In rare cases, a complex Müllerian anomaly requires further assessment. Then, MRI can:
- determine the contour of the fundus
- measure any fundal indentation
- distinguish the nature of a septum (myometrial or fibrous)
- assess for an atrophic horn in a case of unicornuate uterus
- assess for complications associated with a uterine anomaly, such as endometriosis and abnormal location of pregnancy.
Cervical Ca. MRI can be used in cases of cervical cancer to:
- demonstrate the tumor
- allow accurate depiction of its size and location
- aid in treatment selection by showing direct tumor extension to the lower uterus, vagina, paracervical and parametrial tissues, as well as to adjacent bladder and rectum.
Endometrial Ca. MRI can be used to stage endometrial cancer by showing 1) the depth of myometrial invasion and extension into the cervix, broad ligaments, and parametrium and 2) abnormal lymph nodes.
Ovarian Ca. MRI can be used to better define the imaging characteristics of an adnexal mass that is not clearly benign on US. Staging of ovarian cancer, however, is typically performed by CT; MRI is reserved for cases in which the use of iodinated contrast material is contraindicated.
Imaging of the pelvic floor
Dynamic MRI can be utilized when imaging assessment of the pelvic floor in motion is needed to determine whether surgery or other therapy for prolapse or urinary incontinence, or both, is appropriate. The pelvic floor is assessed at rest and during strain in patients with symptoms. MRI can be used to:
- quantify descent
- identify enterocele or rectocele
- assess for the position of the urethra
- assess for muscle atrophy and tears.
US is the first-line modality when endometriosis needs to be assessed by imaging. Sonography depicts focal endometriomas as complex cysts with homogenous, low-level internal echoes.
Small endometrial implants, however, cannot be seen with US; contrast-enhanced MRI with fat saturation can be used to demonstrate small implants and adhesions that involve surrounding organs.
Keep in mind that, typically, laparoscopy is needed for thorough staging of endometriosis because small implants and adhesions are better seen under direct visualization.
Problem: Determining the nature of an indeterminate adnexal mass
Most adnexal lesions seen on US are self-limited physiologic cysts that have a classic appearance; they generally resolve on follow-up. Other lesions—dermoids, endometriomas, and cystadenofibromas—often have a classic appearance on US that allows for confident diagnosis.
At times, however, the diagnosis of an adnexal mass is not definitive on US, and MRI can then be very helpful in problem-solving.
Fibrous lesions. In the case of a fibrous lesion, when it is unclear if the mass is adnexal (fibroma, fibrothecoma) or uterine (an exophytic or pedunculated fibroid), MRI can be helpful in determining the organ of origin of the mass, allowing for avoidance of surgery in cases of fibroids.
Complex cysts. In the case of a complex cyst that is not clearly an endometrioma or a dermoid, MRI can be helpful in making the distinction—and can affect management if used preoperatively to 1) allow the patient to avoid surgery or 2) triage her to a less-invasive surgical procedure.
Dermoids have imaging characteristics of fat that can be brought out with specialized MRI techniques (for example, fat suppression or chemical shift artifact) that show differences between fat and water. MRI is particularly helpful in determining the size of a dermoid that might be difficult to assess sonographically because its echogenicity is similar to that of surrounding pelvic fat.
Endometriomas have blood in many stages of their evolution. The very bright signal intensity seen on T1-weighted images is characteristic of the methemoglobin seen in endometriomas.
Adnexal cysts. At times, the entire wall of an adnexal cyst cannot be assessed adequately by US because the cyst is very large (>7 cm in diameter). In such a case, MRI can help assess the entire cyst and surrounding tissue.
Hydrosalpinx. Last, the distinction between hydrosalpinx and a complex ovarian cyst or neoplasm can, at times, be difficult on US. In such a case, MRI allows for visualization of the ovary distinct from the fallopian tube, thereby providing you with a confident diagnosis of hydrosalpinx and obviating the need for further imaging assessment or surgery.
Left: Transabdominal sonogram of an 18-year-old woman reveals a large, solid mass (M) anterior to the uterus (U). The mass has heterogeneous echo-texture. It is unclear on US whether the mass arises from the uterus—although the echo-texture is similar to what would be expected of a fibroid or fibroma.
Right: A T2-weighted MRI parasagittal image shows the large, lobulated pelvic mass. Other images showed no communication with the uterus but, rather, extension of some of the mass from enlarged neural foramina. Note also the enlarged thecal sac (arrow), which is compatible with dural ectasia. Taken together, these findings are compatible with plexiform neurofibroma. This woman has neurofibromatosis, previously undiagnosed.