Deep infiltrating endometriosis (DIE) of the rectum and rectosigmoid colon represents one of the most severe forms of endometriosis and often requires surgical management when symptomatic and unresponsive to medical therapy. Accurate preoperative assessment of lesion size, extent, and depth of bowel infiltration is essential to guide surgical planning and minimize complications. Transvaginal ultrasound (TVUS) is the first-line imaging technique for the diagnosis of pelvic endometriosis and has high diagnostic accuracy for detecting rectosigmoid lesions. However, its ability to precisely assess infiltration depth and guide the choice of surgical technique may be limited by anatomical distortion and technical factors. Intraoperative ultrasound (IO-US) is a real-time imaging modality that can be performed during laparoscopic surgery after adhesiolysis, allowing direct evaluation of bowel lesions. It may improve the assessment of lesion characteristics and support intraoperative decision-making, potentially reducing unnecessary bowel resections. This prospective single-center comparative study aims to evaluate the agreement between preoperative TVUS and intraoperative ultrasound in measuring rectal and rectosigmoid DIE nodules. Secondary objectives include assessing measurement differences, identifying factors associated with discordance, and evaluating the reproducibility of ultrasound measurements. The findings of this study may improve preoperative counseling, optimize surgical planning, and support the integration of intraoperative ultrasound into the management of bowel endometriosis.

Deep infiltrating endometriosis (DIE) is defined as endometriotic lesions penetrating at least 5 mm beneath the peritoneal surface and represents the most severe form of the disease. Bowel involvement occurs in a significant proportion of cases, with the rectum and rectosigmoid junction being affected in up to 70-90% of intestinal localizations. Patients commonly present with gastrointestinal symptoms such as dyschezia, tenesmus, constipation, or obstructive symptoms, which may significantly impair quality of life.

Surgical management is indicated in patients with severe symptoms or failure of medical therapy. In this setting, accurate preoperative evaluation of lesion size, number, circumferential involvement, and depth of bowel wall infiltration is crucial to guide surgical planning and to select the most appropriate technique (e.g., shaving, discoid excision, or segmental resection). An optimal balance between radical excision and functional preservation is essential to minimize postoperative complications and long-term functional sequelae. Transvaginal ultrasound (TVUS) is currently considered the first-line imaging modality for the diagnosis of pelvic endometriosis. When performed by experienced operators following standardized protocols, TVUS demonstrates high sensitivity and specificity for detecting rectosigmoid DIE. However, its ability to accurately assess the depth of muscular infiltration and to predict the most appropriate surgical approach may be limited by acoustic shadowing, reduced rectal distension, anatomical distortion due to adhesions, and operator dependency.

Intraoperative ultrasound (IO-US) is a real-time imaging technique performed during laparoscopic surgery using probes compatible with standard trocars. Following adhesiolysis and mobilization of the affected bowel segment, IO-US allows direct application of the probe to the lesion, enabling a more precise evaluation of lesion size, number, circumferential involvement, and depth of infiltration. This technique has been widely used in other surgical fields, such as hepatic and renal surgery, and may provide additional information to guide intraoperative decision-making in endometriosis surgery.

Preliminary evidence suggests that IO-US may improve the accuracy of lesion assessment and may influence surgical strategy; however, current data are limited and derived from small series. In particular, the agreement between preoperative TVUS and IO-US in the evaluation of rectal and rectosigmoid DIE has not been systematically investigated. This prospective, single-center, observational comparative study is designed to assess the agreement between preoperative TVUS and IO-US measurements in the same patients using paired data. Each participant will undergo standard preoperative TVUS and intraoperative ultrasound following adhesiolysis. In both assessments, lesion dimensions (craniocaudal and laterolateral diameters), depth of infiltration, and percentage of bowel circumference involved will be recorded.

By directly comparing preoperative and intraoperative ultrasound findings, this study aims to clarify the potential added value of IO-US in the surgical management of rectosigmoid endometriosis. The results may contribute to improving preoperative counseling, refining surgical planning, and optimizing the balance between radicality and functional preservation in patients undergoing surgery for bowel endometriosis.

Inclusion Criteria:

• Women aged 18 to 55 years
• Clinical and/or imaging suspicion of rectal or rectosigmoid deep infiltrating endometriosis (DIE)
• Indication for laparoscopic or robotic surgery for DIE
• Ability and willingness to provide written informed consent

Exclusion Criteria:

• Previous bowel resection for deep infiltrating endometriosis
• Active inflammatory bowel disease
• Pregnancy
• Technical inability to perform transvaginal or intraoperative ultrasound
• Refusal or withdrawal of informed consent

Women with suspected deep infiltrating endometriosis of the posterior compartment involving the rectum or rectosigmoid colon who are scheduled for surgical treatment.