is a Radiologist, Northside Radiology Associates, Atlanta, GA. At
the time this article was written, Dr. Sydow was a radiology
Resident at the Hospital of the University of Pennsylvania.
is an Associate Professor, Department of Radiology, Hospital of
the University of Pennsylvania, Philadelphia, PA.
Magnetic resonance imaging (MRI) is a commonly used technique in
the workup of obstetric and gynecologic abnormalities and in the
pre- and postprocedural evaluation for uterine artery embolization.
This article summarizes the MRI techniques for evaluating the
uterus and describes the MRI findings of the most commonly
encountered conditions involving the uterus.
Optimal MRI of the female pelvis and uterus should be performed
on a high field-strength MRI system that uses local phased-array
coils. Theincreased signal-to-noise ratio provided by the surface
coils allows for small field-of-view imaging that results in higher
spatial resolution. The typical imaging protocol for the uterus
uses both T1-weighted (T1W) and T2-weighted (T2W) images. Axial T1W
images are obtained to evaluate the uterine contour, lymph nodes,
and bone marrow. We perform T2W imaging in 3 orthogonal planes. One
of these planes usually shows the endometrial complex along with
the long and short axis of the uterus to good advantage.
T2-weighted imaging depicts the zonal anatomy ofthe uterus.
Fat-suppressed T1W imaging is used to differentiate between pelvic
masses that contain fat and those that contain protein or
hemorrhage. Contrast enhancement is used to document the extent of
endometrial carcinoma invasion or to detect the presence of
necrosis in uterine leiomyomas. Dynamic contrast injection can be
used in women who are considering uterine artery embolization (UAE)
in order to evaluate the uterine arteries and the potential
collateral gonadal arterial supply.
In the evaluation of congenital uterine anomalies, sagittal T2W
images should be acquired first to determine the long-axis
orientation of the uterus. Subsequently, images should then be
obtained parallel to the long axis of the uterus in order to show
the outer uterine contour.
Normal uterine anatomy
T1-weighted images show poor contrast distinction between the
endometrium and myometrium. The zonal anatomy of the uterus has a
trilaminar appearance on T2W images (Figure 1).
The central endometrium has high signal intensity secondary to
mucinous rich endometrial glands and stroma. The endometrium varies
in thickness with the menstrual cycle and menopausal status. The
endometrium may measure upto 14 mm during the secretory phase in
menstruating women but is thinned during the follicular phase.
Postmenopausal women should have a homogeneous endometrium with a
width of <5 mm.
The myometrium can be separated into the inner myometrium, also
known as the junctional zone, and the outer myometrium (Figure 1).
Thejunctional zone contains compact smooth muscle with a paucity of
intercellular matrix and has relatively low T2 signal intensity.
The normal junctional zone measures <12 mm.
The outer myometrium has less compact smooth muscle and increased
intercellular matrix and vessels compared with the junctional zone,
which results in a higher T2 signal intensity. This zonal anatomy
is best visualized during the reproductive years and may be poorly
depicted or absent in prepubertal and postmenopausal women. In
women taking birth control pills, the junctional zone and
endometrium are thinner than in other women and the outer
myometrium is higher in signal intensity.
Uterine leiomyomas are neoplasms derived from the smooth muscle
cells of the myometrium. Uterine leiomyomas are common, occurring
in >20% in women over 30 years of age. Most patients with
uterine leiomyomas are asymptomatic. Among symptomatic patients,
dysmenorrhea and irregular menstrual bleeding are the most common
complaints. Leiomyomas may be intramural, subserosal, or submucosal
in location. Intramural leiomyomas are centered in the uterine wall
and are the most common subtype. A submucosal leiomyoma has a
component in the endometrial canal. An intracavitary leiomyoma is
almost entirely within the endometrial canal (Figure 2). Subserosal
leiomyomas are centered external to the uterus (Figure 3).
Nondegenerated uterine leiomyomas have lower T2 signal intensity
than the outer myometrium; in addition, they are well circumscribed
and can exhibit mass effect. On postcontrast imaging,
nondegenerated uterine leiomyomas enhance homogeneously. Uterine
leiomyomas can appear heterogeneous in signal intensity on T2W
images and show decreased enhancement when they undergo
degeneration. Some subsets of degeneration include hemorrhagic,
fatty (lipoleiomyoma) (Figure 4), myxoid, hyaline, and cystic.
Leiomyosarcoma may have an appearance similar to a degenerated
leiomyoma, but, fortunately, leiomyosarcoma is rare. It is
difficult to establish a prospective diagnosis of leiomyosarcoma in
the absence of metastatic disease. In our experience, degenerated
atypical leiomyomas are much more common than leiomyosarcomas.
Subserosal leiomyomas can simulate fibrous or smooth-muscle
ovarian masses, such as ovarian fibromas, fibrothecomas, or Brenner
tumors. Subserosal leiomyomas can be differentiated from ovarian
lesions since they show a normal ipsilateral ovary or a bridging
vessel from the uterus to the fibroid.
Subserosal fibroids on a stalk <2 cm in width are considered a
relative contraindication for UAE, as they may lose their
connection to the adjacent uterus.
Submucosal fibroids can simulate endometrial masses such as
endometrial polyps. Leiomyomas can be separated from polyps by
evaluating their signal intensity on T2W images. Leiomyomas usually
have low T2 signal intensity and have a stalk that originates
within the myometrium, while polyps have heterogeneous T2 signal
intensity. Submucosal and intracavitary fibroids are a common cause
of infertility or miscarriages by creating an adverse environment
for implantation or prohibiting sufficient blood fiow to support a
MRI can be used in the evaluation of patients who undergo UAE
for treatment of symptomatic leiomyomas. Preoperatively, MRI can
aid in selecting patients who may benefit from UAE. MRI documents
the size, location, and vascularity of the fibroids. Leiomyomas
that have high signal intensity on T1W images and no enhancement
have a poor response to UAE.
Detection of a large intracavitary fibroid is a relative
contraindication to UAE. Submucosal fibroids may be expelled from
These women may benefit from hysteroscopic resection rather than
Leiomyomas that show high signal intensity on T2W imaging and
homogeneous enhancement have the best responseto UAE.
Magnetic resonance angiography (MRA) can evaluate the uterine
arteries and identify potential collateral arterial supply from
thegonadal vessels that may need to be embolized as well.
MR can also identify other potential causes for a woman's signs or
symptoms, such as adenomyosis or endometriosis.
MR findings of successful UAE include a decrease in size and
enhancement of fibroids, preserved enhancement of the remainder
ofthe uterus, and lack of visualization of the uterine arteries
Treated fibroids have increased T1 signal and do not enhance, in
keeping with hemorrhagic necrosis (Figure 5). Fibroids that
continue to enhance are viable and usually grow in time and may
result in recurrent symptoms.
The angiographic images should be carefully inspected for a
possible cause of failure such as uterine artery revascularization
or collateral arterial supply from the ovarian arteries (Figure
Adenomyosis is the presence of ectopic endometrial tissue in the
uterine myometrium with smooth muscle hyperplasia. Adenomyosis may
be focal or diffuse, with the latter being more common. On T2W
images, adenomyosis appears as a thickening of the
low-signal-intensity junctional zone corresponding to the smooth
muscle hyperplasia (Figure 7).
Thickening of the junctional zone >12 mm is specific for the
diagnosis, while a measurement of 8 to 12 mm is indeterminate and a
measurement <8 mm excludes the diagnosis with high specificity.
One- to 4 mm hyperintense T2 foci within the junctional zone
represent the ectopic foci of endometrial tissue and, when present,
add specificity to the MR diagnosis (Figure 8).
MR can usually differentiate between focal adenomyosis and a
Adenomyosis has poorly defined margins,is often oriented parallel
to the endometrial stripe, contains 1- to 5-mm foci of ectopic
endometrial glands, and has minimal mass effect on the endometrial
canal. Leiomyomas have well-defined margins and mass effect.
Adenomyosis can be treated with uterine artery embolization with
the expectation that >50% of women will have significant
decrease in symptoms after 2 years.
Successfully treated adenomyosis shows a decrease in the width of
the junctional zone on MRI.
Endometrial carcinoma is the most common gynecologic malignancy.
Roughly 75% of endometrial carcinomas occur in postmenopausal
women. Excessive estrogen stimulation is the most recognized
association with endometrial cancer. Women taking tamoxifen are
also at increased risk of endometrial cancer. The most common
symptom of endometrial cancer is postmenopausal bleeding. The
initial procedure of choice in the evaluation of a woman with
suspected endometrial carcinoma is transvaginal sonography or
hysteroscopy with biopsy. MR is not used to screen women for
endometrial carcinoma. However, in women with biopsy-proven
endometrial carcinoma, MRI can be used to determine the depth of
On dynamic contrast-enhanced MRI, endometrial carcinoma enhances
less than the subjacent myometrium.
Malignant adenopathy is associated with muscle-invasive endometrial
carcinomas. Some surgeons use the information provided by
preoperative MRI to determine the need to perform lymphadenectomy.
As opposed to evaluating secondary findings of node-positive
disease (muscle invasion), it would be ideal to develop MRI
techniques to both detect and characterize lymph nodes as benign or
malignant in order to guide therapy.
When abnormal signal within the endometrial canal invades the
junctional zone on T2W or contrast-enhanced images, then
endometrial carcinoma is the likely diagnosis. The differential
diagnosis of a thickened endometrial stripe without myometrial
extension is superficial endometrial carcinoma, endometrial polyps,
and endometrial hyperplasia. Polyps may depict a zonal phenomenon
with a low T2-signal-intensity fibrous core and outer
high-signal-intensity glands. Endometrial hyperplasia often has a “Swiss cheese” configuration on T2W and enhanced imaging, with
internal nonenhancing cysts surrounded by enhancing glandular
Tamoxifen is used in the treatment of breast cancer. While
tamoxifen exhibits antiestrogenic effects within the breast, it can
also show proestrogenic activity within the endometrium. Thus,
tamoxifen can produce endometrial thickening on MRI (Figure 8).
Pathologically, the endometrial abnormalities associated with
tamoxifen use include endometrial atrophy, hyperplasia, polypoid
glandular-cystic proliferation, polyps, and endometrial cancer.
Endometrial sampling is often needed in these women, especially
those with abnormal uterine bleeding.
Mullerian duct anomalies
The incidence of mullerian duct anomalies is approximately 1%
but varies by population. In patients with infertility, it is
estimated to be 3%. Most mullerian duct anomalies are thought to be
sporadic or multifactorial in nature. The most widely quoted
classification scheme formullerian duct anomalies is the American
Fertility Society classification that has 7 classes (Table 1).
A simplified framework for the discussion of mullerian duct defects
consists of 3 categories: duct agenesis and hypoplasia, defects of
vertical fusion of the ducts with the ascending urogenital sinus,
and defects of lateral duct fusion.
Patients with mullerian duct anomalies may manifest with primary
amenorrhea in the adolescent age group. MRI can evaluate for the
presence or absence of the vagina, cervix, or uterus and also
depicts any associated renal anomalies (Figure 9). MRI can show the
level of obstruction of antegrade menstrual fiow in women with
functioning endometrium as well as depict findings of retrograde
menstruation such as hematosalpinx or endometriosis. In the
reproductive years, women with uterine anomalies may present with
spontaneous abortion, premature delivery, and abnormal fetal
Absence of the mullerian ducts (agenesis and
Mayer-Rokitansky-Kuster-Hauser syndrome represents failure of
vaginal development with varying degrees of cervical and uterine
agenesis/hypoplasia. In 90% of cases, there is complete uterine
agenesis. In the remaining 10% of cases, there may be an obstructed
or small rudimentary uterus. The ovaries are usually normal.
Mayer-Rokitansky-Kuster-Hauser syndrome is the most common cause of
amenorrhea in women with breast development, refiecting the normal
ovarian development with this condition. A rudimentary uterus may
contain functioning endometrial tissue. MRI can be used to detect
associated abnormalities such as endometriosis, renal anomalies,
and collecting system abnormalities (Figure 9).
The differential diagnosis of primary amenorrhea with normal breast
development and an absent uterus includes androgen insensitivity
syndrome; affected individuals have rudimentary testes and absent
ovaries on MR.
Unicornuate uterus is a type of uterine hypoplasia in which
there is incomplete or absent development of 1 mullerian duct and
represents 20% of mullerian duct anomalies. The abnormal uterine
horn can be completely absent (one third of cases) or rudimentary
(two thirds of cases). Of those patients with a rudimentary horn,
50% do not contain an endometrial canal and 50% have an
endometrial-lined cavity. The endometrial lined cavity within a
rudimentary horn communicates with the contralateral horn in
approximately one third of women.
A unicornuate uterus is usually an incidental finding unless a
cavitary rudimentary horn is present. These women can present with
nonviable pregnancy, endometriosis, or ectopic pregnancy.
Therefore, rudimentary horns that contain endometrium, whether they
are communicating or noncommunicating, are usually removed. Among
all of the mullerian duct anomalies, unicornuate uteri have the
highest association of renal abnormalities, present in up to 40% of
these women. The renal anomaly is ipsilateral to the abnormal horn.
MRI shows a banana-shapeduterus.
When the endometrium is absent, the horn is of low T2 signal
intensity, with loss of normal zonal anatomy. When the endometrium
is present, zonal anatomy may be preserved.
Disorders of vertical fusion (vaginal septum)
A transverse vaginal septum consists of a band of fibrous
connective tissue with vascular and muscular components. It is the
most commondisorder of vertical fusion. A transverse vaginal septum
can occur anywhere along the vagina, but most commonly occurs at
the junction of the upper and middle third. Patients typically
present with primary amenorrhea. In patients with a uterus and
functioning endometrium, hematocolpos can be depicted with MR with
less severe dilation of the endometrial cavity.
This finding is secondary to the decreased compliance of the more
muscular myometrium. A transverse vaginal septum can be present in
conjunction with other mullerian duct anomalies. The most common
association is a uterus didelphys and complex duplication
anomalies. The differential diagnosis for primary amenorrhea with a
present uterus includes an imperforate hymen, which can also cause
hematocolpos. Imperforate hymen is not a mullerian anomaly, and
distinction from a transverse vaginal septum can be difficult
although the treatment is similar.
Disorders of lateral fusion
Disorders of lateral fusions result in varying degrees of
duplication of the uterus and cervix. Possibilities include
didelphys, septate uterus, and bicornuate uterus. With a septate
uterus (Figure 10), a fibromuscular central septum is incompletely
resorbed after mullerian duct fusion. The septate uterus represents
approximately 55% of mullerian duct anomalies. Septate uteri may
result in first trimester miscarriages caused by implantation on
the septum. Reproductive outcome improves after hysteroscopic
resection of the septum. In uterine didelphys (Figure 11), there is
complete separation of distinct left and right uteri and accounts
for 5% of mullerian duct anomalies. The cervix is usually
duplicated as well. Women with uterine didelphys have normal or
nearly normal fertility. The bicornuate uterus is caused by
incomplete fusion of the uterovaginal horns at the level of the
fundus and represents approximately 10% of mullerian duct
Differentiating between the lateral fusion anomalies has
important implications for treatment decisions. For instance, a
septate uterus isoften treated with hysteroscopic resection of the
septum, while women with bicornuate uteri are treated with a
transabdominal metroplasty if they have a history of repeated
pregnancy loss. The key in imaging lateral fusion anomalies is the
evaluation of the external uterinefundal contour. The best imaging
plane for evaluation of the fundal contour is one that passes
through the long axis of the uterus. In a normal or septate uterus,
the outer contour is convex, fiat, or <10 mm ofconcavity. The
myometrial fundal indentation is smooth and broad, and the signal
intensity of this region is isointense to normal myometrium. The
outer contour concavity of a bicornuate uterus or uterine
didelphys, to the contrary, should be >10 mm. Two measurements
that may be helpful include the intercornual distance and
theintercornual angle. In a septate uterus, the intercornual
distance is <4 cm and the intercornual angle is <60°, as
compared with the bicornuate uterus, in which these values are
>4 cm and >60°, respectively.
Lateral fusion anomalies may also result in vaginal duplication.
Vertical vaginal septa are present in 75% of women with didelphys,
25% with bicornuate, and 5% with septate uteri.
Because of its superb soft tissue contrast and direct
multiplanar capabilities, MRI can detect and characterize normal
uterine anatomy and focal and diffuse uterine conditions. In
patients with primary amenorrhea, MRI can be used to confirm the
absence or presence of the uterus as well as evaluate for any
associated urogenital abnormalities such as renal agenesis. In
patients with infertility, MRI can confirmthe presence and extent
of a septate uterus and define the fibrous and muscular components.
In patients with pelvic pain, MRI is more sensitive and specific
than ultrasound for the findings of adenomyosis. In patients with
known leiomyomas, MRI is used in the preoperative evaluation for
uterine artery embolization. In oncology, MRI can be used to stage
women with known endometrial carcinoma. Understanding the
appearance of the common pathologic entities involving the uterus
along with the strengths and limitations of MRI will help
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