Clinical Correlations

A. First arch syndromes are caused by a lack of migration of neural crest cells into pharyngeal arch 1. They produce various facial anomalies, iwo well-described first arch syndromes are Treacher Collins syndrome (Figure 11-5 A) and Pierre Robin syndrome.

B. DiGeorge syndrome occurs when pharyngeal pouches 3 and 4 fail to differentiate,

Palatine shelf

Intermaxillary segment

Maxillary prominence

Intermaxillary Segment

Intermaxillary segment

Maxillary prominence

Palatine shelf

Neck Cyst Fistula

Palatine raphe

Incisive foramen /

f Philtrum of lip < Four incisor teeth Primary palate

Anomolies The Neural Arch

leading to the absence of the thymus and parathyroid glands. This syndrome is usually accompanied by facial anomalies that resemble first arch syndrome and cardiovascular anomalies that are caused by abnormal neural crest cell migration during the formation of the aorticopulmonary septum.

C. Pharyngeal fistula (Figure 11-5 B) occurs when pharyngeal pouch 2 and pharyngeal groove 2 persist, forming a patent opening from the internal tonsillar area to the external neck. A pharyngeal fistula is generally found along the anterior border of the sternocleidomastoid muscle.

D. Pharyngeal cyst (Figure 11-5 C). A pharyngeal cyst occurs when parts of the pharyngeal grooves that are normally obliterated persist, forming a cyst. This type of cyst is generally found near the angle of the mandible.

E. Ectopic thymus, parathyroid, and thyroid tissue (Figure 11-5 D, E) result from the abnormal migration of the glands from their embryonic position to their definitive adult location. Ectopic thymus and parathyroid tissue can be found in the lateral area of the neck, whereas ectopic thyroid tissue can be found along the midline.

F. Thyroglossal duct cyst. This type of cyst occurs when parts of the thyroglossal duct persist and form a cyst. A thyroglossal duct cyst is most commonly located in the midline near the hyoid bone but may also be located at the base of the tongue (it is then called a lingual cyst).

G. Congenital hypothyroidism (cretinism; Figure 11-5 F) occurs when a thyroid deficiency exists during the early fetal period due to either a severe lack of dietary iodine, thyroid agenesis, or mutations involving the biosynthesis of thyroid hormone.

1. This condition causes impaired skeletal growth and mental retardation.

2. This condition is characterized by dry, rough skin, wide-set eyes, periorbital puffi-ness, a flat broad nose, and a large protuberant tongue.

H. Ankyloglossia (tongue-tie) occurs when the frenulum of the tongue extends to the tip of the tongue, thus preventing protrusion.

I. Cleft palate (Figure 11-5 Q) has many causes. It is classified as anterior or posterior. (Note that the anatomic landmark that separates anterior cleft palate defects from posterior cleft palate detects is the incisive foramen.)

Figure 11-5. (A) Treacher Collins syndrome is characterized by underdevelopment of the zygomatic bones, mandibular hypoplasia (double arrows), lower eyelid colobomas, and malformed external ears (arrow). (13) Pharyngeal fistula. A radiograph after injection of a contrast medium demonstrating the course of the fistula through the neck (arrow). The fistula may begin inside the throat near the tonsils, travel through the neck, and open to the outside near the anterior border of the sternocleidomastoid muscle. (C) Pharyngeal cyst. A fluid-filled cyst (dotted circle) near the angle of the mandible (arrow). (D, E) Ectopic thyroid tissue. A sublingual thyroid mass (dotted circle) is seen in a 5-year-old euthyroid girl. A "mTc pertechnetate scan localizes the position and extent of the sublingual thyroid gland. There is no evidence of functioning thyroid tissue in the lower neck (i.e., normal anatomic position). (F) Congenital hypothyroidim (cretinism). This child shows impaired skeletal growth and mental retardation. Note the dry, rough skin (myxedema) and the protuberant tongue. (G) Unilateral cleft lip and cleft palate. (A, From Smith DW: Recognizable Patterns of Human Malformation: Genetic Embryologic and Clinical Aspects, 3rd ed. Philadelphia, WB Saunders, 1982, p 185. B and G, From Moore KL and Persaud TVN: The Developing Human: Clinically Oriented Embryology, 6th ed. Philadelphia, WB Saunders, 1998, pp 228, 248. C, From Sadler TW: Langman's Mcdical Embryology, 7th cd. Baltimore, Williams Wilkins, 1995, p 325. Courtesy of Dr. A. Shaw, Department of Surgery, University of Virginia. D and E, From Leung AKC, Wong AL, and Robson WLLM: Ectopic thyroid gland simulating a ihyroglossal duct cyst. Can J Surg 38:87, 1995. F, From Warkany J: Congenital Malformations: Notes and Comments. Chicago, Year Book Medical Publishers, 1971, Fig 44.4.)

1. Anterior cleft palate occurs when the palatine shelves fail to fuse with the primary palate.

2. Posterior cleft palate occurs when the palatine shelves fail to fuse with each other and with the nasal septum.

3. Anteroposterior cleft palate occurs when there is a combination of both defects. J. Cleft lip (Figure 11-5 Q)

1. Cleft lip occurs when:

a. The maxillary prominence fails to fuse with the medial nasal prominence b. The underlying somitomeric mesoderm and neural crest fail to expand, resulting in a persistent labial groove

2. Cleft lip may occur unilaterally or bilaterally. Unilateral cleft lip is the most common congenital malformation of the head and neck.

3. Cleft lip and cleft palate are distinct malformations based on their embryologie formation, even though "hey often occur together.

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