Stent

Also known as benign mature teratoma, these lesions are not uncommon and are more frequently identified during the first 3 decades of life. Dermoid cysts are hamartomas and characteristically contain hair, teeth, fat, and mural nodules.^3,5-7 Because of the echogenicity of fat on US, they may be missed. In a series of 22 cases, Bloomfield et al⁵ reported that 27% of dermoid cysts were not identified by US. Conversely, fat is exactly what makes these tumors easily identified on CT and MRI, even if just a small amount is present (Figures 4 and 5). On MRI, fat within dermoids demonstrates high signal intensity on T1-weighted images that is lost with the application of fat suppression (Figure 5).^3,6

The corpus luteum is a normal post-ovulation structure that is characteristically seen as a well-vascularized lesion with crenulated walls (Figure 6). It normally regresses in 14 days if fertilization does not occur, but occasionally it may develop into a cystic lesion. Follow-up typically shows regression after 1 or 2 cycles. These are commonly seen at CT in patients presenting with abdominal pain.^8,9

The most common lesions in this group are hemorrhagic cysts and endometriomas. MRI is usually requested when US shows failure of regression of a suspected hemorrhagic cyst in the context of endometriosis. Endometriomas may have thick irregular walls and septations and can be misdiagnosed as an ovarian malignancy at US. The wall of the endometrioma may show contrast enhancement. The acquisition of T1-weighted images with and without fat suppression is crucial to the diagnosis, since blood products will have high signal intensity on both sequences; however, fat within the mass will lose signal intensity on fat-suppressed images (Figure 5).¹¹ On T2-weighted images, blood products may also have high signal intensity; however, a black rim may be identified surrounding the lesion, which is due to susceptibility artifact from iron secondary to degradation of blood (Figure 9). Simple hemorrhagic cysts are usually resorbed before such chronic changes can occur in red blood cells. A further characteristic of endometriomas is “T2-shading.” This is the internal layering of the blood products that appear as low signal intensity on T2-weighted sequences (Figure 10).¹² Although uncommon, cancer has been reported in as-sociation with endometriosis and should be suspected in the presence of a solid nodule within the lesion (Figure 11).¹³ CT is of limited utility in the distinction of these entities.

While dilated fallopian tubes may be identified at US, they can be misdiagnosed as complex cystic adnexal masses. The multiplanar capabilities of MRI often enable the identification of the serpiginous tubular structure with high T2 signal intensity that may demonstrate T2-shading or high signal intensity on T1-weighted images in the context of endometriosis (Figure 12). CT can also be used to identify these tubular structures (Figure 13).¹⁴

Leiomyomas are the most common neoplasms of the uterus, occurring in 20% to 30% of women over the age of 30 years.¹⁵ MRI may be used to confidently diagnose leiomyomas. Simple leiomyomas are well-circumscribed, rounded lesions of low signal intensity on T1- and T2-weighted sequences (Figure 14), and characteristically demonstrate a high-signal-intensity pseudocapsule on T2-weighted images when intramural.^16,17 Most leiomyomas enhance slightly less or similar to the surrounding myometrium, although avid enhancement is frequently seen and may be helpful to distinguish pedunculated, broad-ligament, or ovarian leiomyomas from fibromas or malignant ovarian neoplasms, which generally show only slight enhancement. Degenerating fibroids typically demonstrate areas of high signal intensity on T2-weighted sequences.^16,18,19 Hemorrhagic or red degeneration is due to massive hemorrhage and infarction and can occur during pregnancy, with the use of oral contraceptives or following embolization. It is recognized by the presence of high signal intensity on T1-weighted images.¹⁶ Cystic degeneration occurs in 4% of leiomyomas and is associated with edema (Figure 15).¹⁹ One unusual kind of leiomyoma is the lipoleiomyoma, which contains a considerable amount of fat. Fat is readily recognized as a region of high signal intensity on T1-weighted sequences that becomes of low signal intensity with the application of fat suppression.¹⁹

Physiologic cysts are a common incidental finding at MRI and CT in women of reproductive age. They are typically less than <3.0 cm in size, contain fluid, and have imperceptible nonenhancing walls (Figure 16).³

Cystadenomas are usually large cystic masses (particularly mucinous cystadenomas), with thin walls and may have a few thin internal septations (Figure 17). The presence of extensive or nodular septations or solid components is suggestive of malignancy.^3,6

Peritoneal inclusion cysts are the result of entrapment of ovarian fluid by adhesions, and are more frequently seen in premenopausal woman with a history of pelvic surgery, pelvic inflammatory disease, or endometriosis. They are likely to slowly increase in size as fluid is constantly secreted by the ovaries but not reabsorbed by the injured peritoneum. Peritoneal inclusion cysts are extraovarian lesions that are adherent to the ovaries, commonly completely surrounding them. This results in the typical appearance of an ovary within a cyst (Figures 18 and 19). Seldom can they be identified at some distance from the ovaries. They may have thin or thick septations, may have nodular projections, and may contain debris and blood.^20,21

Paraovarian cysts are benign lesions that arise from wolffian duct remnants and are usually seen along the broad ligament. They may represent up to 10% to 20% of adnexal masses. A clue to their diagnosis is identification of a normal ovary separate from the adnexal cyst; however, this is not always easily accomplished (Figure 20). They usually do not regress in time and may be complicated by torsion, hemorrhage, rupture, and infection.²²

Malignant-appearing cystic adnexal masses are generally epithelial tumors, usually a cystadenocarcinoma or a borderline tumor. Both have thickened walls or septations and some solid components (Figure 21). It may be difficult to distinguish between these 2 entities, but in the absence of invasion or metastatic disease, a borderline tumor may be considered. Ascites is frequently considered a sign of more aggressive disease.²³

Fibromas are the most common sex cord tumors and represent 4% of all ovarian neoplasms. Because of their solid appearance, they can be misdiagnosed as ovarian cancer at US. On MRI, however, fibromas have a very characteristic appearance with low signal intensity on both T2- and T1-weighted sequences and only slight enhancement after gadolinium administration (Figure 22). Edema and cystic formations (central or eccentric) are recognized and fibromas may be mistaken for cystadenofibromas. Ascites may be present in 40% of cases, particularly if the lesion is large. Fibromas are also associated with pleural effusions (Meigs’ syndrome).^3,6,23

The ovaries are the most common site of metastasis to the female reproductive tract. Gastric, colorectal, and breast cancer are the most frequent extragynecological causes of ovarian metastasis, while primary endometrial and cervical cancers are the usual gynecologic sites of origin.²⁴ Although frequently used as a synonym for ovarian metastases, Krukenberg tumor refers only to metastases composed of mucin signet-ring cells, usually from gastric cancer. Ovarian metastases have no specific appearance, but are commonly bilateral, solid, and strongly enhancing lesions. Cystic and necrotic areas are commonly identified (Figure 23). The primary tumor is usually clinically overt.^27-27

Ovarian lymphoma is exceedingly rare and does not have specific imaging features, but may be suspected in the presence of extensive nodal disease with encasement of vessels (Figure 24).²⁸

Dysgerminomas represent 1% of all ovarian cancers but 20% to 30% of those diagnosed during pregnancy. Eighty percent occur during the first 2 decades of life. Most are unilateral, solid, bosselated tumors with an average size of 15 cm in diameter. Cysts, hemorrhage, and necrosis may be identified. Although dysgerminomas are always malignant and spread to lymph nodes is common, most of these cancers are diagnosed at an early stage and may be treated conservatively.²⁹ A disproportionate amount of adenopathy is sometimes noted, relative to the size and appearance of the ovarian lesion. In these cases, a dysgerminoma should be considered in a young woman and poorly differentiated adenocarcinoma in an elderly patient.

These lesions have variable morphology; they may present with cystic, solid, or a mixture of both components; and they are prone to hemorrhage. Estrogen production is common, and is usually the reason for an early-stage diagnosis. Granulosa cell tumors have a bimodal age distribution: postmenopausal women and those <30 years of age. In the younger age group, recurrence tends to occur within the first 3 years after treatment, but in postmenopausal patients, if the tumor recurs, it happens later in the course of disease. Granulosa cell tumors should be suspected if a solid-appearing ovarian mass has extensive hemorrhage (Figure 25).^23,30,31

Also known as androblastomas and arrhenoblastomas, these rare lesions represent <0.5% of all ovarian tumors. Most of them are diagnosed in women younger than 30 years old, but rarely before puberty. Androgen secretion causes virilization in >50% of patients. Sertoli-Leydig cell tumors are usually benign and diagnosed at an early stage. They are typically unilateral solid masses, although cystic areas may be identified (Figure 26).^23,32 At MRI, these tumors demonstrate high T2 signal intensity, low T1 signal intensity, and enhancement after gadolinium administration.