Ovarian tumours can be benign, malignant or borderline and, based on their cell type, they can be broadly classified into epithelial cell, germ cell, sex cord-stromal, mesenchymal or metastatic tumours. Borderline ovarian tumours (BOT) belong to the epithelial cell type and account for 10-20% of all ovarian neoplasms. They are considered to represent an intermediate phase in the stepwise progression from benign to malignant ovarian cancer and are characterized by increased cell proliferation and nuclear atypia, without frank stromal invasion. Thus, borderline and malignant tumours can coexist histologically in the same surgical specimen.
As for other adnexal masses, BOT present clinically with vague, non-specific symptoms, with abdominal or pelvic pain being the most frequent ones. They can also be asymptomatic and discovered incidentally.
BOT have a favourable prognosis compared to malignant tumours and thus treatment strategies are shifting from a more radical surgical approach to a more conservative one, including fertility-sparing treatments for young patients. This paradigm shift is of paramount importance because BOT occur at a younger age than ovarian carcinomas, commonly in women of reproductive age.
According to the 2020 World Health Organization classification, BOT consist of six subtypes: serous, mucinous, seromucinous, endometrioid, clear cell and Brenner tumours. Of these, the serous and mucinous subtypes are the more frequent ones, accounting for more than 90% of all BOT.
The radiologist needs to be familiar with the more common features of BOT and plays a pivotal role in determining that a lesion is probably of borderline nature, thus allowing for the multidisciplinary team to decide on the most appropriate therapy.
Ultrasound is the first-line modality for the evaluation of adnexal masses and a careful examination must be made to look for septations, papillary projections, mural nodules and Doppler vascularity.
When facing an indeterminate mass, MRI can guide us by providing a morphological evaluation coupled with a functional one, and in most cases allows for the distinction between borderline and malignant lesions. It is known that BOT usually display a type 2 enhancement curve on dynamic post-contrast studies (Figure 1), as opposed to malignant tumours that are associated with a type 3 curve, and that they show higher ADC values than their malignant counterparts. Also, unlike ovarian carcinomas, in the case of BOT, the ovarian parenchyma ipsilateral to the tumour is usually preserved.
CT is indicated for pretreatment staging of malignant lesions and for predicting “difficult to resect” disease.
