These imperfections in fetal development are important in their differentiation from infections such as abscessation. Thyroglossal duct cyst is the result of postnatal persistence of the early embryonic thyroglossal duct. This rare cyst is always single and found in the middle of the neck, usually at the level of the hyoid bone and larynx. It is smoothly rounded with a well-defined border, anchored to the hyoid bone and deep tissues. Unless infection is superimposed, it is seldom attached to the skin. It is not tender and contains fluid.
A branchial (or lateral cervical) cyst develops from branchial apparatus malformation, usually of the second branchial cleft. Unilateral or bilateral branchial cysts occupy a lateral position in the upper neck and are usually only slightly mobile. Their size varies considerably, and an individual cyst may change size periodically as its contents escape through a small opening into the throat or through a small cutaneous fistula (branchial or lateral cervical fistula). A recent retrospective study in horses has identified a bimodal age of presentation: <6 mo of age with clinical signs primarily related to upper respiratory disease and >8 yr of age with esophageal obstructive disease as the predominant clinical feature.
In horses, intramural esophageal cysts or cystic duplication of the esophagus can occur and usually manifests early in life. Surgical removal or omentalization is the treatment of choice. Tubular duplications have also been reported and present clinically as recurring dysphagia or choke; surgical removal is generally corrective.
Dentigerous cysts are of epithelial origin and arise from abnormal tooth development. They often contain tooth fragments and usually involve the maxilla and mandible to varying degrees. These cysts can be found in young (<3 yr) horses or ruminants (primarily sheep). In young horses, they may be difficult to differentiate from cystic sinuses (osteitis fibrosa cystica), which also typically result in facial or mandibular distortion.
Surgical removal of the cyst(s) is required, with definitive diagnosis based on subsequent histopathologic examination.
Last full review/revision March 2012 by Walter Ingwersen, DVM, DVSc, DACVIM