A newborn is taken to the neonatal intensive care unit after delivery due to respiratory distress. The neonate was born full-term, and there were no significant complications during pregnancy or delivery. Once the patient is stabilized, a detailed physical examination is performed. The neonate has an underdeveloped mandible and hypoplastic zygomatic bones. Genetic testing confirms a gene mutation that results in abnormal development of the first and second pharyngeal arches. Which of the following structures is also likely abnormal in this patient?

Question

A newborn is taken to the neonatal intensive care unit after delivery due to respiratory distress.  The neonate was born full-term, and there were no significant complications during pregnancy or delivery.  Once the patient is stabilized, a detailed physical examination is performed.  The neonate has an underdeveloped mandible and hypoplastic zygomatic bones.  Genetic testing confirms a gene mutation that results in abnormal development of the first and second pharyngeal arches.  Which of the following structures is also likely abnormal in this patient?

Quizplus · Accepted Answer

11ec160b_374c_4836_9249_0f92d2b6e222_MD0001_00 The developing embryo has 6 pharyngeal or branchial arches, all but the fifth arch contribute to adult structures. The mesoderm forms muscular and vascular elements, and neural crest cells form the bony and cartilaginous structures. Each arch is also innervated by a specific cranial nerve (CN). The first pharyngeal arch is associated with the trigeminal nerve (CN V). Its bony derivatives include the maxilla, zygoma, mandible, incus, and malleus; its muscular derivatives include the muscles of mastication (eg, masseter, temporalis). The second pharyngeal arch is associated with the facial nerve (CN VII) and gives rise to the styloid process of the temporal bone, lesser horn of the hyoid, and stapes. Muscular derivatives of the second arch include the muscles of facial expression. This neonate's presentation is consistent with Treacher-Collins syndrome (TCS), a genetic disorder resulting in the abnormal development of the first and second pharyngeal arches. The craniofacial abnormalities (eg, mandibular, maxillary, and zygomatic bone hypoplasia) often result in airway compromise and feeding difficulties. In addition, absent or abnormal ossicles (eg, incus, malleus, stapes) lead to profound conductive hearing loss. (Choices A and E) The fourth and sixth arches make up the cartilaginous structures of the larynx, including the cricoid and thyroid cartilages. (Choice B) The glossopharyngeal nerve (CN IX) is derived from the third pharyngeal arch. Dysfunction may lead to impaired taste perception and an absent gag reflex. (Choice C) The hyoid bone at the base of the mandible is derived from 2 pharyngeal arches. The lesser horn of the hyoid is derived from the second arch, and the greater horn of the hyoid is derived from the third arch. (Choice F) The vagus nerve (CN X) is derived from the fourth and sixth arches. Dysfunction results in laryngeal and pharyngeal paralysis and autonomic dysfunction (eg, esophageal motility, gastric acid secretion, heart rate variability). Educational objective: The development of derivatives of the first (eg, trigeminal nerve, mandible, maxilla, zygoma, incus, malleus) and second (eg, facial nerve, stapes, styloid process, lesser horn of hyoid) pharyngeal arches can be disrupted in genetic disorders (eg, Treacher-Collins syndrome), resulting in hypoplasia of the mandibular and zygomatic bones. __________ References: First and second brachial arch syndromes: multimodality approach (http://www.ncbi.nlm.nih.gov/pubmed/20924574) Syndromes of the first and second branchial arches, part 2: syndromes. (http://www.ncbi.nlm.nih.gov/pubmed/20360348)

A Newborn Is Taken to the Neonatal Intensive Care Unit