Commonest site of branchial cyst: September 2012
**Core Concept**
Branchial cysts are congenital anomalies resulting from the incomplete obliteration of the branchial clefts, which are remnants of the embryonic branchial apparatus. The branchial clefts are a series of paired grooves that appear on the lateral surface of the pharyngeal apparatus during embryonic development.
**Why the Correct Answer is Right**
The commonest site of branchial cyst is the second branchial cleft, which is located in the lateral neck, anterior to the upper third of the sternocleidomastoid muscle. The cysts typically present as painless, fluctuant masses in this region, often with a sinus tract opening onto the skin. The second branchial cleft is the most common location due to its relatively incomplete obliteration during embryonic development.
**Why Each Wrong Option is Incorrect**
* **Option A:** The first branchial cleft is a rare location for branchial cysts and is often associated with more complex anomalies.
* **Option B:** The third branchial cleft is a less common location for branchial cysts and is typically found in the lower neck.
* **Option D:** The fourth branchial cleft is a rare location for branchial cysts and is often associated with more complex anomalies.
**Clinical Pearl / High-Yield Fact**
The commonest site of branchial cyst is the second branchial cleft, which is located in the lateral neck, anterior to the upper third of the sternocleidomastoid muscle. This knowledge is essential for diagnosing and managing branchial cysts, which can often be treated with surgical excision.
**Correct Answer: C. Second branchial cleft.**