MRI Pelvis
MRI of the pelvis is a multiparametric study of the uterus, cervix, vagina, ovaries, adnexa, bladder, rectum, pelvic floor, pelvic nodes and bones. It is the main problem solving test in gynaecological and pelvic disease, and the staging test for cervical, endometrial and rectal cancer.
It is done on a 1.5 or 3 tesla scanner with a pelvic phased array coil. Slices are 3 to 5 mm thick. The study takes 30 to 45 minutes.
Core sequences are T2-weighted (small field of view) in axial, sagittal and oblique planes, T1-weighted (with and without fat suppression), and diffusion weighted imaging with an apparent diffusion coefficient map. Dynamic contrast enhanced T1 imaging with gadolinium (0.1 mmol each kg) is added for tumour staging and indeterminate masses.
Antispasmodic (hyoscine butylbromide 20 mg or glucagon) reduces bowel motion. The patient may be asked to have a moderately full bladder.
Pelvic masses are found in 5 to 10% of women, and most adnexal masses are benign. Ultrasound is the first test. MRI has a sensitivity of about 90% and a specificity of 85 to 95% in characterising indeterminate adnexal masses, and it reduces unnecessary surgery.
Cervical cancer is the fourth commonest cancer in women. MRI gives accurate local staging, with a sensitivity of about 90% for parametrial invasion. Endometrial cancer depth of invasion is assessed with an accuracy of 85 to 90%.
Indications.
- Indeterminate adnexal mass on ultrasound.
- Staging of cervical, endometrial, vaginal and vulvar cancer, and assessment of recurrence.
- Staging of rectal cancer (tumour, mesorectal fascia, nodes) and anal fistulas.
- Bladder cancer staging (muscle invasion).
- Endometriosis (deep infiltrating disease) and adenomyosis.
- Uterine fibroids before treatment (embolisation, surgery), and mapping.
- Congenital uterine and vaginal anomalies (septate, bicornuate, unicornuate).
- Pelvic pain with an inconclusive ultrasound.
- Pelvic inflammatory disease and tubo ovarian abscess.
- Pregnancy: placenta accreta spectrum, foetal anomalies when ultrasound is limited, and appendicitis.
- Pelvic floor disorders and fistulas (dynamic MR).
- Pelvic bone and soft tissue tumours, sacral lesions, and lymph node assessment.
- Infertility workup.
- Post-treatment assessment of cancer.
Not for the first look at simple pelvic pain or early pregnancy, which are for ultrasound.
Contraindications and precautions.
- The usual MRI safety screening. Copper intrauterine devices and most contraceptive implants are safe (conditional).
- Gadolinium: avoid in severe renal impairment and in pregnancy unless essential.
- Hyoscine is avoided in glaucoma, prostatic obstruction and tachyarrhythmia. Glucagon is avoided in phaeochromocytoma and insulinoma.
- Claustrophobia: preparation and sedation.
- Hip prostheses cause artefact, so sequences are adjusted.
- Fasting for 4 hours reduces bowel motion.
Preparation and technique.
The patient fasts for 4 hours and empties the bladder an hour before the scan, so the bladder is only moderately filled. A vaginal gel (50 to 60 mL) is sometimes instilled for vaginal and cervical tumours. Rectal gel is used in rectal and anal fistula studies.
The patient lies supine, with the coil over the pelvis. The antispasmodic is given just before scanning.
Small field T2 images are taken in planes perpendicular and parallel to the cervix or the tumour axis. Diffusion weighted imaging uses b values of up to 800 to 1000. Dynamic contrast imaging is taken at 30-second intervals.
For endometrial cancer, sagittal oblique T2 images across the uterus are acquired. For rectal cancer, high resolution T2 perpendicular to the tumour axis is acquired. For fistulas, three plane T2 with fat suppression is used.
