**Core Concept**
Gartner's duct cysts are a type of benign, congenital cystic structure that arises from the remnants of the Wolffian duct, a precursor to the male reproductive system. These cysts occur in the female genital tract due to the incomplete regression of the Wolffian duct during embryonic development.

**Why the Correct Answer is Right**
Gartner's duct cysts typically present as a painless, palpable mass in the labia majora or along the vaginal wall. They are usually filled with a clear or serous fluid and can range in size from a few millimeters to several centimeters. The exact mechanism of their formation is not fully understood, but it is thought to involve the abnormal persistence of Wolffian duct cells and their subsequent cystic dilation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Gartner's duct cysts are not typically associated with the Bartholin glands, which are a separate type of glandular structure in the female genital tract.
* **Option B:** This option is incorrect because hydrosalpinx is a condition characterized by the accumulation of fluid within a fallopian tube, which is distinct from Gartner's duct cysts.
* **Option C:** This option is incorrect because a Bartholin gland cyst is a separate type of cystic structure that occurs in the female genital tract, distinct from Gartner's duct cysts.

**Clinical Pearl / High-Yield Fact**
Gartner's duct cysts can be easily differentiated from other types of cystic structures in the female genital tract by their characteristic location along the vaginal wall or in the labia majora, as well as their smooth, painless nature.

**Correct Answer:** D.