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Background
CT scan is not the imaging modality of choice for noninvasive diagnosis of endometriosis. However, abdominopelvic pain is a common initial presentation in women with endometriosis, for which they usually undergo a CT scan as the first imaging study. Lack of knowledge of CT appearances of endometriosis can cause a delay in appropriate diagnosis and management. The goal of this educational exhibit is to review the CT features that should raise the suspicion for deep endometriosis and triage the patient appropriately for making an early and accurate diagnosis.

Educational Goals / Teaching Points
Learn to recognize and suspect deep endometriosis on abdominopelvic CT studies through case-based examples. Understand the next best imaging test for confirmation of CT findings based on disease location. Demonstrate the few indications where a CT study does play a role in this patient population.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
CT features of deep endometriosis in the abdomen and pelvis can be divided by anatomic location. Pelvic endometriosis: ovarian endometriomas (hyperdense adnexal masses); uterine surface plaques (nonspecific soft tissue surface deposits, more commonly on the posterior uterine surface at the torus uterinus); and bridging soft tissue plaques in the posterior pelvic compartment (linear, nodular, or spiculated soft tissue in the rectouterine pouch and rectovaginal septum). Bowel endometriosis: large bowel (commonly affecting the rectosigmoid colon with soft tissue infiltration into the anterior wall); ileocecal region (soft-tissue mass bridging the ileum to cecum); appendix (nodular enhancing tissue, commonly at the tip or tethering of appendix to right adnexa); and small bowel (recurrent small bowel obstructions, multifocal involvement, fan-shaped extrinsic small bowel soft-tissue causing the “fortune cookie” sign). Urinary tract endometriosis: urinary bladder (nodular soft tissue at the dome and base). Ureteral endometriosis: uni or bilateral hydroureteronephrosis, with commonest site of obstruction being the distal third of the ureter at 3–4 cm from the ureterovesical junction. Abdominopelvic wall: scar endometriosis; umbilical “villar” nodule; and canal of Nuck endometriosis. Atypical locations: perihepatic (may cause spontaneous bleeding resembling hepatic mass rupture); peritoneal disease (nodular omental and mesenteric soft tissue resembling peritoneal carcinomatosis); pelvic nerve involvement (asymmetric thickening of pelvic nerves, such as the sciatic nerve); and diaphragmatic surface (tiny soft tissue nodules, often difficult to visualize by CT but may present with spontaneous/ recurrent pneumothorax). Indications where CT is useful in this patient population: diagnosis of small bowel obstruction; tuboovarian abscess, especially after oocyte retrieval for fertility treatment; and detection of complications after endometriosis surgery.

Conclusion
Knowledge of CT features of abdominopelvic endometriosis can greatly help suspect this indolent multisystem disease, thus helping make an early diagnosis; however, CT cannot be considered as the imaging modality of choice for diagnosis of endometriosis.