Risk stratification:

Based on IOTA simple rules this is likely malignant.
There are 2 "M" features present - irregular solid tumor (M1) and very strong blood flow (M5). No "B" features.

Based on the ADNEX model, the risk of malignancy is 52%.

O-RADS Category 5; high risk - >50%; recommend management by a gynae-oncologist.

Histology:

Ovarian dysgerminoma.
Intact capsule. Widespread lymphovascular invasion.

Discussion:

Large, solid mass in an adolescent female patient. Note the lobulated internal architecture of this lesion, which is typical for this entity.