What is the most likely diagnosis for a tender and warm cystic mass on the lower edge of the left labia majora in a sexually active woman?

The presence of a tender and warm cystic mass on the lower edge of the left labia majora in a sexually active woman strongly suggests a Bartholin's gland abscess. Bartholin's glands, located bilaterally at the 4 o'clock and 8 o'clock positions at the vaginal opening, can become obstructed due to various factors, including infection, trauma, or inflammation. When this occurs, fluid accumulates, and if the cyst becomes infected, it can lead to an abscess that is typically painful, tender, and may exhibit redness and warmth upon examination.

Symptoms often include localized pain, swelling, and discomfort during intercourse or sitting, which correlates with the description of the cystic mass. The choice of "Bartholin's gland abscess" is thus consistent with these clinical findings.

In contrast, conditions like Skene's gland cysts, cystoceles, and lymphogranuloma venereum present differently. Skene's gland cysts are usually asymptomatic and may be more medial, while cystoceles involve the urinary bladder protruding into the anterior vaginal wall, which wouldn't typically present as a distinct cystic mass on the labia. Lymphogranuloma venereum, a sexually