While the most commonly encountered branchial cleft cysts arise from the second branchial apparatus, third and fourth branchial cleft cysts do exist. Third branchial cleft cysts are usually encountered posterior to the carotid artery and are sometimes mistaken for retropharyngeal abscesses. After passing through the thyro-hyoid membrane the third branchial sinus passes between the internal and external carotid arteries. Fourth branchial cleft cysts lie medial to the carotid artery and are more common on the left than the right. Both forms of lower branchial cleft cysts may present with symptoms suggestive of recurrent left side thyroiditis and are much more common on the left than the right because of the longer migrational course. Endoscopically, differentiation between third and fourth branchial cleft cysts is made based on the location of the orifice into the pyriform sinus. A third branchial cleft sinus will have its pyriform sinus opening above the apex and anterior to the internal laryngeal nerve while a fourth branchial cleft cyst will have its origin at the apex. Unfortunately, endoscopy was not performed in this patient.

Reference:
Cote. Fourth Branchial Cleft Cysts. Otolaryngology Head & Neck Surgery, Jan. 1996.

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