Ovarian cancer, the most lethal of all gynecologic cancers, is a complex grouping of tumors that often have a silent progression, spreading over surfaces of intraperitoneal structures. This article discusses the use of a variety of imaging modalities in the detection, assesment, and tissue characterization of ovarian malignancies. The individual features and abilities of ultrasound, CT and MRI each address different aspects of imaging needs of patients with ovarian cancer
Dr. Schweitzer is an Instructor in Radiology and Dr. Majid
is a Resident in Radiology at the Medical College of Virginia
of Virginia Commonwealth University; and Dr. Paredes is a
gynecologist with the Department of Obstetrics & Gynecology
at St. Mary's Hospital, Richmond, VA.
Ovarian cancer, the most lethal of all gynecologic cancers, is
responsible for approximately 14,500 deaths annually in American
women, and remains a challenging enigma. Its natural history
remains a mystery, and, despite the new therapeutic modalities, the
treatment of the disease is yet an unresolved riddle.
These disturbing facts are better understood when the unusual
features of this complex disease are considered. Ovarian cancer
represents a subtle array of many types and subtypes of
malignancies, each with unique histologic features and
idiosyncratic biologic behavior.
Because of these facts, no consensus for a standard classification
of the disease exists, and the establishment of a standard seems
Early diagnosis of ovarian cancer is not yet within reach,
because of the silent progress of the disease and the lack of
specific and sensitive tests at present. The utilization of family
history, genetic testing (BRCA-1 and BRCA-2), CA 125 testing, and
vaginal and Doppler ultrasound targeted to those patients who are
at high risk may be helpful.
Ovarian carcinoma is basically a disease of surfaces, however,
in that it spreads not by infiltrating adjacent organs, but by
settling on the surfaces of surrounding tissues. Free-floating
cancer cells carried by the intra-abdominal peritoneal fluid are
responsible for the occult and silent dissemination and for the
inaccurate diagnosis of a localized disease.
Theoretically, for the diagnosis of ovarian cancer to be effective
at a very early stage, biochemical markers would be used to detect
the expression of the disease. Since no such markers are available,
prophylactic oophorectomy at the time of unrelated pelvic surgery
is a reasonable option to discuss with selected patients.
Pathology of ovarian cancer
More than 85% of ovarian cancers are of coelomic epithelial
The remaining are derived from germ cells, specialized gonadal
stroma, nonspecific mesenchyma, or are metastatic lesions to the
ovary. The epithelial ovarian cancers consist of the following
subtypes: 50% serous, 17% undifferentiated, 15% endometrioid, 12%
mucinous, and 6% clear cell carcinomas.
Serous tumors occur at any age, but their peak incidence is in
the fourth to fifth decade. Serous carcinomas are the most common
bilateral ovarian neoplasms and the most often widely disseminated
at the time of diagnosis, with widespread intraperitoneal
Endometrioid carcinomas are less likely to be bilateral or
widely disseminated in the abdominal cavity. These tumors are more
likely to be associated with coexisting adenocarcinoma of the
and with non-neoplastic endometriosis. The main age at presentation
is 55 to 60 years. Common symptoms include abnormal vaginal
bleeding, abdominal pain, and/or mass.
Mucinous carcinomas occur mostly in the fourth to seventh
decades, are bilateral in 15% to 20% of cases
and are mostly (95%) confined to the ovaries at laparotomy. About
5% of mucinous cancers are associated with dermoid cysts and range
in size up to 50 cm in diameter. Rare gigantic lesions have been
documented as weighing over 100 kg.
Clear cell tumors occur most often in the fifth to seventh
decades, and one-half to two-thirds of patients are nulliparous.
The most common presenting symptom is an enlarging abdominal mass.
At laparotomy, 50% are confined to the ovary and are uncommonly
associated with paraneoplastic hypercalcemia.
Imaging of ovarian malignancy
Once a pelvic mass is found, the role of the diagnostic
radiologic modalities is important to clarify its origin and
characteristics. Radiology plays an important role in the
diagnosis, preoperative staging, surgical treatment, and evaluation
of tumor recurrence of ovarian carcinomas. Ovarian carcinoma has
characteristic tumor appearances and modes of tumor spread within
the peritoneal cavity. By recognizing these features, the
radiologist can assist the clinicians in treatment planning.
Ultrasound is usually used for the evaluation of an asymptomatic
or a symptomatic pelvic mass found on clinical exam. A combination
of transvaginal and transabdominal ultrasound (US) is 80% accurate
in detecting ovarian masses.
When an ovarian mass is detected, US is performed to evaluate the
other ovary and uterus, as ovarian cancer has a high propensity for
uterine cavity and contralateral ovarian involvement. This pattern
of involvement is found in endometrioid ovarian cancers and in 66%
of malignant serous neoplasms.
US is an inexpensive means of evaluating ovarian masses. It has
been shown that ultrasound is 90% sensitive in detecting pelvic
masses and their origins.
However, considerable overlap is present in the imaging features of
benign and malignant lesions and, therefore, US cannot be used to
differentiate benign from malignant ovarian masses.
US is also limited in evaluating the extent of disease;
specifically, US is not accurate in evaluating the spread of
metastatic ovarian disease to the omentum, mesentery, bowel serosa,
Transvaginal ultrasound and color Doppler sonography have
improved characterization of ovarian pathology.
Ultrasound characteristics that suggest malignancy are
multiloculated masses that are >10 cm in diameter with thick
septations and solid components
Color Doppler sonography is used to aid in differentiating
malignant blood flow patterns from benign or physiologic
Malignant blood flow is characterized by an increase in diastolic
flow, which is secondary to neovascularization.
The ovarian arterial blood flow is evaluated by calculating the
resistive index (RI) or the pulsatility index (PI).
The RI is calculated from the difference between the systolic peak
and diastolic trough. The values are found between 0 and 1. The PI
is calculated by evaluating the difference over the mean velocity
of the cardiac cycle.
The PI is considered more accurate than the RI, and values range
between 0 and 10. Regardless of which index is used, the lower the
value, the more diastolic flow. Doppler waveforms with RI <0.4
and PI <1 suggest malignancy, but there are many other
nonmalignant causes of low RI or PI.
Once ultrasound confirms a mass found on physical examination,
other imaging studies are often used to further differentiate the
mass and evaluate the extent of disease. The role of
cross-sectional imaging in the preoperative evaluation of ovarian
cancer is still not universally accepted and is somewhat
If a clinical diagnosis of ovarian cancer is of little doubt,
preoperative performance of cross-sectional imaging will not change
Surgery remains at the central point in the management of ovarian
Laparotomy, surgicopathologic staging, and tumor debulking are
performed. The gold standard is the performance of a total
abdominal hysterectomy, bilateral salpingo-oopherectomy, and
omentectomy in addition to aspiration of ascites or peritoneal
lavage for cytologic examination. In addition, random peritoneal
biopsies are taken from the paracolic gutters, undersurfaces of the
hemidiaphragms, and lymph nodes.
For patients with advanced disease, chemotherapy is initiated
following laparotomy. The routine preoperative use of CT or MRI has
not been advocated, as staging and debulking occur at the time of
However, cross-sectional imaging has a role in preoperative
surgical planning, as well as in determining patients who may
benefit from preoperative adjuvant chemotherapy.
Cross-sectional imaging is used preoperatively to plan the
optimal surgery when the diagnosis is uncertain, and as guidance
for percutaneous biopsy or paracentesis for symptomatic relief of
For surgical planning, imaging can direct the surgeon to areas of
disease that may be difficult to assess surgically, such as the
dome of the diaphragm and retroperitoneum.
In addition, the identification of bowel invasion can alter
surgical approach and treatment.
The identification of nonresectable tumors is another important
aspect of preoperative imaging. Tumor nonresectability has been
defined as tumor larger than 2 cm at the mesenteric root, porta
hepatis, omentum of the lesser sac, intersegmental fissure of the
liver, gastro-splenic ligament, diaphragm, or liver dome.
Lymphadenopathy >1 cm at or above the celiac axis and the
presence of presacral and extraperitoneal disease are also criteria
Currently, CT is considered the most useful preoperative imaging
technique, with a reported accuracy of 70% to 90%.
On CT, malignant ovarian tumors may be entirely solid or cystic,
or have mixed solid and cystic components, including septations or
papillary fronds. Fine or coarse calcifications may be present.
Contrast enhancement is variable and, if present, is seen in cyst
walls and solid areas (figures 2 and 3).
The early stages of ovarian cancer include direct invasion to
local structures. Metastatic disease occurs via three pathways: 1)
intraperitoneal seeding, 2) lymphatic invasion, and 3) hematogenous
Intraperitoneal metastatic disease has a classic appearance.
Peritoneal implants frequently occur on the omental and peritoneal
surfaces. These include the cul-de-sac, infundibulopelvic
ligaments, right paracolic gutter, right subdiaphragmatic surface,
liver surface, and mesenteries.
Other common sites of organ involvement include the spleen and
bowel; bowel obstruction can occur late in the disease secondary to
tumor invasion. Less frequently, extra-abdominal and intrahepatic
metastases occur late in the disease (figure 4).
Previously reported limitations of CT include the lack of
visualization of peritoneal implants <5 mm in diameter.
On CT, peritoneal implants appear as soft-tissue or
fluid-attenuated masses; if ascites is present, tumor implants are
more readily visible (figure 5). Current CT scanners can detect 50%
of peritoneal implants as small as 5 mm.
Buy et al
reported identification of peritoneal implants as small as 2 to 3
mm when large amounts of ascites was present. The most common sites
of peritoneal implants identified by CT preoperatively were the
right subphrenic space, pouch of Douglas, and greater omentum.
Involvement of the greater omentum with spread of tumor is known as
omental "caking." The omental "cake" on CT is shown by confluent
soft-tissue nodules between the anterior abdominal wall and
adjacent bowel, with obliteration of the intervening fat.
Lymphatic involvement with ovarian cancer is shown on CT by
enlarged retroperitoneal lymph nodes. Specifically, lymph nodes
>1 cm may occur in the para-aortic, external iliac, obturator,
and hypogastric lymph node chains.
One important complication of lymphadenopathy is hydronephrosis due
to extrinsic ureteral compression. Metastatic disease occurs in the
anterior mediastinum and right thoracic duct via retrosternal
Sites of hematogenous spread of ovarian cancer are also seen on
CT. The most common sites of hematogenous spread are the liver,
lung, spleen, pancreas, and kidney (figure 6).
Postoperative imaging is used in three situations: 1) to
identify disease progression, 2) to define treatment endpoints, and
3) to determine if further surgery or a "second-look" operation is
Imaging evaluation is used in conjunction with clinical examination
and CA-125 levels in postoperative patient management.
Like CT, MRI can diagnose ovarian malignancy in the evaluation
of the abnormal pelvis approximately 80% of the time and can detect
abdominal spread 80% to 90% of the time.
Advantages of MRI include tissue characterization, identification
of local tumor extension, and identification of tumor implants
involving the hemi-diaphragm, liver surface, and liver parenchyma.
Because of its multiplanar capability, MRI can distinguish between
uterine and ovarian origin of a pelvic mass.
MR appearances of ovarian tumors vary and are based upon tissue
T1-weighted images enable detection of hemorrhage or fat in an
ovarian mass as well as the presence of lymphadenopathy. The high
signal intensity of the ovarian follicles helps to differentiate
the adjacent bowel and uterus from the ovary on T2-weighted images.
The T2-weighted images are also used for tissue characterization.
Contrast-enhanced T1-weighted images provide higher resolution of
tissue characteristics and identify peritoneal and omental
On MRI, these appear as nodules of medium signal intensity.
Fat-saturation and gradient-recall echo technique (GRE), are used
to further evaluate tissue character. Finally, fast spin echo (FSE)
technique decreases image acquisition time, thereby decreasing
motion artifact and improving resolution.
Ovarian carcinoma, the most lethal gynecologic cancer, is a
complex grouping of tumors that often have a silent progression,
spreading over surfaces of intraperitoneal structures. An initial
evaluation of a pelvic mass is done with ultrasound. Transabdominal
ultrasound is performed in conjunction with transvaginal ultrasound
and color Doppler evaluation. While ultrasound is a useful,
noninvasive, and inexpensive modality to confirm an ovarian mass,
its inability to differentiate benign from malignant disease and
disease extent limits its utility in the assessment of ovarian
carcinoma. CT has been established as the primary imaging modality
in the evaluation of ovarian tumors, preoperative staging of
disease, and posttreatment response. This is due to its easier
accessibility, quicker imaging and interpretation time, physician
familiarity, and lower cost than MRI.
MRI offers a variety of techniques and has multiplanar capability.
It is usually reserved for patients with contraindications to CT
scan, such as pregnancy, contrast allergy, or abnormal renal
However, MRI is becoming more widely used for tissue
characterization, and for the evaluation of local and distant
spread of disease, especially in evaluation of the liver surface
and diaphragm. AR
The authors gratefully thank Ms. Louise Logan for her
preparation of the manuscript.
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