A 26-year-old female presents with cyclic pelvic pain and a palpable adnexal mass. What is the most likely diagnosis?

The presentation of cyclic pelvic pain along with a palpable adnexal mass strongly suggests endometriosis as the most likely diagnosis. Endometriosis is characterized by the growth of endometrial tissue outside the uterus, which can lead to the formation of cysts, often referred to as endometriomas, on the ovaries. These cysts can present as palpable adnexal masses during a pelvic examination and are typically associated with cyclic pain that corresponds with the menstrual cycle due to hormonal influences on ectopic endometrial tissue.

The cyclic nature of the pelvic pain is particularly indicative of endometriosis, as the pain can worsen during menstruation when hormonal fluctuations increase inflammation and the presence of ectopic tissue. This condition often presents in women of reproductive age, which aligns with the age of the patient described.

While other options such as ovarian cancer, functional ovarian cysts, and pelvic inflammatory disease could also present with pelvic pain and adnexal masses, the specific combination of cyclic pain and the typical patient demographic makes endometriosis the most likely diagnosis in this scenario. Ovarian cancer and pelvic inflammatory disease might present differently, and functional ovarian cysts typically produce pain but may not always create a palpable mass, particularly if they are small or resolving.