(3-5) There are several theories for the pathogenesis of these cysts, including remnants of branchial clefts
, retention cysts, coalescence of numerous minute cystic lesions, or degeneration of an adenoma.
(4) During embryonic development, the second arch grows caudally and it covers the second, third, and fourth branchial clefts
. The cervical sinus of his is formed by the fusion of this second arch with the enlarging epi pericardial ridge of the fifth arch.
The fetal branchial apparatus develops in the 2nd gestational week and consists of 6 pairs of mesodermal arches separated by 5 ectoderm-lined branchial clefts
externally and 5 endoderm-lined pharyngeal pouches internally.
The ectoderm, joining the arches, forms the branchial clefts
, and the endoderm the branchial pouches.
anomalies occur as a result of incomplete obliteration of the branchial clefts
He suggested that these cysts were results of impaired obliteration of branchial clefts
(18) The cysts arise from the third and fourth branchial clefts
, and, therefore, thymic cysts may have a similar appearance to third and fourth branchial cleft
cysts, being differentiated only by the presence of thymic tissue within thymic cysts.
However, in general, the branchial apparatus structures develop between the 4th and 6th week of gestation and consist of 6 pairs of mesodermal branchial arches separated by 5 paired endodermal pharyngeal pouches internally and 5 paired ectodermal branchial clefts
FIRST BRANCHIAL ANOMALY: First branchial clefts
comprise 5-25% of all branchial anomalies (3, 4).
Adjacent arches are separated externally by ectodermal branchial clefts
or grooves and internally by endodermal pouches.
A developmental alteration of the branchial clefts
or pouches can result in cysts, sinuses, and/or fistulas.