Branchial Cleft Cysts

Etiology

Branchial cleft cysts result from elements of the cervical sinus of His becoming entrapped without an external or internal opening, forming an epithelial lined cyst. They have also been proposed to develop from epithelial rests of tissue from Waldeyer’s ring. Pure branchial cleft cysts/sinuses are relatively rare, and often there is a combination of the 2.[3][4]

Embryology

Branchial cleft cysts develop early during gestation. During week 4 of embryonic development, four branchial (pharyngeal) clefts form five ridges. These ridges contribute to the formation of portions of the head, neck, and thorax. These mesodermal ridges form the 6 branchial (pharyngeal) arches. The branchial arches form grooves or clefts externally and pouch internally. A pouch is associated with a ventral or dorsal wing and is lined by endoderm. The branchial arch derivatives are lined with mesoderm. Ectoderm lines the branchial cleft derivatives. Each arch is associated with a cartilaginous bar, carotid artery derivative,  cranial nerve, and vein. The nerves run anterior to the artery associated with each arch, except for in the case of the sixth arch where the nerve runs posterior to the artery.

The first branchial arch also known as the mandibular arch is associated with the trigeminal (V) nerve while the artery degenerates. The second arch is associated with the facial (VII) nerve and the second aortic arch degenerates. If this artery does not degenerate, then a stapedial artery persists. The third branchial arch is associated with cranial nerve IX, the glossopharyngeal nerve. The common and internal carotid arteries are associated with the third arch. The fourth arch is associated with the superior laryngeal nerve, a branch of the vagus (X) nerve. On the left, the fourth arch gives rise to the aorta, while on the right the fourth arch gives rise to the proximal subclavian artery. The fifth branchial arch degenerates. The sixth branchial arch gives rise to the pulmonary artery on both the left and right in addition the ductus arteriosus on the left. The sixth arch also gives rise to a branch of the vagus (X) nerve, the recurrent laryngeal nerve. The 12th cranial nerve lies caudal to all arches.

Epidemiology

Branchial cleft cysts are the most frequent cause of congenital neck masses, comprising approximately one-third of all congenital neck masses. They are the most common lateral neck mass, with 2% to 3% occurring bilaterally. While they occur more frequently in patients with a family history, there is no reported predilection for gender or race. They are more commonly found during childhood but can be seen in adults.[5]

Pathophysiology

Branchial cleft cysts represent incomplete involution of branchial cleft structures. A branchial cleft cyst has no opening in the skin or digestive tract. A branchial cleft sinus has a single opening to the skin or digestive tract versus a branchial cleft fistula which has an opening to skin and digestive tract. Stratified squamous epithelium lines branchial cleft cysts in 90% of cases.

Histopathology

The majority of branchial cleft cysts are lined with stratified squamous epithelium. The inside of the cyst may reveal a keratinous plug. In rare cases, the cyst may be lined with ciliated columnar epithelium. If infected, an inflammatory infiltrate may be present.

History and Physical

A branchial cleft cyst is typically present as a non-tender, fluctuant, lateral neck mass. They may become inflamed, tender and possibly suppurate during an upper respiratory tract infection.

Specific Features of Each Level of Cyst

First Branchial Cleft Cyst

First branchial cleft cysts comprise 5% to 25% of all branchial cleft cysts. There are two different subtypes within the first branchial cleft category. A Work’s type I first branchial cleft cyst presents as a preauricular cyst. There is a duplication of the external auditory canal which is comprised of ectodermal elements only. The tract of the type I cleft passes lateral to cranial nerve VII, parallels the external auditory canal and ends in the mesotympanum. A Work’s type II branchial cleft cyst is found along the angle of the mandible, periauricular area or in the submandibular area. Type II first branchial clefts are more common and contain both ectoderm and mesoderm. Fifty-seven percent of type II first branchial cleft cysts pass laterally to cranial nerve VII, while 30% of them pass medially. These cysts end within or near the external auditory canal.

Second Branchial Cleft Cyst

Second branchial cleft cysts are the most common type and have been reported to comprise up to 95% of all branchial cleft cysts. Second branchial cleft cysts run between internal and external carotid arteries, pass deep to cranial nerve VII, superficial to cranial nerves XII and IX, and end internally in the tonsillar fossa if there is an associated sinus. They run deep to second arch derivatives such as the manubrium of the malleus, the long process of the incus and the stapes superstructure and superficial to third arch derivatives such as the greater cornu of the hyoid.

Third Branchial Cleft Cyst

A third branchial cleft cyst is more commonly found on the left side in the lower portion of the anterior neck. These cysts may present as an abscess, neck mass or thyroiditis. Third branchial cleft cysts run superficially to cranial nerve X and the common carotid artery, superficial to cranial nerve XII and deep to cranial nerve IX. The associated tract, if present, then passes through the thyrohyoid membrane above superior laryngeal nerve and opens into the upper piriform sinus.

Fourth Branchial Cleft Cyst

These branchial cleft cysts are rare. A fourth branchial cleft cyst typically presents as a low anterior neck mass, beneath the platysma and anterior to the sternocleidomastoid muscle. The tract of a fourth branchial cleft cysts loops around cranial nerve XII then runs posterior to the common carotid artery and thyroid following the recurrent branch of cranial nerve X. It then runs through the cricothyroid membrane below superior laryngeal nerve with recurrent laryngeal nerve deep to its path and drains into the apex of the piriform sinus.

Evaluation

Various imaging modalities have been used to evaluate for the presence of a branchial cleft cyst. Three commonly used techniques are ultrasound, computed tomography (CT) scanning, and magnetic resonance imaging (MRI). Larger cystic lesions can be seen with ultrasound. A CT with contrast will also show a cystic appearing, well circumscribed, enhancing lesion. CT imaging can also assist with identification of structures both deep and superficial to the lesion to better categorize the type of branchial cleft cyst. MRI with gadolinium may show a (KA21) branchial cleft with wall enhancement. MRI is typically better for evaluation of type II first branchial cleft cyst because it provides for better evaluation of the parotid gland and involvement of surrounding neural structures.[6]

Treatment / Management

Treatment of a branchial cleft cyst is complete surgical excision. If a cyst is found during an infection, the surgeon should allow adequate time for the infection to resolve before scheduling the procedure. Incision and drainage should be avoided if possible as it can make definitive excision more difficult. For treatment of third and fourth branchial cleft cysts, a partial thyroidectomy may be required. Direct laryngoscopy with visualization of any opening in the pyriform sinus can aid in localization of tract. Some consider cautery of pyriform sinus tract alone as adequate for treatment of third and fourth branchial cleft cysts.[1]

Differential Diagnosis

• Hemangioma
• Ectopic thyroid or salivary gland tissue
• Lymphadenopathy

Complications

• Infection
• Abscess formation
• Damage to adjacent nerves during excision