|ECR 2018 / C-3194|
|Deep endometriosis of the posterior pelvic compartment:a MRI pictorial guide.|
Findings and procedure details
When endometriosis invades the subperitoneal space for more than 5 mm in depth, it's called deep endometriosis .
Accuracy, sensitivity and specificity of MRI in the evaluation of deep endometriosis were > 90% in different studies [5-6].
It is frequently associated with dysmenorrhea, dyspareunia, pelvic pain, backaches, urinary tract symptoms and infertility .
Posterior compartment of the pelvis is the most common localization of deep endometriosis [3-4]. Fig.1-4 show the main anatomical sites of disease.
A correct execution of the MRI examination is based on the acquisition of T2w and T1w images on axial, sagittal and coronal planes.
Our acquisition protocol consists of :
- axial, sagittal and coronal T2w TSE images
- axial T2w SPAIR images
- axial T1w TSE images
- axial and sagittal T1w SPAIR images after intravenous contrast medium injection (if necessary).
Slice thickness: 4-5 mm.
Fluid distension of vaginal and rectal cavities is recommended because collapsed hollow organs prevent the correct depiction of small foci of disease involving visceral walls, and seems to improve sensitivity and specificity of the technique [7-8].
Contrast medium injection helps in the differentiation between deep endometriosis and scars, allowing the demonstration of the activity of the disease, improving specificity .
Post-contrast acquisitions are also useful when endometriosis is suspected during examination performed for other reasons or when patients refused fluid distension of the cavities, improving sensibility.
At histological examination, fibromuscular hyperplasia surrounding ectopic endometrial glands are typical findings of deep endometriosis. This explains the MRI appearance of endometriosis as hypointense lesions on T2w acquisitions with hyperintense spots inside (Fig.5), sometimes with hyperintese foci on T1w images due to haemorrhagic phenomena (Fig.6) [2-3,8-9] .
Endometriotic lesions are usually detected as plaques (Fig.7) , nodules (Fig.8) or focal or diffuse thickening (Fig.9) ; star-like appearance lesions with spicules and adhesions to sorrounding structures can be seen due to fibrotic reaction characterizing the disease (Fig.10 and Fig.11) [2-3,8-9].
The “mushroom cap” sign (Fig.12) , described on sagittal or axial planes as a T2 heterogeneous hypointense mushroom cap shaped lesion, due to hypertrophic muscolaris propria, growing into the bowel lumen, surrounded by hyperintense mucosal and submucosal layers, is a typical sign of deep rectosigmoid colon endometriosis .
Posterior deep endometriosis usually involves retroperitoneal and dependent posterior intraperitoneal regions often resulting in adhesions between adjacent peritoneal surfaces of the anterior rectal wall and posterior vaginal fornix with consequent invasion of the muscolar layers of both organs .
Based on the location on transrectal ultrasonography and MRI imaging retroperitoneal lesions were classified in :
- rectovaginal septum lesions (Fig.7) , extending from posterior wall of the vaginal mucosa to the anterior wall of the rectal muscolaris, under the peritoneal fold of the Douglas pouch (type 1);
- posterior forniceal lesions (Fig.8), small lesions involving the posterior fornix and the retrocervical area-torus uterinus, without deep infiltration of the rectovaginal septum or rectal wall (type 2);
- hourglass-shaped lesions (Fig.13), expanding from posterior fornix and retrocervical area-torus uterinus toward the anterior rectal wall infiltrating its muscolaris (type 3) [9,11].
Retrocervical endometriosis usually involves the uterosacral ligaments that appear thickened or with internal small nodules (Fig.9).
Retroversion of the uterus and angular rectal attraction (Fig.14) are often seen due to the fibrotic behavior of the disease .
Recto-sigmoid walls endometriosis (Fig.15-18) usually involves the serosal layer but can also extend into the muscolaris propria, causing bowel strictures and cyclic haemorrhage .
The involvement of the other surrounding pelvic structures as ovaries or fallopian tubes (Fig.19-20) can be seen.