Fate of pharyngeal cleft and anomalies related to it скачать в хорошем качестве

Fate of pharyngeal cleft and anomalies related to it

After the pharyngeal arches are formed, the region of the neck is marked by a series of grooves or ectodermal clefts. First cleft has 2 parts- dorsal and ventral. Dorsal develops into the epithelial lining of the external acoustic meatus (EAM) whereas the ventral part gets obliterated. EAM is surrounded by pinna/auricle which develops from 6 mesenchymal proliferations or hillocks arising on the first and second arches surrounding the first pharyngeal cleft. They fuse and form the definitive auricle. Second arch grows much faster than the rest of the arches and overhangs them thereby fusing with the Epicardial ridge. The space enclosed is called cervical sinus which normally obliterates. if it persists, it lies in the neck along the anterior border of sternocleidomastoid just below the angle of mandible. It is then known as branchial cyst and if there is an opening, it is termed as branchial sinus. Branchial fistulas may either be internal or external . If internal which are very rare,the opening is in the region of tonsil when the membrane between second pouch and cleft dissolves at some time during development.