Most cases of ovarian CAF/AF demonstrate a cystic mass combined with a solid component, which makes accurate preoperative diagnosis difficult. Misdiagnosis may increase the psychological burden of patients as well as the occurrence of unnecessary interventions. Although pathological diagnosis is the gold standard, image diagnosis is superior in comprehensively determining the benign, malignant, adjacent condition, and the treatment choice before surgery . In this study, we investigated the imaging characteristics of 11 patients with ovarian CAF/AF to correlate their respective imaging characteristics with histopathologic findings. Imaging features of these tumors included a cluster of papillary nodular structures inside the cyst wall (45.5%, 5/11), diffusely or partially thickened wall/septa (81.8%, 9/11), unilocular (63.6%, 7/11), and a well-encapsulated, cystic mass, and in some cases black sponge sign (18.2%, 2/11). More than half of the cases had pattern II (72.7%, 8/11), papillary nodule clusters or thickened wall/septa (solid accounted for less than one-third) contained in the cystic masses.
In the current study, 63.6% (7/11) of the lesions were unilocular. However, Dae et al  reported a unilocular rate of 7.7%. We speculated that this difference could be ascribed to the small samples of both studies. The morphology of the solid component demonstrated a mass (18.2%, 2/11), a solid region with a septum (18.2%, 2/11), a diffusely or partially thickened wall (81.8%, 9/11) like carpet, or a cluster of papillary nodular structures inside the cyst wall (45.5%, 5/11). Yen et al  referred to the diffusely thickened wall-like carpet as the “carpet sign.” The rate of papillary nodular clusters in our study was consistent with that of previous studies (range, 33–80%) [8–12]. Our study demonstrated that a diffusely or partially thickened wall was the most common feature (81.8%, 9/11), and rate was close to that reported by Bohyun . Consistent with previous studies [4–8, 11], the solid component demonstrated an isointense or hypointense signal on T2WI, and a hypointense signal intensity on DWI, similar to skeleton muscles. A T2 dark signal intensity solid component containing small cystic locules on MRI was called the black sponge sign, which was observed in only 2 cases (18.2%, 2/11) in our study, a rate that is lower than that reported in previously studies [2, 4, 6–8].
In addition, case 5 in our study combined with infarction presented a solid mass, the signal intensity of which was also distinctive in this group but consistent with the other tumors accompanied by infarction: isointense on T2WI, hypointense on DWI, and lack of enhancement.
Ovarian CAF/AF is an epithelial-derived tumor [1–3]. It is categorized into 2 subtypes based on the cytologic features of the glandular element: benign and borderline. In our study, 8 benign and 3 borderline cases were included. The solid mass, diffusely or partially thickened wall/septa and papillary nodular clusters inside the cyst wall represented a dense fibrous component, correlated with histopathologic findings. Microscopically, small cystic glandular structures scattered in the fibrous stroma manifested very high signal intense tiny cysts presented in very low signal intense solid components on T2WI, which was called the black sponge sign. Moreover, we observed 1 cystic-solid mass, 2 solid masses, and 8 cystic masses during surgical operations, which were not consistent with CT/MRI (1 cystic-solid mass, 1 solid mass, and 9 cystic masses). The main discrepancy was case 4 combined with torsion of pedicle. The inside wall of the cyst in cases 6 and 10 was described as smooth during the surgical operations, but papillary nodular clusters of structures were shown inside the wall on T2WI. The above imaging findings were confirmed by pathology.
CAF/AF is a rare ovarian tumor. A previous study reported that the onset age span is wide (range, 23–70 years) and most patients who developed the disease are postmenopausal . Abdominal/pelvic mass, abdominal distension or pain, and postmenopausal vaginal bleeding are the main symptoms. In the present study, postmenopausal women accounted for 72.7% (8/11), and a total of 8 patients (72.7%, 8/11) manifested abdominal/pelvic mass. This was consistent with past reports. However, in this study, only 2 patients (18.2%, 2/11) developed postmenopausal vaginal bleeding. In addition, the levels of both CA125 and CA199 were elevated in only 2 cases (18.2%, 2/11). One case was accompanied by endometrial implantation, and the other was accompanied by cervical polyp. Those complications may account for the elevation we presumed. No patient enrolled in our study had elevated serum HE 4, CEA, or AFP levels.
In addition, we observed several novel findings in our study. First, a small vesicle with an acute angle to the inner wall of the cysts was seen in cases 2 and 8. Second, a solid region with a septum, such as honeycomb (case 1) and onion peel (case 10). Third, among all 11 cases in our study, cases 2, 3, 4, 5, and 8 demonstrated residual ovary follicles and stromal signals on MRI, whereas these were relatively rare in borderline cases, seen only in case 3. We referred to this as residual ovary sign. It is well-known that MRI has the highest resolution for the ovary, but cases 6 and 9 (benign) underwent CT only. That is probably why the ovaries in the 2 benign cases did not show as clear, like we presumed. Despite the selection of examination methods (CT or MRI), we speculated that it may also be related to the natural quality of the begin, borderline, or malignant tumor. Fourth, ascites was not found in pure benign CAF/AF in our study. Only 2 borderline and 2 benign lesions in the current study were combined with ascites, the latter of which were case 4 complicated with a torsion and case 7 complicated with dilatation of the fallopian tube, local congestion, and bleeding in the wall with scattered chronic inflammatory cell infiltration. We speculated that the complications above may be accounted for by the production of ascites. In conclusion, the amount of ascites associated with CAF/AF is small, which is significantly different from ovarian malignant tumors, such as serous cystadenocarcinoma.
Our study has some limitations. First, to verify the novel findings found in the current study, a prospective study with a large sample containing all classifications of CAF/AF is needed. Second, because the surgeon may not be the same gynecologist in all cases, the consistency between surgical and image findings remains to be further verified.