Ovarian cancer is a silent killer; however, improvements in identification of women at high risk for ovarian cancer, as well as improved imaging techniques, increase the likelihood of early detection. [1, 2, 3] (See the images and video below.)
Pelvic ultrasonography is the examination of choice, followed by magnetic resonance imaging (MRI) and/or computed tomography (CT) scanning. [4, 5, 6] The ovary may be difficult to delineate in some women who are postmenopausal, because of its relatively small size (<2 × 2 cm), its position deep within the pelvis, and the lack of identifiable contained structures, such as cysts. [7, 8, 9, 10]
Relatively simple ultrasound-based rules can be used to diagnose ovarian malignancy, such as the International Ovarian Tumor Analysis (IOTA) rules [2, 3] . A multicenter trial  evaluated 1938 patients with an adnexal mass: 1396 (72%) had benign tumors, 373 (19.2%) had primary invasive tumours, 111 (5.7%) had borderline malignant tumours, and 58 (3%) had metastatic tumors in the ovary. Five simple (M) rules were used to predict malignancy: (1) irregular solid tumor; (2) ascites; (3) at least four papillary structures; (4) irregular multilocular-solid tumor with a largest diameter of at least 100 mm; and (5) very high color content on color Doppler examination. Five simple (B) rules were used to suggest a benign tumor: (1) unilocular cyst; (2) presence of solid components where the largest solid component is <7 mm in largest diameter; (3) acoustic shadows; (4) smooth multilocular tumor less than 100 mm in largest diameter; and (5) no detectable blood flow on Doppler examination. If one or more M features were present in the absence of a B feature, the mass was classified as malignant. If one or more B features were present in the absence of an M feature, it was classified as benign. If both M features and B features were present, or if none of the features was present, the simple rules were inconclusive. The simple rules yielded a conclusive result in 1501 masses (77%), for which they resulted in a sensitivity of 92% (95% confidence interval 89% to 94%) and a specificity of 96% (94% to 97%).
The primary use of CT scanning is in the evaluation of metastatic disease rather than of the ovarian mass; for the evaluation of the ovarian mass, ultrasonography and MRI are more valuable.  CT scanning is helpful in diagnosing cystic teratomas, 93% of which contain fat and 56% of which are calcified. If a large (>10 cm) soft-tissue mass is present, malignant transformation should be suspected. 
CT scanning also can aid in the evaluation of cystadenomas. A serous cystadenoma has an attenuation similar to that of water, whereas a mucinous cystadenoma has an attenuation closer to that of soft tissue.
The presence of wall and septal thickness and irregularity, as well as the existence of enhancing nodules, suggests malignancy. Although CT scan findings can suggest malignancy, they are not definitive for diagnosis unless metastases are present.
CT scan findings of complex functional cysts, benign ovarian tumors, and inflammatory and/or infectious masses, such as tubo-ovarian abscesses, can mimic ovarian malignancies.
Magnetic Resonance Imaging
The primary advantage of using MRI in the evaluation of ovarian masses is the ability to employ this modality in the characterization of tissue. The presence of fat, hemorrhage, mucin, fluid, and solid tissue within an ovarian mass can be determined with the aid of MRI. The ability to characterize tissue in this way is most useful in determining whether a mass is definitely benign. [1, 8]
To determine the potential of malignancy for epithelial tumors, assessing the internal architecture is useful. In this situation, for example, gadolinium enhancement can be employed in the differentiation of solid papillary tissue (which can enhance) from clot or debris (which does not). Gadolinium enhancement is useful in the evaluation of the internal architecture of predominately cystic lesions. In addition, if the mass is malignant, gadolinium enhancement may aid in the depiction of peritoneal implants.
Obtain images in at least 2 planes with T1- and T2-weighted sequences. 
For masses with high signal intensity on T1-weighted images, the addition of fat-saturated, T1-weighted images is useful in differentiating fat from hemorrhage.  Gadolinium enhancement is useful in evaluating the internal architecture of predominately cystic lesions. In addition, if the mass is malignant, gadolinium-enhancement may help to denote peritoneal implants.
If the signal intensity of a lesion is high on the T1-weighted image, the lesion can contain fat, hemorrhage, or mucin. If the lesion loses signal intensity after fat saturation, it contains fat; most likely, it is a cystic teratoma. If it does not lose signal, the lesion most likely contains hemorrhage, and it may represent an endometrioma or hemorrhagic cyst. Endometriomas are often dark on T2-weighted images.  In addition, high-viscosity mucin can be bright on T1-weighted images. Low-viscosity mucin is dark on T1-weighted images. 
If a lesion is dark on T1- and T2-weighted images, it may contain fibrotic tissue and be a fibroma. Consider a fibrothecoma or Brenner tumor.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.
Degree of confidence
In a multivariate analysis, the accuracy of gadolinium-enhanced MRI in the diagnosis of ovarian malignancy was 93%.  The findings most predictive of malignancy were necrosis in a solid lesion (odds ratio, 107) and vegetations in a cystic lesion (odds ratio, 40). In addition, ancillary findings, such as ascites, peritoneal metastases, and hemorrhage, on MRI scans had a high predictive value for malignancy. The use of gadolinium-based contrast agents improves tissue characterization and increases the degree of confidence for MRI findings.
As with CT scans, MRI scans may depict numerous benign processes, such as complex functional cysts, tubo-ovarian abscesses, and benign tumors, that can mimic an ovarian malignancy.
Malignant ovarian tumors tend to have papillary excrescences, irregular walls, and/or thick septations. [4, 1, 15, 16, 17] The tumor can contain echogenic material arising from mucin or protein debris. The more solid the areas are, the greater the likelihood that a tumor is present. Typically, intraperitoneal fluid is present; this is a sign of peritoneal spread.
On color Doppler ultrasonograms, tumors tend to have vessels with low impedance because of the lack of muscular media in the vessel wall and arteriovenous shunts. The vessels tend to be clustered (see the images and video below).
The ultrasonographic finding that is most indicative of ovarian cancer is papillary excrescence, which is present in more than 50% of ovarian malignancies. Low impedance and clustered vessels have a 70-80% diagnostic accuracy. 
Tubo-ovarian abscesses may mimic the ultrasonographic appearance of ovarian cancer, but patients with abscesses typically present with symptoms that are attributable to an inflammatory process.