What condition should be suspected in females with pelvic fullness and urinary frequency due to a large cyst?

The most likely condition to consider in females presenting with symptoms of pelvic fullness and urinary frequency related to a large cyst is a physiological ovarian cyst. Physiological ovarian cysts, which include follicular and corpus luteum cysts, typically develop in response to the normal menstrual cycle and can grow large enough to cause pressure symptoms on surrounding structures, including the bladder. This pressure can lead to urinary frequency, as the cyst may compress the bladder and reduce its capacity.

The description of pelvic fullness aligns well with the presence of a large cyst. Unlike other conditions, physiological ovarian cysts usually do not present with severe symptoms unless they rupture, which is less common. Their occurrence is particularly relevant during the reproductive years when hormonal fluctuations are frequent.

In contrast, conditions like uterine fibroids might also cause pelvic fullness but are typically associated with additional symptoms such as heavy menstrual bleeding, rather than predominantly urinary frequency. Ovarian torsion would present with acute pain and potentially nausea, rather than gradual-onset urinary symptoms. Lastly, pelvic inflammatory disease typically presents with lower abdominal pain and fever, stemming more from an infection rather than from a cystic mass. Therefore, the symptoms described most directly correlate with a physiological ovarian cyst, making it the most appropriate diagnosis in this context