B

common sex cord-stromal tumor of the ovary and is benign. It is composed of fibroblasts and collagen and is without estrogenic activity.71 It may be associated with ascites and Meigs syndrome. Ovarian fibromas are worth mentioning from an imaging standpoint because they have a relatively specific appearance on imaging that may suggest the diagnosis. The characteristic appearance of fibroma on ultrasound is a homogeneous hypoechoic mass with posterior acoustic shadowing.59 On CT, it has been reported that most ovarian fibrothecomas appear as solid masses with delayed accumulation of contrast medium.73 On MRI, fibromas and fibrothecomas are predominantly of low signal intensity on T2-weighted images because of the abundant collagen and fibrous components. Dense calcifications in the mass can often be seen.59 Although a broad spectrum of imaging appearances has been reported with ovarian fibromas and fibrothecomas, which cannot always be easily differentiated from other ovarian tumors, the above imaging features, when present, are highly suggestive of an ovarian fibroma or fibrothecoma.74 However, a differential diagnosis needs to be considered for such a mass, that is, a pedunculated subserosal uterine leiomyoma or a broad-ligament leiomyoma, which may appear as an adnexal mass and also frequently demonstrates very low signal intensity on T2-weighted MRI and low echogenicity on ultrasound59 (Fig. 5-7). Since leiomyomas are supplied by the uterine artery branches coursing through the adjacent myometrium, feeding vessels sometimes can be seen at the interface between a pedunculated subserosal leiomyoma and the adjacent uterus.59 These can be detected by both Doppler ultrasound and MRI.75,76 On the other hand, ovarian masses are most likely fed directly by the ovarian arteries or by ovarian branches of the uterine arteries coursing along the fallopian tube. Therefore, no feeding vessels should be expected between an ovarian mass and the uterus.

The term collision tumor describes the coexistence of two adjacent but histologically distinct tumors with no histologic admixture at the interface.59 Ovarian collision tumors are rare and most commonly composed of teratoma and cystadenoma or cystadenocarcinoma, although case reports of other histologic combinations have been published.77 Therefore, the possibility of a collision tumor should be considered

Peritoneal Tumors Mri
Figure 5-7. A 39-year-old woman with a history of breast cancer. Axial T2-weighted MRI of the pelvis demonstrates a heterogeneous mass in the right adnexal region. Surgical pathology revealed a broad ligament leiomyoma.

when an ovarian tumor has imaging findings that cannot be explained solely by one histologic type, especially in the presence of a teratoma.77

It should be noted that although primary ovarian cancer is generally the main concern when a suspicious ovarian mass is identified at imaging, approximately 10% of ovarian tumors are metastatic.78,79 Primary cancers that may metastasize to the ovaries include colon, stomach, breast, pancreas, lung, gallbladder, small intestine, and kidney cancers, as well as melanoma, sarcoma, and carcinoid tumors. Most ovarian metastases arise from the gastrointestinal tract, with colon and gastric primaries being the most common; ovarian metastases from colon and gastric primary tumors are often referred to as Krukenberg tumors80,81 (Fig. 5-8). Differentiation between primary and metastatic neoplasms of the ovary is of obvious importance for appropriate clinical management. A number of studies have shown that on CT the metastatic ovarian lesions are variable in appearance and may be cystic, mixed, or solid and in some cases may simulate the appearance of a primary ovarian carci-noma81,82 (Fig. 5-9). Therefore, some investigators have suggested that a careful search for signs or symptoms of gastrointestinal tract tumor should be carried out in any patient with an ovarian mass81 and the ovaries routinely examined in the preop-erative CT staging of gastric or colon carcinoma.81 A more recent multi-institutional

Figure 5-8. A 32-year-old woman with colorectal cancer. A and B, Axial contrast-enhanced images demonstrate a mass in the left ovary that contains fat, soft tissue mural nodule, cystic components and calcification (arrows). The right ovary contains a mass of both fat and soft tissue components (arrowhead). Subsequent surgical pathology demonstrated a mature cystic teratoma in the left ovary, metastatic colorectal adenocarcinoma, and mature teratomatous components in the right ovary.

Figure 5-8. A 32-year-old woman with colorectal cancer. A and B, Axial contrast-enhanced images demonstrate a mass in the left ovary that contains fat, soft tissue mural nodule, cystic components and calcification (arrows). The right ovary contains a mass of both fat and soft tissue components (arrowhead). Subsequent surgical pathology demonstrated a mature cystic teratoma in the left ovary, metastatic colorectal adenocarcinoma, and mature teratomatous components in the right ovary.

Figure 5-9. A 59-year-old woman with lymphoma and a newly detected left ovarian mass. A, Sagittal T2-weighted MRI demonstrates a complex cystic and solid mass in the left adnexa (vertical arrow). In addition, there is omental caking (horizontal arrow) and a small amount of ascites (arrowhead). Infiltration of the omentum is also demonstrated on B, axial T2-weighted MR (arrow) and C, contrast-enhanced axial T1-weighted fat-suppressed MR image (arrow). Surgical pathology revealed serous type adenocarcinoma limited to the endometrium (not shown) with metastasis to the left fallopian tube. Metastatic serous adenocarcinoma to the omentum was confirmed.

Figure 5-9. A 59-year-old woman with lymphoma and a newly detected left ovarian mass. A, Sagittal T2-weighted MRI demonstrates a complex cystic and solid mass in the left adnexa (vertical arrow). In addition, there is omental caking (horizontal arrow) and a small amount of ascites (arrowhead). Infiltration of the omentum is also demonstrated on B, axial T2-weighted MR (arrow) and C, contrast-enhanced axial T1-weighted fat-suppressed MR image (arrow). Surgical pathology revealed serous type adenocarcinoma limited to the endometrium (not shown) with metastasis to the left fallopian tube. Metastatic serous adenocarcinoma to the omentum was confirmed.

Radiology Diagnostic Oncology Group study using all three modalities (ultrasound, CT, and MRI) showed that for malignant ovarian masses, multilocularity somewhat favors the diagnosis of primary ovarian malignancy, and a solid nature favors diagnosis of a secondary neoplasm. However, no imaging feature seems to be adequate for making the distinction between primary and secondary ovarian malignancies.83

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