OSCTs are ovarian tumours composed entirely or mostly of cells that secrete steroid hormones. OSCTs can secrete one or more steroid hormones, such as androgens, oestrogen, cortisol, aldosterone, and progesterone, resulting in corresponding symptoms and signs, such as hyperandrogenaemia, hyperestrogenaemia, Cushing syndrome, and refractory hypertension [7], and androgenaemia is the most common. In female hyperandrogenism, adrenal and/or ovarian sources need to be distinguished. The cause of hyperandrogenaemia caused by adrenal tumours is the secretion of excessive dehydroepiandrosterone sulphate [8], and the androgens secreted by most ovarian tumours are not regulated by gonadotropins or adrenocorticotropic hormone (ACTH). Therefore, adrenal CT and medium-dose dexamethasone suppression tests can be used to exclude adrenal sources.
The clinical manifestations of OSCTs are determined by the steroid hormones produced, and OSCTs can be divided into high-androgen types and high-oestrogen types. Most OSCTs (80%) are of the high-androgen type, and approximately 20% of OSCTs are of the high-oestrogen type [9, 10]. High-androgen-type tumours mainly cause symptoms such as hirsutism, acne, a low and thick voice, an enlarged clitoris, laryngeal knots, breast atrophy, hair loss, and a low posterior hairline. High-oestrogen-type tumours mainly cause symptoms such as irregular vaginal bleeding and endometrial hyperplasia. All patients in this case series exhibited high-androgen-type OSCTs. In case 1, the patient showed progressive hirsutism, and the patients in cases 2 and 3 showed no obvious clinical symptoms. Some scholars [3] conducted a pathological review of approximately 90 OSCT cases reported in domestic and foreign literature from 2000 to 2017 and found that the corresponding clinical manifestations caused by endocrine abnormalities were the main clinical features of OSCTs, but there were still approximately 6% of patients with clinical manifestations with no obvious correlation with endocrine abnormalities.
Due to the low incidence of OSCTs, corresponding imaging reports are rare, and most of them are case reports, so the typical imaging features are not fully understood. On histology, OSCTs are generally well-defined and spherical, while LCTs are significantly smaller than SCT-NOS lesions. OSCTs are dominated by solid components; because most of them contain fat components, they were once called lipocytomas. On microscopy, the tumour cells are rich in lipids, and there are abundant capillary networks and vascular sinusoid structures in the tumour [11]. Ultrasound is the first choice for the detection and diagnosis of ovarian tumours due to its convenience, speed and non-invasiveness. OSCTs tend to occur in one ovary, and grey-scale ultrasound usually shows solid, round or oval nodules with clear boundaries. The internal echo is mainly slightly hyperechoic. The echo intensity may be related to the internal fat content. Because testosterone has the effect of increasing vasodilatory substances, most OSCTs exhibit rich blood flow signals dominated by low-resistance blood flow [12]. Tan et al. [13] performed contrast-enhanced ultrasound in two cases of OLCTs and found that the LCTs had a rich blood supply, and the new capillaries around the tumours were more obvious than those in the tumours. Since LCTs are very small and lack typical imaging features, this may cause poor visibility on ultrasound and CT examinations [14, 15]. At the same time, in menopausal women, due to the reduced oestrogen level and insufficient perfusion by the ovarian artery blood, the appearance of the ovaries is reduced, and the echo of the ovaries is increased. CDFI usually indicates no blood flow signals in the ovaries [16]. Therefore, it is difficult to distinguish between OLCT tissue and normal atrophic ovarian tissue by ultrasound. At present, it is believed that SCT-NOS lesions are more easily recognized on imaging than LCTs.
Mature teratomas contain liquid fat and appear as a clear hyperechoic mass on grey-scale ultrasound. Thus, teratomas need to be differentiated from OSCTs. Especially when a small, hyperechoic mass appears on one ovary in menopausal women, the possibility of an OLCT cannot be ignored. However, most teratomas are mixed tumours with cystic and solid component. Lipid stratification can occur in the cystic part, and some of the lesions can contain bone tissue or teeth, appearing as hyperechoic nodules with rear acoustic shadows. CDFI usually shows no obvious blood flow signal these masses. Because teratomas contain very few non-secretory tissues that produce testosterone, they very rarely cause hyperandrogenism [17].
Follicular membrane cell tumours that secrete oestrogen are composed of lipid-rich ovarian membrane cells. Histologically, these tumours are mainly solid, with a hard texture and intact capsule, which can be combined with various forms of degeneration, such as calcification. On grey-scale ultrasound, these tumours appear as a round or lobulated, hypoechoic mass with a smooth surface and are often accompanied by varying degrees of posterior sound attenuation, with clear or unclear boundaries; the internal echoes may be uniform or uneven. CDFI shows no obvious blood flow signals in these tumours, and oestrogen secretion is the main distinguishing feature of OSCTs [18]. McGonagall syndrome can occur when the tumour is large.
Follicular membrane fibroids are derived from spindle-shaped collagen fibroblasts. They are sex cord-stromal tumours that occur in perimenopausal or postmenopausal women, with very few malignant changes. Follicular membrane fibromas and follicular cell tumours have similar features on grey-scale ultrasound. CDFI shows that these mass have no blood supply or secretory function, which are key to distinguishing follicular membrane fibromas from OSCTs.
Ovarian Sertoli-Leydig cell tumours, which also commonly show androgen secretion, are composed of Sertoli cells and/or mesenchymal cells of different levels. Histologically, these tumours mainly manifest as a hard, lobulated mass with a complete capsule [19]. Unlike OSCT patients, approximately 75% of patients with Sertoli-Leydig cell tumours are 30 years old or younger, and on grey-scale ultrasound, these tumours are mainly solid/cystic masses with clear boundaries. Because the tumour cells contain more fibrous interstitium, the solid part of the tumour is less echogenic. Most of these tumours are rich in blood vessels, so they can show an abundant blood supply on imaging.
Granulosa cell tumours of the ovary are rare, low-grade ovarian stromal tumours with a granular cell morphology, and most secrete oestrogen. Because granulosa cell tumour tissue is fragile and easily becomes detached, causing haemorrhagic necrosis and cystic transformation, solid/cystic masses are typical imaging features of ovarian granulosa cell tumours, and they are mostly arranged in intervals in a radial pattern. CDFI shows minimal to moderate blood flow signals in these tumours [20], with mostly low-resistance blood flow due to the vasodilator effect of oestrogen. It is not difficult to distinguish ovarian granulosa cell tumours from OSCTs using both clinical and imaging features.
When broad ligament leiomyomas become large and show degenerative changes, it is difficult to distinguish them from ovarian tumours. Therefore, accurate positioning of the ovary is the key to distinguishing between the two. Whirlpool or woven hypoechoic masses and pseudocapsules are characteristic ultrasound manifestations of leiomyomas. CDFI shows low blood flow signals inside and around these tumours. Similarly, the lack of endocrine function is also key to distinguishing leiomyomas from OSCTs.
SCT-NOS lesions are the most prone to malignant transformation among OSCTs, with a malignant transformation rate of approximately 25–43% [12]. When OSCTs undergo malignant transformation, necrosis, haemorrhage and cystic transformation may occur, and these OSCTs need to be differentiated from ovarian cystadenocarcinomas. Cystadenocarcinomas are malignant ovarian epithelial tumours, with an age at onset later than that of OSCTs. The grey-scale ultrasound features of serous cystic carcinomas include a single sac or cystic mass with compartments, usually accompanied by papillary protrusions. Mucinous cystadenocarcinomas are very large and are usually multilocular cystic masses with solid wall nodules, turbid cyst fluid and poor sound transmission. Since ovarian malignant tumour cells can produce vascular endothelial growth factor, etc., they can induce the formation of new blood vessels lacking smooth muscle tissue, which will lead to a low blood flow RI [21]. On CDFI, the solid component of ovarian cystadenocarcinomas shows abundant low-resistance blood flow signals. At the same time, the presence of endocrine function can also help further distinguish the type of tumour.
In summary, the diagnosis of postmenopausal OSCTs is mainly based on typical symptoms and signs, sex hormone determination, imaging features and pathological findings. The corresponding symptoms caused by endocrine abnormalities are the most intuitive clinical manifestations of the disease, especially virilization caused by hyperandrogenaemia, which is more common, but there are still some patients who are completely asymptomatic. A solid, slightly hypoechoic, round or oval mass with a uniform internal echo and an abundant blood supply with low resistance are more typical imaging features of OSCTs. Diagnosing OSCTs is challenging, and surgery can be used for both diagnosis and clear treatment. Of course, histological examination is the gold standard for the final diagnosis of OSCTs.