ª Springer Science+Business Media New York 2016 Abdominal Radiology Abdom Radiol (2016) DOI: 10.1007/s00261-016-0956-8 Deep pelvic endometriosis: a radiologist’s guide to key imaging features with clinical and histopathologic review Ayeh Darvishzadeh ,1 Wendaline McEachern,2 Thomas K. Lee,3 Priya Bhosale,4 Ali Shirkhoda,1 Christine Menias,5 Chandana Lall1 1 Department of Radiology, University of California Irvine School of Medicine, 1001 Health Sciences Road, Irvine, CA 92617, USA Department of Radiology, Mayo Clinic, Rochester, MN, USA 3 Department of Pathology, University of California Irvine School of Medicine, Irvine, CA, USA 4 Division of Diagnostic Imaging, UT MD Anderson Cancer Center, Houston, TX, USA 5 Department of Radiology, Mayo Clinic, Phoenix, AZ, USA 2 Abstract While endometriosis typically affects the ovaries, deep infiltrating endometriosis can affect the gastrointestinal tract, urinary tract, and deep pelvis, awareness of which is important for radiologists. Symptoms are nonspecific and can range from chronic abdominal and deep pelvic pain to nausea, vomiting, diarrhea, constipation, hematuria, and rectal bleeding. Ultrasound and computed tomography may show nonspecific soft-tissue density masses causing bowel obstruction and hydronephrosis. This constellation of presenting symptoms and imaging evidence is easily mistaken for other pathologies including infectious gastroenteritis, diverticulitis, appendicitis, and malignancy, which may lead to unnecessary surgery or mismanagement. With this, deep pelvic endometriosis should be considered in the differential diagnosis in a female patient of reproductive age who presents with such atypical symptoms, and further work up with magnetic resonance imaging is imperative for accurate diagnosis, treatment selection, and preoperative planning. Key words: Endometriosis—Deep infiltrating endometriosis—Gastrointestinal tract—Pelvis—Cul-desac—Ultrasound—Magnetic resonance imaging (MRI)—Computed tomography (CT) Endometriosis was first reported by Rokitansky in 1860 and affects 1–7% of women, including 6–10% of preCorrespondence to: Ayeh Darvishzadeh; email: [email protected] menopausal women and 2.5% of postmenopausal women [1–3] with an average age of diagnosis usually between 25- and 29-year old, increasing with age. Risk factors include prolonged use of an intrauterine device, uninterrupted menstrual cycles, and a history of a first-degree relative with endometriosis [4]. The incidence of endometriosis increases to 17% in women with infertility and to 50% of women who complain of pelvic pain [5, 6]. Typically, endometriosis implants in the ovaries and uterosacral ligaments with the classic clinical presentation being a female of reproductive age with cyclical pelvic pain with menstruation and dyspareunia [7]. Endometriosis, however, can affect other areas including the pericardium, lungs, and the peritoneum. Roughly 5–15% of endometriosis affects the gastrointestinal tract [5, 8]. Most commonly, gastrointestinal endometriosis involves the rectosigmoid colon, followed by the sigmoid colon, rectum, ileum, appendix, and cecum; this is often but not always present in conjunction with pelvic endometriosis. Deep infiltrating endometriosis (DIE) is defined as subperitoneal endometrial implants, greater than 5 mm in depth affecting the gastrointestinal tract, urinary tract, and pelvic cul-de-sac and is usually associated with reactive inflammation, fibrosis, adhesions, and smooth muscle hyperplasia (Fig. 1). Gastrointestinal DIE typically involves the rectosigmoid, small bowel, colon, and appendix. DIE of the urinary tract can affect the ureters and urinary bladder while DIE of the cul-de-sac can involve the uterosacral ligaments, vagina, and cervix. Patients with endometriosis usually present with chronic, nonspecific symptoms including nausea, vomiting, diarrhea, constipation, rectal bleeding, dyschezia, deep dys- A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 2. Colonoscopy images of female with endometriosis of the colon showing A mucosal induration with areas of fibrosis and punctate hemorrhagic foci and B mass-like protrusion into the colon. Fig. 1. Schematic of the female reproductive system and pelvis illustrating typical locations of deep infiltrating endometriosis. A Uterus and associated structures and colon. B Sagittal view of the pelvis. pareunia, and even crippling, chronic pelvic pain [9, 10]. Roughly 27% of intestinal endometriosis results in bowel obstruction and can necessitate emergency surgery [11, 12]. Since symptoms tend to be nonspecific, the estimated delay in diagnosis is between 3 and 9 years and is greater in patients whose primary complaint is pelvic pain as opposed to those reporting infertility [12, 13]. Furthermore, physical exam is usually insensitive to detect endometriosis [14] with highly variable findings on exam depending on size and location of ectopic tissue and clinical experience of examiners. The most common clinical findings include palpable nodules at the uterosacral ligament, rectovaginal space, Pouch of Douglas, rectosigmoid, and posterior wall of the urinary bladder [15]. However, the diagnostic value of a physical examination is limited by the inability of an examiner to palpate deep enough into the pelvis, specifically in the rectosigmoid space. Subsequent delayed diagnosis is costly, with an estimated cost of $12,419 per woman per year due to health care costs and loss of productivity [16, 17]. Delay in diagnosis leads to more progressive disease, which increases the risk of organ damage and greater need for invasive surgical intervention [15]. A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 3. An asymptomatic 44-year-old woman with a significant family history of colon cancer who on screening colonoscopy was found to have a mass in the sigmoid colon that did not penetrate through the mucosa. Differential diagnosis at time of surgery was gastrointestinal stromal tumor, leiomyoma, or endometriosis. A, B Coronal and axial contrast-enhanced CT images show a subtle, soft-tissue density thickening in the sigmoid colon (arrows). Inlet image is zoomed in image of coronal CT showing circumscribed mass in colon with hyper- attenuation at mass borders and heterogenous soft-tissue density body. C Specimen of resected sigmoid colon showing intramural mass protruding into the sigmoid. D–F Pathology images of mass shown in C. D Low-power image of histological, showing colonic mucosa (arrow) with areas of hypertrophic muscularis propria and endometriosis (asterisk). E High-power images of benign endometrial gland and endometrial stroma. F High-power image of endometrial gland and stroma stained positive with estrogen-receptor immunostaining (brown). A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 4. 40-year-old female with rectal pain and hematuria. A, B Transvaginal ultrasound imaging showing a hypoechoic mass between the urinary bladder and anterior uterus rectum. C, D Axial and sagittal contrast-enhanced CT images showing a mildly enhancing mass in between the urinary bladder and anterior uterus (asterik). Typically, patients with endometriosis are often diagnosed with pelvic inflammatory disease, irritable bowel syndrome, Crohn disease, infectious colitis, diverticulitis, appendicitis, and malignancy [13]. Small, scattered deep endometrial foci can be especially difficult to detect with computed tomography (CT) and magnetic resonance imaging (MRI) secondary to limiting in spatial resolution. Recent developments in soft-tissue characterization on MRI, however, allow for excellent preoperative assessment of DIE. Laparoscopic surgery with histological confirma- tion remains the gold standard diagnostic method to date. However, unanticipated intraoperative biopsies showing endometriosis often result in a second surgery after reassessment and proper bowel preparation [18]. Given this, diagnosis of endometriosis involving the colon and pelvis is important to allow for preoperative planning, which may include a general surgeon or urologist. The objective of this article is to review and discuss the symptoms and imaging of deep pelvic endometriosis of the gastrointestinal and urinary tract in order to A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 5. 41-year-old female presented to the Emergency Department with severe deep pelvic pain. A–C Axial CT images with enteral contrast showed a lobulated soft-tissue density mass causing extrinsic compression and severe luminal narrowing at the rectosigmoid junction. Imaging find- ings on CT raised concern for a colorectal neoplasm. D Single-contrast barium enema shows a 7 cm stricture with serrated appearance and mucosal crenation at the rectosigmoid junction. Subsequent pathology revealed rectosigmoid endometriosis. familiarize clinicians with the typical and atypical appearance of suspected DIE on various imaging modalities. depth. Understanding the imaging of deep infiltrating endometriosis relies on some factors of its pathophysiology. DIE is associated with reactive inflammation of the surrounding area, including proliferation of smooth muscle cells, fibrosis, and adhesions [19]. Endometriotic implants may also include small, interspersed hemorrhagic foci. Clinical features and pathophysiology Deep infiltrating endometriosis consists of subperitoneal endometrial implants that are greater than 5 mm in A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 6. 33-year-old female with a 3-year history of severe pelvic and abdominal pain, constipation, and catamenial rectal bleeding. A Transvaginal ultrasound images of adenomyosis showing cystic anechoic spaces throughout the myometrium that show low velocity flow with Doppler sonog- raphy. B, C Axial and coronal contrast-enhanced CT images show circumscribed broad-based soft-tissue density thickening at the sigmoid colon (arrows). D High-power pathology section showing endometrial glands and stroma infiltrating the submucosal and muscularis propria. A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 7. 34-year-old female presenting with severe right lower quadrant pain and mild rectal bleeding. A Coronal contrastenhanced CT image of the abdomen and pelvis showing a hypodense mass at the cecal base and appendix (asterix). B Delayed urographic phase CT image of the abdomen and pelvis showing right hydronephrosis and extrinsic ureteral involvement at the middle right ureter. C Magnetic resonance urogram and D retrograde right ureteral injection showing mild hydronephrosis and extrinsic compression and narrowing of the right ureter at the upper pelvis (blue arrows) E, F Axial contrastenhanced CT images showing dilation of the right ureter proximal to external compression at the area of endometriosis. G Final specimen of the appendix showing endometrial glands and stroma in the lumen of the appendix (asterix). Final diagnosis was endometriosis of the appendix and right ureter. A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 9. 46-year-old female with a 1-year history of episodic c crampy abdominal pain in the mid-epigastric and right upper quadrant region, presenting to the Emergency Department with a 1-day history of severe right and epigastric abdominal pain, nausea, chills and sweats, denies changes in bowel habits, diarrhea, constipation, or hematochezia. Physical exam showed tenderness to palpation in epigastric and left and right lower quadrants of the abdomen. Abdominal ultrasound showed no evidence of liver, common bile duct, or gallbladder abnormality. A–C, Coronal, sagittal, and axial contrast-enhanced CT images of the abdomen shows a lowlying cecum that is positioned medially within the mid-pelvis with an ill-defined soft-tissue density mass with scattered lowattenuation areas that appear to be emanating from the cecal base. D, E Coronal and sagittal-delayed CT images with intraluminal contrast filling the cecum and distal small bowel showing the cecal mass. Differential diagnosis at time of imaging included cecal or appendiceal neoplasm, and inflammatory mass relation to initial presentation of inflammatory bowel disease or subclinical appendicitis. F Final pathology confirms endometriosis with histology showing endometrial glands and stroma in the colonic mucosa (dashed circles) and submucosal (asterix). G Endoscopic image showing large erythematous mass at the cecum that was soft and fluctuant with positive pillow sign when compressed. Fig. 8. Contrast-enhanced coronal abdominal CT image of 38-year-old female with history of episodic right lower quadrant abdominal pain showing heterogeneous soft-tissue density mass in the cecum (straight arrow). Circumscribed areas of hypoattenuation suggestive of hemorrhagic foci (round arrow). Differential diagnosis included acute appendicitis, cecal malignancy, Crohn’s disease, enterocolitis, and ileocecal tuberculosis. Pathology confirmed cecal endometriosis. Gastrointestinal tract In the bowel, DIE implants at the antimesenteric edge of the serosa and infiltrates through the muscularis propria into the wall in a progressive manner [20]. Furthermore, depending on the location of ectopic tissue and depth of invasion, bowel endometriosis can present in various, surprising ways. Superficial endometriosis involving only the serosa can be asymptomatic. Classically, we would expect patients with DIE to report pelvic pain that peaks and troughs in a cyclical manner synchronized with the proliferation and shedding of the ectopic endometrial tissue with the menstrual cycle [21, 22]. However, patients report chronic deep pelvic pain nausea, vomiting, diarrhea, constipation, reduced stool caliber, abdominal bloating, and even ascites [11, 21–27]. Although DIE rarely infiltrates through to the mucosa, patients may also present with hematochezia, thought to occur when swelling of underlying endometrial tissue causes colonic mucosa to tear [20, 25]. Endometriosis of the appendix can also occur and may present with profuse rectal bleeding or mimic acute appendicitis, chronic appendicitis, or a peptic ulcer [28–32]. Patients who present with changes in bowel movements and abdominal pain often undergo colonoscopy and CT for initial analysis, but the findings can mislead physicians toward diagnoses of malignancy, inflammatory bowel disease (IBD), ischemic bowel, or chronic enteritis. On endoscopy, deep endometriosis can present with slight induration or hyperplastic surface epithelium of the mucosa (Fig. 2), intramural masses protruding into the colon causing extrinsic compression and luminal narrowing (Fig. 3), or as masses with central ulceration and indurated, rolled borders that can mimic carcinoma [19, 33]. On biopsy, mucosal changes include distorted colonic glands, blunting of intestinal villi, pyloric metaplasia, polypoid granulation tissue, and deep fissures also found in IBD, ischemic bowel, and chronic enteritis [19]. Urinary tract Deep infiltrating endometriosis of the urinary tract most commonly affects the bladder (15%) and the ureters (4.5%), in women with severe endometriosis [34, 35]. Endometriosis of the bladder can present with hematuria, dysuria, urinary frequency, urinary tract infections, pelvic pain, constipation, diarrhea, and both urgency or stress urinary incontinence [35–39]. Diagnosis of bladder endometriosis is confounded by a clinical presentation that is similar to urinary tract infections, A. Darvishzadeh et al.: Deep pelvic endometriosis A. Darvishzadeh et al.: Deep pelvic endometriosis overactive bladder syndrome, painful bladder syndrome, and interstitial cystitis [40]. Bladder endometriosis may also be associated with ovarian and rectosigmoid lesions, with one study reporting co-existing disease in 49.2% and 28.9% of cases, respectively [38]. Ureteral endometriosis typically implants on the external surface of the ureters and causes external constriction of the ureteral wall, leading to significant pathology such as progressive renal function loss. Thus, diagnosing ureteral endometriosis is critical to prevent kidney damage and significant hydronephrosis but can be difficult due to either a complete lack of or nonspecific symptoms. Unfortunately, 47% of patients with ureteral endometriosis require nephrectomy at the time of diagnosis [41]. Common presenting symptoms include dysuria, recurrent urinary tract infections, and hematuria [35]. Correlations between ureteral and rectovaginal endometriosis and between ureteral and uterosacral ligament endometriosis have also been reported and should be considered with women who have evidence of either other locations [34, 35]. Imaging modalities Ultrasound Gastrointestinal tract Transvaginal ultrasound after bowel preparation (TVUS-BP) remains the best initial imaging method for endometriosis, since it can detect foci of deep endometriosis including which layer of bowel has been infiltrated, while also being low cost, vastly available, and not exposing the patient to radiation [37, 42–46]. It is, however, operator-dependent, time-consuming and may miss or underestimate the extent of disease. Improvements in patient preparation allow increased visualization of the bowel for examination. These include adequate bowel preparation to minimize fecal contents and intestinal gas, placing ultrasound gel in the upper third of the vagina to distend the vaginal dome, and injecting ultrasound gel in the rectum gain a better view of the bowel wall [37, 47]. Using TVUS-BP, bowel endometriosis appears as an irregular hypoechoic mass with or without hypoechoic or hyperechoic foci penetrating into the hypoechoic muscularis propria layer wall. It may also show as long, nodular hypoechoic lesions along the intestinal wall [20, 42]. Submucosal lesions appear as hypoechoic gaps in the hyperechoic submucosa. On color Doppler imaging, the masses show no blood flow. A number of characteristic appearances of endometriosis of the rectosigmoid area have been reported, including the ‘‘pyramid sign,’’ the ‘‘comet sign,’’ and the ‘‘Indian headdress sign’’ [48–50]. The lesions are Fig. 10. 43-year-old female with history of endometriosis c presenting with 3 months of right lower flank pain and hematuria. A–C Axial contrast-enhanced images of the pelvis showing a, irregular contour at the right bladder with a mildly hyperdense mass extending into the vescicular space. B Delayed imaging showing intravenous-contrast filling the bladder outlining the irregular mass and C post-contrast image showing mild hyperattenuation of the mass with attenuation again similar to myometrium. D Axial T1-weighted MRI image showing the mass in the lower right bladder wall that appears isointense to muscle with foci of hyperintensity indicative of hemorrhagic cysts. E Axial T2-weighted MRI image showing the mass is hypointense to muscle with hyperintense foci again indicative of hemorrhagic products. F Final pathology of the lesion in the bladder wall showing endometrial glands at the level of the muscularis propria with E, estrogen-receptor staining positive on immunohistochemistry. described as pyramidal shaped and are attached to the anterior rectal wall, pointing anteriorly toward the uterus [48]. Furthermore, the margins are irregular and one end appears thinner than the other, similar to a comet, and thin band-like echoes that spread out from the center of the mass have been described as like an ‘‘Indian head dress’’ [49, 50]. Examiners can also look for pelvic adhesions by assessing the movement of the uterus, ovaries, and bowel loops with movement of the transducer [37]. TVUS-BP, however, is most useful when detecting endometriosis of the bladder, rectum, and rectovaginal septum, with limitations of examining the proximal gastrointestinal tract [51]. Trans-rectal ultrasound (TRUS) has also shown high sensitivity and specificity for detecting endometriosis of the rectovaginal region [52]. Like with TVUS, endometriosis of the rectosigmoid presents as irregular hypoechoic masses on the intestinal wall, protruding through the muscularis layer, and a characteristic ‘‘C’’ shape has been described that identifies the retraction of the endometriotic nodule due to fibrosis and adhesions [53]. TRUS is limited in which it cannot be used to assess DIE of the anterior pelvic cul-de-sac, including the uterovesical space and bladder, and may require the patient to be sedated. However, it offers the benefits for the examiner to perform a fine needle aspiration for histological confirmation and is better able to determine the extent of endometriosis infiltration into the intestinal wall than TVUS [53, 54]. Urinary tract Ultrasound is the initial imaging method of choice for urinary tract endometriosis. TVUS the first line method of diagnosing bladder endometriosis from which the size A. Darvishzadeh et al.: Deep pelvic endometriosis A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 11. ‘‘Mushroom cap sign’’ seen with a deep, infiltrating deposit in the rectum (A sagittal T2, B sagittal T1 FS postgadolinium; C fluoroscopic barium enema with end-to-side anastomosis; arrows). There is T2 hypointense, enhancing fibrosis between the torus uterinus and the rectum (A, B; arrowheads), with obliteration of the rectocervical space (D axial T1 FS postgadolinium; arrow). of the lesions and infiltration into the detrusor muscle can be assessed [51]. The endometrial lesions typically appear as solid ‘‘comma-shaped’’ or spherical hypoe- choic or isoechoic to the bladder wall masses with numerous anechoic spaces within, described as ‘‘bubblelike’’ [55–57]. Color Doppler shows few vessels within the A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 12. 46-year-old female with obliterated anterior and posterior cul-de-sac secondary to chronic fibrotic endometriosis. A Sagittal T1FS post-gadolinium and B sagittal T2 imaging shows tethering to the urinary bladder (arrows). C Sagittal T2 image shows tethering to the rectum (arrow). D Axial T1 FS and E sagittal T2 images show bilateral ovarian endometriomas which are T1 hyperintense (D, arrows) with T2 shading with tethering to the uterine fundus (E, arrows) creating a ‘‘kissing ovaries’’ appearance (F coronal T2, arrow). A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 13. A nodular submucosal mass protrudes into the urinary bladder with punctate foci of T1 hyperintense (A axial T1 FS, arrow) and predominantly T2 hypointense (B axial T2, arrow) signal. C Axial T1FS post-gadolinium shows mild enhancement (arrow). D Cystoscopy with mild mucosal bulge (arrow). endometriotic implants [57]. They are typically found at the posterior bladder wall and cause external compression into the bladder (Fig. 4A, B). TVUS is also used to assess the ureters, both at rest, while peristalsing in order to look for endometriosis, ureteral dilation, abnormal bending, or evidence of obstruction [56, 58]. Ureteral endometriosis appears as heterogeneous hypoechoic nodules. Hydronephrosis can be visualized on renal ultrasound and dilated ureters above the site of endometriosis may be seen on pelvic or abdominal ultrasound. These findings can mimic ureteral obstruction by cervical cancer [37]. plasms (Figs. 5, 6). Usually these patients do not undergo workup for DIE, instead undergo explorative laparotomy or laparoscopy usually with inadequate preoperative planning, preparation, and patient consent prior to surgery. Understanding CT imaging of endometriosis is essential for accurate diagnosis, prompting appropriate further imaging to evaluate locations and depth of other ectopic foci. Typically endometriosis of the colon presents as a soft-tissue density intraluminal mass with mild to moderate contrast enhancement and may cause eccentric stenosis of the intestinal lumen. Furthermore, the intestinal wall in close proximity to the nodule displays mural thickening and scalloping. Bowel may be angulated or displaced from the expected locations. Evaluation of cecal and appendiceal endometriosis can be further complicated due to stenosis by muscular contraction, incomplete distention, or presence of feces [59]. Due to these confounding factors, two of our cases of endometriosis were mistaken for appendicitis, cecal malignancy, and inflammatory bowel disease (Figs. 7, 8, 9). Notably, inflammatory changes of the nearby bowel and mildly enhancing lymph nodes may also appear on CT. Computed tomography and fluoroscopy Patients with endometriosis with clinical symptoms of appendicitis, chronic pelvic pain, gastrointestinal symptoms of diarrhea, constipation and possibly reduced stool caliber, or hematochezia often undergo CT imaging for diagnosis. On contrast-enhanced CT imaging, DIE typically appears as a soft-tissue density mass, indistinguishable from other gastrointestinal pathologies including diverticulitis, and benign or malignant neo- A. Darvishzadeh et al.: Deep pelvic endometriosis Fig. 14. ‘‘Kissing ovaries’’ morphology with tethering to the uterus. A Axial T2 image demonstrates ‘‘kissing ovaries’’ (arrow), the ‘‘dark spot sign’’ (arrowhead), and dark peripheral rind (double arrowhead). B Sagittal T1 FS image demonstrates bilateral hyperintense endometriomas (arrows). C T2 hypointense tethering to the uterine serosa (arrow). D Coronal T2 shows thickening of the uterosacral ligaments (arrows). Advancements in the use of CT for endometriosis have been noted. Roman et al. created a virtual colonoscopy (CTC) that provides an accurate preoperative roadmap of the length of the colon affected by DIE and degree of stenosis when compared to magnetic resonance imaging [60]. CT urography is useful for assessing ureteral involvement (Fig. 7). Iosca et al. report using multislice CT with colon water distention (MSCT-c) and intravenous injection of iodinated contrast medium to identify endometriosis of the intestinal tract and the ureters [61]. On CT, endometriosis of the bladder can present as an irregular, mildly enhancing mass in the bladder wall with associated mural thickening (Figs. 4, 10). Furthermore, endometriosis of the ureters causes fibrosis, leading to hydronephrosis, dilated ureters proximal to location of implantation and can pull the lower portion of the ureter medially from the lateral position (Fig. 7B). A. Darvishzadeh et al.: Deep pelvic endometriosis Double-contrast barium enema (DCBE) is not currently recommended for the diagnosis of endometriosis due to low specificity. Classically, however, it had been a helpful method of imaging endometriosis of the gastrointestinal tract, specifically the rectosigmoid colon. On DCBE, endometriosis appears with characteristic findings including strictures caused by extrinsic mass effect, shortening, tethering, or flattening of the bowel wall. Additionally, intramural endometriosis with subsequent scalloping of antimesenteric border creates the characteristic crenulation pattern seen on DCBE, which may be the only distinguishing finding (Fig. 5D) [9, 59, 62, 63]. Given that these findings, however, are nonspecific and are similar to the findings of malignancy, the diagnostic value of DCBE is limited. In general, given that most patients are of reproductive age, the use of CT and fluoroscopy is limited by the patient’s desire to forgo radiation exposure. Magnetic resonance imaging MRI is the imaging modality of choice for evaluation of deep infiltrating endometriosis due to inherent high sensitivity for detecting blood products and global evaluation of structures compared to the limited reach of TVUS [59, 64]. Although not implemented at all institutions, MRI sensitivity can be improved by bowel preparation, administration of an antispasmodic agent to reduce bowel peristalsis, and administration of vaginal gel [36]. Use of rectal gel is disputed since it can increase bowel peristalsis and distort rectal retraction caused by the endometriosis implants [37, 65]. The timing of MR is also controversial, however, some authors suggest performing MR 12 days after the first day of the patient’s last menstrual period when the endometrial blood products are at their maximum [66]. Evaluation should include investigation of the gastrointestinal tract and the deep pelvis, typically based on a tri-compartmental approach, i.e., the anterior, middle, and posterior pelvic compartments [67, 68]. DIE of the gastrointestinal tract appears as irregular, eccentric mass/masses infiltrating into the intestinal wall causing luminal narrowing with associated fibrosis and smooth muscle hyperplasia appearing at times as irregular, speculated, hypointense lesions on T2-weighted images. Fat-saturated T1-weighted images show a mass or thickening, which is isointense to muscle, possibly with interspersed hyperintense foci that reflect hemorrhagic blood products [37, 65, 66]. Restricted diffusion with low apparent diffusion coefficient (ADC) values, although not specific, is also noted [66]. The ‘‘mushroom cap’’ sign refers to the appearance of rectosigmoidal le- Fig. 15. 34-year-old female with tri-compartmental involve- c ment. A axial T1 and B axial T2 images demonstrate an obliterated posterior cul-de-sac with left ovarian endometrioma (T1 hyperintense, T2 hypointense; arrows). The uterus is retroflexed and there is a ‘‘kissing ovaries’’ morphology (B). C sagittal T2 image shows T2 hypointense fibrotic thickening from the torus uterinus and lower uterine segment to the rectum (arrows). D sagittal T1 FS shows left ovarian serosal deposits (hyperintense foci; arrow). E axial T2 shows involvement of the right distal ureter (hypointense thickening; arrow). There is T2 thickening of the bilateral uterosacral ligaments (F coronal T2; arrows) and round ligaments (G axial T2; arrows). H Laparoscopy showing obliterated posterior culde-sac. sions on T2-weighted images as a hypointense fibrotic mass in the muscularis layer that protrudes into the intestinal lumen with hyperintense submucosal and mucosal layers that cover the mass and create an outline similar to that of a mushroom cap (Fig. 11) [64]. Other findings include bowel wall thickening, loss of fat planes between bowel segments and adjacent organs, and abnormal angulation of the bowel loops [59, 69]. Increased spatial resolution with the use of a 3.0T MRI compared to a 1.5T MRI allows for improved detection of smaller DIE lesions and superficial endometriosis by showing adhesions and peritoneal irregularities [65]. The anterior compartment includes the bladder, vesico-uterine pouch, vesico-vaginal septum, and distal ureters. Superficial, serosal implants are typically T2 hypointense and result in ante-flexion and obliteration of the anterior cul-de-sac (Fig. 12). Lesions that invade through to the bladder mucosa may demonstrate more typical T1 hyperintense and T2 hypointense glandular elements [35, 70] (Figs. 10, 13). Given the rarity of bladder mucosal invasion, these implants may be missed at cystoscopy and the patient may be asymptomatic [67]. MR urography and retrograde ureteral injection are used to determine extent of ureteral involvement (Fig. 7). Middle compartment evaluation includes the uterus, ovaries, fallopian tubes, and uterine ligaments. The hallmark findings of ovarian endometriomas are T1 hyperintense cysts that demonstrate T2 dark shading and a T2 dark rind due to the accumulation of degraded hemorrhagic blood products. More recently, however, the T2 ‘‘dark spot sign’’ has proven to have greater specificity in discerning endometriomas from other hemorrhagic cysts. The T2 ‘‘dark spot sign’’ is characterized by discrete, circumscribed areas of increased hypointensity on T2 weighted images within the T2-shaded cyst or against the cyst wall [71]. Tiny serosal deposits on the ovaries may A. Darvishzadeh et al.: Deep pelvic endometriosis A. Darvishzadeh et al.: Deep pelvic endometriosis A. Darvishzadeh et al.: Deep pelvic endometriosis 43-year-old female with small bowel obstruction and circumferential mass at the terminal ileum. A Coronal T2 and c axial T2 show a hypointense, circumferential mass (arrows). B Coronal T1 FS post-gadolinium shows mass enhancement (arrow). D B600 showing diffusion restriction (arrow). E Colonoscopy with tight stricture at the terminal ileum (arrow). b Fig. 16. have punctate areas of T1 hyperintensity with diffusion restriction. Abutting, retro-positioned ovaries, secondary to endometriotic adhesions, may create a ‘‘kissing ovaries’’ appearance. Thickening and nodularity of the broad and round ligaments may also be present (Figs. 14, 15). The posterior compartment may be significantly involved by deep invasive endometriosis. This compartment includes the rectum, Pouch of Douglas, torus uterinus, uterosacral ligaments, posterior vaginal fornix, and rectovaginal septum. Fibrotic changes are commonly seen in this area, manifest as predominantly T2 dark bands [72]. Retrocervical bands extending from the torus uterinus, uterosacral ligaments, and rectum may cause partial or complete obliteration of the cul-de-sac [67]. Obliteration of the cul-de-sac may hide areas of endometrial involvement on laparoscopic examination and thus underestimate disease extent at surgery [73]. Serosal deposits involving the rectosigmoid colon may be superficial, with potential for deeper invasion into the muscularis propria. Despite the lack of mucosal invasion, serosal involvement may result in colonic obstruction or narrowing/stricture (Figs. 11, 15). Other sites of involvement include the vagina, the small intestine, the ischio-anal fossa, the sciatic nerve, abdominal organs such as the liver, and extra-abdominal locations such as the pleura (Fig. 16) [67]. MR urography and retrograde ureteral injection are used to determine extent of ureteral involvement (Fig. 7C, D). Laparoscopy Ultimately, laparoscopy or laparotomy with histological confirmation of endometriosis remains the gold standard for diagnosis. Typically, endometriosis is characterized on laparoscopy as adhesions and serosal fibrosis with patchy gray-brown discoloration, also called ‘‘powderburn’’ lesions. Macroscopically, the lesions are small nodules of large cystic glands and endometrial type stroma that appear on the peritoneal surface as raised, punctate hemorrhagic areas with hemosiderin deposits, whitish opacfications, or reddish-blue irregularly shaped lesions [20, 74]. Summary Endometriosis is a common disease affecting up to 50% of women with pelvic pain and can present with a variety of symptoms making diagnosis difficult. Patients may suffer due to a delayed diagnosis, incurring health care costs, and lost income due to decreased productivity with a significant personal impact. The typical delay in diagnosis ranges from 3 to 9 years and may lead to progressive disease requiring surgical intervention [16, 17]. Thus, an early and precise diagnosis of DIE is ‘‘key.’’ Familiarity with the pathophysiology, clinical presentation, and the imaging features of DIE can aid in the radiologic diagnosis and guide appropriate and timely patient management. Acknowledgements The authors acknowledge the assistance of Eric J. Gray and Sonia Watson, Ph.D., for editing the manuscript and Christopher M. Brown for illustration design. Compliance with ethical standards Funding No funding was received for this study. Conflicts of interest The authors declare that they have no conflict of interest. Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. 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