Chapter 51. Malformations Related to The Branchial Apparatus - Review of Medical Embryology Book

Malformations of the head and neck generally originate during the transformation of the branchial apparatus into adult structures

CONGENITAL AURICULAR PITS AND CYSTS: blind pits or cysts in the skin are commonly found in a small area anterior to the ear and are probably ectodermal folds sequestered during the formation of the external ear
BRANCHIAL OR LATERAL CERVICAL SINUSES are relatively rare and almost always open externally on the side of the neck. They are due to a failure of the second branchial cleft or groove to obliterate

A blind pit or channel opens on the lower third of the neck near the sternocleidomastoid muscle

A branchial sinus opening into the pharynx is rare, but one may open into the tonsillar fossa as a result of the persistence of part of the second pharyngeal pouch

BRANCHIAL FISTULA is an abnormal tract opening both on the side of the neck and in the pharynx (tonsillar fossa)

It is the result of the persistence of parts of the second branchial groove and second pharyngeal pouch
It provides drainage for a lateral cervical cyst (remnants of the cervical sinus) and is found most often just below the angle of the jaw

BRANCHIAL VESTIGE is rare; and seen as cartilaginous or bony remnants of branchial arch cartilages, which normally disappear. It is seen on the side of the neck in front of the lower third of the sternocleidomastoid muscle
THE FIRST ARCH SYNDROME: a number of malformations result from the disappearance or abnormal development of various parts of pharyngeal arch They are probably due to insufficient migration of arch I neural crest cells and are associated with anomalies of the mandibular swelling and ear. Two rare symptom complexes are described

Treacher Collins syndrome (mandibulofacial dysostosis): due to a dominant gen One sees abnormal external ears, anomalies of the middle and inner ears, hypoplasia of the malar bone and mandible, defects of the lower eyelid, and downslanting of the palpebral fissures
Pierre Robin syndrome: hypoplasia of the mandible, cleft palate, and defects of the eye and ear

DIGEORGE'S SYNDROME: congenital thymic aplasia and absence of the parathyroid glands. Characterized by congenital hypoparathyroidism, susceptibility to infection, mouth malformations, low-set notched external ears, nasal clefts, thyroid hypoplasia, and cardiac anomalies

Due to a failure of the third and fourth pharyngeal pouches to differentiate into a thymus and parathyroid glands. Some abnormal development of arch I components also are seen

CERVICAL THYMUS AND ACCESSORY THYMUS: very rare; cords of thymus are seen in the course of its descent from the third pharyngeal pouches

Doubling of the cephalic extremity at the time of gastrulation (15-20 days) leads to

Major type (cyclopy): incompatible with life
Median type (archiencephaly): agenesis of the corpus callosum
Minor type (agenesis of the nasal septum): a median nasal fissure with a median cleft lip