to the pelvis and para-­aortic lymph node were seen, whereas 13.5% was reported for pelvic resp for para-aortic lymph node metastases only (Bachmann et al. 2016).

Hematogenous spread occurs later in the course of the disease. Distant metastases are most commonly found in the liver, lung, pleura, and kidneys. At the time of the initial presentation, parenchymal liver metastases are extremely rare, and patients are more likely to present with liver surface metastases (Akin et al. 2008).

7.3\ Staging of Ovarian Cancer

Staging of ovarian cancer is determined by the extent and location of disease found at surgical staging. The latter is considered the gold standard for staging and aims for obtaining the histopathological diagnosis and a complete cytoreductive surgery. It includes a total abdominal hysterectomy, bilateral salpingo-oophorectomy, infracolic omentectomy, and lymphadenectomy (Jayson et al. 2014; Ozols et al. 2001). Furthermore, peritoneal cytology and multiple peritoneal biopsies are obtained throughout the pelvis and upper abdomen. In an attempt for optimal debulking, agressive surgery techniques including multidisciplinary surgery teams may be needed (Jayson et al. 2014). Laparoscopic staging procedures for ovarian cancer have also been introduced. In clinical practice, understaging of ovarian cancer remains a common problem (20–40%). This may occur when the initial surgery had been performed under the presumption of a benign tumor, due to laparoscopy technique, and lack of oncologic specialist expertise (Ozols et al. 2001).

Ovarian cancer is staged using the TNM or the FIGO (International Federation of Gynecology and Obstetrics) classification. According to the 2014 revised FIGO classification, not only the tumor stage but also the histological subtypes and grade should be documented. Most important change is the fusion of epithelial ovarian, fallopian, and primary peritoneal cancers. The revised staging classification is also used in germ cell and sex-cord stromal malignancies (Kandukuri and Rao 2015).

7.3.1\ Staging by CT and MRI

Surgical staging can be preceded by preoperative imaging. According to the ACR appropriateness criteria, radiographic studies such as contrast enema and urography have been replaced by CT and other cross-sectional imaging for staging ovarian cancer (Mitchell et al. 2013). Preoperative assessment by imaging has a major impact on treatment stratification, as the extent and anatomic location of peritoneal implants are major determinators for treatment decision (Forstner et al. 2010; Nougaret et al. 2012; Sala et al. 2013; Javadi et al. 2016).

Accurate mapping of the disease contributes to optimized surgery planning (Sala et al. 2013). This may also alert to need of multidisciplinary surgery teamwork. In case of extensive cancer load on CT or MRI, patients may also be triaged to undergo a neoadjuvant radiochemotherapy prior to surgery (Forstner et al. 2010; Sala et al. 2013).

Imaging Findings According to Tumor Stages

The FIGO classification system of ovarian cancer is summarized in Table 3.

Imaging findings in CT and MRI have also been adapted to the FIGO classification system (Forstner et al. 2010, 2016b; Nougaret et al. 2012; Javadi et al. 2016).

In stage I, tumor is confined to one ovary or the fallopian tube (stage IA) (Fig. 2) or both ovaries or the fallopian tubes (stage IB). The capsule of the tumor is intact, and there is no evidence of spread of the tumor outside of the ovary. In stage IC disease, tumor is detected on the ovarian or fallopian tube surface or capsule rupture has occurred. Malignant pelvic ascites may also be present (Fig. 1).

Stage II is characterized by local tumor extension into the pelvic soft tissues and to pelvic organs below the pelvic brim. In stage IIA, either direct tumor extension or implants on the uterus, ovaries, or fallopian tubes can be identified. Findings suggesting this stage include distortion or irregularity between the interface of the tumor and the myometrium. Stage IIB is characterized by involvement of pelvic tissues, such as the

bladder, rectum, and pelvic peritoneum. Invasion of the sigmoid colon or rectum is diagnosed when loss of tissue plane between the solid components of the tumor, encasement, or localized wall thickening is noted (Fig. 10). A distance of less than 3 mm between the lesion and the pelvic sidewall or displacement or encasement of iliac vessels is suggestive of pelvic sidewall invasion (Fig. 11).

Stage III consists of extrapelvic peritoneal implants and/or retroperitoneal lymphadenopathy. Retroperitoneal lymph node metastases as the only disease outside the pelvis are found in less than 10%, but they demonstrate favorable prognosis than lymph node metastases in stages IIIB or IIIC (Kandukuri and Rao 2015). In imaging the diagnosis of lymphadenopathy is based on the short-axis diameter of lymph nodes of ≥1 cm. Peritoneal implants outside the pelvis, omental or mesenteric implants, and hepatic or splenic surface metastases are other findings defining stage

III ovarian cancer. Stages IIIA2–IIIC differ in the size of abdominal peritoneal lesions. In stage IIIA2, tumor is grossly limited to the pelvis; however, large amounts of ascites are a sign of upper abdominal peritoneal tumor spread. In stage IIIB, lesion size is 2 cm or less and in stage IIIC it exceeds 2 cm (Fig. 12). Ascites is a common finding in stage III disease. In delayed contrastenhanced MR imaging, ascites may enhance and thus obscure peritoneal implants.

Stage IV ovarian cancer is characterized by distant metastases that include pleura, ­parenchymal organs outside the pelvis, and extraabdominal lymph nodes. Malignant pleural effusion presents stage IVA1 and is characterized by pleural metastases proven either by positive cytology or biopsy. Typical imaging findings include pleural effusion associated with pleural nodularity and focal pleural thickening. Quantification of pleural effusion as small, moderate, or large has shown to be related with

Fig. 10  Sigmoid colon wall invasion in CT. A peritoneal implant (*) shows a broad contact and impression of the colon wall. The ovarian cancer is located in the midline and compresses the bladder. Multiple pelvic lymph node metastases are seen, the largest in the right obturator region. U uterus

Fig. 11  Pelvic sidewall invasion. Transaxial CT at the level of the iliac bifurcation. A mixed solid and cystic adnexal tumor, which was nondifferentiated ovarian cancer at histopathology, is located in the pelvis. The left pelvic sidewall, including iliac vessels and psoas muscle, is clearly separated by fat. The right pelvic sidewall (arrow) is in direct contact with the solid tumor component. Furthermore, external and internal iliac arteries are displaced; the latter is encased by tumor (arrowhead)

Fig. 12  Stage IIIC ovarian cancer. Peritoneal nodular implants are shown at the diaphragm and in the Morison’s pouch (arrows). A surface metastases invading the spleen larger than 3 cm is also demonstrated (arrow). Ascites (*) is found in the pelvis and upper abdomen. Ovarian cancer (arrowhead)

Fig. 13  Ovarian cancer stage IVB. Large amounts of ascites indicate peritoneal metastases. Umbilical metastasis (arrow) is a finding typical of stage IVB ovarian cancer