L27 Developmental Disorders of the Head & Neck PDF

IBSSD 1525 Samuel Gutherz, Ph.D. 2024 [email protected] L27: Developmental Disorders of the Head & Neck Background reading: Langman’s Medical Embryology, 15th edition, Chapter 10: The...

IBSSD 1525 Samuel Gutherz, Ph.D. 2024 [email protected] L27: Developmental Disorders of the Head & Neck Background reading: Langman’s Medical Embryology, 15th edition, Chapter 10: The Axial Skeleton (just read Skull), Chapter 17: Head & Neck Definitions - Disease – an affliction in which the initiate of the disease process (etiology) and the process that maintains the disruption (pathogenesis) are understood - Syndrome – an affliction in which the etiology is understood but the pathogenesis is unknown - Sequence – an affliction in which the etiology is unknown, but the pathogenesis is understood Treacher Collins Syndrome - Treacher Collins Syndrome (TCS) is a rare genetic disorder in which derivatives of the 1st & 2nd pharyngeal arches fail to develop completely, resulting in cosmetic facial deformities. o It is an autosomal dominant disorder in which there is a loss of function of the TCOF1 gene on chromosome 5 o This mutation results in hypoplasia (underdevelopment) of the maxilla, mandible, zygomatic arches, and palate - It is generally bilateral, although the cosmetic changes are often asymmetrical - Common presentations o Downward slanting of the palpebral fissures o Increased distance between the eyes o Palatal clefts o Defective development of the ear ossicles, resulting in conductive hearing loss o Impaired vision o Retrusion of 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 - This mutation disrupts neural crest cell function and can affect the development of multiple pharyngeal arches - The presentation of this series of disorders is highly variable but symptoms may include: o Heart and aortic arch defects o Underdeveloped or absent thymus  This results in immunodeficiency 1 Text © Samuel Gutherz 2024 IBSSD 1525 Samuel Gutherz, Ph.D. 2024 [email protected] o Mild cosmetic facial deformities o Learning difficulties o Increased risk of mental illness Ankyloglossia - During typical development, the frenulum (the part of the tongue that attaches it to the floor of the mouth) is partially obliterated. However, sometimes it remains fully intact, attaching to the tip of the tongue, restricting lingual movement - This intact frenulum may stretch with use, restoring normal function. Function may be restored with therapy, or in extreme cases, by surgical removal of part of the frenulum Thyroglossal Cyst - A thyroglossal cyst may form anywhere along the path of the descent of the thyroid gland, the result of a remnant of the thyroglossal duct o Most commonly found at or just below the body of the hyoid - Thyroglossal cysts are always in the midline - These cysts can connect to the external environment and become a thyroglossal fistula Facial Clefts - There are a variety of defects that can occur due to failure of midline palatal structures o These typically result in cosmetic abnormalities, speech and feeding difficulties, ear infections or hearing loss, dental malocclusion - The causes are varied but include: o Genetic factors, exposure to teratogenic compounds (e.g., medications, cigarette smoking/alcohol use during fetal development), nutritional deficits - The incisive foramen demarcates anterior and posterior cleft disorders o Anterior and posterior cleft disorders may occur in any combination - Anterior cleft disorders o Lateral cleft lip – can be unilateral or bilateral o Cleft upper jaw o Cleft between primary and secondary palates - Posterior cleft disorders o Cleft secondary palate – can be unilateral or bilateral o Cleft uvula – typically the least complicated but can still affect speech Branchial cleft cyst - Branchial cleft cysts typically occur when the 2nd pharyngeal arch fails to develop caudally to cover the 3rd & 4th pharyngeal arches. This leaves pharyngeal clefts 2, 3, and/or 4 intact, which can later form cysts, sinuses, or fistulas. 2 Text © Samuel Gutherz 2024 IBSSD 1525 Samuel Gutherz, Ph.D. 2024 [email protected] o Pharyngeal cleft 2 most often remains intact for cyst formation, with remnants of clefts 1, 3, and 4 being relatively rare. - These cysts or fistulas are located just anterior to the sternocleidomastoid, most commonly directly beneath the angle of the mandible o Typically become visible during adolescence - If a fistula forms, they are most commonly connected to the external surface, although in rare cases they can connect to the pharynx. Pierre Robin Sequence - This disorder can occur in association with other syndromes or independently due to mutations on chromosomes 2, 3, 11, or 17 - The cause of Pierre Robin sequence is unknown, but the disruption begins with underdevelopment of the mandible, followed by posterior placement of the tongue (glossoptosis) and then the development of either/both cleft palate and airway disruption Hemifacial microsomia - 2nd most common craniofacial developmental disorder after facial clefts - Results from the underdevelopment or malformation of the 1st & 2nd pharyngeal arches o Typically affects the maxilla, temporal, and zygomatic bones, as well as underdevelopment of the external ear o Commonly asymmetrical - Cause is unknown Supernumerary teeth - Hyperdontia is the presence of excessive teeth - Hyperdontia is more common in permanent teeth than deciduous teeth - More common in the maxilla than the mandible o Most common around the maxillary incisors, followed by the teeth distal to the maxillary 3rd molar, or the premolar region of either jaw - Causes are uncertain o There appears to be a genetic component o Persistent dental placodes o Hyperactivity of dental lamina - Hyperdontia may delay eruption of adjacent teeth, malocclusion, cause 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 a series of skin and nerve syndromes called ectodermal dysplasias - Has a variety of causes 3 Text © Samuel Gutherz 2024 IBSSD 1525 Samuel Gutherz, Ph.D. 2024 [email protected] o Congenital o Endocrine dysfunction o Excessive radiation exposure 4 Text © Samuel Gutherz 2024