Serous Cystadenoma: This is a common benign ovarian neoplasm that can present as a large, cystic adnexal mass. The pervasively cystic nature of the lesion is consistent with this diagnosis.

Mucinous Cystadenoma: Another type of benign ovarian tumor that can appear as a large, cystic mass. While less common than serous cystadenomas, they are still a likely consideration for a pervasively cystic adnexal lesion.
Dermoid Cyst (Mature Cystic Teratoma): Although often containing solid components, dermoid cysts can sometimes appear predominantly cystic. They are a common adnexal mass, especially in younger women.
Simple Ovarian Cyst: These are benign, fluid-filled sacs that can occur on the ovaries. While usually smaller, they can grow large enough to be considered in the differential for a pervasively cystic adnexal lesion.

Ovarian Cancer (e.g., Serous or Mucinous Cystadenocarcinoma): Although less common than benign cystic lesions, ovarian cancer is a critical diagnosis not to miss due to its significant implications for patient management and prognosis. A pervasively cystic appearance can sometimes be seen in malignant ovarian tumors.
Tubovarian Abscess: This is an infectious process involving the tubes and ovaries, often resulting from pelvic inflammatory disease (PID). It can present as a complex cystic adnexal mass and is crucial to diagnose promptly due to the need for antibiotic treatment and potential surgical intervention.
Ectopic Pregnancy: While typically presenting early in pregnancy, an ectopic pregnancy can occasionally manifest as a cystic adnexal mass. This diagnosis is critical to identify quickly due to the risk of rupture and severe hemorrhage.

Cystic Dysgerminoma: A rare type of ovarian germ cell tumor that can have a cystic component. While predominantly solid, the presence of cystic areas can sometimes lead to consideration in the differential for pervasively cystic lesions.
Yolk Sac Tumor: Another rare ovarian germ cell tumor, which can occasionally present with cystic components. It is more common in children and young adults.
Lymphangioma or Other Rare Benign Tumors: Extremely rare tumors that can affect the adnexa and present as cystic masses. Their rarity makes them less likely considerations but should be kept in mind for unusual or atypical presentations.