**Core Concept**
Gartner's duct cysts are a type of benign, congenital anomaly that arises from the remnants of the paroophoric Wolffian ducts, which are embryological structures responsible for the development of the male reproductive system. These cysts are typically found in the labia majora of females.

**Why the Correct Answer is Right**
Gartner's duct cysts are a result of the abnormal persistence and dilatation of the Wolffian ducts during embryonic development. They are usually lined by a single layer of columnar epithelium and may contain a central core of fibrous tissue or a few smooth muscle cells. The cysts can become symptomatic if they become large enough to cause discomfort or if they undergo torsion.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because Gartner's duct cysts are not typically found in the labia minora.
**Option B:** This is incorrect because Gartner's duct cysts are not a type of neoplasm, but rather a benign congenital anomaly.
**Option C:** This is incorrect because hydrosalpinx refers to a type of fluid-filled fallopian tube, which is a different condition altogether.

**Clinical Pearl / High-Yield Fact**
It's essential to distinguish Gartner's duct cysts from other types of vulvar masses, such as Bartholin's gland cysts or epidermoid cysts, which may present similarly but have different treatment approaches.

**Correct Answer: D.**