A branchial cleft cyst (BCC) is a congenital, fluid-filled neck mass that forms due to a developmental anomaly during fetal growth. It appears on the side of the neck, typically along the front edge of the large neck muscle. Although present from birth, the cyst may not become noticeable until childhood or early adulthood, often presenting as a painless lump. It represents one of the most common causes of a mass in the side of the neck in the pediatric population.
Embryological Origin and Definition
The formation of the branchial cleft cyst is a direct consequence of incomplete regression of structures called the branchial apparatus during the fifth to seventh weeks of gestation. This apparatus consists of four pairs of arches, clefts, and pouches that are responsible for developing the head and neck structures. The arches form cartilage, bone, muscles, and blood vessels, while the clefts and pouches normally involute by the time the embryo is about seven weeks old.
If a portion of one of these ectoderm-lined clefts fails to fully close, the entrapped remnant can form an epithelial-lined cavity that fills with fluid. This results in the congenital cyst. The vast majority of these cysts arise from the second branchial cleft, making them the most common type of BCC. While the lesion is present at birth, fluid accumulation or a subsequent infection often causes it to enlarge and become visible later in life.
Recognizing the Signs
The primary sign of a branchial cleft cyst is a soft, noticeable, and typically painless swelling on the side of the neck, usually between the jawline and the collarbone. This lump is frequently found along the anterior border of the sternocleidomastoid muscle. The mass may fluctuate in size, often becoming more prominent during or after an upper respiratory tract infection.
Sometimes, the anomaly presents not as a closed cyst but as a sinus tract or fistula. This opening may intermittently drain a mucous-like fluid onto the neck surface. If the cyst becomes infected, the patient will experience secondary signs, including localized pain, tenderness, redness, and rapid swelling. In rare cases, a large or infected cyst can cause difficulty swallowing or noisy breathing due to compression of nearby structures.
Medical Diagnosis and Classification
Diagnosing a branchial cleft cyst typically begins with a thorough physical examination and medical history, focusing on the location and characteristics of the neck mass. The specific location of the cyst or any associated external opening often provides clues to its origin. Medical imaging is necessary to confirm the diagnosis and determine the extent of the anomaly.
Ultrasound is usually the initial imaging study, which can visualize the fluid-filled nature of the cyst. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scans are often used to gain a more detailed anatomical understanding. These advanced scans help define the cyst’s full size and its precise relationship to surrounding structures, such as blood vessels and nerves, which is essential for surgical planning. BCCs are categorized into four types (first, second, third, or fourth) based on which branchial arch remnant caused the anomaly. Classification is important because each type follows a distinct anatomical path, influencing the complexity of surgical removal and the risk to nearby nerves.
Treatment and Management
The definitive treatment for a branchial cleft cyst is complete surgical excision of the cyst and any associated sinus tract or fistula. Surgery is recommended to prevent repeated infections and abscess formation, which can damage surrounding tissues. Before definitive surgery, any acute infection must be managed first, typically with antibiotics. If a significant abscess has formed, surgical incision and drainage may be required.
The procedure is often delayed until the patient is older, typically at least three months of age, to allow for better surgical outcomes. During the operation, the surgeon must carefully dissect the cyst and its tract to ensure total removal. The main risks associated with the surgery include the potential for injury to adjacent cranial nerves, such as the facial nerve for first arch cysts, and the possibility of recurrence if any part of the tract is left behind.