DOI:10.2214/AJR.05.2226
AJR 2006; 187:S460-S466
© American Roentgen Ray Society
Radiological Reasoning: Imaging Characterization of Bilateral Adnexal Masses
Susanna I. Lee1
1 Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston,
MA 02114.
Received December 27, 2005;
accepted after revision March 13, 2006.
This Radiological Reasoning article is available for SAM credit and
CME credits when completed with the additional educational material provided
in "Imaging Evaluation of Adnexal Masses: Self-Assessment Module."
See page S457 for
details.
Address correspondence to S. I. Lee.
(slee0{at}partners.org).
Abstract
Objective
A 46-year-old woman presented with bilateral adnexal masses on pelvic
sonography, a complex cystic mass on the right, and a homogeneously
hypoechoic, solid-appearing mass on the left. Pelvic MRI showed a T1
hypointense, T2 hyperintense, nonenhancing mass in the right ovary and a
homogeneously T1 hyperintense lesion with mixed T2 signal in the left ovary.
Fat-saturated T1-weighted sequences showed the left ovarian lesion to be an
endometrioma containing a high concentration of hemoglobin breakdown products
and revealed other endometriotic implants in the right ovary, broad ligament,
and cul-de-sac. Follow-up pelvic sonography 9 weeks later showed resolution of
the right complex cystic ovarian mass, indicating that it was a physiologic
hemorrhagic cyst.
Conclusion
Imaging features of benign and malignant ovarian masses overlap. If imaging
is inconclusive in characterizing an adnexal mass as benign, the mass will be
resected rather than followed up because of the concern for a rapidly growing
ovarian cancer. Thus, the goal of imaging is to identify unequivocally the
benign lesions that can be left untreated. Pelvic MRI provides a powerful
adjunct to pelvic sonography in characterizing adnexal masses as benign.
Keywords: adnexa • genitourinary imaging • MRI • ovaries • pelvic imaging • sonography • uterus • women's imaging
Case History
A 46-year-old woman presented to the emergency department with right-sided
pelvic pain that had been gradually increasing in intensity over the past 14
hours. She was premenopausal, and the onset of her last menstrual period had
been 11 days earlier. She had no associated fevers, bowel symptoms, or vaginal
discharge. Her serum ß-HCG was negative. A pelvic examination revealed
fullness and mild tenderness in the right adnexa. Pelvic sonography was
performed.
Sonography
Transabdominal imaging (Fig.
1A) shows a normal uterus and two masses posterior to the uterus.
Transvaginal images show a 6.6-cm cystic lesion with solid components in the
right adnexa (Fig. 1B) and a
3.9-cm solid-appearing left adnexal mass
(Fig. 1C). Neither ovary was
seen separate from these lesions.
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Fig. 1A —46-year-old woman who presented to emergency department with
right-sided pelvic pain of gradually increasing intensity. Pelvic sonography
was performed first.p Transverse sonogram from transabdominal examination
shows two adnexal lesions (arrows) posterior to normal-appearing
uterus.
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Fig. 1B —46-year-old woman who presented to emergency department with
right-sided pelvic pain of gradually increasing intensity. Pelvic sonography
was performed first.p Transvaginal sonograms reveal complex cystic mass on
right (B) and a more solid-appearing hypoechoic mass on left
(C). Neither ovary was seen separate from these adnexal lesions.
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Fig. 1C —46-year-old woman who presented to emergency department with
right-sided pelvic pain of gradually increasing intensity. Pelvic sonography
was performed first.p Transvaginal sonograms reveal complex cystic mass on
right (B) and a more solid-appearing hypoechoic mass on left
(C). Neither ovary was seen separate from these adnexal lesions.
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Expert Discussion (Dr. Lee)
Although acute-onset pelvic pain in a nonpregnant woman has many possible
causes, the one requiring the most urgent diagnosis is ovarian torsion. Pelvic
sonography is often performed to look for underlying lesions that might cause
torsion, but this diagnosis must ultimately be made on clinical assessment.
Acute ovarian torsion can present with normal pelvic sonographic findings
[1], and Doppler flow can be
detected in up to 93% of torsed ovaries
[2]. Because this patient
lacked any history of sudden acute onset of pain and because extreme adnexal
pain was not elicited on examination, the attending gynecologist excluded
ovarian torsion on clinical grounds.
Pelvic sonography shows two lesions, one in each adnexum. Once emergent
diagnoses have been excluded, adnexal lesions must next be evaluated for the
possibility of malignancy. In this context, four characteristics on sonography
should be assessed: location (of ovarian rather than extraovarian origin),
size, morphology (simple cyst, mixed solid and cystic, or homogeneously
solid), and persistence or resolution on follow-up after at least one
menstrual cycle.
Doppler sonography is rarely useful for assessing ovarian lesions. Color
Doppler signal, if present, is occasionally helpful in distinguishing a
soft-tissue component of a complex cystic epithelial tumor from a clot in a
hemorrhagic cyst. However, studies on the usefulness of color and pulsed-wave
Doppler sonography for distinguishing malignant from benign ovarian lesions
[3,
4], although prolific, have not
proven sufficiently conclusive or definitive to dictate management
decisions.
When an adnexal mass can be shown to be separate from the ipsilateral ovary
(i.e., extraovarian), it is considered benign
[5-7].
However, lesions of ovarian origin can be malignant. The masses in this
patient cannot be definitively shown to be extraovarian because neither ovary
is seen separate from these lesions. Thus, the lesions should be considered of
ovarian origin and further characterized to exclude malignancy.
Size is important because smaller lesions are much less likely to be
ovarian cancer. Ovarian cancers can grow rapidly. Studies evaluating
surveillance sonography to screen for ovarian cancer consistently reveal
patients who present with cancer less than 12 months after sonography with
normal findings
[8-10],
which indicates that ovarian cancer develops and becomes advanced in a matter
of months rather than years. This observation explains why incidentally
identified primary ovarian cancer is usually large, with a mean size of 6.5 cm
[11]. Although consensus has
not been reached as to a cutoff size above which ovarian lesions are
considered suspicious for malignancy, generally ovarian masses larger than 3
or 4 cm in mean diameter, such as the masses seen in this patient, are
recommended for further evaluation
[12].
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Fig. 2A —In same patient as in Figures
1A,
1B, and
1C, pelvic MRI was performed
for further characterization of lesions. Axial T2-weighted image shows two
lesions in right ovary, one large (solid white arrow) and the other
small (black arrow), and single lesion in left ovary (dashed
white arrow).
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Fig. 2B —In same patient as in Figures
1A,
1B, and
1C, pelvic MRI was performed
for further characterization of lesions. Axial T1-weighted image shows that
small right (black arrow) and left (dashed white arrow)
ovarian lesions are homogeneously hyperintense, whereas large right ovarian
lesion (solid white arrow) is hypointense.
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Fig. 2C —In same patient as in Figures
1A,
1B, and
1C, pelvic MRI was performed
for further characterization of lesions. Sagittal T1-weighted image after
administration of gadolinium shows no internal enhancement of large right
ovarian lesion (arrow). Uterus (asterisk) and bladder
(dot) are also seen.
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Fig. 2D —In same patient as in Figures
1A,
1B, and
1C, pelvic MRI was performed
for further characterization of lesions. Axial T1-weighted images with fat
saturation show that small right (black arrow, D) and left
(dashed white arrow, D) ovarian lesions continue to be
homogeneously hyperintense. Other tiny T1 hyperintense foci are seen in pelvis
(arrowheads). Solid white arrow in D indicates large lesion in
right ovary.
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Fig. 2E —In same patient as in Figures
1A,
1B, and
1C, pelvic MRI was performed
for further characterization of lesions. Axial T1-weighted images with fat
saturation show that small right (black arrow, D) and left
(dashed white arrow, D) ovarian lesions continue to be
homogeneously hyperintense. Other tiny T1 hyperintense foci are seen in pelvis
(arrowheads). Solid white arrow in D indicates large lesion in
right ovary.
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Morphology is helpful in deciding whether a lesion should be further
evaluated. Simple cysts (cysts with an imperceptible wall and no solid
components such as septations, mural nodules, or papillary projections) need
no further imaging evaluation when presenting in a premenopausal woman.
Although such cysts could represent benign epithelial tumors (e.g.,
cystadenomas), they are usually physiologic ovarian cysts or inclusion cysts
and are not malignant
[13-15].
Large simple cysts are often resected because they cause pain and may
predispose the ovary to torsion.
Mixed solid and cystic lesions include epithelial ovarian malignancies and
should be further evaluated. The right ovary in this patient is mixed solid
and cystic with a papillary projection and a thin septum. Although the linear
border of the solid component is strongly suggestive of a retracting clot of a
hemorrhagic cyst [16,
17], this lesion was
nevertheless classified as indeterminate. A follow-up sonography examination
in 6 weeks was recommended to assess lesion resolution.
Homogeneously solid-appearing lesions, in the absence of a history of prior
malignancy, are usually benign
[11,
18-20].
The most common solid adnexal lesions are pedunculated uterine or broad
ligament fibroids, benign ovarian stromal tumors (e.g., fibroma or
fibrothecoma), dermoids, and endometriomas. Although dermoids and
endometriomas are pathologically cysts, they are protean in their sonographic
appearance and can sometimes appear homogeneously solid on sonography. Each of
the solid lesions listed displays a characteristic appearance on MRI. This
patient's left ovarian lesion appears solid. On the basis of its low-level
internal echoes [21], the
diagnosis of endometrioma was suggested. However, MRI was recommended for
complete characterization.
MRI
The right ovary shows two lesions. The larger, homogeneously T2
hyperintense lesion (Fig. 2A)
corresponds in size to the 6.6-cm complex cystic mass seen on sonography. On
T1-weighted images (Fig. 2B),
this lesion is homogeneously hypointense. After gadolinium administration
(Fig. 2C), it shows a thin
smooth margin without any internal enhancement, consistent with a cyst. The
second right ovarian lesion is smaller and is homogeneously T2
(Fig. 2A) and T1
(Fig. 2B) hyperintense.
The left ovary contains a lesion with heterogeneous T2 signal
(Fig. 2A) corresponding in size
to the 3.9-cm solid-appearing mass seen on sonography. On T1-weighted images,
this lesion is homogeneously hyperintense
(Fig. 2B).
The two T1 hyperintense lesions, the smaller right and the left ovarian
masses, remain hyperintense to surrounding tissues on fat-suppression
sequences (Figs. 2D and
2E). Their hyperintensity is
enhanced by compression of the dynamic range of signal received by the
receiver coils. Thus, the observed T1 hyperintensity is not fat but probably
represents products of hemoglobin breakdown. Additional extraovarian foci of
T1 hyperintensity are seen in the right broad ligament
(Fig. 2D) and in the cul-desac
(Fig. 2E).
Expert Discussion (Dr. Lee)
MRI was performed to characterize the left ovarian lesion, the sonographic
appearance of which was suggestive of an endometrioma. Characteristics of the
lesion on MRI are diagnostic of an endometrioma. On T1-weighted sequences, one
sees "light-bulb" bright lesions that show extremely high T1
signal because of high concentrations of paramagnetic products of hemoglobin
breakdown. Endometriomas are particularly easy to spot on fat-saturated
T1-weighted images because they are light-bulb bright in the surrounding dark
pelvic soft tissue. Using this sequence, one can see that not only is this
patient's left ovarian lesion an endometrioma, but so is the smaller right
ovarian lesion. In addition, MRI identifies an extraovarian implant of
endometriosis in the right adnexum and in the cul-desac. Interestingly, only
the left endometrioma shows the areas of T2 hypointensity described as shading
[21], whereas the right
endometrioma appears homogeneously hyperintense on the T2-weighted images.
The larger right ovarian lesion, suggested to be a hemorrhagic cyst on
sonography, appears to be a cyst on MRI as well. It is homogeneously
hyperintense on T2-weighted images and shows no gadolinium enhancement.
However, it is T1 isointense, an imaging feature that is compatible with but
not diagnostic for blood. Thus, this lesion is still considered
indeterminate.
On a cautionary note, the differential diagnosis of T1 hyperintense lesions
that show persistent signal on fat-suppression sequences includes potentially
malignant lesions. These include the rare epithelial ovarian tumors containing
high concentrations of mucin
[22] and endometriomas that
have evolved into endometrial carcinoma from chronic exposure to unopposed
estrogen [23]. However, these
lesions, in contrast to endometriomas, show heterogeneous T1 signal and T1
isointense soft-tissue components that often enhance. Thus, if the
"light bulb" is not uniformly bright, or the lesion shows darker
T1 components that enhance with contrast material, a definitive diagnosis of
endometrioma cannot be made on MRI.
Follow-Up Sonography
Nine weeks after the original sonography, the transvaginal sonogram of the
right ovary (Fig. 3A) shows
complete resolution of the complex cystic lesion. The small right ovarian
endometrioma seen on MRI is now identified on sonography. The left ovary
(Fig. 3B) again shows the
endometrioma seen in the prior studies.
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Fig. 3A —Follow-up pelvic sonography 9 weeks after initial examination of
patient shown in Figures 1A,
1B,
1C,
2A,
2B,
2C,
2D, and
2E. Transvaginal sonogram of
right ovary shows resolution of large complex cystic lesion. Smaller right
ovarian lesion (arrow) is still present.
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Expert Discussion (Dr. Lee)
Complex cystic ovarian masses that resolve on sonography after at least one
menstrual cycle are, by definition, physiologic cysts and benign. The
disappearance of the 6.6-cm right ovarian mass on follow-up imaging is
consistent with the diagnosis of a physiologic hemorrhagic cyst. The
persistence and stability of the smaller right ovarian and the 3.9-cm left
ovarian masses are consistent with the previous MRI diagnosis of
endometriomas.
Clinical Management
Overall, the imaging evaluation resulted in a diagnosis of endometriosis.
Because the patient was past child-bearing and nearing menopause, she elected
to undergo hysterectomy. Surgical findings, confirmed on pathology, showed an
endometrioma in each ovary and endometriotic implants in the broad ligaments
bilaterally, in the cul-de-sac, and on the appendix.
Commentary
The traditional first step in the evaluation of the female pelvic organs is
sonography. In the evaluation of adnexal lesions in adult women, the primary
concern is to not miss malignancy. Consequently, much literature has been
devoted to evaluating sonographic criteria (e.g., size, Doppler flow, septal
thickness and number, and amount of free fluid) that might predict malignancy.
Some authors have evolved elaborate statistical models calculating the
likelihood of malignancy [24,
25]. Although these studies
have been useful in pointing out worrisome features of ovarian masses, they
are not sufficiently sensitive to ensure identification of all cancers while
simultaneously excluding most benign lesions, nor are the multifactorial
analyses sufficiently simple to assess ovarian masses encountered in everyday
sonography practice.
The difficulty in trying to distinguish benign from malignant ovarian
masses is that the imaging features overlap between the two categories. If the
radiologist cannot definitively identify an ovarian lesion as benign, a
complex ovarian mass will likely be surgically resected because of the concern
for malignancy. As noted, ovarian cancer grows quickly, and one of the best
prognostic indicators for survival is resection at an early stage
[26]. If imaging is
inconclusive in characterizing an ovarian lesion as benign, the lesion will
undergo prompt resection, even if the likelihood of malignancy is low by
imaging criteria. Thus, the goal of imaging should not be to identify the
malignant lesions that will be taken out, but to identify and definitively
characterize the benign lesions that can be left untreated.
Pelvic MRI has proven to be powerful as an adjunct to pelvic sonography in
characterizing adnexal masses as benign
[27,
28]. With its accessibility
and high resolution, transvaginal sonography is still the best method for
characterizing a lesion as a simple cyst, a complex cyst, or a homogeneously
solid mass. However, sonography is limited in its range of tissue
characterization and field of view. Although MRI is less accessible and has
lower resolution than sonography, it has the benefit of a wide range of tissue
specificity and a much larger field of view. MRI can be used to definitively
characterize fat, blood, and simple fluid, and the enhancement properties of
solid tissues can be measured with the administration of gadolinium. The
larger field of view proves useful for characterizing large masses or for
evaluating lesion location relative to the ovary in patients with large
uterine fibroids when the adnexal anatomy is significantly distorted.
MRI can characterize two categories of lesions as definitively benign.
First are the cystic lesions suspected to be of extraovarian origin. These
include paratubal cyst, peritoneal inclusion cyst, and hydrosalpinx. Second
are the solid-appearing lesions in patients without a history of prior
malignancy in whom metastases are extremely unlikely. The common solid adnexal
lesions are pedunculated uterine or broad ligament fibroid, benign ovarian
stromal tumor (fibroma and fibrothecoma), dermoid, and endometrioma. Fibroids
show a discrete round margin and a distinctive whirling internal structure,
and they typically enhance intensely with gadolinium. Benign ovarian stromal
tumors show T2 hypointensity, homogeneous internal structure, and a low level
of enhancement with the administration of gadolinium. Dermoids contain fat and
endometriomas contain high concentrations of blood breakdown products. If a
lesion is suspected on sonography of being one of these benign lesions, the
patient should be referred to MRI for further evaluation and, in many cases,
definitive characterization.
The diagnosis of endometriosis poses a special problem for the
gynecologist. In the context of a patient presenting with chronic or recurrent
pelvic pain, endometriosis is often on the list of suspected causes. However,
a definitive diagnosis requires laparoscopy, an invasive procedure that is
often not warranted given the degree of symptoms or the level of suspicion. In
this context, a noninvasive sensitive imaging method to look for
endometriosis, MRI, is a useful and popular diagnostic tool. Pelvic MRI has
proven to be more sensitive than sonography in the diagnosis of endometriosis
[29,
30], as has been shown by the
patient presented here. MRI detected both the additional endometriotic
components outside the ovary (where sonography rarely finds disease) and the
smaller implant in the right ovary, which was obscured by the large
hemorrhagic cyst. The detection of these small implants requires the use of a
specific pulse sequence, a T1-weighted sequence with fat saturation. The
addition of fat saturation to the T1-weighted sequence significantly improves
the conspicuity of small implants
[31,
32] and hence the sensitivity
of the MRI examination for detecting endometriosis.
Because most complex cystic ovarian lesions seen in premenopausal women are
physiologic cysts, follow-up imaging is usually performed to document the
persistence of a lesion before resection. Imaging is recommended after the
passage of one menstrual cycle, typically after 6 weeks. If the lesion is
likely to be one of the benign lesions that can be definitively characterized
with imaging, MRI should be chosen as the technique for follow-up. However, if
the lesion is just a complex cystic lesion with no features suggestive of
benignity, the best way to characterize it as benign is to document that it
resolves. Under these circumstances, follow-up imaging should be performed
with repeated sonography. If this algorithm still fails to result in
characterization of an ovarian mass as benign, surgical resection should be
considered.
In postmenopausal women, in whom physiologic cysts are rare, lesions should
be considered persistent on first presentation. Rather than being followed,
they should be triaged directly to MRI or surgical resection for definitive
characterization. The only lesions that are occasionally followed up with
sonography are small simple cysts because of the rare but reported possibility
of their evolving into complex cystic lesions
[15].
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S. I. Lee
Imaging Evaluation of Adnexal Masses: Self-Assessment Module
Am. J. Roentgenol.,
September 1, 2006;
187(3_Supplement):
S457 - S459.
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