Conversely, Low et al. reported the superiority of MRI over CT to predict optimal cytoreduction (Low et al. 2015). A prospective multicenter trial identified three clinical and six CT criteria correlating with suboptimal debulking (Suidan et al. 2014). Another study reported lung metastases of >7 mm in size, pleural effusion, deposits of >10 mm in size on largeand small-bowel mesentery, and infrarenal para-aortic lymph node metastases to be associated with low debulking status (Borley et al. 2015). Despite advanced surgery techniques in both studies, bowel involvement is a major limitation for optimal cytoreduction. Thus, careful analysis of CT signs of bowel and mesenteric involvement, e.g., of bowel wall thickening and adhesions and mesenterial tethering, is warranted (Nougaret et al. 2012).

7.4\ Tumor Types

Ovarian neoplasms are categorized as surface epithelial cell tumors, germ cell tumors, and sex-­cord stromal tumors. The vast majority comprise epithelial cancers, whereas malignant germ cell and malignant stromal neoplasms are responsible for 7% each.

In epithelial tumors benign, malignant, and borderline tumors are differentiated according to their

Fig. 14  Nonoptimally resectable ovarian cancer. Multiple peritoneal implants (arrows) are demonstrated on the liver surface and lesser sac. The latter is distended due to ascites. The implants located in the interlobar fissure (*) and lesser sac (*) are considered nonoptimally resectable

histological features. Malignant tumors of the ovary and borderline tumors account for 21% and 4–15% of primary ovarian tumors, respectively (Lengyel 2010; Koonings et al. 1989). In epithelial cancer distinct subtypes can be identified that not only differ in histopathology and genetic profiles but also in their imaging findings and clinical course. This is also reflected in the new WHO classification of ovarian, fallopian tube, and primary peritoneal cancer (Kurman et al. 2014). Clinicopathological and radiological characteristics of the major ovarian cancer subtypes are summarized in Table 4 (Forstner et al. 2016b; Höhn et al. 2014; Lalwani et al. 2011).

7.4.1\ Epithelial Ovarian Cancer

High-Grade Serous Ovarian Cancer

High-grade serous epithelial cancer accounts for the majority (70–80%) of epithelial ovarian cancers. Two-thirds of these tumors involve both ovaries (Clarke-Pearson 2009; Ozols et al. 2001). Macroscopically, it displays typically as multilocular cystic tumors with intracystic papillary projections. These excrescences fill the cyst cavity, or they may contain serous, hemorrhagic, or turbid fluid (Fig. 1) (Lalwani et al. 2011). Some of these tumors may also present as solid masses with irregular contours. The typical imaging feature is advanced peritoneal disease with large amounts of ascites and often bilateral adnexal masses (Fig. 15) (Forstner et al. 2016b; Höhn et al. 2014; Tanaka et al. 2016). In up to 12%, the ovaries may be small and display predominantly surface involvement, a finding that previously defined primary carcinoma of the peritoneum but is now recognized as a variant of high-grade serous cancer (Kurman and Shih 2011). Almost all cancers related to BRACA1 and BRACA2 mutations fall into this tumor category (Jayson et al. 2014).

Low-Grade Serous Ovarian Cancer

This subtype accounts for approximately 5% of ovarian cancers. It seems to develop in a stepwise fashion from cystadenomas and serous borderline tumors. In imaging cystic and septate lesions or cystic lesions with papillary mural nodules

Table 4  Clinicopathological and radiological characteristics of ovarian cancer subtypes

Adapted from Forstner et al. (2016b), Höhn et al. (2014), Lalwani et al. (2011), and Tanaka et al. (2016) STIC serous tubal intraepithelial cancer, HG high grade, LG low grade, BT borderline tumor aPredominant pattern

Carcinoma Ovarian in MRI and CT

303

Fig. 15  Typical high-grade serous cancer in CT. Bilateral adnexal tumors and large amounts of ascites and peritoneal deposits in the abdomen (arrows) as sign of peritoneal spread outside the pelvis at time of diagnosis

may be found unior bilaterally. Both borderline tumors and low-grade serous cancers may coexist at diagnosis. Psammoma bodies within the tumor or implants, presenting tiny calcifications, are detected in 30% at histology but only in 12% of cases in CT (Ozols et al. 2001; Jung et al. 2002). Dissemination occurs later in the course of the disease, and nodular implants are identified throughout the abdomen (Höhn et al. 2014).

Mucinous Epithelial Ovarian Cancer

Mucinous cancers comprise approximately 3–5% of ovarian carcinomas. They tend to be large at diagnosis and contain loculi with hemorrhagic or proteinaceous content similar to their precursors mucinous borderline tumors. They present smooth contours and multiloculated cystic architecture with solid areas and intracystic nodules (Fig. 16). Rarely, the tumor may be predominantly solid. They are mostly unilateral and detected in early stages. Bilateral involvement is only found in 5–10% (Seidman et al. 2002).

Fig. 16  Stage IA mucinous ovarian cancer arising within a BL mucinous tumor. A large multiloculated ovarian mass with loculi of different SI is shown on the T2WI indicating a mucinous lesion. At its superior aspect, areas of invasive cancers were found at surgery

Pseudomyxoma peritonei with cystic peritoneal implants may be associated with mucinous ovarian cancers but seems more likely to result from spread by mucinous primaries of the GI tract.

Endometrioid Ovarian Carcinomas

Endometrioid carcinomas represent 10–20% of all ovarian carcinomas. They occur with synchronous endometrial carcinomas or endometrial hyperplasia in up to 33% of cases (Seidman et al. 2002). Endometrioid carcinoma may also arise from endometriosis (Tanaka et al. 2010). Bilateral ovarian involvement is encountered in 30–50% of cases. Macroscopically, these tumors are solid and cystic; the cysts may contain mucinous or greenish fluid. Rarely, solid tumors with extensive hemorrhage or necrosis may be found (Seidman et al. 2002). Another feature is cancer developing within an endometrioma (Lalwani et al. 2011; Tanaka et al. 2010).