Various congenital anomalies of branchial origin are found in the neck region. Understanding the varied radiologic appearances of these anomalies is greatly aided by familiarity with their embryologic origins. By considering the anatomic location and radiologic appearance, the precise embryologic origin can be accurately predicted. Defects of the branchial apparatus include branchial, thymic, and parathyroid anomalies, which may manifest as cysts, sinuses, fistulas, and ectopic glands. The embryologic model is used to explain the origins of all branchial apparatus anomalies. The most accepted theory proposes that vestigial remnants result from incomplete obliteration of the branchial apparatus or buried cell rests, and, thus, if cells are trapped in the branchial apparatus during the embryologic stage, they can form branchial cysts later in life. By understanding the embryologic basis for these defects, the radiologist is better able to interpret the findings encountered with the various imaging modalities used in the evaluation of these anomalies.

Familiarity with the embryology of the lymphatic system is helpful in understanding the pathogenesis and radiologic appearance of lymphangiomas of the cervicothoracic region. By considering anatomic location and radiologic appearance, one can predict the type of lymphangioma present, the primordial lymph sac from which the malformation arose, and when it formed in embryonic life. Cystic hygromas are composed of large, dilated lymphatic spaces. They form when a primordial lymph sac fails to reestablish communication with the central venous system from which it arose. These lesions may also resuit from an aberrant bud arising from a primordial lymph sac. Cayernous and capillary lymphangiomas are composed of smaller lymphatic channels. They form from abnormally sequestered buds of the developing lymphatic mesenchyme responsible for the fine meshwork of terminal branches in the periphery of the embryo. Their growth may be inhibited by the relatively tougher tissues in the periphery (eg, skin and muscle) compared with the relatively loose fatty connective tissue in which cystic hygromas form. Not only can all types of lymphangioma occur in one lesion, but lymphatic and vascular malformations may also coexist.

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