Uterine artery embolization (UAE) is used as an alternative to hysterectomy in selected patients and MRI assessment is key in allowing not only pre-procedure assessment but also assessing post-procedural outcome.
For a general discussion of the underlying condition refer to the article on uterine fibroids. For discussion of the indications and technique, refer to the article on uterine artery embolization.
Radiographic features
MRI
MRI is used for patient selection, planning and documenting baseline appearances prior to uterine artery embolization (UAE). Additionally, MRI is also useful following UAE, where it is used to assess post-embolization outcome and complications.
MR technique
T1 and T2 fast spin echo (FSE) in sagittal, coronal and axial planes
MR angiography using 3D gradient recalled echo with IV gadolinium (e.g. 20 ml gadodiamide)
20 mg IV hyoscine butylbromide is given to suppress uterine and intestinal peristalsis
Pre-embolization assessment
Pre-embolization imaging should assess appearance, location, size, and vascularity as well as ensure that uterine findings do not represent other pathology.
Appearance
MRI appearances of uterine fibroids are variable, and depends on whether the fibroids are:
non-degenerate
-
degenerate:
hyaline or cystic
myxoid
red
Non-degenerate fibroids appear as well-circumscribed masses of homogenous decreased signal intensity (cf. outer myometrium) on T2 images. Cellular leiomyomas show a slightly higher signal intensity on T2 images as well as enhancement on post-contrast images.
Degenerate fibroids show variable appearances on T2 images and contrast-enhanced images.
Fibroids with cystic degeneration show high signal intensity on T2 images. Cystic areas do not show enhancement.
Fibroids with hyaline or calcific degeneration show low signal intensity on T2 images, this is similar to a typical fibroid 3. Fibroids with hyaline degeneration may show a cobblestone appearance on post-contrast images 1.
Fibroids with myxoid degeneration demonstrate very high signal intensity on T2 images and minimal enhancement on contrast-enhanced images 4.
Fibroids with red degeneration may show peripheral or diffuse high signal intensity on T1 images (probably due to the proteinaceous content of blood or T1 shortening effects of methemoglobin). They may show variable signal intensity on T2 images, with or without a low signal intensity rim.
Location
Uterine fibroids are, usually, seen within the uterine corpus, ~8% occur within the cervix.
They may be classified as follows:
submucosal: projecting within the endometrial cavity
intramural: within the substance of the myometrium
subserosal: lie beneath the serosa
Pedunculated fibroid: can be subserosal or submucosal in location, this is defined by the presence of a stalk which <50% of the fibroid diameter.
Fibroid size
Although the relationship between the size of the fibroid and post-embolization outcome is not entirely clear, most operators select a threshold of 13-15 cm. It is suspected that embolization of larger leiomyomas may still result in bulk symptoms due to residual fibroid mass. Additionally, with larger amount of necrotic tissue, prolonged post-embolization syndrome might occur 1.
Vascularity
Enhancement of the fibroids depends on their vascularity which is assessed on post-contrast images. The goal of uterine artery embolization (UAE) is to cause infarction of the fibroid while maintaining endometrial and myometrial perfusion. Fibroids that are already infarcted are unlikely to show volume reduction following UAE.
Vascular anatomy is assessed on 3D contrast-enhanced MRA. This permits assessment of the anatomy of the uterine vessels. It also has a role in depicting ovarian artery contribution to the uterine fibroid blood supply.
Differential diagnosis
MRI helps in confirming the diagnosis of uterine fibroids and differentiating it from a variety of gynecological conditions.
solid adnexal mass
Post UAE MRI appearances
Vascularity
Lack of enhancement on post-contrast images in a previously enhancing fibroid represents fibroid infarction. Complete fibroid infarction has been shown to have a higher symptom control and a lower rate of gynecological intervention at 5 years when compared to incomplete infarction.
Persistent fibroid enhancement on post-contrast images or visualization of the uterine arteries on MRA is considered treatment failure.
Liquefaction
With increased interval between 3 months and 1 year following embolization, there is progressive liquefaction of necrotic fibroids. This results in increased signal intensity on T2 images.
Size reduction
Successful embolization may result in some reduction of fibroid size.
Location
Some fibroids (1-5%) may demonstrate change in location, e.g. a submucosal fibroid may become endocavitary. Similarly subserosal fibroids may develop a submucosal or intramural component.
Fibroid recurrence
This is considered a late treatment failure.
Complications
Some complications are evidence of post UAE MRI:
-
uterine enlargement
T1 hyperintense intracavitatory hematoma
gas associated with endometritis appears as a signal void on all sequences (the presence of gas alone does not indicate infection)
-
uterine infarction is a very rare complication
non-enhancement of uterine corpus
widening of the endometrial stripe
the uterus shows homogeneous low signal intensity on T1 images and areas of high signal intensity on T2 images
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