Magnetic Resonance Imaging in Evaluation of Endometriosis: Case-Based Pictorial Essay

Gayatri Ulhas Harshe^1*, Mitusha Verma¹, Deeppak Patkar¹

¹Department of Radiology, Nanavati Max Super Speciality Hospital Mumbai

Abstract: We present a pictorial exhibit of endometriosis with a case-based overview of magnetic resonance imaging (MRI) findings in both pelvic and extra pelvic locations. All the cases with a clinical history of suspected endometriosis were reviewed retrospectively from the Picture Archiving and Communication System (PACS) database from 2020 to 2024. Cases with features of deep endometriotic implants, endometriomas, and surface endometriotic deposits were identified. Additionally, other spectrums of endometriosis, like adenomyosis, were also included.

An MRI is the best imaging diagnostic tool for preoperative staging of endometriosis as it allows for performing a complete assessment of all the pelvic compartments and extrapelvic locations simultaneously. It helps to plan a multidisciplinary approach, which decreases the postoperative complication rates. It is helpful in followup cases after the surgical excision of deep endometriotic implants. Understanding the imaging findings and thorough knowledge about the pelvic anatomy increase the accuracy of endometriosis diagnosis.

Key words: DIE (Deep Infiltrating Endometriosis), Surface Peritoneal Implants, Endometriomas, Endometriotic Implants, Deposits, Torus Uterinus.

Background

Endometriosis is a chronic condition that affects women of reproductive age group. It causes chronic pelvic pain and infertility or subfertility. 1-3 It is characterised by the growth of functional ectopic endometrial stroma and glands in an extrauterine location. The disease process is as follows:

It predominantly covers three different manifestations4-7: Ovarian endometriomas: endometrium-like tissue in the form of ovarian cysts.

Surface peritoneal implants: the presence of endometrium-like tissue involving the peritoneal surface.
Deep pelvic endometriosis: endometriotic lesions penetrating the retroperitoneal space or the wall of the pelvic organs to a depth of at least 5mm

The primary locations are in the pelvis; extrapelvic endometriosis may rarely occur.

Table 1: Common sites of endometriosis

Table 2: Anatomical compartments and their contents7 (Figure 1)

Pathogenesis of endometriosis^{9, 10, 11:}

Metastatic theory: Transplantation of endometrial tissue from the uterus to an ectopic location
a) Retrograde menstruation

b) Vascular and lymphatic spread
c) Iatrogenic
Metaplastic theory: Retroperitoneal deep endometriosis. This may originate from metaplasia of Mullerian remnants located in the recto-cervical septum
Induction theory: Transformation of circulating stem cells. The shed endometrium releases substances that induce undifferentiated mesenchymal cells to form endometriotic tissue.

Diagnosis requires a combination of clinical history, invasive and non-invasive techniques. Laparoscopy and histological confirmation are the key diagnostic tools.8

Invasive: Laparoscopy and histopathology
Non-invasive: Transvaginal ultrasonography (TV USG) 1,3:Focused Magnetic Resonance Imaging (MRI)3: Global overview (article is limited to MRI imaging findings)

Diagnostic imaging is essential for treatment planning, with MRI as a second-line technique after ultrasound. The MRI appearance of endometriotic lesions is variable and depends on the quantity and age of haemorrhage, the amount of endometrial cells and stroma, smooth muscle proliferation, and fibrosis. The purpose of surgery is to achieve complete resection of all endometriotic lesions in the same operation.

Patient preparation

Fasting: Less than 2 hrs of fasting is required (Instructions should be provided with caution for diabetic patients, or patients on any medication)
Bladder distention: Potential issues
a: Empty bladder: May miss smaller deposits

b: Full bladder: Can cause patient discomfort

c: Partially distended bladder: Ensures that by the
end of the study, the bladder is moderately full or full which is adequate for the detection of smaller implants.
Antiperistaltic agents like buscopan and glucagon: Can prevent bowel peristalsis-related artefacts

MRI Protocol: All cases were performed using a 3T magnet on the GE Avanto with pelvic phased array coil.

Anterior compartment:

Pre-vesical space, bladder, the terminal portion of the ureters and vesicovaginal septum

Medial compartment:

Content: ovaries, uterus (torus uterinus), uterine tubes and vagina

Posterior compartment:

Rectum and uterosacral ligament

Description of cases are as follows:

Case 1: Anterior compartment, bladder involvement (Figure 2)

A 43-year-old lady, known case of endometriosis, post-hysterectomy, and previous urinary bladder deep infiltrating endometriosis (DIE) with ureteric involvement, with post-excision of the implant, and ectopic ureteric reimplantation status. She presented with pain while micturition. Evaluation revealed a deep infiltrating endometriotic implant along the posterior and inferior wall of the urinary bladder. It was heterogeneously hypointense on T2- weighted images with few T1 and T2 hyperintense foci. An ectopic reimplanted left ureter was also observed. DIE was seen extending along the left side of the uterosacral ligament and adherent to the rectal wall.

Learning points:

Depth of detrusor muscle involvement
Distance from the ureteral meatus (for assessment of the ureteric reimplantation).
Differential diagnosis includes carcinoma bladder.

Figure 1: Yellow outline:anterior compartment; Red outline: middle compartment; Blue outline: posterior compartment

Figure 2: (Case 1): a. An ill-defined T2 hypointense endometriotic deposit with few T2 hyperintense foci within along the posteroinferior wall of the urinary bladder in a partially distended bladder. (yellow arrow). b. An ill-defined T1 hypointense deposit with T1 hyperintense foci along the posterior wall of the urinary bladder (yellow arrow), star shows rectal adhesion, and red arrow indicates uterosacral ligament (USL) extension. c. Reimplantation status of the left ureter. (yellow arrow) d. Postcontrast and distended bladder determine the involvement of the serosa (by long yellow arrow) short arrow indicates non-involvement of the mucosa.

Figure 3: (Case 2): a. and b An ill-defined T2 hypointense endometriotic deposit with few T2 hyperintense foci within by yellow arrow. c. The lesion shows few T1 hyperintense foci within represented by horizontal yellow arrow. d. This lesion shows mild enhancement in the postcontrast study shown by the red arrow.

Case 2: Anterior compartment, perivesical space endometriotic deposit (Figure 3) A 28-year-old lady presented with cyclical abdominal pain in the right-side lower pelvis. She was a known case of adenomyosis and left chocolate cyst and with a post-hysterectomy status. MRI revealed an ill-defined T2 hypointense lesion in the prevesical space with a few T1 hyperintense foci, consistent with an endometriotic implant in the prevesical space. The exact understanding of anatomy and knowledge of endometriosis, along with correlation with the clinical history, led to the diagnosis of a prevesical endometriotic implant in this known case of endometriosis.

Learning points:

Differential diagnoses include haemorrhagic cysts, dermoid cysts, and ovarian carcinomas.
T1 fat-saturated sequence is one of the key sequences.⁶
It is important to mention the largest dimension of each endometrioma and the number of the endometriotic cysts. If multiple endometriomas are seen. the total combined dimension of the largest measurements of each endometrioma on each side must be noted.⁵

Figure 4: (Case 3): a. Multiple well-defined T2 iso to hyperintense cysts are seen in the bilateral ovaries, few of them on right side show shedding sign. (yellow arrow) and kissing sign positive suggestive of adhesions, b. These are T1 hyperintense, c. Same cysts on T1 fat-saturated images

Case 4: Middle compartment, endometrioma with malignant transformation (Figure 5)

A 45-year-old unmarried female patient, a known case of adenomyosis and right ovarian endometrioma was on follow-up for 2 years. On follow-up USG imaging, there was a suspicious solid component in the previously seen endometrioma. Further MRI imaging revealed a multilocular cyst replacing the right ovary, appearing hyperintense on T2, T1, and T1 fat-saturated images, suggestive of endometrioma with a solid T2 hypointense central component. Due to surrounding T1 hyperintensity, demonstrating enhancement on the post-contrast study was challenging. However, subtracted images better delineated the contrast enhancement in the solid component. Histopathology confirmed malignant transformation of the endometrioma

Learning points:

Although malignant transformation is rare, we should consider its possibility.^2,10
Acquiring and interpreting subtracted images (with dynamic contrast study) provides an advantage in arriving at the diagnosis.

Figure 5:(Case 4): a. A fairly well-defined, multilobulated, T2 hyperintense lesion in the right adnexa suggestive of endometrioma with T2 iso- to hypointense central solid component (yellow arrow). b. T1 fat-saturated image suggestive of T1 hyperintense lesion with T1 hypointense central component (yellow arrow), c. On postcontrast T1 fat-saturated image mild enhancement in the central solid component, but not well appreciated. d-i. and d-ii. Precontrast subtracted image and postcontrast subtracted image with only demonstration of contrast enhancement in the central component. e. Focal adenomyoma (yellow arrow) in a case of adenomyosis

Case 5: Posterior compartment, endometriotic deposit at the torus uterinus and rectal adhesion and USL involvement (Figure 6)

A 49-year-old lady presented with chronic abdominal pain and constipation. An MRI scan revealed an ill-defined T2 hypointense endometriotic implant at the torus uterinus with few T1 hyperintense foci within. There were also a few adhesions between the torus uterinus and the anterior wall of the rectum.

Learning points:

T2 sequence plays an important role in the detection of endometriotic implants.
A key is to select the exact plane to acquire oblique axial images.

Figure 6: (Case 5): a. a. Ill-defined T2 hypointense endometriotic deposit at the torus uterinus (yellow arrow), b. Adhesion between the torus uterinus and anterior wall of the rectum yellow arrow) Thickening and irregularity of the uterosacral ligament on the left side suggestive of endometriotic disease process (red arrow)

Case 6: Posterior compartment, rectal endometriotic implant with diffuse adenomyosis of the uterus (Figure 7)

A 42-year-old lady presented with rectal bleeding, constipation, and dysmenorrhoea. MRI scan revealed a bulky uterus with heterogeneous myometrium and loss of interface between the junctional zone and myometrium. A large DIE endometriotic deposit was identified along the anterior wall of the rectum. Administration of rectal contrast improved the depiction of rectal mural involvement compared to cases without rectal gel.

Learning points:

Distance from the anal verge of the rectal implant.
Number and length of each implant.
Depth of the mural wall of implant.
Percentage of circumferential involvement

Figure 7: (Case 6): a. Adenomyotic uterus with rectal wall endometriotic deposit. b and c. Mushroom cap sign: fibrotic, T2 hypointense endometriotic implant extends into muscularis propria (yellow arrow) with submucosa is T2 hyperintense (red arrow) and gives mushroom cap sign in a case of the endometriotic implant in the anterior wall of the rectum

Case 7: Extra-pelvic endometriosis, scar endometriosis (Figure 8)

A 34-year-old lady presented with cyclical pain at the C-section scar site. Imaging revealed an ill-defined, spiculated T2 and T1 hypointense implant with mild enhancement on postcontrast images, consistent with scar endometriosis, which was confirmed by excision biopsy.

Learning points:

Intrinsic T1 hyperintense foci within MRI.10 Differential diagnoses include suture granuloma, incisional hernia, and primary or metastatic cancer.

Figure 8: (Case 7): a. An ill-defined T2 hypointense lesion in the left side of the rectus abdominus muscle at scar site. b. and c. It appears hypointense on T1-weighted images and shows contrast enhancement respectively. d. It exhibits diffusion restriction.

CONCLUSION:

MRI is the most effective imaging diagnostic tool for preoperative staging of endometriosis, as it allows for a comprehensive assessment of all pelvic compartments and extrapelvic locations.8 It facilitates the planning of a multidisciplinary approach, which helps decrease the postoperative complication rates. MRI is also valuable for follow-up cases after the surgical excision of deep endometriotic implants. Understanding the imaging findings and thorough knowledge of pelvic anatomy, enhances the diagnostic accuracy of endometriosis. Tailoring the MRI protocol with knowledge of different imaging patterns of endometriosis and detailed anatomical knowledge further helps improve diagnostic precision

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Magnetic Resonance Imaging in Evaluation of Endometriosis: Case-Based Pictorial Essay

Background

Pathogenesis of endometriosis9, 10, 11:

Patient preparation

Anterior compartment:

Medial compartment:

Posterior compartment:

Description of cases are as follows:

Learning points:

Learning points:

References

Pathogenesis of endometriosis^{9, 10, 11:}