Malignant Ovarian Tumors
Approximately 90% of ovarian cancers are of epithelial origin.
Malignant epithelial tumors are subtyped as: - serous (50%), - mucinous (20%), - endometrioid (20%), - clear cell (10%), - undifferentiated (1%).
Non-epithelial cancers include malignant granulosa cell tumor, dysgerminoma, immature teratoma, endodermal sinus tumor, and metastases to the ovary.
Ovarian carcinoma accounts for 3% of all cancers in females. It is the second most common malignancy of the female reproductive tract, but the most frequent cause of death from gynecological malignancy (Jemal et al. 2007).
Serous cystadenocarcinomas are the most common type of malignant epithelial tumors. They are frequently bilateral and usually appear as mixed solid and cystic masses with irregularly shaped solid components. The solid components show avid enhancement and areas of necrosis. These appearances in combination with a disproportionately large amount of ascites compared to the tumor size, presence of enlarged lymph nodes and peritoneal and/or serosal implants are suggestive of diagnosis.
Mucinous cystadenocarcinomas tend to be larger, more often unilateral, occur in an older age group, and usually have better prognosis than do their serous counterparts. They are usually multiloculated and may be of higher signal intensity on T1-weighted images due to high protein concentration within the mucoid material. Presence of ascites and peritoneal implants is rare. Mucinous cystadenocarcinomas may be associated with Pseudomyxoma peritonei although 90% of P. peritonei originate from the appendix. MRI findings include the presence of mucinous loculated collections of low signal intensity on T1- weighted images and high signal intensity on T2-weighted images, which cause scalloping of the liver and splenic surfaces and displacement of the bowel loops due to pressure effects.
Clear cell carcinoma
Clear cell carcinoma accounts for only 5% of ovarian cancers and it is almost invariably malignant. It is associated with endometriosis in 25% of cases. The diagnosis should be considered when a nodule is seen within a predominantly cystic endometrioma.
Endometrioid carcinomas are usually bilateral and associated with endometrial hyperplasia or carcinoma in 20–30% of cases. They are mainly solid with areas of necrosis and avid enhancement.
TNM FIGO classification of ovarian carcinoma is presented in Table 7.1.6. Cross-sectional imaging is better accepted and more commonly used in the evaluation and staging of ovarian carcinoma than for other gynecologic malignancies (Tempany et al. 2000; Woodward et al. 2004). CT is the most commonly performed study for the preoperative staging of a suspected ovarian carcinoma (Coakley 2002). The role of MRI in patients with known ovarian carcinoma is still evolving. Currently, the appropriate role of MR is characterization of ovarian masses rather than staging of histologically proven ovarian cancer. When MR is used for staging of ovarian carcinoma, imaging of the whole abdomen and pelvis should be performed using both T1-weighted and T2-weighted sequences in at least two planes. The coronal plane is useful in the evaluation of the liver surface and diaphragm. Contrast-enhanced fat-suppressed T1-weighted imaging is essential for optimal staging of ovarian cancer as it improves tumor delineation and increases the conspicuity of peritoneal or serosal deposits.
Intraperitoneal dissemination is the most common route of spread of ovarian carcinoma. Peritoneal implants appear as nodular or plaque-like enhancing soft tissue masses of varying size. MRI is very sensitive (95%) for detection of peritoneal metastases, which show delayed enhancement on contrast-enhanced MRI (Ricke et al. 2003).
Ascites is a non-specific finding but, in a patient with ovarian cancer, usually indicates peritoneal metastases (Hricak et al. 2000). Ascitic fluid may outline small implants, facilitating detection. Peritoneal implants may occur anywhere in the peritoneal cavity, but the most common sites include the pouch of Douglas, paracolic gutters, surface of the small and large bowel, greater omentum, surface of the liver (perihepatic implants), and subphrenic space.
MRI is useful in differentiating between subcapsular liver implants and parenchymal liver metastasis, which alters staging and therapy. These implants are best seen on the delayed (5 min) contrast-enhanced fat-suppressed T1-weighted images. Surface implants are usually well defined, biconvex, and peripheral, and they indent the liver. True intraparenchymal metastases are often ill-defined, circular, and partially or completely surrounded by liver tissue.
Ovarian cancer is a genetically heterogeneous disease with a poor prognosis (overall 5-year survival of < 45%). Five-year survival rates vary between 93% for stage I disease and 30% for stage IV disease (Jemal et al. 2007). In general, ovarian cancer is a disease of the postmenopausal woman and, occasionally, prepubescent girls. The cause of ovarian cancer is unknown, although a number of risk factors have been identified. Chronic anovulation, oral contraception, multiparity, and history of breast feeding seem to be protective, whereas genetic factors appear to play an important role in the development of progression of ovarian cancer.