What is the most likely diagnosis for a woman with an enlarged ovary presenting with irregular menstrual intervals?

The most likely diagnosis for a woman with an enlarged ovary and irregular menstrual intervals is a functional ovarian cyst. These cysts are common in women of reproductive age and typically arise during the normal menstrual cycle as follicles develop and release eggs. When a follicle fails to rupture or when the corpus luteum forms but does not regress, it can lead to a functional cyst, which may cause menstrual irregularities due to hormone imbalances.

Functional ovarian cysts can often resolve on their own without treatment, resulting in a normalization of menstrual cycles once they dissipate. The enlargement of the ovary in this case aligns with the presence of such a cyst, particularly since they can lead to delayed or missed periods.

In contrast, ovarian carcinoma generally presents with more severe and persistent symptoms, and while it can also cause an enlarged ovary, it is less likely to solely present with irregular periods in this demographic. Endometriosis often involves other symptoms, such as chronic pelvic pain, and typically does not result in enlarged ovaries without the presence of endometriomas. A benign cystic teratoma, or dermoid cyst, is also a possibility for an enlarged ovary, but it is less common and usually does not directly cause irregularities in menstrual cycles