Magnetic resonance imaging findings of cystic ovarian tumors: major differential diagnoses in five types frequently encountered in daily clinical practice

Abstract

There are many types of ovarian tumors, and these different types often form cystic masses with a similar appearance, which can make their differentiation difficult. However, with the exclusion of rare ovarian tumors, the number of ovarian tumors encountered in daily practice is somewhat fixed. It goes without saying that magnetic resonance imaging (MRI) is useful for differentiating ovarian tumors. In this review, we summarize the differential diagnoses for each of the five types of MRI findings commonly encountered in daily practice. First, unilocular cystic masses without mural nodules/solid components include benign lesions such as serous cystadenoma, functional cysts, surface epithelial inclusion cysts, paratubal cysts, and endometriosis. Second, multilocular cystic ovarian lesions include mucinous tumors and ovarian metastases. It should be noted that mucinous tumors may be diagnosed as borderline or carcinoma, even if no solid component is observed. Third, cystic lesions with mural nodules that are unrelated to endometriosis include serous borderline tumor and serous carcinoma. Cystic lesions with solid components are more likely to be malignant, but some may be diagnosed as benign. Fourth, ovarian tumors deriving from endometriosis include seromucinous borderline tumors, endometrioid carcinoma, and clear cell carcinoma. These tumors sometimes need to be differentiated from serous tumors. Finally, cystic lesions with lipid contents include teratoma-related tumors. In mature cystic teratoma, mural nodules (called "Rokitansky protuberance" or "dermoid nipple") are sometimes seen, but they do not suggest malignancy. Some of these lesions can be diagnosed accurately by considering their characteristic imaging findings, their changes over time, MRI findings other than those of the primary lesion, and information from other modalities such as tumor markers. To ensure the optimal treatment for ovarian tumors, it is important to estimate the histological type as well as to diagnose whether a lesion is benign or malignant.

Keywords: Cystic ovarian tumor; Differential diagnosis; Magnetic resonance imaging.

Fig. 1

Lesions that need to be differentiated from serous cystadenoma. a, b Unilateral cystic mass of the right ovary in a woman in her 40 s. The inside of this thin-walled cystic lesion is hyperintense on T2WI (a) and hypointense on T1WI (b). There is no mural nodule inside the cystic lesion. The lesion was diagnosed as serous cyst adenoma. c: Unilateral small cyst (< 10 mm) (arrow) of the left ovary in a woman in her 80 s. The inside of this cystic lesion is markedly hyperintense on T2WI. The lesion was diagnosed as surface epithelial inclusion cyst. d–f Unilateral cystic mass of the left ovary in a woman in her 30 s. The inside of this thin-walled cystic lesion is markedly hyperintense on T2WI (d) and hypointense on T1WI (e). There is no mural nodule inside the cystic lesion. It could not be identified on fat-suppressed T2WI (FS-T2WI) after 3 months, and was considered to be a functional cyst (f). g Right paratubal cyst in an adolescent girl. FS-T2WI shows an extraovarian unilateral cystic lesion (arrowhead) bordering the right ovary (arrow). h, i Hydrosalpinx in a woman in her 50 s. T2WI shows a cystic lesion with marked hyperintensity on the left side of the uterus (arrow) (h). Linear structures showing plica of the fallopian tubes are visible inside (h). Sagittal FS-T2WI shows the cystic lesion is a tubular lesion with a C-shaped appearance (i)

Fig. 2

Endometriotic cyst. a, b Endometriotic cyst of the left ovary in a woman in her 40 s. It has a smooth wall and the inside of the cyst shows hypointense on coronal T2WI (a). The inside intensity of the cyst is higher than that of fat on T1WI (b). c Endometriotic cyst of the right ovary in a woman in her 40 s. The coronal T2WI shows a cystic lesion in contact with the uterus and a hypointense area in the myometrium at the site of adhesion, suggestive of adenomyosis

Fig. 3

Mucinous tumors. a–c Mucinous cystadenoma of a woman in her 30 s. A multifocal cystic mass greater than 10 cm is observable in the pelvis. On FS-T2WI and fat-suppressed T1WI (FS-T1WI), the signal intensity varies across the different loculi of the mass, giving it a stained-glass appearance (a, b). Gd-enhanced FS-T1WI shows no solid components in the mass (c). d–f Mucinous borderline tumor in a woman in her 20 s. T2WI and FS-T1WI show different signal intensities across the loculi of the mass (d, e). The sizes of the loculi are smaller than in mucinous cystadenoma, and they are more numerous. There are loculi that are hypointense on T2WI and hyperintense on FS-T1WI (arrowhead) (d, e). Gd-enhanced FS-T1WI shows no solid components in the mass (f). g–i Mucinous carcinoma of a woman in her 60 s. T2WI and FS-T1WI show variations in signal intensity across the loculi of the mass (g, h). The loculi are as small as in mucinous borderline tumor. There are loculi that are hypointense on T2WI and hyperintense on FS-T1WI (arrowhead) (g, h). Gd-enhanced FS-T1WI shows enhanced solid components in the mass (arrow) (i)

Fig. 4

Bilateral ovarian metastasis from colon cancer in a woman in her 70 s. a Two multilocular cystic masses are seen at the head of the uterus and in the Douglas fossa on FS-T2WI. b The T1WI shows variation in the signal intensity of the loculi inside the mass, giving a ‘stained-glass’ appearance

Fig. 5

Struma ovarii in an adolescent girl. a FS-T2WI shows a lobulated multilocular cystic mass in the pelvis. Some loculi are as hypointense as skeletal muscle. A nodular area with hyperintensity is observable in the center of the mass (arrowhead). b On FS-T1WI, the majority of the mass is slightly hyperintense compared with skeletal muscle. A nodular area in the center of the mass is hypointense (arrowhead). c Gd-enhanced FS-T1WI shows no enhancement in the majority of the mass, but marked enhancement in the central nodular area (arrowhead). d The central nodular area is hyperintense on DWI (arrowhead) and ADC maps (e; arrowhead); hence, the area has no diffusion restriction. f Unenhanced CT shows the majority of the mass to be hyperdense compared with skeletal muscle, with the exception of the central nodular area

Fig. 6

Adult granulosa cell tumor in a woman in her 40 s. a An internal heterogeneous mass in the left ovary appears spongy on FS-T2WI with marked hyperintense areas clustered in the center of the mass. b FS-T1WI shows hyperintense areas suggestive of hemorrhage (arrowhead). c The margins and septa of the mass show enhancement on Gd-enhanced FS-T1WI

Fig. 7

Non-neoplastic lesion presenting as a multilocular cystic mass. a Hyperreactio luminalis in a woman in her 30 s at 14 weeks of pregnancy. The right ovary is enlarged and a multilocular cystic mass can be seen on T2WI. Each loculus appears to be an overly-enlarged normal follicle. b, c Peritoneal inclusion cyst after uterine myomectomy in a woman in her 40 s. A cystic mass with septa can be seen along the right pelvic wall on FS-T2WI (b). The bilateral ovaries are inside the cystic lesion on FS-T2WI. The periphery of the cystic lesion is in line with the peritoneum (c)

Fig. 8

Serous borderline tumor in a woman in her 50 s. a A unilocular cystic mass is found at the head of the uterus. The inside of the cyst is markedly hyperintense on T2WI. A papillary mural nodule can be seen rising from the inferior wall into the lumen. The mural nodule has a dendritic hypointense area at its center and a marked hyperintense area around it. This forms the so-called ‘papillary architecture and internal branching pattern.’ The signal intensities of the cyst content and papillary mural nodule margins are similar, and the contour of the mural nodule is, therefore, unclear. b On FS-T1WI, the mural nodule margins are hypointense compared with the cyst content, and the contour of the mural nodule is clear. c Dendritic enhancement of the mural nodule can be seen on Gd-enhanced FS-T1WI

Fig. 9

Bilateral serous borderline tumor in a woman in her 20 s. a Bilateral ovarian multilocular cystic masses with solid components have formed. The right ovarian mass has exophytic solid components (arrowhead), whereas the left ovarian mass has intracystic solid components. T2WI shows that the solid components of the bilateral ovarian mass are composed of markedly hyperintense areas with dendritic hypointense areas. b, c The solid components are hypointense on T1WI (b) and show strong enhancement on Gd-enhanced T1WI (c). The cystic content is hyperintense; hence, the lesion needs to be differentiated from tumors associated with endometriosis. d On the coronal T2WI, the exophytic solid components (arrowhead) of the right ovarian mass shows well-depicted papillary architecture and an internal branching pattern

Fig. 10

High-grade serous carcinoma. a FS-T2WI shows bilateral ovarian solid and cystic masses. Solid components show hypointensity compared with serous borderline tumor. A large amount of ascites is visible. b FS-T2WI shows some peritoneal dissemination (arrowhead). c The solid components are markedly hyperintense on DWI (high b value). d The solid components are markedly hypointense on ADC maps

Fig. 11

Cystic tumor with solid components showing hypointensity on T2WI and DWI. a–c Fibroma in a woman in her 40 s. A solid and cystic mass is present in the left ovary. The solid components are hypointense on FS-T2WI, comparable to skeletal muscle (arrowhead) (a). The solid components are hypointense on FS-T1WI, comparable to skeletal muscle (arrowhead) (b). The solid components are hypointense on high b value DWI (arrowhead) (c)

Fig. 12

Seromucinous borderline tumor in a woman in her 60 s. a FS-T2WI shows the right ovarian cystic mass to have slightly hyperintense content with a papillary mural nodule. The papillary mural nodule shows marked hyperintensity with central dendritic hypo-intensities. This finding resembles those of serous borderline tumor. b On T1WI, the right ovarian cystic mass has slightly hyperintense content with a hypointense mural nodule. c On DWI (high b value), the central area of the mural nodule is slightly hyperintense. d On ADC maps, the central area of the mural nodule is slightly hypointense but the peripheral area of the mural nodule is markedly hyperintense

Fig. 13

Endometrioid carcinoma in a woman in her 60s. a T2WI shows a mass in the left ovary consists of a cyst and solid components. b FS-T1WI shows a hyperintense area inside the mass, suggesting hemorrhage. c Gd-enhanced FS-T1WI shows that the solid components have the same degree of enhancement as the myometrium. d On DWI (high b value), the solid components are hyperintense compared with the myometrium. The hemorrhage area shows marked hyperintensity. e ADC maps show the solid components to be hypointense compared with the myometrium. f Sagittal T2WI shows the solid components to be multicentric

Fig. 14

Endometrioid carcinoma of the right ovary with endometrioid carcinoma of the uterine corpus in a woman in her 40s. a A cystic mass is present in the right ovary. FS-T2WI shows mural nodules with a moderate signal intensity. One mural nodule is focal and eccentric. This is a finding that is more likely to be associated with clear cell carcinoma. b Sagittal FS-T2WI shows that a mass suspected to be endometrial carcinoma is present in the uterine cavity and is hanging down into the cervix. Based on the above, the mass in the right ovary is strongly suspected to be endometrial carcinoma

Fig. 15

Clear cell carcinoma of a woman in her 40s. a A mass consisting of cysts and solid components was found in the left ovary. The center of the mass has a solid component with moderate hyperintensity on FS-T2WI (arrowhead). There is also a papillary mural nodule in the posterior mass loculus that shows a markedly hyperintense area with a dendritic hypointense area in the center on FS-T2WI (arrow). b A papillary mural nodule is clearly depicted on coronal T2WI (arrow). c On DWI (high b value), the solid component in the center of the mass is slightly hyperintense (arrowhead), whereas the papillary mural nodule is hypointense (arrow). d On ADC maps, the solid component in the center of the mass is hypointense (arrowhead), whereas the papillary mural nodule is hyperintense (arrow)

Fig. 16

Polypoid endometriosis in a woman in her 30s. a A lesion consisting of cystic and solid components is visible in the pelvis. The solid components are moderately hyperintense on FS-T2WI (arrowhead). b Some of the cystic components are markedly hyperintense on fat-suppressed FS-T1WI (arrow). c Solid components have moderate enhancement on Gd-enhanced FS-T1WI (arrowhead) and are hyperintense on DWI (d: arrowhead). e On ADC maps, the solid components are iso-intense compared with skeletal muscle (arrowhead). f Sagittal FS-T2WI shows the solid component as iso-intense compared with endometrium (arrowhead), and there is a hypointense rim on the surface of the solid component (arrow)

Fig. 17

Decidualized endometriosis in a woman in her 20s at 14 weeks of pregnancy. a A cystic mass with a mural nodule is observable in the right ovary. On FS-T2WI, the mural nodule is as hyperintense as the placenta (arrowhead). b On FS-T1WI, the mural nodule is iso-intense compared with the placenta (arrowhead). c On DWI, the mural nodule is as hyperintense as the placenta (arrowhead). d On ADC maps, the mural nodule is as hypointense as the placenta (arrowhead)

Fig. 18

Mature cystic teratoma in a woman in her 20s. a A coronal T2WI shows an 8-cm cystic mass in the right ovary with a protruding structure with a palm tree appearance. b The cystic content and central area of the protruding structure are hyperintense on T1WI and hypointense on FS-T1WI (c). From the above, it can be seen that there is fat inside the protruding structure, and that it is a Rokitansky protuberance

Fig. 19

Malignant transformation of mature cystic teratoma in a woman in her 20 s. a FS-T2WI shows a cystic mass with an internal fluid–fluid level. A moderately hyperintense 2-cm mural nodule on the posterior wall of the mass (arrowhead) is observable on FS-T2WI. T1-weighted gradient-echo in-phase (b) and opposed-phase (c) imaging shows that the mural nodule has no fat or lipid content (arrowhead). d FS-T1WI shows lipid-rich fluid and a hypointense mural nodule (arrowhead). e Gd-enhanced FS-T1WI shows mild enhancement of the mural nodule (arrowhead). f 18F-FDG-PET/CT shows significant accumulation in the mural nodule (arrowhead). Surgery was performed and malignant transformation (squamous cell carcinoma) of mature cystic teratoma was diagnosed