Developmental Disorders of the Head & Neck

Developmental Disorders of the Head & Neck

• Disease: The etiology and pathogenesis of the disease are understood.
• Syndrome: The etiology is understood, but the pathogenesis is unknown.
• Sequence: The etiology is unknown, but the pathogenesis is understood.

Treacher Collins Syndrome

• A rare genetic disorder.
• Results from incomplete development of the 1st and 2nd pharyngeal arches.
• This leads to facial deformities.
• Autosomal dominant disorder with a mutation in the TCOF1 gene on chromosome 5.
• Characterized by hypoplasia (underdevelopment) of the maxilla, mandible, zygomatic arches, and palate.
• Usually bilateral, but cosmetic changes can be asymmetrical.
• Common presentations include:
  • Downward slanting palpebral fissures.
  • Increased distance between the eyes.
  • Palatal clefts.
  • Defective ear ossicles, causing conductive hearing loss.
  • Impaired vision.
  • Retrusion of the mandible and/or maxilla.

22q11.2 Deletion Syndromes (e.g., DiGeorge Syndrome)

• A de novo mutation in which a portion on the long arm of chromosome 22 is deleted.
• Affects neural crest cell function and can interfere with development of multiple pharyngeal arches.
• Highly variable presentation but may include:
  • Heart and aortic arch defects.
  • Underdeveloped or absent thymus, leading to immunodeficiency.
  • Mild facial deformities.
  • Learning difficulties.
  • Increased risk of mental illness.

Ankyloglossia

• The frenulum (tongue attachment to the floor of the mouth) remains intact, restricting tongue movement.
• The frenulum may stretch with use, restoring normal function.
• Therapy or surgical removal of the frenulum can restore function.

Thyroglossal Cyst

• Develops along the path of the thyroid gland descent due to a remnant of the thyroglossal duct.
• Most commonly located at or just below the hyoid bone.
• Always in the midline.
• May connect to the external environment, forming a thyroglossal fistula.

Facial Clefts

• Defects resulting from failure of midline palatal structure development.
• Can lead to:
  • Cosmetic abnormalities.
  • Speech and feeding difficulties.
  • Ear infections or hearing loss.
  • Dental malocclusion.
• Causes include:
  • Genetic factors.
  • Exposure to teratogens (e.g., medications, cigarette smoking/alcohol use during fetal development).
  • Nutritional deficiencies.
• The incisive foramen divides anterior and posterior cleft disorders, which may occur in any combination.
• Anterior cleft disorders:
  • Lateral cleft lip (unilateral or bilateral).
  • Cleft upper jaw.
  • Cleft between primary and secondary palates.
• Posterior cleft disorders:
  • Cleft secondary palate (unilateral or bilateral).
  • Cleft uvula (least complicated, but can still affect speech).

Branchial Cleft Cyst

• Occurs when the 2nd pharyngeal arch fails to completely cover the 3rd and 4th arches, leaving pharyngeal clefts 2, 3, and/or 4 intact.
• The most common type involves pharyngeal cleft 2.
• Located just anterior to the sternocleidomastoid, often beneath the angle of the mandible.
• Typically becomes visible during adolescence.
• May form a fistula, usually connecting to the external surface, but rarely may connect to the pharynx.

Pierre Robin Sequence

• Can occur alone or in association with other syndromes due to mutations on chromosomes 2, 3, 11, or 17.
• The etiology is unknown, but the sequence of events is:
  • Underdevelopment of the mandible.
  • Posterior placement of the tongue (glossoptosis).
  • Cleft palate and airway disruption.

Hemifacial Microsomia

• The second most common craniofacial developmental disorder after facial clefts.
• Results from underdevelopment or malformation of the 1st and 2nd pharyngeal arches.
• Typically affects the maxilla, temporal, and zygomatic bones, and causes underdevelopment of the external ear.
• Usually asymmetrical.
• Cause is unknown.

Supernumerary Teeth

• Hyperdontia is the presence of excessive teeth, more common in permanent than deciduous teeth.
• Occurs more frequently in the maxilla than mandible.
• Most common around maxillary incisors, followed by distal to the maxillary 3rd molar, or premolar region of either jaw.
• Causes are uncertain, but may involve:
  • Genetic component.
  • Persistent dental placodes.
  • Hyperactivity of the dental lamina.
• Can delay eruption of adjacent teeth, cause malocclusion, dental crowding, or tooth displacement.

Anodontia

• Can be partial (one to several teeth) or complete.
• Most commonly affects the permanent 3rd molar, maxillary lateral incisor, and mandibular 2nd premolar.
• Often associated with ectodermal dysplasias, a group of skin and nerve syndromes.
• Multiple causes:
  • Congenital.
  • Endocrine dysfunction.
  • Excessive radiation exposure.

Developmental Disorders

• Disease - etiology and pathogenesis are known
• Syndrome - etiology known, pathogenesis unknown
• Sequence - etiology unknown, pathogenesis known

Treacher Collins Syndrome

• Rare genetic disorder
• Derivatives of the first and second pharyngeal arches fail to develop completely
• Autosomal dominant disorder
• Loss of function of the TCOF1 gene on chromosome 5
• Hypoplasia (underdevelopment) of maxilla, mandible, zygomatic arches and palate
• Can present with:
  • Downward slanting of the palpebral fissures
  • Increased distance between the eyes
  • Palatal clefts
  • Defective development of the ear ossicles, resulting in conductive hearing loss
  • Impaired vision
  • Retrusion of mandible and/or maxilla

22q11.2 deletion syndromes (e.g. DiGeorge Syndrome)

• De novo mutation
• Portion of the long arm of chromosome 22 is deleted
• Disrupts neural crest cell function
• Can affect the development of multiple pharyngeal arches
• Symptoms can include:
  • Heart and aortic arch defects
  • Underdeveloped or absent thymus
  • Mild cosmetic facial deformities
  • Learning difficulties
  • Increased risk of mental illness

Ankyloglossia

• Frenulum remains fully intact, attaching to the tip of the tongue
• Restricts lingual movement
• May stretch with use, restoring normal function
• Can be treated with therapy or surgical removal of the frenulum

Thyroglossal Cyst

• Forms anywhere along the path of the thyroid gland's descent
• Remnant of the thyroglossal duct
• Most commonly found at or just below the body of the hyoid
• Always in the midline
• Can connect to the external environment and become a thyroglossal fistula

Facial Clefts

• Variety of defects that can occur due to failure of midline palatal structures
• Can result in:
  • Cosmetic abnormalities
  • Speech and feeding difficulties
  • Ear infections or hearing loss
  • Dental malocclusion
• Causes include:
  • Genetic factors
  • Exposure to teratogenic compounds
  • Nutritional deficits
• Incisive foramen demarcates anterior and posterior cleft disorders
• Anterior cleft disorders:
  • Lateral cleft lip - can be unilateral or bilateral
  • Cleft upper jaw
  • Cleft between primary and secondary palates
• Posterior cleft disorders:
  • Cleft secondary palate - can be unilateral or bilateral
  • Cleft uvula

Branchial Cleft Cyst

• Occurs when the second pharyngeal arch fails to develop caudally to cover the third and fourth pharyngeal arches
• Leaves pharyngeal clefts 2, 3 and/or 4 intact, which can later form cysts, sinuses, or fistulas
• Pharyngeal cleft 2 most often remains intact for cyst formation
• Cysts or fistulas located just anterior to the sternocleidomastoid, commonly beneath the angle of the mandible
• Typically become visible during adolescence
• If a fistula forms, they are most commonly connected to the external surface

Pierre Robin Sequence

• Can occur in association with other syndromes or independently due to mutations on chromosomes 2, 3, 11, or 17
• Cause unknown
• Begins with underdevelopment of the mandible
• Followed by posterior placement of the tongue (glossoptosis)
• Development of either/both cleft palate and airway disruption

Hemifacial Microsomia

• Second most common craniofacial disorder after facial clefts
• Results from underdevelopment or malformation of the first and second pharyngeal arches
• Typically affects the maxilla, temporal, and zygomatic bones, as well as underdevelopment of the external ear
• Commonly asymmetrical
• Cause unknown

Supernumerary Teeth (Hyperdontia)

• Presence of excessive teeth
• More common in permanent teeth than deciduous teeth
• More common in the maxilla than the mandible
• Most common around the maxillary incisors
• Causes are uncertain:
  • Genetic component
  • Persistent dental placodes
  • Hyperactivity of dental lamina
• Can delay eruption of adjacent teeth, malocclusion, cause dental crowding or tooth displacement

Anodontia

• Partial or complete absence of teeth
• Most commonly affects the 3rd molar, maxillary lateral incisor and mandibular 2nd premolar
• Often associated with ectodermal dysplasias
• Causes include:
  • Congenital
  • Endocrine dysfunction
  • Excessive radiation exposure