**Core Concept**
A branchial cyst, also known as a branchial cleft cyst, is a congenital anomaly resulting from the incomplete closure of the branchial clefts during embryonic development. It is a type of neck mass that can present in various ages, from infancy to adulthood. The cysts typically arise from remnants of the second branchial cleft.

**Why the Correct Answer is Right**
Branchial cysts are usually lined by squamous epithelium and contain lymphatic fluid. They are often found in the upper neck, near the anterior border of the sternocleidomastoid muscle, and can cause symptoms such as swelling, pain, and infection. The most common treatment for branchial cysts is surgical excision, which can be performed through an external incision or endoscopically.

**Why Each Wrong Option is Incorrect**
**Option A:** Branchial cysts are typically lined by stratified squamous epithelium, not pseudostratified columnar epithelium. This distractor is incorrect because pseudostratified columnar epithelium is more commonly associated with respiratory or genitourinary tract tissues.

**Option B:** While branchial cysts can present in various sizes, the statement that they are always large is incorrect. Some branchial cysts can be small, ranging from a few millimeters to several centimeters in diameter.

**Option C:** The statement that branchial cysts are always infected is incorrect. While branchial cysts can become infected, many are asymptomatic and discovered incidentally during imaging studies or surgical procedures.

**Clinical Pearl / High-Yield Fact**
To remember the common locations of branchial cysts, recall the "2-3-4" rule: most branchial cysts arise from the second branchial cleft (2), are located near the anterior border of the sternocleidomastoid muscle (3), and are found in the upper neck (4).

**Correct Answer:** A.