Deep Endometriosis introduction

Endometriosis is defined by the presence of endometrial-like glands and stroma in ectopic locations such as the pelvic peritoneum, ovaries and rectovaginal septum. Symptoms include pain (i.e. dysmenorrhea, dyspareunia, dyschezia, dysuria and chronic pelvic pain) and/or infertility(1, 2). Phenotypically, three types of endometriosis lesions can be distinguished: 1.) superficial (mainly peritoneal) endometriosis, 2.) deep endometriosis (nodules) and 3.) ovarian endometriotic cysts (endometriomas) (3). 

Deep endometriosis (DE) is defined as more than 5mm infiltration of endometriosis below the surface of the peritoneum (4). DE may be located in the anterior compartment of the pelvis (vesicouterine fold, bladder wall and distal ureters) or in the posterior compartment of the pelvis (the vaginal wall, rectovaginal septum, utero-sacral ligaments, anterior rectal wall and the sigmoid wall). Ovarian endometriosis is associated with an increased risk of intestinal DE involvement (5). 

N80: endometriosis 
-    N80.3: endometriosis of pelvic peritoneum
-    N80.4: endometriosis of rectovaginal septum and vagina 
-    N80.5: endometriosis of intestine
-    N80.8: other endometriosis 
 

Endometriosis is a common chronic inflammatory problem, affecting approximately 10% of women and people assigned female at birth (3, 6). The prevalence may be as high as  30–50% in those with infertility and/or pain (7). The prevalence of DE is estimated to be 1-2% (8). The anatomical distribution of DE is asymmetric i.e., DE is more frequently present in the posterior compartment and is more often located on the left side. The most common sites of DE in the posterior compartment are uterosacral ligaments (52.7%), posterior vaginal fornix (16.2%), rectum/rectosigmoid junction and sigmoid colon (22.7%). Bladder DE is less frequent (6.3%), as is ureteral DE (2.1%) (9). 

The exact pathogenesis of endometriosis is still unknown and different theories on its pathogenesis exists. For peritoneal endometriosis, the most widely accepted hypothesis is retrograde menstruation . During the menstruation, some effluent flows retrogradely through the lumen of the Fallopian tubes into the pelvic cavity. In the pelvic cavity they can implant, grow and invade onto pelvic structures (10-12). DE may also be explained by the coelomic metaplasia theory (the transformation of peritoneal mesothelium   into glandular endometrium)(11) or by the theory of embryogenic remnants (residual embryonic cells developing into endometriotic lesions)(13). A last hypothesis is the lymphatic and vascular metastasis (i.e., the transport of endometrial cells through lymphatic and blood vessels). The latter hypothesis may explain the rare occurrence of extra-pelvic endometriosis (3). 

The histological diagnosis of endometriosis is made by the presence of endometrial   glands and/or endometrial stroma and/or hemosiderin-laden macrophages (13). The glands have an endometrioid appearance ranging from inactive to proliferative (or occasionally secretory) to hyperplastic histology. The endometriotic stroma typically resembles eutopic inactive or proliferative endometrial stroma, including the presence of a network of small arterioles (14). 

DE has long been defined as at least 5mm infiltration of endometriosis below the surface of the peritoneum, while superficial endometriosis is defined as less than 1mm infiltration depth. The term intermediate endometriosis historically was used to describe lesions with 2 to 4mm infiltration (4, 15). Recently, a new International Terminology for Endometriosis publication defines DE as endometrium-like tissue lesions in the abdomen, extending on or under the peritoneal surface. DE lesions are usually nodular, able to invade adjacent structures, and associated with fibrosis and disruption of normal anatomy(16).

While a detailed clinical history and gynecological examination may raise the suspicion of endometriosis, the gold standard for the diagnosis of endometriosis is a laparoscopy with biopsy. A clinical diagnosis can be made when DE involves the vaginal wall, i.e. by visualization of endometriotic lesions at speculum examination (17). 

Non-invasive imaging methods, such as magnetic resonance imaging (MRI) and transvaginal ultrasound, have proven to be accurate in the detection of DE and endometriomas, and allow mapping the exact location and extent of lesions. Transrectal ultrasound may be considered if transvaginal ultrasound is impossible or inappropriate (18). Superficial endometriosis often remains undetected on MRI or ultrasonography and necessitates laparoscopy for proper diagnosis. However, since ultrasound is a dynamic exam, site-specific tenderness and reduced organ mobility on transvaginal ultrasound are indirect signs of superficial endometriosis (19). Superficial endometriosis will be discussed in a separate VISUOG article.  Transvaginal ultrasound is the first-line imaging technique in the diagnosis of pelvic endometriosis and in particular for DE (20). 

In 2016, the International Deep Endometriosis Analysis (IDEA) group published a consensus opinion on terms, definitions and measurements to describe the sonographic features of the pelvis in women with suspected endometriosis (18). 

Assessment of both the anterior and posterior compartment is necessary. All DE nodules should be measured in three orthogonal planes.

1.    Anterior compartment: 
Ultrasound appearance of anterior compartment DE is variable including hypoechoic lesions, with or without regular contours involving the muscularis and/or (sub)mucosa of the bladder (21, 22). 

To assess the anterior compartment, the transducer is positioned in the anterior fornix of the vagina. The anterior compartment includes following anatomical localizations: urinary bladder, uterovesical region and ureters. 

1.1.    Urinary bladder can be divided in four zones: the trigonal zone, the bladder base, the bladder dome and the extra-abdominal bladder. If bladder endometriosis is suspected, patient should be asked not to empty their bladder completely before the ultrasound examination. A slightly filled bladder facilitates evaluation of the bladder wall. The dimensions of the bladder nodule should be measured in three orthogonal planes. Bladder DE is diagnosed only if the muscularis is involved.

1.2.    The uterovesical region can be evaluated using the sliding sign. Sliding of the posterior bladder relative to the anterior uterine wall can be evaluated. If the posterior bladder wall slides freely over the anterior uterine wall, the sliding sign is reported positive. If the bladder does not slide freely over the anterior uterine wall, the sliding sign is reported negative and the uterovesical region is deemed obliterated. This may be due to adhesions following surgery, pelvic infection or endometriosis. 

1.3.    The distal ureters should be evaluated by transvaginal ultrasound. Furthermore, in all women with DE, a transabdominal scan of the kidney must be performed to detect hydronephrosis. When DE with ureteral involvement is noticed, the distance between the distal ureteric orifice and the DE lesion should be measured. 

2.    Posterior compartment:
Ultrasound appearance of posterior compartment DE is characterized by a hypoechoic thickening of the wall of the bowel or vagina, or as hypoechoic solid nodules which may vary in size and have smooth or irregular contours (23). 

To assess the posterior compartment, the transducer is positioned in the posterior fornix of the vagina. Bowel preparation can be used, however this is not mandatory (24). The posterior compartment includes following zones: uterosacral ligaments (USL), posterior vaginal fornix, anterior rectum/anterior rectosigmoid junction and sigmoid colon (9). 

2.1.    Isolated DE in the rectovaginal septum is rare, the nodules are usually extending to the posterior vaginal wall, the anterior rectal wall or both. ‘Diabolo’-like or ‘hourglass’-shaped nodules are found when the posterior vaginal fornix DE extends into the anterior rectal wall. Bowel DE typically involves the anterior rectum, rectosigmoid junction and/or sigmoid colon. These lesions can all be visualized by ultrasound. Bowel DE can be isolated, multifocal (multiple lesions affecting the same segment) and/or multicentric (multiple lesions affecting several bowel segments). To assess both multifocal and multicentric involvement additional imaging may prove of value including double contrast barium enema, computed tomographic colonography or magnetic resonance imaging of the pelvis. Rectal DE is associated with a second intestinal lesion in 55% of cases (25). Endometriotic nodules infiltrating the bowel may have a regular outline or may present (a combination of) specific ultrasound features, reported as the ‘comet’ sign (DE nodule with progressive narrowing), the ‘moose antler’ sign (DE nodule with prominent spikes towards the bowel lumen) or the ‘pulling sleeve’ sign (DE with extrinsic retraction). When detecting bowel DE, lesion length (26) and the affected segment of the rectum or sigmoid colon should be specified as well as an estimation of the distance between the lower margin of the lesion and the anal verge (27). 

2.2.    DE involving the uterosacral ligaments   are visible as hypoechogenic lesions within the more hyperechogenic tissue of the ligaments    (28). Since nodules within the uterosacral ligaments may exert extrinsic force on the ipsilateral ureter leading to stricture and proximal hydroureter or even hydronephrosis, diagnosing these DE lesions is of utmost importance. Large uterosacral nodules (≥17mm) generally indicate DE infiltration into the parametrium, increasing the expected surgical complexity. (28)

2.3.    Sliding of the anterior rectum relative to the retrocervical region and posterior vaginal wall should be evaluated. A negative sliding sign is indicative for posterior compartment obliteration (29, 30).      

Based on epidemiological findings, DE is not associated with an increased risk of cancer in general (31). Concerning ovarian cancer, the overall risk was not increased among women with DE. However, women with ovarian endometriosis have a slightly increased risk of ovarian cancer (32). Although endometriosis is a benign gynecological disorder, it has a negative impact on quality of life and fertility (33). 

Treatment of endometriosis must be individualized, taking into consideration the clinical problem in its entirety, including the impact of the disease and the expected effect of treatment on quality of life. Evidence-based recommendations are continuously updated and summarized in the ESHRE guidelines for the clinical management of endometriosis (33). 

Medical treatment of deep endometriosis (DE) (with non-inflammatory steroidal inflammatory drugs, (combined) contraceptives or GnRH-agonists) is based on suppression of the symptoms and is a valuable therapeutic option for many women (34-36). A surgical approach can be offered to women with failed medical treatment, contraindications or intolerance for hormonal treatment, couples seeking natural conception, patient preference for surgery and specific surgical indications (i.e. bowel stenosis associated with sub-occlusive symptoms or ureteral stenosis) (33). 

Transvaginal ultrasound is the first-line imaging technique in the diagnosis of pelvic endometriosis and in particular for DE (20). Therefore, ultrasound is of pivotal in the preoperative evaluation of patients with clinical suspicion of DE to provide correct patient counseling, assess the expected operative complexity (37) and select the appropriate surgical team. 

Recurrence of endometriosis after surgery is often ill-defined or poorly recorded. In general, the recurrence rate in studies with a follow-up period >2 years varies between 5 and 25%(35).

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