Introduction: Endometriosis affects 10%-15% of women in reproductive age and may cause no-cyclic chronic pelvic pain, dysmenorrhea, dyspareunia, urinary tract symptoms, and it is frequently associated with infertility. The peak of incidence is between 24 and 29 years old and the clinical diagnosis of endometriosis is generally delayed by 6-7 years. Laparoscopy with surgical biopsies is the "gold standard" for the diagnosis of endometriosis, with histological verification of endometrial ectopic glands and/or stroma. However, nowadays two different non-invasive modalities are routinely used for a presumptive diagnosis: Transvaginal Ultrasound (TVUS) and Magnetic Resonance Imaging (MRI).
Evidence acquisition: A structured search using PubMed was performed starting from October 2020 and including all relevant original and review articles published since 2000. The search used the following key word combinations: "endometriosis MRI" AND "DIE and MRI" (45); "MRI endometriosis and pelvic pain" OR "endometriosis and MRI technical development" (296). Ultimately, 87 articles were deemed relevant and used as the literature basis of this review.
Evidence synthesis: TVUS represents the first imaging approach for endometriosis showing a good diagnostic performance, but it is highly operator dependent. MRI is a second level examination often used in complex cases indeterminate after TVUS and in preoperative planning. MRI is considered the best imaging technique for mapping endometriosis since it provides a more reliable map of deep infiltrating endometriosis than physical examination and transvaginal ultrasound. We have analyzed and described the main forms of endometriosis: adnexal endometriosis, adenomyosis, peritoneal implants and deep infiltrating endometriosis, showing their appearance in the two imaging modalities.
Conclusions: Endometriosis is one of the most common gynecologic disorders correlated to chronic pelvic pain whose treatment is still today complex and controversial. In this context, MRI has become an important additional non-invasive tool to investigate cases of chronic pelvic pain related to deep infiltrating endometriosis (DIE) with or without neural involvement.