Pelvic MRI is a method of choice for confirmation and characterization of uterine fibroids.
MRI protocol varies among institutions,
mostly in terms of the plane selection,
however,
required sequences are T2WI in three planes,
T1WI with and without fat saturation and dynamic postcontrast T1WI sequences. Diffusion sequences (DWI and ADC) are also acquired but of lesser significance in diagnosis of leiomyomas.
In this educational exhibit we will try to accentuate what is important for diagnostic radiologist to report and explain what information the gynecologist and interventional radiologist expect to find in MRI report in order to plan further management.
MRI before UFE - what should be reported
•Uterus: - Size
- Position
- Zonal anatomy
•Uterine fibroids (UFs): - Number
- Size
- Location
- Morphology (T2WI)
- Degeneration
- Enhancement (T1WI Gd+)
- Vascularity (MRA)
- Pressure on adjacent organs
•Exclude potential pelvic pathology/differential diagnosis
The report should start with usual information we describe in the MR analysis of uterus.
Size of the uterus in three dimensions (Fig.
3) is important to mention because lesion or uterus diameter longer than 20 cm may be a contraindication for embolization (Fig.
4),
although recent studies show that it is actually a relative contraindication and that even such myomas can be embolized.
Fig. 3: Size of the uterus in all three dimensions should be reported: craniocaudal and anteroposterior diameter in sagittal plane (A) and laterolateral diameter in axial/transverse plane (B).
Fig. 4: Uterine or leiomyoma size exceeding 20 cm in longest diameter may be contraindication for UFE.
Regarding position of the uterus,
possible findings are: normal,
anteflexion,
anteversion,
retroflexion and retroversion of the uterus (Fig.
5 and 6).
Fig. 5: Normal position of uterus (A), retroflexion - RF (B).
Fig. 6: Anteversion - AV (A) and anteflexion - AF (B) of the uterus.
One should also appreciate zonal anatomy of the uterus (endometrium,
junctional zone or inner myometrium and outer myometrium) and look whether it's neat or there is a pathology that disturbs it (Fig.
7).
Fig. 7: Zonal anatomy of uterus
As far as number and size of UFs are concerned,
there can be a single fibroid or the entire uterus may be changed (uterine leiomyomatosis),
and sizes vary from a few millimeters to over 10 cm (Fig.
8 and 9).
Fig. 8: Number of uterine fibroids: single (A) vs. multiple (B), also referred to as uterine leiomyomatosis.
Fig. 9: Size of the UF: from very small (A) to very large (B).
It is important to determine the exact location of the dominant leiomyoma: anterior wall,
posterior wall,
fundus,
isthmus or cervix of the uterus.
Regarding position of leiomyoma in relation to the uterus wall,
we differentiate between submucosal,
intracavitary,
intramural,
subserosal and pedunculated UFs (Fig.
10 and 11).
Fig. 10: Position of UFs: submucosal (A), intracavitary (B) and intramural (C).
Fig. 11: Position of UFs: subserosal (A) and pedunculated (B).
Intramural fibroids are the most common type of fibroids and usually do not cause significant symptoms.
Submucosal fibroids often present with prolonged and excessive menstrual bleeding.
For intracavitary fibroids there is a risk of expulsion through the vaginal canal after embolization.
For pedunculated subserosal UFs it is important to measure the thickness of the stalk because those thinner than 2 cm may be a contraindication for embolization due to the risk of leiomyoma being detached.
If solitary,
laparoscopic surgery is better option for these UFs,
rather than embolization.
In addition,
for this type of leiomyomas,
torsion and consequently inflammation,
peritonitis,
intraperitoneal adhesions,
acute abdominal pain and protracted pain syndrome are possible.
Sometimes we can also come across an unusual location.
Fibroids located in broad ligament of uterus may be mistaken for ovarian masses which are also of homogeneously low signal intensity (SI) on T2WI,
such as ovarian fibroma and Brenner tumor.
But,
if we prove continuity of the lesion with uterus on consecutive images and unremarkable appearance of ovaries,
uterine origin of the lesion can be confirmed (Fig.
12).
Fig. 12: UF (yellow elipse) in the broad ligament of uterus. The continuity of lesion with the fundus of uterus (yellow arrow) and the normal appearance of both ovaries (white arrows) confirm uterine origin of detected lesion.
The morphology we are analyzing on anatomical T2 weighted sequences can sometimes directly decide on the choice of therapeutic method.
How we want UF to look like in ideal circumstances?
To be homogeneously iso- to moderately low T2 SI,
well-defined,
with intense and homogeneous postcontrast enhancement (Fig.
13). This appearance of leiomyoma usually guarantees the success of UFE.
Fig. 13: Preferable morphology and appearance of UF (*) before and after embolization (T2WI and postcontrast T1WI sequences).
Recently,
we find this MRI classification in the literature (Fig.
14): three types of UFs depending on signal intensity on T2WI (visual inspection) in comparison with SI of myometrium and skeletal muscle (m.
psoas major,
m.
rectus abdominis or other skeletal muscle shown in a specific plane).
T2 signal intensity of UFs:
- type I: SI of UF ≤ SI of skeletal muscles
- type II: SI of skeletal muscles < SI of UF < SI of myometrium
- type III: SI of UF > SI of myometrium.
Fig. 14: Three types of UFs comparing SI of leiomyoma to SI of myometrium and skeletal muscle.
It is believed that the very low signal intensity UFs,
those similar to signal intensity of skeletal muscle (type I) have been strongly degeneratively changed.
It has also been described that types II and III have the best response to UFE.
Leiomyomas with homogeneously high signal intensity on T2WI,
in which smooth muscle component dominates over fibrous tissue and are consequently hypercellular,
have intense postcontrast enhancement (Fig.
15).
Because of high cellularity they may also show diffusion restriction and imitate other uterine lesions.
This type of UFs are considered to have very good response to UFE.
Fig. 15: Hypercellular UF (*): homogeneously high T2WI SI, homogeneous enhancement and diffusion restriction.
UF may outgrow their vascular supply,
resulting in different types of degeneration that we demonstrate in our pictorial examples:
• Hyaline degeneration (> 60 %),
• Cystic degeneration (4%),
• Myxoid degeneration and
• Red degeneration.
The most common type is hyaline degeneration which occurs in more than 60% of fibroids and is characterized by extremely low signal intensity on T2WI (Fig.
16 and 17).
These myomas can be calcified and the postcontrast enhancement is much weaker than of the rest of the uterus.
Uterine fibroids with hyaline or calcific degeneration are difficult to distinguish from non-degenerated fibroids on pelvic MRI.
Areas of calcification can appear as signal voids on MRI.
Fig. 16: UFs with hyaline degeneration (yellow circles): T2 hypointense, T1 isointense and low enhancement in comparison to regular UFs.
Fig. 17: Example of hyaline degeneration of uterine fibroids with very poor, almost none postcontrast enhancement.
There is also a cystic degeneration that is recognized by the cystic zones of very high signal intensity on T2WI and by the absence of postcontrast enhancement of the same zones (Fig.
18).
Fig. 18: Cystic degeneration of UF (yellow circle): very hyperintense on T2, no enhancement at all.
Myxoid degeneration is presented by irregular areas of moderately high T2 signal intensity but unlike cystic,
there is minimal enhancement of myxoid components (Fig.
19).
Fig. 19: Myxoid degeneration of UF: hyperintense on T2 with minimal postcontrast enhancement.
A specific type of degeneration that occurs more frequently in pregnant women and presents with acute pain is the red or hemorrhagic degeneration (Fig.
20).
It is characterised by variable SI onT2 depending on the age of the blood,
high SI on T1 (sometimes across whole lesion but more often only on the periphery of the lesion),
with no signs of postcontrast enhancement.
To be sure,
we can obtain T1WI with fat saturation,
where the high SI of hemorrhagic component is still visible.
Fig. 20: Red (hemorrhagic) degeneration of UF is characterised by variable signal intensity on T2, hyperintense T1 areas representing blood products (arrows) and absence of enhancement.
We can often encounter a peripheral ring of high SI in UFs on T2WI,
with postcontrast enhancement (Fig.
21 and 22).
Such morphology,
ie pseudocapsule,
is explained by the existence of dilated lymphatic vessels or ectatic veins on the periphery of the lesion,
or the edema where the enhancement is explained by retention of contrast in the interstitial space.
Fig. 21: Uterine fibroid with peripheral ring of high T2 SI with enhancement.
Fig. 22: Enhancement of peripheral high T2 SI ring.
Description of enhancement of the lesion and vascular supply of leiomyoma on MR angiography is of the utmost importance for the report.
As we have already mentioned,
it is desirable that fibroid enhances vividly and homogeneously (Fig.
23).
Fig. 23: Preferable vivid and homogeneous enhancement of uterine fibroid.
On MR angiography we monitor the anatomy,
origin and course of uterine arteries,
anatomy of the iliac arteries,
possible dominant vascular supply on one side and the presence of collateral circulation to the UF through the ovarian arteries,
which may be a cause of failed embolization and persistent symptoms following UFE (Fig.
24).
Fig. 24: A. Uterine fibroid vascular supply from both uterine arteries (Source: Department of Radiology, University Hospital Centre "Sisters of Mercy" - Zagreb/HR);
B. Arrows indicate ovarian artery collaterals that supply UF on both sides (Source: Kröncke T.J. (2014) When to Consider Ovarian Artery Embolization in UAE. In: Reidy J., Hacking N., McLucas B. (eds) Radiological Interventions in Obstetrics and Gynaecology. Medical Radiology. Springer, Berlin, Heidelberg).
References: Kröncke T.J. (2014) When to Consider Ovarian Artery Embolization in UAE. In: Reidy J., Hacking N., McLucas B. (eds) Radiological Interventions in Obstetrics and Gynaecology. Medical Radiology. Springer, Berlin, Heidelberg
MRI is also effective in assessment of postembolization success by measuring volume reduction and enhancement of UF and also in detecting possible complications.
This diagnostic approach facilitates and directly affects the planning of intervention,
saves time and protects the patient from additional radiation during DSA angiography.
We also have to report any significant mass effect or pressure on the surrounding organs,
because sometimes leading symptoms of uterine fibroids can be constipation or urinary incontinence (Fig.
25).
Fig. 25: Pressure on adjacent organs: uterine mass effect on colon and rectum (white arrows) and on urinary bladder (yellow arrow) may be present. Notice how very large UF on image B pushed bladder anteriorly and cranially to the level of L4 vertebra.
MR is also done to exclude any other pelvic pathology that may be the cause of the symptoms.
Differential diagnosis
• Adenomyosis
• Solid adnexal masses
• Leiomyosarcoma of the uterus
• Focal contraction of myometrium.
In addition to the solid adnexal masses mentioned above,
sometimes a leiomyosarcoma of the uterus comes in consideration,
which is,
unlike the uterine fibroids,
poorly defined,
ie has irregular border.
Sometimes radiomorphologically these two entities (uterine leiomyoma and leiomyosarcoma) can not be distinguished with certainty and the final diagnosis is pathohistological (nuclear atypia,
high mitotic index and infiltrative margins being consistent with leiomyosarcoma).
Focal contractions of myometrium that can mimic the mass will be recognized by disappearance in the consecutive sequences,
and focal adenomyosis can often be found in coexistence with leiomyomas.
Adenomyosis,
or ectopic endometrial tissue within the myometrium is characterized by diffuse low T2 SI area with punctate foci of high T2 SI representing the ectopic endometrial glands,
some of which have high signal intensity on T1WI too,
in terms of hemorrhage (Fig.
26).
This ectopic glandular tissue is surrounded by reactive hypertrophy of myometrial smooth muscle.
Adenomyosis is usually more or less ill-defined,
has no significant mass effect,
and is defined already by thickness of the junction zone of 12 milimeters or more.
Fig. 26: Adenomyosis: low T2 SI ill-defined mass (yellow elipse in image A) and small foci of high T2 SI within which represent ectopic endometrial glands (yellow arrows in images B and C). Some of these have high T1 SI consistent with hemorrhage (white arrow in image D).
When we observe this comorbidity (both adenomyosis and uterine fibroids; Fig.
27),
it is important to determine the dominant pathology for interventional radiologist.
Indeed,
adenomyosis is not contraindication and can also be treated by embolization,
but in this case it is necessary to embolize it with smaller particles (300-500 μm instead of 500-900 μm) because vessels within adenomyosis are of smaller calibre than those in uterine fibroids.
Fig. 27: Coexistence of focal adenomyosis of posterior wall of the uterus (A) and several uterine fibroids (UF) in same organ.
Some other pathologies can also be found occasionally,
such as glandular cervical polyp that can be hard to differentiate from hypercellular uterine fibroid (Fig.
28).
Fig. 28: Here we have an example of well-defined cervical/uterine mass (*) whose etiology could not be determined reliably by MRI. Although reminiscent of the leiomyoma (hypercellular because of moderate hyperintensity on T2WI), a pathohistological analysis has demonstrated that this is a glandular polyp of the cervix.
MRI after UFE - what should be reported
• Size of UF (volume reduction)
• Morphology of UF
• Enhancement of UF
• Possible complications
After embolization,
the best indicator of success is regression of the symptoms but the morphological criteria on MRI also tell us about the success of the procedure and the potential risk of disease recurrence (development of collateral supply of UFs on MRA).
On the follow-up MRI we describe the morphology of the treated leiomyoma,
contrast enhancement and the diameter and volume reduction (details in Fig.
29,
30 and 31).
Volume reduction of 30-50 % is considered to be good response to treatment of uterine fibroid.
Submucosal UFs respond better to UFE than intramural or subserosal leiomyomas.
(Hyper)cellular UFs have also very good postprocedural response.
Degenerated UFs have smaller volume reduction after UFE.
Fig. 29: Patient with solitary leiomyoma of fundus of the uterus initially presenting with pain and excessive menstrual bleeding has been referred to UFE. Great response to UFE: images before (A,B) and 6 months after the procedure (C,D) show 30% diameter reduction and more than 60 % volume reduction of embolized uterine fibroid. There is no enhancement of the lesion (representing infarction) on follow-up MRI and the symptoms have disappeared.
Fig. 30: Another good response to UFE in patient with prolonged and excessive menstrual bleeding: uterine fibroid before (A,B) and 6 months after the procedure (C,D) shows 31 % diameter reduction and 50 % volume reduction.
Fig. 31: Good response to UFE even in very low T2 SI leiomyoma that is considered to be degeneratively changed and thus, less prone to successful treatment; before (A,B) and 6 months after the procedure (C,D). Size reduction and lack of enhancement on follow-up MRI.
Complications
- Transient pain / Postembolization syndrome
- Transcervical expulsion of UF
- Premature menopause (loss of ovarian function)
- Postembolization infection (endometritis,
tubo-ovarian abscess,
PID,
pyomyoma)
Most of these rarely occur and are again diagnosed by MRI.