Magnetic resonance imaging findings for discriminating clear cell carcinoma and endometrioid carcinoma of the ovary

This study was approved by the institutional review board of Nara Medical University. Written informed consent was obtained from each patient. The inclusion criteria were as follows: the medical records of patients with CCC and EC who underwent surgical treatment at Nara Medical University Hospital between January 2008 and September 2018 were reviewed. Tumor staging I-IV was performed in accordance with the FIGO classification. A baseline MRI scan was obtained for all patients before any intervention. Contrasted MRI scans were performed less than 2 months before surgery. Patients were excluded from the study if they had no pathology, other pathological subtype of epithelial ovarian cancer, and/or salvage treatment for recurrence and metastatic ovarian cancer at study initiation. One radiologist and one gynecologic oncologist with 10–20 years of experience independently reviewed the MR images of all patients; these reviewers were blinded to the clinical and histopathologic data. This study included 98 patients who met the inclusion and exclusion criteria (primary CCC (n = 52) and EC (n = 46)).

Data were collected from all enrolled patients and were compared between the two groups. Assessments included baseline characteristics such as age, BMI, parity, and menopausal status.

MRI scans were performed on a 3.0 Tesla system (Magnetom Verio; Siemens Healthcare, Erlangen, Germany) with a 32-element body array coil. The protocol of our MRI examination was performed as described previously [24]. MRI scans were T1-weighted, T2-weighted, T1-weighted with fat suppression and gadolinium-enhanced, and DW.

The following MRI morphologic features were assessed with both T1 and T2 phases, such as the maximal diameter of the cyst, tumor margin, multilocularity, growth patterns and surface irregularities of mural nodules, characteristics of solid components, and the presence of malignant ascites; all of these features are considered significant factors in distinguishing between benign and malignant ovarian tumors [23, 24]. A mural nodule was defined as a wall-based lesion projecting into the cystic space. Several variables involving mural nodules were selected in this study. As described previously, we defined the size of a mural nodule according to its “Height” and “Width” [24]. The term “Height” indicated maximum vertical length from the bottom of the cyst to the top of the nodule. The term “Width” indicated maximum perpendicular length to the “Height.” For each case, the largest dimensions of mural nodules were used to determine “Height” and “Width.” Mural nodular HWR was also calculated. The appearances of tumor margins were classified into two types: a well-defined margin (clear-cut margin) or an ill-defined margin (uncertain margin). The growth pattern of the mural nodules or solid components was designated as one of two categories. The mural nodules were either broad-based nodular structures or polypoid structures. When more than three solid components existed along the inner cystic surface, the pattern was defined as “multifocal, concentric, or broad-based nodular structures” [23]. If one or two mural nodules existed on the inner surface of the cyst, the pattern was defined as “focal, eccentric, or polypoid structures.” When the mural nodules arose from more than one-third of the tumor wall, the pattern was defined as “continuing.” The surface irregularity pattern of the mural nodules or solid components was also divided into two categories: a smooth or regular surface; or a rough, irregular, or lobulated surface. The degree of ascites was graded by using standard criteria, as either negative or positive.

Patient demographic factors of the study population are summarized in Table 1. All patients were of Japanese ethnicity. There were no significant differences between the CCC and EC groups in variables such as age, body mass index (BMI), parity, menopausal status, clinical stage, or International Federation of Gynecology and Obstetrics (FIGO) stage (postsurgical stage). The imaging findings associated with tumor characteristics on MRI were compared between the two groups via univariate analysis (Table 2). There were no significant differences between the CCC and EC groups in variables such as the maximum diameter of the cyst, ill-defined margin, or locularity.

On univariate analysis, six variables, such as the “Width,” “Height-to-Width” ratio (HWR), growth pattern, and surface irregularity of mural nodules, as well as the presence of ascites and continuity of mural nodules, were significant factors for prediction of CCC. The mural nodule “Width” in patients with EC was statistically significant, compared with that width in patients with CCC (5.42 ± 2.14 cm versus 3.91 ± 1.93 cm, p = 0.0013). The patients with EC, when compared with those with CCC, had a smaller HWR (0.69 ± 0.41 cm versus 0.91 ± 0.50 cm, p = 0.0022). The multifocal, concentric, or broad-based nodular structures were observed in 29 (63.0%) of 46 patients with EC and 16 (30.7%) of 52 patients with CCC (p = 0.0017). Compared with CCC, the mural nodule was significantly wider and more multifocal in EC. Twenty-nine patients (63.0%) with EC showed a continuing mural nodule pattern, whereas 16 patients (38.1%) with CCC showed the continuing pattern (p = 0.0017). Among the 98 patients with EAOC, 50 were classified as “negative” and 48 as “positive,” respectively. Among all patients, 36.5% (19/52) and 63.0% (29/46) had ascites in CCC and EC, respectively (p = 0.0097). A round and polypoid mass with high HWR, as well as the absence of ascites, were findings significantly associated with CCC.

Figure 1 shows the typical imaging appearances of CCC (A) and EC (B). MRI diagnosis of CCC and EC comprised a large unilocular or multilocular cystic mass associated with several mural nodules protruding into the cystic space. The following imaging characteristics may be aid in diagnosis of CCC: a large cystic mass with a small mural nodule, representing a focal, eccentric, or polypoid growth pattern. In contrast, EC mural nodules exhibited a large, heterogenous mixed mass, representing a multifocal, concentric, or broad-based nodular growth pattern.

All variables showing significant values in the univariate analysis were included in the multivariate analysis. Multivariate logistic regression analysis revealed that HWR and the growth pattern of the mural nodules resulted in the best discrimination of patients with CCC from those with EC (Table 3). Receiver operating characteristic (ROC) curves showed that the area under the curve (AUC), 95% confidence interval (CI), optimum diagnostic cutoff value, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) predicted CCC. The AUC for HWR was 0.706 (95% CI: 0.263–0.609), followed by 0.677 (95% CI: 0.286–0.769) for “Width” of a mural nodule (Table 4). The focal growth pattern yielded a sensitivity of 91.3% (95% CI, 82.4–96.4%), specificity of 57.7% (95% CI, 49.8–62.2%), PPV of 65.6% (95% CI, 59.2–69.3%), and NPV of 88.2% (95% CI 76.1–95.1%). The HWR yielded a sensitivity of 70.8% (95% CI, 61.3–79.1%), specificity of 61.9% (95% CI, 51.0–71.4%), PPV of 68.0% (95% CI, 58.8–76.0%), and NPV of 65.0% (95% CI 53.5–74.9%). The focal growth pattern of mural nodules demonstrated a higher HWR for diagnostic sensitivity and improved predictive values for negative test results.