VP05.06: Differential diagnosis of deep rectal endometriosis by ultrasound

In the past decade, the use of transvaginal ultrasound according to the IDEA protocol increased the ultrasound detection rate of rectal deep endometriosis foci. Due to the nature of the disease, such as distorted pelvic anatomy and the variety of phenotypes of endometriotic lesions, a complete sonographic evaluation is often difficult. Several conditions can mimic rectal deep endometriosis. This was a prospective study of patients presenting for possible pelvic deep endometriosis between January 2019 and May 2021. Patients were examined by transvaginal ultrasonography and sonoelastography based on the IDEA protocol. Histology after laparoscopy was the gold standard of the study. Of the 450 patients who underwent ultrasonography for the suspicion of pelvic deep endometriosis in 291 (64,7%) cases were rectal localisation the indication. Deep endometriosis was confirmed by 279 patients. In the remaining 12 (4,3%) patients the diagnoses were: vaginal cyst (3/12), anorectal abscess (3/12), rectal cancer (2/12), hydrosalpinx (2/12) metastatic endometrial cancer (1/12) and Crohn's disease (1/12). Vaginal cysts were round, anechogenic masses with smooth wall at the level of the rectovaginal septum. Anorectal abscesses have mixed hyperechogenic content and high vascularity in the soft wall of the lesion. Rectal cancer can bulge in the lumen of the bowel, but it usually grows outward contrary to deep infiltrating endometriosis lesions infiltrating inward. With a colour Doppler ultrasound examination, rectal cancer shows also increased vascularity. Metastastic tumour was an irregular solid lesion with a leading vessel. In Crohn's Disease elastography shows diffuse fibrosis. For the diagnosis of rectal deep endometriosis a trained ultrasound operator, combining ultrasound modalities and interdisciplinary approach are important. The best scenario is when laparoscopic surgeons are performing the sonography, or the sonographer receives feedback from them.