Branchial arches
§ Branchial apparatus appears around 4th wk of gestation
§ The structures of head are derived from 5 pairs of branchial arches, their intervening clefts externally, & pouches internally
§ At first there are 6 arches
§ 5th arch disappears & only 5 are left ---------- no structure develops from 5th arch
§ Ventral ends of arches of both sides meet in midline
§ Endoderm lining inside forms---------- pouches
§ Surface ectoderm forms --------- clefts
§ Each branchial/pharyngeal arch contains------ skeletal muscle(cartilage that forms bone),striated muscle,nerve of arch,arterial arch
Derivatives of skeletal elements of arches
| Cartilage of 1st arch ( Meckel’s cartilage ) | § maxilla , § incus, § malleus, § anterior ligament of malleus (from sheath/perichondrium) |
| Cartilage of 2nd arch (Reichert’s cartilage) | § stapes, § styloid process, § stylohyoid ligament (from sheath/perichondrium), § smaller/lesser cornu of hyoid bone, § superior part of body of hyoid bone |
| Cartilage of 3rd arch | § greater cornu of hyoid bone, § lower part of body of hyoid bone |
| Cartilage of 4th arch | § thyroid cartilage, § epiglottic cartilage |
| Cartilage of 6th arch | § Cricoids, § arytenoids, § Corniculate |
Nerves & muscles of pharyngeal arches
| Arch | nerve | Muscles |
| 1 | mandibular | Muscles of mastication § Medial pterygoid § Lateral pterygoid § Masseter § Temporalis Mylohyoid Ant. Belly of Digastric Tensor tympani Tensor palate |
| 2 | Facial | Muscles of facial expression Occipito-frontalis Platysma Stylohyoid Post. Belly of digastrics Stapedius Auricular muscles |
| 3 | glossopharyngeal | Stylopharyngeus |
| 4 | Cricothyroid | |
| 6 |
Fate of clefts
§ 1st ectodermal cleft------------ external acoustic meatus
Fate of pouches
§ 1st endodermal pouch(& a part of 2nd ) ----------- tubotympanic recess---------- middle ear , auditory tube
§ 2nd pouch---------- palatine tonsil
§ 3rd pouch------- inferior parathyroid gland(so called parathyroid III), thymus
§ 4th pouch ----------- superior parathyroid gland(so called parathyroid IV), some contribution to thyroid
Arteries of arches
| Pharyngeal arch | |
| 3rd | |
| 4th | |
| 6th |
Foramen caecum at floor of pharynx gives rise to --------- Median diverticulum-------- Thyroglossal duct---------- thyroid gland
Branchial anomolies
| 1st arch branchial remnants | § located in front or back of ear or in upper neck in the region of mandible § Fistulas typically commence through the parotid gland & end in external auditory canal |
| 2nd branchial remnants are m.c. | § fistulas/sinuses with external opening along anterior border of sternocleidomastoid & internal opening at tonsillar fossa § Fistulous track passes b/w internal & external carotid arteries |
| 3rd branchial cleft remnants— | § No associated sinuses/fistula § Located in in suprasternal notch/ clavicular region § Most often contain cartilage & present as firm mass or subcutaneous abscess § Rarely sinus may occur which open internally into pyriform sinus |
§ Branciogenic anomalies occur with equal frequency on each side of neck & 15% are bilateral
§ Fistulas & sinuses appear at birth
§ Cysts appear in late childhood & adults
§ Cysts are characteristically found anterior & deep to the upper 3rd of sternocleidomastoid (inferior to the angle of mandible)
§ Sinuses & cysts are prone to become repeatedly infected producing cellulitis & abscess formation
§ Children ---------- fistulas>sinuses>cysts
§ Cysts are more common in adults BUT they may occur at any age
§ Adults ------ cysts > sinuses
§ t/t
o All branchial abnormalities should be excised early in life
o Complete surgical removal necessary
o A series 2-3 small transverse incisions in stepladder fashion
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