What are the branchial arches and their derivatives?

Branchial Arches and Their Derivatives

The branchial arches (pharyngeal arches) are embryological structures that form the foundation of face and neck development, giving rise to critical anatomical structures through a complex process of differentiation and migration. 1

Embryological Development of Branchial Arches

• Branchial arches develop during the 4th-5th week of embryonic life as paired structures on either side of the developing pharynx
• Six pairs of arches form (numbered 1-6, with the 5th arch being rudimentary or absent in humans)
• Each arch consists of:
  • External covering of ectoderm
  • Internal lining of endoderm
  • Mesenchymal core containing:
    • Cartilaginous element
    • Muscular component
    • Arterial supply
    • Neural component

Branchial Arch Components and Derivatives

First Branchial Arch (Mandibular Arch)

• Cartilage: Meckel's cartilage
• Skeletal derivatives:
  • Malleus and incus of middle ear
  • Mandible (via intramembranous ossification)
  • Sphenomandibular ligament
  • Anterior ligament of malleus
• Muscles:
  • Muscles of mastication (temporalis, masseter, medial and lateral pterygoids)
  • Mylohyoid, anterior belly of digastric
  • Tensor tympani, tensor veli palatini
• Nerve: Mandibular branch of trigeminal nerve (CN V3)
• Artery: First aortic arch (mostly disappears, contributes to maxillary artery)

Second Branchial Arch (Hyoid Arch)

• Cartilage: Reichert's cartilage
• Skeletal derivatives:
  • Stapes of middle ear
  • Styloid process of temporal bone
  • Stylohyoid ligament
  • Lesser horn and upper portion of hyoid bone
• Muscles:
  • Muscles of facial expression
  • Stapedius
  • Stylohyoid
  • Posterior belly of digastric
• Nerve: Facial nerve (CN VII)
• Artery: Second aortic arch (contributes to stapedial and hyoid arteries)

Third Branchial Arch

• Skeletal derivatives: Greater horn and lower portion of hyoid bone
• Muscles: Stylopharyngeus
• Nerve: Glossopharyngeal nerve (CN IX)
• Artery: Third aortic arch (forms common carotid and proximal part of internal carotid arteries)

Fourth and Sixth Branchial Arches

• Skeletal derivatives: Laryngeal cartilages (thyroid, cricoid, arytenoid, corniculate, cuneiform)
• Muscles:
  • Pharyngeal constrictors (4th arch)
  • Intrinsic laryngeal muscles (6th arch)
  • Cricothyroid (4th arch)
• Nerves:
  • Superior laryngeal branch of vagus (CN X) for 4th arch
  • Recurrent laryngeal branch of vagus (CN X) for 6th arch
• Arteries:
  • Fourth aortic arch (forms arch of aorta on left, proximal right subclavian artery on right)
  • Sixth aortic arch (forms pulmonary arteries and ductus arteriosus)

Branchial Clefts and Pouches

Branchial Clefts (Ectodermal)

• First cleft: External auditory meatus
• Other clefts: Obliterated during normal development

Branchial Pouches (Endodermal)

• First pouch: Middle ear cavity, mastoid air cells, Eustachian tube
• Second pouch: Palatine tonsil and tonsillar fossa
• Third pouch: Inferior parathyroid glands, thymus
• Fourth pouch: Superior parathyroid glands, ultimobranchial body (parafollicular C cells of thyroid)

Clinical Significance

Branchial Arch Anomalies

• Second most common congenital lesions of head and neck in children 2
• Present as cysts, sinuses, or fistulae
• Second branchial arch anomalies account for approximately 95% of cases 2
• Diagnosis depends on high index of suspicion and knowledge of typical locations

Branchial Arch Syndromes

• First and second branchial arch syndromes represent the second most common craniofacial malformation after cleft lip and palate 3
• Include:
  • Hemifacial microsomia
  • Mandibulofacial dysostosis (Treacher Collins syndrome)
  • Branchio-oto-renal syndrome
  • Pierre Robin sequence
  • Nager acrofacial dysostosis

Imaging Considerations

• Multimodality imaging approach is essential for diagnosis and grading of branchial arch syndromes 3
• Imaging modalities include:
  • Orthopantomogram (OPG)
  • Lateral and posteroanterior cephalometric radiographs
  • CT and MRI

External Carotid Artery Development and Branches

The external carotid artery develops from the third aortic arch and has eight major branches that supply structures derived from the branchial arches 4:

• Anterior branches: Superior thyroid, lingual, facial
• Medial branch: Ascending pharyngeal
• Posterior branches: Occipital, posterior auricular
• Terminal branches: Maxillary, superficial temporal

These branches form important collateral pathways to the brain through connections with the internal carotid and vertebral arteries 4.

Embryological Significance of Branchial Derivatives

Understanding branchial arch development is crucial for:

• Interpreting congenital anomalies of the head and neck
• Surgical planning for craniofacial reconstruction
• Understanding the anatomical basis of cranial nerve distribution
• Recognizing patterns in branchial arch syndromes

The complex embryological development of branchial arches explains the intricate relationships between structures in the adult head and neck, particularly the pathways of cranial nerves and the distribution of muscles and skeletal elements 5.