Embryology Flashcards
Preauricular sinus
improper fusion of 1st and 2nd branchial arches
Hillocks of Hiss
1-3 from first branchial arch, 4-6 from second branchial arch
Hillocks of Hiss - 1-3
1 - tragus, 2 - crus of helix, 3 - helix
Hillocks of Hiss - 4-6
4 - antihelix, 5 - antitragus, 6 - lobule
Jacobsons nerve
glossopharyngeal branch to ear
Arnold’s nerve
vagus branch to ear
Location of 1st Branchial Cleft Cyst Type I?
Work Classification
Type I
- Preauricular mass or sinus
- Duplication of EAC
- Ectoderm
- Sinus tract is anterior and medial to the EAC
- Preauricular region - Lateral to CN VII - Parallels EAC - Ends in EAC or middle ear
Location of 1st Branchial Cleft Cyst Type II?
Work Classification
Type II
- More common than Type I
- Presents at the angle of mandible or submandibular region
- Angle of mandible - Lateral or medial to CN VII - Ends in concha or bony-cartilaginous junction of EAC.
Location of 2nd Branchial Cleft Cyst?
95% of all branchial cleft anomalies arise from second cleft
- They are found along the anterior border of the SCM
- Pass through the carotid bifurcation
- Superficial to CN IX and XII
- Into the tonsillar fossa.
Location of 3rd Branchial Cleft Cyst?
Closely associated with thyroid gland
Usually on the left
- Lateral neck (similar or lower location than 2nd)
- Deep to carotids
- Deep CN IX, superficial to CN XII
- Superficial to superior laryngeal nerve
- Piercesthyrohyoid membrane
- Opens into apex of pyriform sinus
Location of 4th Branchial Cleft Cyst?
VERY rare
- Low in neck (anterior to SCM)
- Deep to common carotid
- Loops around aortic arch on the left
- (subclavian on the right)
- Deep to superior laryngeal nerve
- Superficial to recurrent laryngeal nerve
- Opens into pyriform sinus
1st branchial arch
Mandibular Arch
Skeletal components:
Meckel’s cartilage
Framework for mandible
Malleus head and neck
Incus body and short process
Muscles:
Muscles of mastication
Anterior digastric
Mylohyoid
Tensor tympani
Tensor veli palatini
**Nerve**: CN V (Trigeminal)
Artery:
Maxillary; external carotid
2nd branchial arch
Hyoid Arch
Skeletal components:
Reichert’s cartilage
Stapes
Malleus manubrium
Incus long process
Styloid process
Hyoid bone (lesser horn and upper body)
Muscles:
Facial expression, buccinator, platysma, stapedius, stylohyoid,
posterior digastric
**Nerve**: CN VII (Facial)
Artery:
Stapedial
3rd branchial arch
Skeletal components:
Hyoid (greater horn and lower body)
Muscles:
Stylopharyngeus
**Nerve**: CN IX (Glossopharyngeal)
Artery:
Common/Internal carotid
4th branchial arch
Skeletal components:
Thyroid, epiglottic, cuneiform cartilages
Muscles:
Cricothyroid, inferior constrictors
Nerve:
Superior laryngeal
Artery:
Subclavian, aortic arch
6th branchial arch
Skeletal components:
Cricoid, arytenoids, corniculate
Muscles:
All intrinsic muscles of larynx (except
cricothyroid)
Nerve:
Recurrent laryngeal
Artery:
Pulmonary artery
1st pharyngeal pouch
Eustachian tube, middle ear, mastoid, inner layer
of tympanic membrane
2nd pharyngeal pouch
Tonsils, root of tongue, foramen cecum,
pharynx(part)
3rd pharyngeal pouch
ventral and dorsal wings
Ventral wing
Thymus
Dorsal wing
inferior parathyroid glands
4th pharyngeal pouch
Superior parathyroid glands
Parafollicular C-cells of thyroid gland
5th pharyngeal pouch
Contributes to Parafollicular C-cells
6th pharyngeal pouch
Contributes to laryngeal musculature and
cartilage
Thyroglossal duct cyst
7% of population
Failure of ablation of TGD
Anywhere from base of tongue to upper
mediastinum
Typical finding is cystic lesion just below hyoid in midline that moves with deglutination and tongue protrusion
May contain thyroid tissue
Potentially the only functioning thyroid
Perform U/S or CT to look for thyroid and to
assess lesion
1st branchial arch derivatives?
