A 1-week-old boy is brought to the emergency department with poor feeding, lethargy, and unusual "muscle movements" involving the left thumb and hand over the last 2 days. The patient's mother had appropriate prenatal care, a normal pregnancy, and took no medications other than prenatal vitamins. The infant's vital signs are normal, but unusual flexion of the left wrist and thumb and extension of the fingers are observed with cuff blood pressure measurement. Physical examination reveals a hypoplastic mandible, low-set ears, bifid uvula, and cleft palate. A chest x-ray reveals decreased soft-tissue attenuation in the right anterior mediastinum. These findings most likely suggest impaired development of which of the following embryonic structures?

Question

A 1-week-old boy is brought to the emergency department with poor feeding, lethargy, and unusual "muscle movements" involving the left thumb and hand over the last 2 days.  The patient's mother had appropriate prenatal care, a normal pregnancy, and took no medications other than prenatal vitamins.  The infant's vital signs are normal, but unusual flexion of the left wrist and thumb and extension of the fingers are observed with cuff blood pressure measurement.  Physical examination reveals a hypoplastic mandible, low-set ears, bifid uvula, and cleft palate.  A chest x-ray reveals decreased soft-tissue attenuation in the right anterior mediastinum.  These findings most likely suggest impaired development of which of the following embryonic structures?

Quizplus · Accepted Answer

11ec160b_373c_6998_9249_dbbad4a638b5_MD0001_00 A 22q11.2 microdeletion underlies the spectrum of physical features seen in DiGeorge syndrome (DGS). Embryologically, the neural crest fails to migrate into the derivatives of the third (affects inferior parathyroid and thymus) and fourth (affects superior parathyroid) pharyngeal/branchial pouches. The consequent parathyroid and thymic hypoplasia results in hypocalcemia and T cell deficiency, respectively. The hypocalcemia in DGS leads to increased neuromuscular excitability, which manifests as tetany, carpopedal spasms, or seizures. Tapping on the facial nerve usually elicits twitching of the nose and lips (Chvostek sign), and inflation of the blood pressure cuff leads to carpal spasm (Trousseau sign). Normally, the thymic shadow is visible on a newborn's x-ray. Its absence reflects thymic hypoplasia, which leads to T cell dysfunction and results in recurrent viral, fungal, and protozoan infections. Conotruncal cardiac anomalies (eg, interrupted aortic arch, truncus arteriosus) may also result from failure of neural crest migration. If there is additional involvement of the first and second pharyngeal/branchial pouches, patients with DGS may have features such as hypertelorism, short palpebral fissures, micrognathia, bifid uvula, and cleft palate. (Choice A) Failure of the anterior neuropore to close leads to neural tube defects such as anencephaly. Neural tube defects can be prevented with maternal folic acid supplementation. (Choice B) The foramen cecum is a depression on the tongue that represents the embryological remnant of the superior end of the obliterated thyroglossal duct. A persistent duct results in a thyroglossal cyst that presents as a midline neck mass. (Choice C) Rathke pouch represents an invaginated oral ectoderm that eventually develops into the anterior pituitary. Craniopharyngiomas arise from remnants of this pouch and can result in hypopituitarism, hydrocephalus, and diabetes insipidus, but not hypocalcemia. (Choice D) The second branchial cleft (ie, second pharyngeal groove) is normally obliterated in utero. Persistence leads to a branchial cleft cyst between the angle of the mandible and sternocleidomastoid muscle. Educational objective: DiGeorge syndrome results from maldevelopment of the third (inferior parathyroid and thymus) and fourth (superior parathyroid) pharyngeal/branchial pouches. Subsequent parathyroid and thymic hypoplasia results in hypocalcemia and T cell deficiency. __________ References: Velocardiofacial syndrome, DiGeorge syndrome: the chromosome 22q11.2 deletion syndromes. (http://www.ncbi.nlm.nih.gov/pubmed/17950858)

A 1-Week-Old Boy Is Brought to the Emergency Department with Poor