There are multiple causes of adnexal mass development. Gynecologic causes, meaning that masses originate from the reproductive system, are the most common. In some cases, however, there may be non-gynecologic causes that involve the digestive or urinary system.
Adnexal masses are usually associated with the female reproductive system and occur more frequently in individuals of childbearing ages. In fact, ectopic pregnancy is a very common cause of adnexal masses. An ectopic pregnancy is when an embryo implants somewhere other than in the uterine cavity—most frequently in the fallopian tube. In cases of pregnant individuals for whom ectopic pregnancy has been ruled out, adnexal masses are usually benign and occur as a result of hormonal changes identified during pregnancy.
In non-pregnant individuals, the most common types of gynecologic adnexal masses are functional ovarian cysts (i.e., luteal cysts), which form on the surface of the ovary after ovulation occurs. Notably, the presence of such cysts increases the risk of ovarian torsion, a medical emergency that presents when the ovary rotates around its ligaments and interferes with the blood supply. Additionally, adnexal masses may present as multiple small cysts on enlarged ovaries (i.e., polycystic ovaries), which is characteristic of polycystic ovary syndrome (PCOS). Other adnexal masses include leiomyomas -- benign, fibrous tumors usually occurring in the uterus -- and endometriomas, which are cysts that form when endometrial tissue grows in or around the ovaries. Pelvic inflammatory disease or other causes of tubo-ovarian abscesses (i.e., collections of pus in the ovaries and fallopian tubes) can also cause adnexal masses. If the mass is suspected to be malignant, ovarian cancer is the most common cause.
On the other hand, non-gynecologic adnexal masses often originate from the gastrointestinal or urinary system. Common types of these adnexal masses include inflammatory masses of the
appendix,
colorectal cancer, as well as pelvic kidneys, which occur when the kidneys do not fully ascend during fetal development. Lastly, breast and
colon cancer, when spread to other organs, can metastasize in the
pelvis and create adnexal masses.
