Pelvic MRI: Is Endovaginal or Rectal Filling Needed?

Magnetic resonance imaging (MRI) is widely recognized as the imaging modality of choice for the evaluation of the pelvis. Magnetic resonance (MR) examinations are based on T2-weighted MR imaging, allowing depiction of the uterus cavity, rectum lumen and vagina. The anatomy of these structures is best observed when the walls, that may spontaneously be collapsed, are distended. Distension of these cavities during pelvic MRI for evaluation of gynecologic or rectal diseases has been conducted with a variety of methods: vagina may be filled with ultrasound gel (1, 2), saline solution (3), and rectum may be distended, among other materials, with air (“air balloon technique”) (4) or potato starch combined with gadolinium-based contrast media (5, 6, 7).

Among these different agents, ultrasound gel has the advantage to ensure stable distension of cavities and to provide high contrast with adjacent structures on T2-weighted images, thus facilitating, in some cases, diagnosis and evaluation of benign and malignant gynecologic or rectal conditions. The purpose of this review is to report and illustrate our experience in this field as well as to review literature findings in terms of use of vaginal and rectal opacification for various indications.

Table 1
Summarizing MRI Sequences and Use of Endovaginal/Rectal Filling for Each Disease, Both in Literature and in Our Experience (including Advantages)

• Click for larger image
• Click for full table
• Download as Excel file

Pelvic MRI may be conducted either using 1.5T or 3T MR units. Although 3T MR imaging has inherent higher resolution, yields high contrast between tissue and fluid could thus provide more detailed depiction of rectal/vaginal walls, there has not been clear evidence in literature, to support superiority of 3T vs. 1.5T pelvic MR imaging in the field of rectal or gynecological disorders. The only study addressing an intra-patient comparison of 1.5T and 3T MRI performances for staging in patients with rectal cancer did not reveal improvement with 3T MRI. No rectal filling was conducted before imaging in that study (8). Another recent study comparing results of pelvic MRI conducted for rectal cancer in 50 patients imaged without and after rectal filling concluded that rectal distension improved visualization of tumors, even though studies were conducted on a 3T MR unit (9).

Three different types of distension may be conducted depending on studied pathology. Vaginal distension may be conducted alone in conditions such as cervix and endometrial carcinomas, developmental abnormalities and vaginal cysts, while vaginal and rectal filling may be undertaken in endometriosis or pelvic floor disorders such as cystocele, vaginal prolapse and rectocele. Last, rectal distension can be conducted alone to evaluate rectal cancer. When vaginal and/or rectal distension is scheduled, the patient should be familiarized with intention and course of the procedure. With adequate information provided to the patient before administration, tolerability is good with an acceptance rate ranging from 91.3% to 98.7% (10, 11, 12). The approach to the patient preparation depends on the indication. Most gynecological pathologies do not require colonic preparation.

However, in case of endometriosis, most authors ask their patients to undergo bowel cleansing to maximize detection of a rectal implant (11, 13, 14, 15) and fasting is recommended (14, 15), in studies using 1T and 1.5T scans. Many methods are being used throughout literature for bowel cleansing, mainly on 1.5T devices (1, 3, 4, 6, 7, 8, 10, 13, 14, 15, 16, 17, 18). They include administration of two doses of an oral laxative the day before the study (15), or of an oral mild laxative senna extract for 3 days (16, 17), or of a 120-mL single dose of ready-to-use enema kept by the patient for 15 minutes before bowel movement (18). In their recent guidelines, European Society of Urogenital Radiology (ESUR) recommend fasting prior to MRI (3–6 hours before MRI) and consider bowel preparation as “best practice” for detection of deep pelvic endometriosis (DPE) (19).

To reduce bowel peristalsis and avoid gastrointestinal tract artifacts, an antispasmodic agent is generally administered (10, 11, 13, 18, 20), intravenously or intramuscularly, in absence of contraindication. Specifically, ESUR's guidelines recommend use of anti-peristaltic agent in the evaluation of DPE (19).

As far as endometriosis is concerned, the vagina and the rectum may be filled immediately before examination, with the patient in left lateral decubitus position inside the MR scanner. Most centers use ultrasound gel, either sterile (10, 11, 21) or not sterile (16, 17, 18), as gel is a widely available contrast agent, low-cost, easy to use and administer, and convenient for vaginal and rectal distension. As it is viscous, it allows good expansion of hollow organs and doesn't leak during the procedure. The amount of gel used to fill the vagina and the rectum is a matter of debate. Usually, using 1.5T units, 50 mL (14, 15, 16, 17, 18, 21) to 100 mL (10) can be used to fill the vagina. Rectum should be filled with approximately 100–150 mL of sonographic gel (11, 14, 16, 17, 18).

Regarding dynamic pelvic study, ESUR and European Society of Gastrointestinal and Abdominal Radiology (ESGAR)'s recommendations suggest that the rectum should be filled with a large amount of gel (180–200 mL) to improve capacity to defecate (22). In literature, the amount varies between 100–300 mL (1, 2, 6, 23, 24, 25, 26). Investigators either use standardized amount of gel or administer gel until the patient expresses an urge to relieve the bowel (1, 6). A recent study has revealed that decreasing rectal gel volume from 180–120 mL did not compromise defecation performance (24). Although no consensus could be obtained among experts from the ESGAR and the ESUR (22), a rectal cleansing enema prior to examination is beneficial. When vaginal opacification is conducted, quantity introduced is generally between 20 mL and 50 mL, in studies conducted on 1.5T units (1, 22, 23, 26, 27).

As far as rectal cancer evaluation is conducted, when used, the amount of ultrasound gel should not exceed 60 mL to avoid potential compression of the mesorectum (28). In our experience, 50 mL and 250 mL of non-sterile ultrasound gel are used to fill the vagina and the rectum, respectively, for evaluation of DPE and dynamic pelvic studies. For evaluation of cervix or endometrial carcinomas, developmental anomalies and vaginal cysts, we conduct a vaginal opacification with 50 mL of ultrasound gel. For rectal cancer evaluation, we gently fill the rectum with 60–80 mL of ultrasound gel, but do not consider it mandatory. Last, patients do not fast prior to our pelvic MRI studies, nor undergo colonic preparation nor receive antispasmolytic agents.

Vaginal and rectal opacification with ultrasound gel before MR imaging is an inexpensive, well tolerated procedure. While use of rectal opacification is widely recognized as necessary in evaluation of dynamic pelvic floor disease, use of rectal and/or vaginal opacification is a matter of debate. We believe from our experience that, as far as endometriosis is concerned, opacification may be beneficial particularly for small vaginal lesions, lesions infiltrating posterior vaginal fornix and anterior rectal wall, and that it enables less-experienced radiologists to better interpret deep endometriosis. Regarding cervical and endometrial cancer, endovaginal filling is useful when vaginal extension of the tumor is suspected. Development anomalies, such as vaginal septum, vaginal agenesis, as well as vaginal cysts are often better characterized and localized, when vaginal opacification is conducted. Finally, in the case of rectal tumor, we presume that rectal opacification may enable radiologists to measure distance from inferior pole of the tumor to the anal margin and to assess relationship of the tumor with the sphincter.