures such as posterior deep infiltrating endometriosis surgery, centralization may help reduce the risk of serious complications and potentially improve recovery.
For patients, practical considerations include asking whether the center performs endometriosis surgery regularly, whether a multidisciplinary team is available, and what pathways exist for managing complications if they occur.
For healthcare systems, the findings may inform regional referral pathways, quality improvement efforts, and the organization of specialized endometriosis units.
Study Strengths and Limitations
A major strength of this study is its nationwide design, which minimizes selection bias and reflects real-world practice across France. The large sample size also allowed a robust analysis of uncommon but clinically important severe complications.
The use of a validated classification system for complications adds reliability, and adjustment for multiple confounders strengthens the findings.
However, there are limitations. As with all database studies, some clinical details are not available, such as lesion size, exact disease extent, surgeon-specific experience, imaging findings, operative complexity beyond coded procedures, and patient preferences. Administrative coding may also miss some complications or misclassify others. In addition, the study shows association rather than direct causation, so lower complication rates in high-volume centers may partly reflect unmeasured factors such as team structure or referral patterns.
Conclusion
In this nationwide French study, hospitals performing 40 or more posterior deep infiltrating endometriosis surgeries per year had lower rates of severe postoperative complications than lower-volume hospitals. The findings suggest that surgical experience at the center level is an important determinant of short-term outcomes after complex endometriosis surgery.
For patients, this supports consideration of referral to specialized, high-volume centers when surgery for posterior deep infiltrating endometriosis is planned. For clinicians and health systems, it underscores the value of centralizing care and strengthening multidisciplinary expertise for this challenging condition.