Endometriosis is a chronic inflammatory gynecologic disorder characterized by presence of endometrial-like tissue outside of the uterus. It is a common condition that affects approximately 10% of reproductive age women worldwide. Common symptoms include dysmenorrhea, dyspareunia, chronic pelvic pain, dyschezia, dysuria, and is associated with infertility. The reference standard for the diagnosis is direct visualization by laparoscopy and biopsy of lesions with a suspicious appearance. There are three types of endometriosis: superficial endometriosis (SPE), deep infiltrating endometriosis (DIE), and ovarian endometriotic cyst. Several guidelines have been developed by different national and international societies to diagnose and classify endometriosis, yet areas of controversy and uncertainty remain. The purpose of this exhibit is to explain the importance of imaging in endometriosis and review the findings of transvaginal ultrasound (TVUS) and MRI.
Educational Goals / Teaching Points
This exhibit aims to review the characteristic features of endometriosis seen in TVUS and MRI; discuss the importance of these imaging modalities in endometriosis; describe the common protocols used; and provide a case-based review of different manifestations of endometriosis.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
TVUS is the primary imaging modality for evaluation of endometriosis. The four components of TVUS are: evaluation of the uterus and adnexa, dedicated search for DIE, assessment of the sliding sign, and detection of sonographic soft markers. Endometriomas are bilateral in up to half of the cases. They exhibit diffuse low-level internal echoes, with the “classic” endometrioma being described as a homogeneous, hypoechoic focal lesion within the ovary. DIE appears as hypoechoic linear or round nodules with smooth or irregular borders and no to minimal internal vascularity at color Doppler US. MRI protocols have proven to be useful in establishing a diagnosis and in preoperative planning. The advantages of MRI include further characterization of US findings, confirmation of disease in the setting of a negative US, and identification of extra pelvic deep endometriosis not reachable with TVUS, such as in the liver or small bowel. On MRI, ovarian endometriomas have a characteristic homogeneous T1-weighted (T1W) hyperintensity that becomes hypointense on a T2-weighted (T2W) image, a feature known as “shading.” DIE typically shows low to intermediate signal intensity on T1W sequences and variable T2W signal. All protocols should include T1W fat-suppressed sequences, as this enables detection of smaller endometriomas and facilitates differentiation of cystic teratomas from endometriomas.
TVUS is the first-line imaging tool for suspected endometriosis, and MRI is considered a second-line imaging technique. The imaging features of endometriosis are highly varied because it is a complex disease process with a heterogeneous phenotype. TVUS and MRI can play a significant role in predicting staging of disease and surgical planning.