Intraoperative ultrasound in minimally invasive surgery for deep endometriosis: time for new approaches

Abstract

Endometriosis is a complicated and growing health concern, affecting approximately 2–3% of individuals assigned female at birth worldwide1, 2. Advances in ultrasound and magnetic resonance imaging (MRI) allow assessment of disease, to some extent obviating the ‘(g)old standard’ of diagnostic laparoscopy3. Use of standardized examination criteria for deep endometriosis (DE) on transvaginal ultrasound assessment, as well as terms and definitions of DE, as suggested by the International Deep Endometriosis Analysis (IDEA) group, allow for prediction of the involvement of most pelvic structures with satisfactory diagnostic accuracy4, 5. Despite these significant advances, transvaginal ultrasound for DE is operator dependent and prone to limitations, for example, in cases of severely distorted pelvic anatomy or cul-de-sac obliteration5. This necessitates the employment of innovative tools and techniques, allowing better intraoperative planning and precise intraoperative decisions. One such tool is intraoperative ultrasound (IO-US), which has been employed since the 1960s for the detection of common bile duct and renal stones in cases of profound inflammation6, 7. The application of IO-US in gynecology, specifically for DE, has been more limited, despite the progress of sonography in gynecological diagnostics7. In this Opinion, we undertook a comprehensive search of the literature using terms for intraoperative ultrasound/sonography and deep endometriosis in PubMed (MEDLINE), ScienceDirect and Google Scholar. All study types written in the English language were considered for inclusion. Herein, we summarize the evidence on the use of IO-US in surgery for DE, providing perspectives on the use of IO-US and its applicability in disease management. IO-US describes a wide variety of sonographic techniques that can be employed in all types of gynecological surgery. It is considered a low-risk tool with a ‘real-time’ scanning nature. Different ultrasound probes can be used depending on the surgical procedure, route and purpose of use. In a recent systematic review, Galazis et al.8 described five different types of IO-US applied in fertility-sparing gynecological surgery: transabdominal, transvaginal, transrectal, laparoscopic and contact ultrasound. For transabdominal ultrasound, the ultrasound probes used have a frequency range of 1–5 MHz. For transvaginal and transrectal ultrasound, a variety of probe types can be used, including convex-array, two-dimensional, three-dimensional and transverse endocavitary transducers, with frequencies ranging from 2–20 MHz. Additionally, laparoscopic ultrasound (using probes with a frequency range of 2–15 MHz) and contact ultrasound, which includes the use of linear, convex or T-shaped finger-grip probes during open surgery (using probes with a frequency range of 1–15 MHz), have also been described8-10. Each type of ultrasound technique can find an application in a different setting. For example, contact ultrasound has been used in open surgery, primarily for the detection of metastasis in oncological cases. Transabdominal ultrasound has been used to guide dilation and curettage and hysteroscopic procedures or the placement of intrauterine devices to reduce the risk of perforation7. Owing to the proximity of the transvaginal probe to ovarian tissue compared with that used in transabdominal ultrasound, transvaginal ultrasound has been applied in the context of guidance for fertility/ovary-sparing surgery of adnexal masses, paving the way for future studies in endometrioma surgery11. With respect to endometriosis, researchers have attempted excision of rectal endometriosis under transvaginal ultrasound guidance, but procedures can also be performed under laparoscopic ultrasound guidance. As far as laparoscopic ultrasound is concerned, it can be used for detection of lesions up to 3–5 mm in diameter during conventional laparoscopy and robotic surgery12. The ultrasound probes used are typically linear or conv