Birth Defects Involving the Pharyngeal Region PDF

Birth Defects Involving the Pharyngeal Region Fevziye Figen Kaymaz M.D., Ph.D. Prof. of Histology & Embryology [email protected] 1 OBJECTIVES The student should be able to: 1. Explain the developmental disorders of pharyngeal apparatus 2 Ectopic Thymic and Parathyroid Tissue • Because gl...

Birth Defects Involving the Pharyngeal Region Fevziye Figen Kaymaz M.D., Ph.D. Prof. of Histology & Embryology [email protected] 1 OBJECTIVES The student should be able to: 1. Explain the developmental disorders of pharyngeal apparatus 2 Ectopic Thymic and Parathyroid Tissue • Because glandular tissue derived from the pouches undergoes migration, it is not unusual for accessory glands or remnants of tissue to persist along the pathway. This is true particularly for thymic tissue, which may remain in the neck, and for the parathyroid glands. The inferior parathyroids are more variable in position than the superior ones and are sometimes found at the bifurcation of the common carotid artery. 3 Ectopic Thyroid Gland The head and neck, showing the usual sites of ectopic thyroid tissue. The broken line indicates the path followed by the thyroid gland during its descent, as well as the former tract of the thyroglossal duct. • Ectopic Parathyroid Glands found anywhere near or within the thyroid gland or thymus. The superior glands are more constant in position than the inferior ones. Occasionally, an inferior parathyroid gland remains near the bifurcation of the common carotid artery. In other cases, it may be in the thorax. • Accessory Thymıc Tıssue An isolated mass of thymic tissue may persist in the neck and often lies close to an inferior parathyroid gland • Abnormal Number Of Parathyroid Glands PIRIFORM SINUS FISTULA • The piriform sinus fistula is thought to result from persistence of remnants of the ultimopharyngeal body along its path to the thyroid gland 6 Branchial (servical) FistuIas • Branchial fistulas occur when the second pharyngeal arch fails to grow caudally over the third and fourth arches leaving remnants of the second, third, and fourth clefts in contact with the surface by a narrow canal • Such a fistula, found on the lateral aspect of the neck directly anterior to the sternocleidomastoid muscle, usually provides drainage for a lateral cervical cyst • These cysts, remnants of the cervical sinus, are most often just below the angle of the jaw, although they may be found anywhere along the anterior border of the sternocleidomastoid muscle. Frequently, a lateral cervical cyst is not visible at birth but becomes evident as it enlarges during childhood. • Internal branchial fistulas are rare; they occur when the cervical sinus is connected to the lumen of the pharynx by a small canal which usually opens in the tonsillar region. Such a fistula results from a rupture of the membrane between the second pharyngeal cleft and pouch at some time during development. 8 • External cervical sinuses are uncommon, and most result from failure of the second groove and cervical sinus to obliterate • The sinus typically opens along the anterior border of the sternocleidomastoid muscle in the inferior third of the neck. Anomalies of the other pharyngeal grooves occur in approximately 5% of neonates. External sinuses are commonly detected during infancy because of the discharge of mucus from them • The external cervical sinuses are bilateral in approximately 10% of affected neonates and are commonly associated with auricular sinuses. Thyroglossal Duct Cysts and Sinuses A typical thyroglossal duct cyst in a girl. The round, firm mass (indicated by the sketch) produced a swelling in the median plane of the neck, just inferior to the hyoid bone. • A thyroglossal cyst may lie at any point along the migratory pathway ofthe thyroid gland but is always near or in the midline of the neck • Cysts may form anywhere along the course of the thyroglossal duct. • The duct typically atrophies and disappears, but a remnant of it may persist and form a cyst in the tongue or in the anterior part of the neck, usually just inferior to the hyoid bone. • As indicated by its name, it is a cystic remnant of the thyroglossal remnant of the thyroglossal duct. Although approximately 50% of these cysts are close to or just inferior to the body of the hyoid bone • they may also be found at the base of the tongue or close to the thyroid cartilage. Sometimes, a thyroglossal cyst is connected to the outside by a fistulous canal, a thyroglossal fistula. Such a fistula usually arises secondarily after rupture of a cyst but may be present at birth. Thyroglossal Duct Cysts and Sinuses A typical thyroglossal duct cyst in a girl. The round, firm mass (indicated by the sketch) produced a swelling in the median plane of the neck, just inferior to the hyoid bone. • Most cysts are observed by the age of 5 years. Unless the lesions become infected, most of them are asymptomatic. The swelling produced by a thyroglossal duct cyst usually develops as a painless, progressively enlarging, movable mass • The cyst may contain some thyroid tissue. If infection of a cyst occurs, a perforation of the skin may develop, forming a thyroglossal duct sinus that usually opens in the median plane of the neck anterior to the laryngeal cartilages. • when they produce a slowly enlarging, painless swelling in the neck A boy with swelling in the neck produced by a (cervical) branchial cyst. Branchial cysts often lie free in the neck, just inferior to the angle of the mandible, or they may be found anywhere along the anterior border of the sternocleidomastoid muscle. Neural Crest Cells and Craniofacial Defects • Neural crest cells are essential for formation of much of the craniofacial region. Consequently, disruption of crest cell development results in craniofacial malformations. First Pharyngeal Arch Syndrome • result from insufficient migration of neural crest cells into the first arch during the fourth week. • various birth defects of the eyes, ears, mandible, and palate, which together constitute the first arch syndrome Treacher Collins Sendromu Pierre Robin sendromu 1st arch syndrome: deficiency of neural crest cell migration Treacher Collins Syndrome (mandibulofacial dysostosis) • an autosomal dominant disorder occurring in 1/50,000 live births with 60% of cases arising as new mutations • hypoplasia of the maxilla, mandible, and zygomatic arches, which may be absent. • Cleft palate is common as are external ear defects accom— panied by atresia of the auditory canals and abnormalities of the middle ear ossicles, such that bilateral conductive hearing loss is often present. • The eyes are usually involved with down-slanting palpebral fissures and lower eyelid colobomas. Mutations in the TCOF1 gene [5q32] are responsible for most cases. • The product of this gene is a nucleolar protein called treacle that appears to be necessary for preventing apoptosis and maintaining prolif— eration in neural crest cells but not for regulating their migration, which occurs normally Pierre Robin Syndrome • • • • • Like Treacher Collins syndrome, Robin sequence alters first-arch structures, with development of the mandible most severely affected. associated with hypoplasia (underdevelopment) of the mandible, cleft palate, and defects of the eyes and ears. Infants usually have a triad of micrognathia, cleft palate, and glossoptosis [posteriorly placed tongue) it is inherited in an autosomal dominant pattern. It may be due to environmental factors. occurs in approximately1/8,500 births. the initiating defect is a small mandible (micrognathia), which results in posterior displacement of the tongue and obstruction to full closure of the palatal processes, resulting in a bilateral cleft palate Digeorge Syndrome • • • • • • • • • • born without a thymus and parathyroid glands and have defects in the cardiac outflow tracts. In some cases, ectopic glandular tissue has been found characterized by congenital hypoparathyroidism, increased susceptibility to infections (from immune deficiency, specifically defective T-cell function), birth defects of the mouth (shortened philtrum of upper lip), low-set and notched ears, nasal clefts, thyroid hypoplasia, and cardiac abnormalities (defects of the aortic arch and heart). 3th & 4th branchial pouches failes to developes to the thymus and parathyroid. This is the result of a breakdown in signaling between pharyngeal endoderm and adjacent neural crest cells. Hypoparathyroidism Immune Deficiency Mouth abnormalities Abnormality of auricle Nasal Clefts Thyroid hypoplasia Cardiac abnormalities References 1. Sadler TW, Langman's Medical Embryology 13E 2. Moore KL, Persaud TVN, Torchia MG Developing Human 9e 3. Carlson BM Human Embryology & Developmental Biology, 5E 21