Dermoid cyst: This is a common type of ovarian tumor, especially in younger women. The solid appearance on ultrasound (US) is consistent with a dermoid cyst, which often contains a mixture of solid and cystic components, including hair, teeth, and other tissues.

Mucinous cyst: While typically more cystic than solid, a large mucinous cystadenoma can have solid components and present as a predominantly solid mass on US. These tumors are often large and can be benign or malignant.
Ovarian fibroma: These are solid ovarian tumors composed of fibrous tissue. They can grow to be quite large and are more common in older women. The solid appearance on US is consistent with an ovarian fibroma.

Ovarian cancer: Although less likely, it is crucial not to miss a potential malignancy. A solid ovarian mass, especially one that is large, warrants further investigation to rule out ovarian cancer. This includes obtaining tumor markers (e.g., CA-125) and considering a biopsy or surgical exploration.
Germ cell tumor: These tumors can present as solid masses and are more common in younger women. They can be benign or malignant, and some types, like dysgerminomas, can grow rapidly.

Sclerosing stromal tumor: A rare type of sex cord-stromal tumor that can present as a solid ovarian mass. These tumors are usually benign but can cause significant symptoms due to their potential to produce androgens or other hormones.
Ovarian metastasis: In rare cases, a solid ovarian mass can be a metastasis from another primary cancer site. This would be more likely in a patient with a known history of cancer.