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CONGENITAL ANOMALIES OF THE HEAD AND NECK
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The critical period of cervicofacial growth and differentiation occurs between weeks 4 through 8 of embryologic development. The beginning of this stage is characterized by the appearance of the frontonasal process—the precursor of the forebrain and upper face—with development soon thereafter of the optic and otic vesicles; the nasal placodes; the primitive mouth, or stomodeum; and 5 ridges on the ventrolateral surface of the embryonic head, which is known as the branchial system. Many of the symmetrically paired skeletal and neuromuscular structures of the head and neck arise from the first (mandibular), second (hyoid), third (pharyngeal), and fourth (laryngeal) arches of this fetal branchial system (Table 367-1). The skull, facial, and neck bones have begun to ossify by the end of the eighth fetal week, which coincides with a recognizable human embryonic face with easily discernible ears, eyelids, cheeks, nose, and upper and lower lips.
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Most of the congenital anomalies of the face and neck are thought to arise from altered or arrested growth during this critical developmental stage. Such anomalies may manifest initially at birth as an asymptomatic palpable mass or a sinus or fistula opening; they alternatively may remain unnoticed until secondary infection causes acute presentation later in childhood. The anatomic location of such lesions often suggests their embryologic origin (Table 367-2).
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