When it comes to medical imaging of the female pelvis, many physicians hold by the standard of “ultrasound first”. Advancements in ultrasound (US) technology have risen dramatically in recent years, and the modality now includes functions like 3D volume imaging and real time evaluation of pelvic organs.1 However, some would say that ultrasound’s greatest benefit is that it is inexpensive, widely available, and involves no exposure to radiation.
The American Institute of Ultrasound in Medicine recently began advocating for the use of US examinations before other imaging modalities when evidence shows that US is at least equally, if not more effective for the anatomic area. This applies particularly to gynecologic patients.1 In many instances US is accurate and effective, however, there are times when ultrasound is inconclusive about diagnosis or doesn’t provide enough information to confirm treatment direction, allowing magnetic resonance imaging (MRI) to operate as an effective problem solver.
Why use MRI to image the female pelvis?
While ultrasound is the standard for initial imaging of the female pelvis, it does have its shortcomings. For example, limited field of view, obscuration of pelvic organs by the presence of bowel gas, dependency on patient size, and dependency on the skill and experience of the operator. MRI on the other hand is known for its detailed, high-quality, and high-contrast images, its ability to provide good tissue characterization, and its multiplanar imaging capabilities.2
Physicians generally hesitate to recommend MRI initially because the cost of an MRI scan is higher than an ultrasound exam. Therefore, an MRI is often not ordered until an ultrasound scan is performed and is shown lacking diagnostic capabilities. When a radiologist needs a more detailed view of anatomy, characterizing information about tissues, or multi-planar imaging, then an MRI is often the next step.
During a discussion at the 2017 RSNA conference, Deborah Levine, MD, from Beth Israel Deaconess Medical Center and Harvard Medical School in Boston discussed the benefits of using MRI in certain instances when imaging the pelvis. She explained how “MRI can provide additional information about the nature of a mass that may change the decision to perform surgery, such as when the mass is an exophytic fibroid.” In addition, Dr. Levine discussed how, when a uterine artery embolization is planned, MRI can show the exact number, size, and location of fibroids, and it can guide decisions regarding a hysteroscopy or laparoscopic approach.3
Dr. Levine also noted that MRI can be a very useful tool when imaging women who are pregnant. She stated that MRI should be utilized if there is a suspicion of fetal abnormality, prior to any fetal surgery, when the surgeon wants to be certain that the abnormality being treated is the only condition present.3 Ultimately, Dr. Levine believes that when pelvic surgery is being considered, MRI can provide valuable additional information that can confirm or alter the direction of treatment, as well as assist with patient counseling.
MRI of ovarian cysts
Ovarian cancer is the second most common of all gynecologic malignancies, and it is the leading cause of death in this category of disease.4 Approximately 75% of women with ovarian cancer are diagnosed at an advanced stage of the disease.
The imaging and staging of ovarian cancer is critical as it affects the prognosis and treatment of the patient. Women who are diagnosed at stage one of the disease have a five-year survival rate of 80%, while women who are diagnosed at stage four of the disease have a five-year survival rate of only 8%.5 MRI plays a significant role in the detection, characterization, and staging of ovarian masses. The ability to characterize masses as benign or malignant is essential, as the number of benign ovarian masses vastly exceeds the number of malignant abnormalities.5
The ovaries are mainly made of three types of cells, and each type can develop into a different type of tumor.
- Epithelial tumors- These tumors start from cells that cover the surface of the ovary. Epithelial tumors account for nearly 85%-90% of all ovarian malignancies.5
- Germ cell tumors- These tumors start from the cells that produce the eggs.
- Stromal tumors- These tumors start from structural tissue cells that hold the ovary together and produce the female hormones. 6
MRI can be extremely accurate in the diagnosis of benign lesions, such as mature cystic teratomas, endometriomas, and nondegenerative leiomyomas located on the ovaries. In fact, many studies have shown MRI to be superior to both US and CT scans in diagnosing malignancy in indeterminate ovarian masses. Furthermore, a gadolinium-based contrast agent can be used during an MRI to characterize the internal architecture of cystic lesions. For example, a contrast enhanced MRI can readily detect papillary projections, necrosis in a solid tumor, and septations.5
There are many possible pelvic/ovarian MR imaging protocols, however the sequences are the basic building blocks for most MRI protocol. Post-contrast fat-saturated axial T1-weighted images are extremely useful in detecting peritoneal implants, necrosis in a solid mass, and enhancing septations or vegetations in a cystic mass. On T2-weighted scans, ovarian masses with fibrous components, such as firbome, fibrothecome, and cystadenofibroma, tend to have very low signal intensity. In addition, Hemorrhagic cysts can be diagnosed by the signal intensity of the hemorrhage within the cyst, at a high T1 signal intensity and of variable T2 signal intensity.5
A study conducted in 2007 by Sohaib et al., showed that the most predictive characteristics of malignancy are vegetations in a cystic lesion, presence of ascites, a maximal diameter greater than 6cm and necrosis in a solid lesion. 7
Ultimately, MRI is a key problem-solving tool when imaging tumor abnormalities in the female pelvis. The modalities’ ability to characterize masses in the structures related to the uterus, ovaries, and Fallopian tubes provides powerful diagnostic and prognostic information. Furthermore, MRI has the advantage of being able to use contrast enhancement agents, it’s scans are high resolution and extremely detailed, and it does not expose patients to ionizing radiation. While ultrasound might be the initial imaging modality of choice for examining the pelvis, radiologists should be aware of the significant value offered by MR.
1. Benacerraf, Beryl R., et al. "Consider ultrasound first for imaging the female pelvis." ajog.org. April 2015. Web. 29 August 2018. <https://www.ajog.org/article/S0002-9378(15)00151-9/pdf>.
2. Hubert, Jenifer, Bergin, Diane. "Imaging the female pelvis: When should MRI be considered?" Applied Radiology. 11 October 2011. Web. 29 August 2018. <https://appliedradiology.com/articles/imaging-the-female-pelvis-when-should-mri-be-considered>.
3. Allyn, Jennifer. "Ultrasound vs. MRI for Imaging of the Female Pelvis." RSNA 2017. 30 November 2017. Web. 29 August 2018. <https://rsna2017.rsna.org/dailybulletin/index.cfm?pg=17thu04>.
4. Velduis, Wouter et al. "Diagnostic Work up of Ovarian Cysts." Radiology Assistant. 14 May 2011. Web. 29 August 2018. <http://www.radiologyassistant.nl/en/p4d85aa9a92bbb/diagnostic-work-up-of-ovarian-cysts.html>.
5. Balachandran, Aparna et al. "Imaging of ovarian cancer." Applied Radiology. 12 September 2005. Web. 29 August 2018. <https://appliedradiology.com/articles/imaging-of-ovarian-cancer>.
6. "What is Ovarian Cancer?" American Cancer Society. 11 April 2018. Web. 29 August 2018. <https://www.cancer.org/cancer/ovarian-cancer/about/what-is-ovarian-cancer.html>.
7. Foti, Pietro V., et al. "MR imaging of ovarian masses: classification and differential diagnosis." NCBI. 16 December 2015. Web. 29 AUgust 2018. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4729709/>.