Fig. 18  Endometrioma mimicking ovarian cancer in CT. Coronal (a) and sagittal CT (b). In a 47-year-old woman with elevated tumor markers, a multicystic mass with a diameter of 25 cm occupies the pelvis and midabdomen. Focal mural and septal thickening (arrow) and high density within some cysts are demonstrated. There

was no evidence of lymph node enlargement or ascites. At surgery, extensive endometriosis of the ovaries and peritoneum was found. Furthermore, mural wall thickening of the rectum and sigmoid colon by endometriosis (arrowhead) and thickening of the uterine corpus due to endometriosis were detected (b)

and papillary thyroid cancer (Kawamoto et al. 1999). Malignant ovarian germ cell and stromal tumors may display imaging characteristics similar as ovarian cancer. Age and hormonal effects may help in the differential diagnosis. Other differential diagnoses include benign cystic and/or solid tumors, e.g., cystadenofibroma and rarely dermoids without fat. In the majority of cases, tubo-ovarian abscesses can be distinguished from ovarian cancer based upon imaging and clinical findings. Endometriomas can be differentiated by MRI by typical findings such as shading, thick capsules, and lack of enhancing solid components. However, in CT, endometriomas may be a diagnostic problem and mimic ovarian cancer (Fig. 18). Enhancement of a mural nodule within an endometrioma is highly suggestive of malignant transformation.

Borderline Tumors

Borderline tumors account for up to 15% of all ovarian malignancies (Alvarez and Vazquez-­ Vicente 2015). They are distinct from invasive ovarian cancer in terms of younger age at presentation, better prognosis, and fertility-preserving treatment options. Histologic and cytogenetic features include atypical epithelial proliferations, multilayering of the epithelium, increased mitotic activity, nuclear atypia, and mostly KRAS and BRAF gene mutations but the absence of stromal invasion (Lalwani et al. 2010). Borderline tumors most commonly affect women in reproductive age. Most of these present with early-stage (70– 80%) disease and are associated with an excellent prognosis. A 7-year follow-up of survival of stage I diseases was 99% and for stage II and III disease 92% (Ozols et al. 2001; Leake et al. 1992). In the presence of invasive elements, recurrence rates approach 45% and progression to invasive cancers may be found (Lalwani et al. 2010).

Borderline tumors may be large, with diameters ranging from 7 to 20 cm. Bilaterality is more common in serous tumor BT (25–50%) compared to the mucinous subtypes (5–10%) (Alvarez and Vazquez-Vicente 2015). Mucinous BT tends to be larger and may be associated with pseudomyxoma peritonei (Bent et al. 2009).

Imaging Findings

Borderline tumors tend to be large unilateral or bilateral ovarian tumors that cannot reliably be distinguished from invasive ovarian cancers in CT or MRI (Fig. 19). Imaging findings suggesting borderline tumors include a multicystic mass with papillary projections ranging from 10 to 15 mm in size protruding into the cyst wall (Jung et al. 2002). Rarely, BT may present as a purely cystic or solid lesion (Fig. 20), and psammoma bodies may be present (Bent et al. 2009). In a series of 60 borderline tumors, 6 were purely cystic and 29

mainly cystic with papillary projections and nodules; out of these one-third displayed vegetations of less than 1 cm in size; 14 were mixed cystic and solid and 10 mainly solid or solid (Zhao et al. 2014a). ADC values of the papillary projections tend to be higher than in invasive cancers. Using a threshold value of 1.039 × 103, Zao et al. attained sensitivity of 97% and specificity of 92.2% in

a

b

Fig. 19  Serous borderline tumor in CT. A large thin-­ walled cystic pelvic lesion is shown demonstrating slightly irregular enhancing septa at the cephalad aspect and a central irregular thickened septum with tiny calcifications (arrow)

Fig. 20  Stage I borderline tumor. Coronal (a) and parasagittal (b) CT. A 7 cm predominantly solid tumor (*) with cystic areas is located in the cul-de-sac. The sagittal plane shows broad-based contact to the uterus (b). No evidence of ascites was found in the pelvis or abdomen. At surgery, a grayish tumor deriving from the left ovary was found. Histopathology revealed the rare endometrioid subtype of ovarian tumor of low malignant potential, which was classified as FIGO stage IA