DOI:10.2214/AJR.07.3509
AJR 2008; 191:364-370
© American Roentgen Ray Society
MRI of Adnexal Masses in Pregnancy
Nicholas A. Telischak1,
Benjamin M. Yeh1,
Bonnie N. Joe1,
Antonio C. Westphalen1,
Liina Poder1 and
Fergus V. Coakley1
1 All authors: Department of Radiology, University of California, San Francisco,
Box 0628, Rm. M-372, 505 Parnassus Ave., San Francisco, CA 94143-0628.
Received December 6, 2007;
accepted after revision February 13, 2008.
A. C. Westphalen was supported by the National Institute of Biomedical
Imaging and Bioengineering (NIBIB T32 training grant no. 1 T32 EB001631).
Address correspondence to F. V. Coakley
(fergus.coakley{at}radiology.ucsf.edu).
Abstract
OBJECTIVE. The objective of this article is to provide a practical
review of the incremental benefit of MRI in the assessment of adnexal masses
in pregnancy.
CONCLUSION. MRI can assist sonographic assessment of adnexal masses
in pregnancy by depicting the characteristic findings of exophytic leiomyoma,
red degeneration of leiomyoma, endometrioma, decidualized endometrioma, and
massive ovarian edema. Accordingly, MRI should be considered as a useful
adjunct when sonography is inconclusive or insufficient to guide management of
adnexal masses discovered in pregnancy.
Keywords: adnexal mass • fetal imaging • MRI • obstetrics • women's imaging
Introduction
A pathologic adnexal mass is found in 1–2% of pregnancies
[1] (by definition, the
physiologic corpus luteum cyst of early pregnancy is excluded). The relative
frequency of the more common diagnoses encountered is illustrated by a
sonographic series of 131 adnexal masses seen after 12 weeks of gestation in
which 38% were functional cysts; 32%, dermoid cysts; 12%, benign cystic
tumors; and 11%, endometriomas
[1].
Only 1–3% of adnexal masses are malignant, but even benign masses can
cause symptoms or obstetric complications. Sonography is the primary method of
detection and evaluation, but findings may be nonspecific and then MRI may
assist characterization [2].
The use of MRI in pregnancy has expanded because of improvements in rapid
breath-hold sequences and because better imaging helps avoid the potential
hazards of surgery during gestation. This pictorial essay aims to provide a
practical review of the incremental benefit of MRI in the assessment of
adnexal masses in pregnancy and consists of a description of MRI technique
during pregnancy accompanied by a review of MRI findings of these masses
categorized as mimics, nonneoplastic, and neoplastic.
Technique
Standard MRI safety screening should be performed. The patient should fast
for 4 hours to reduce bowel peristalsis artifact and prevent postprandial
fetal motion and should empty her bladder immediately before scanning. Written
consent is not mandatory, although arguably it is advisable to explain to the
patient the negligible nature of the risks posed by MRI in pregnancy
[3] and document this
discussion in either the chart or the radiology report. A pelvic surface coil
will improve image quality, but it can be omitted if the scanner bore will not
accommodate both patient and coil. Most pregnant patients can be scanned in
the supine position, but left lateral decubitus positioning should be
considered during later gestation to avoid caval compression by the gravid
uterus.
After a localizer is acquired, rapid T1- and T2-weighted imaging, which
will eliminate respiratory motion artifact and minimize fetal motion artifact,
can be performed during a maternal breath-hold with multislice spoiled
gradient-echo and single-shot RARE sequences, respectively. Axial images are
usually adequate for T1-weighted evaluation. T1-weighted images with
frequency-selective fat saturation should be obtained if an adnexal mass is of
high T1 signal intensity, because this sequence can distinguish fat from
blood.
Axial, sagittal, and coronal images are often helpful for T2-weighted
assessment. Slower breathing-averaged RARE T2-weighted sequences may provide
greater spatial and contrast resolution than T1-weighted sequences but have
the disadvantages of longer imaging times and potential for greater motion
artifact. TR and TE values used locally for nonpregnant patients can be used
in pregnant patients to produce appropriately T1- and T2-weighted images.
Slice thickness and matrix can be adjusted to optimize coverage and resolution
while remaining within the breath-hold capacity of the patient. Typically,
slice thickness would be 5–8 mm with an interslice gap of 0–1 mm
and a matrix of 256 x 128–256.
Gadolinium is teratogenic in animal studies and crosses the placenta where
it is presumably excreted by the fetal kidneys into the amniotic fluid. In the
era of nephrogenic systemic fibrosis, this characteristic of gadolinium raises
theoretic concerns of toxicity related to disassociation and persistence of
free gadolinium. Gadolinium is classified as a category C drug by the U.S.
Food and Drug Administration (FDA) and can be used if considered
critical—that is, to be administered only "if the potential
benefit justifies the potential risk to the fetus." More stable
macrocyclic agents (e.g., gadoteridol or gadobutrol) may be preferable to
gadolinium [4]. In reality,
contrast administration for adnexal masses is used primarily to assess for the
presence of solid components in a cystic mass and is used to a lesser extent
to evaluate nonenhancement in a torsed mass. Such information can generally be
derived from gray-scale and Doppler sonography; thus, it is unlikely that IV
gadolinium would be considered critical for MRI of an adnexal mass in
pregnancy.
Mimics of Adnexal Masses
This category consists of masses that do not arise primarily from the
ovaries or fallopian tubes and includes exophytic uterine leiomyoma and
ectopic pregnancy. Exophytic leiomyomas are a common cause of an apparent
adnexal mass at sonography. MRI is superior to sonography in differentiating
leiomyomas from other masses
[5], and the correct diagnosis
is suggested when a well-circumscribed lesion with low-T2-signal-intensity
solid components is seen to have a beak- or claw-shaped interface with the
uterus (Figs. 1A,
1B, and
1C). Bridging vessels between
the uterus and an apparent adnexal mass are also a useful sign of an exophytic
leiomyoma. Occasionally during pregnancy, leiomyomas undergo spontaneous
hemorrhagic infarction, known as "red degeneration," or growth and
can present with acute pain. There are no specific sonographic features of
leiomyoma, but MRI characteristically shows a leiomyoma with uniform or
peripheral high T1 signal intensity
[6] (Figs.
2A,
2B, and
2C).
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Fig. 1A —36-year-old pregnant woman who presented for routine early
pregnancy sonography. Routine early pregnancy transabdominal sonogram obtained
at 7 weeks' gestation shows solid mass (arrow) of indeterminate
origin and nature in pelvis posterior to uterus (UT).
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Fig. 1B —36-year-old pregnant woman who presented for routine early
pregnancy sonography. Sagittal single-shot RARE T2-weighted image shows large
mixed solid and cystic pelvic mass inferoposterior to gravid uterus. Note that
solid parts (arrow) of mass are of low T2 signal intensity.
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Fig. 1C —36-year-old pregnant woman who presented for routine early
pregnancy sonography. Axial RARE T2-weighted image with fat saturation shows
mass has beak- or clawlike interface with myometrium (arrows),
consistent with uterine origin. Overall findings are those of cystic
degeneration in exophytic uterine leiomyoma.
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Fig. 2A —34-year-old pregnant woman who presented with lower abdominal
pain. Transvaginal sonogram obtained at 25 weeks' gestation shows solid 3.8-cm
mass (between calipers) thought to be of right adnexal origin.
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Fig. 2B —34-year-old pregnant woman who presented with lower abdominal
pain. Axial RARE T2-weighted image shows mass (arrow) arises from
uterus and is of low T2 signal intensity; also, note "claw sign,"
similar to Figures 1A,
1B, and
1C. Findings are those of
exophytic uterine leiomyoma.
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Fig. 2C —34-year-old pregnant woman who presented with lower abdominal
pain. Axial spoiled gradient-echo T1-weighted MR image shows exophytic uterine
leiomyoma (arrow) is of increased T1 signal intensity; this finding
indicates red degeneration (i.e., spontaneous hemorrhagic infarction).
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Ectopic pregnancy is usually diagnosed clinically and sonographically. MRI
serves as an adjunct when sonography is occasionally limited by inadequate
soft-tissue contrast, resolution, or field of view. The key MRI feature of
ectopic pregnancy is a gestational sac that is outside the uterus
[7]
(Fig. 3), generally in the
absence of an intrauterine pregnancy. The ectopic gestational sac typically
appears as a cystic saclike structure that is frequently associated with
surrounding acute hematoma of distinct low intensity on T2-weighted
images.
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Fig. 3 —Sagittal single-shot RARE T2-weighted image in 29-year-old
woman with ectopic pregnancy at 22 weeks' gestation shows fetus in
extrauterine location. Empty endometrial cavity (arrow) is seen
anterior to large leiomyoma (Fibroid).
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Nonneoplastic Adnexal Masses
This category includes hemorrhagic cyst, endometrioma, theca lutein cyst
(hyperreactio luteinalis), tuboovarian abscess, and massive ovarian edema.
Hemorrhagic cysts may have a variable course and sonographic appearance,
including internal heterogeneity, thickened rim, septations, and solid
components thought to represent clot
[8]. Although high T1 signal
may suggest the diagnosis of hemorrhagic cyst, MRI may also be inconclusive in
these difficult cases (Fig.
4).
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Fig. 4 —Axial RARE T2-weighted image with fat saturation obtained at
24 weeks' gestation in 29-year-old woman shows complex mixed solid and cystic
left adnexal mass (arrow). No increased signal was seen on
T1-weighted images (not shown). MRI appearances are nonspecific, although
diagnostic considerations include cystic malignancy. Mass was resected and
found to be benign hemorrhagic cyst.
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On MRI, endometriomas are somewhat thick-walled cystic structures of
characteristically high T1 and variably reduced T2 signal intensity (the
latter is known as "T2 shading"). High T1 signal intensity is due
to blood products and does not suppress with fat saturation
[6] (Figs.
5A,
5B,
5C, and
5D). Solid components within
an endometrioma can be due to the rare complication of malignant
transformation but when seen in pregnancy may reflect ectopic decidualization
(i.e., ectopic occurrence of the endometrial changes that normally form the
vascular decidual lining of the uterus). Decidualized endometrioma can mimic
ovarian malignancy during pregnancy, but a prospective diagnosis may be
possible when solid smoothly lobulated nodules with prominent internal
vascularity within an endometrioma are seen on sonography from early in
pregnancy, and the nodules show marked similarity in signal intensity and
texture to the decidualized endometrium in the uterus at MRI
[9] (Figs.
6A,
6B, and
6C). That is, smooth
lobulation and prominent vascularity on Doppler imaging and isointensity to
decidualized endometrium on MRI are features of solid nodules in an
endometrioma that suggest decidualization rather than malignant
transformation.
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Fig. 5C —37-year-old pregnant woman. Axial spin-echo T1-weighted MR
image with fat saturation shows mass (arrow) remains of increased
signal intensity, excluding macroscopic fat and suggesting blood.
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Fig. 5D —37-year-old pregnant woman. Axial single-shot RARE
T2-weighted MR image shows mass (arrow) of reduced T2 signal
intensity ("T2 shading"). Overall findings are consistent with
endometrioma.
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Fig. 6A —34-year-old pregnant woman. Axial Doppler sonography image
obtained at 21 weeks' gestation shows right adnexal mass (arrow) with
smoothly lobulated mural nodules and prominent internal vascularity.
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Fig. 6B —34-year-old pregnant woman. Axial T1-weighted spoiled
gradient-echo MR image shows that fluid in cystic part of mass is of high T1
signal intensity (arrow), which is consistent with blood.
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Fig. 6C —34-year-old pregnant woman. Axial RARE T2-weighted MR image
shows solid component (white arrow) of mass is strikingly similar to
decidualized endometrium (between black arrows) in uterus, both with
respect to signal intensity and texture. Findings are considered consistent
with decidualized endometrioma; postnatal resection confirmed diagnosis.
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Theca lutein cysts (hyperreactio luteinalis) are rare functional ovarian
masses that are due to overstimulation of the ovaries by endogenous or
exogenous gonadotropins, usually in the setting of assisted fertility,
gestational trophoblastic disease, or multiple gestation. Theca lutein cysts
are large and have a typical multilocular cystic appearance across all imaging
techniques, and there is usually little incremental benefit to MRI in
diagnosis [6]
(Fig. 7).
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Fig. 7 —Coronal single-shot RARE T2-weighted MR image obtained at 22
weeks' gestation in 31-year-old woman. Large bilateral multilocular adnexal
masses (vertical arrows) are typical of theca lutein cysts, which in
this case were associated with twin pregnancy; note two fetal heads
(horizontal arrows) in uterus.
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Tuboovarian abscess may complicate pregnancy, typically in patients
presenting with fever, elevated WBC count, pelvic pain, and vaginal discharge.
Patients with more severe symptoms or who are unresponsive to initial therapy
may need to undergo imaging, and MRI is sometimes superior to transvaginal
sonography for radiologic assessment
[10]. An abscess appears as a
thick-walled, fluid-filled mass in the adnexal region that is hypointense on
T1-weighted images and hyperintense or heterogeneous on T2-weighted images.
However, in practice, the workup of tuboovarian abscess usually begins with
sonography and proceeds to CT if exclusion of other inflammatory or
gastrointestinal abnormalities or if imaging-guided percutaneous drainage is
required, so the incremental role of MRI is debatable. MRI may be helpful if
sonography is inconclusive or nondiagnostic or when abscesses containing gas
cannot be differentiated from gas within bowel.
Massive ovarian edema is characterized by marked enlargement of one ovary
(rarely both) due to gross diffuse stromal edema that results in peripherally
displaced follicles and may be due to subacute or chronic torsion without
frank infarction [11]. MRI
shows an enlarged ovary that is hyperintense on T2-weighted images. T2
hyperintensity may even suggest the lesion is cystic, but correlation with
sonography will help avoid this pitfall (Figs.
8A and
8B).
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Fig. 8B —32-year-old woman with persistent right-sided pelvic pain.
Sagittal RARE T2-weighted MR image shows right ovary (asterisk) is of
markedly increased T2 signal intensity to degree that mass might be considered
cystic if MRI findings had not been interpreted in conjunction with
sonographic findings. Appearance is of massive ovarian edema. Cause of this
condition is not well understood but may reflect chronic or subacute low-grade
torsion. Beaklike pedicle (arrow) arising from superior aspect of
ovary is compatible with this pathogenesis.
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Neoplastic Adnexal Masses
This category includes cystadenoma, dermoid cyst, borderline tumor, primary
ovarian cancer, and metastases to the ovary. Cystadenomas are typically
benign-appearing cysts of variable size and MRI generally adds little to
sonography (Fig. 9), although
occasionally MRI may help in evaluation of the overall dimensions and site of
origin of the mass by showing a displaced ovary not seen at sonography.
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Fig. 9 —Axial RARE T2-weighted MR image obtained at 18 weeks'
gestation in 29-year-old woman shows large predominantly cystic right adnexal
mass with somewhat thickened internal septae (arrow). Resection
showed benign cystadenofibroma.
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Dermoid cysts are also usually distinctive at sonography, but the
diagnostic finding on MRI, if performed, is the presence of macroscopic fat
(Figs. 10A and
10B). It should be remembered
that dermoid cysts may undergo torsion. Borderline tumors show a greater
degree of complexity, with thickened walls or septae and internal solid
components [6] (Figs.
11A and
11B).
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Fig. 10A —22-year-old pregnant woman. Axial spin-echo T1-weighted MR
image obtained at 24 weeks' gestation shows adnexal mass is posterior to
uterus and contains focus (arrow) of increased T1 signal
intensity.
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Fig. 10B —22-year-old pregnant woman. Axial spin-echo T1-weighted MR
image with fat saturation shows that focus of increased T1 signal intensity in
A is now of low signal intensity (arrow), confirming presence
of macroscopic fat and indicating diagnosis of mature cystic teratoma (dermoid
cyst).
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Fig. 11A —24-year-old pregnant woman. Axial T1-weighted spoiled
gradient-echo MR image with fat saturation obtained at 25 weeks' gestation
shows bilateral cystic adnexal masses (arrows) with thick septations
and stained-glass appearance due to variable signal intensity among different
compartments of lesion.
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Fig. 11B —24-year-old pregnant woman. Axial RARE T2-weighted MR image
shows internal complexity in masses (white arrows) with thick
septations (vertical black arrow) and solid nodules (horizontal
black arrow). Findings are considered suggestive of malignancy. Resection
showed bilateral mucinous cystic tumors of low malignant potential (borderline
tumors).
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Frank ovarian malignancies account for approximately 1% of pathologic
ovarian masses in pregnancy
[12] and are characterized by
prominent solid components within a cystic mass, necrosis in a solid mass, or
peritoneal metastases (Figs.
12A and
12B). Any cystic mass should
be carefully examined for mural or septal thickening or mural nodules,
papillary excrescences, or other solid components because these findings may
indicate malignancy. Although all these features within the primary tumor can
be seen on both sonography and MRI, MRI has the advantages of depicting more
distant findings, such as widespread ascites, peritoneal implants, and pelvic
or retroperitoneal adenopathy, and of being more accurate overall than
sonography in the distinction of benign from malignant ovarian masses
[13].
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Fig. 12B —34-year-old pregnant woman. Axial RARE T2-weighted MR image
through upper abdomen shows large tumor deposit (arrow) abutting
liver. Appearances are considered indicative of malignancy. Cesarean
hysterectomy and bilateral salpingo-oophorectomy were performed at 28 weeks'
gestation because of progression of subphrenic tumor with diaphragmatic
irritation. Pathology results showed benign metastasizing leiomyoma. Masses
spontaneously regressed after surgery and patient remains free of disease 3
years after surgery.
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Conclusion
MRI can assist sonographic assessment of adnexal masses in pregnancy by
showing the uterine origin and reduced T2 signal intensity of exophytic
leiomyoma; the increased T1 signal intensity in red degeneration of leiomyoma;
the increased T1 signal intensity of endometrioma; and the characteristic
findings of dermoid cyst, decidualized endometrioma, and massive ovarian
edema. The distinction and specific characterization of these different
neoplastic and nonneoplastic abnormalities require close attention to lesion
morphology and signal characteristics and are often aided by review of
sonographic findings. Accordingly, MRI should be considered a useful adjunct
when sonography is inconclusive or insufficient to guide management of adnexal
masses discovered in pregnancy.
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Abstract
Introduction
