A 5-year-old boy is brought to the office by his parents for evaluation of cyanosis with minimal exertion. The boy has had occasional episodes of "turning blue" that first began during infancy and are now occurring more frequently. During the episodes, the boy assumes a squatting position as it makes him "feel better." The family recently immigrated to the United States; the boy has never had a medical checkup prior to this visit. Physical examination reveals a prominent right ventricular impulse and a harsh systolic murmur. Which of the following embryological events is the most likely mechanism that caused this patient's condition?

Question

A 5-year-old boy is brought to the office by his parents for evaluation of cyanosis with minimal exertion.  The boy has had occasional episodes of "turning blue" that first began during infancy and are now occurring more frequently.  During the episodes, the boy assumes a squatting position as it makes him "feel better."  The family recently immigrated to the United States; the boy has never had a medical checkup prior to this visit.  Physical examination reveals a prominent right ventricular impulse and a harsh systolic murmur.  Which of the following embryological events is the most likely mechanism that caused this patient's condition?

Quizplus · Accepted Answer

11ec160b_3736_eb51_9249_4bc72aa7bd89_MD0001_00 This patient's clinical presentation (cyanotic spells that improve with squatting, prominent right ventricular impulse, systolic murmur) is consistent with tetralogy of Fallot (TOF). Abnormal neural crest cell migration leads to anterior and cephalad deviation of the infundibular septum during embryologic development, resulting in a malaligned VSD and an overriding aorta. TOF is characterized by 4 distinct anatomic abnormalities: Cyanosis occurs due to the presence of right-to-left shunt in patients with severe or worsening RVOT obstruction. The typical harsh, systolic ejection murmur over the mid-to-left upper sternal border is due to the presence of RVOT obstruction (subvalvular, pulmonary valve stenosis or supravalvular narrowing in the main pulmonary artery). Squatting increases the peripheral systemic vascular resistance (afterload) and decreases the degree of right-to-left shunting across the VSD, thereby improving cyanosis. (Choice A) In anomalous pulmonary venous return, blood from both the pulmonary (oxygenated) and systemic (deoxygenated) venous systems flow into the right atrium, leading to right atrial and ventricular dilation. Patients also have obligatory right-to-left atrial shunting. (Choice B) Aortic arch constriction results in coarctation of the aorta and is most commonly located just distal to the left subclavian artery (juxtaductal). Common manifestations include brachial-femoral pulse delay and blood pressure discrepancy between the upper and lower extremities. (Choice D) Failed fusion of the superior and inferior endocardial cushions (eg, endocardial cushion defect) results in defects of the atrioventricular septum and valves (mitral and tricuspid valves). These typically manifest initially as atrial defects and/or VSDs with left-to-right shunting of blood. Over time, the increased right-sided blood flow leads to pulmonary hypertension with reversal of blood flow through the shunt and development of cyanosis (Eisenmenger syndrome). This patient has had cyanotic symptoms since birth that would not be expected with an isolated endocardial cushion defect. (Choice E) Transposition of the great arteries results from linear, rather than spiral, development of the aorticopulmonary septum in utero. Educational objective: Tetralogy of Fallot results from anterior and cephalad deviation of the infundibular septum during embryologic development, resulting in a malaligned ventricular septal defect (VSD) with an overriding aorta. As a result, the patient has right ventricular outflow obstruction (resulting in a systolic murmur) and squats to increase the peripheral systemic vascular resistance (afterload) and decrease right-to-left shunting across the VSD. __________ References: Evaluation and management of heart murmurs in children. (http://www.ncbi.nlm.nih.gov/pubmed/22010618) Tetralogy of Fallot. (http://www.ncbi.nlm.nih.gov/pubmed/19683809) When 'blue babies' grow up: what you need to know about tetralogy of Fallot. (http://www.ncbi.nlm.nih.gov/pubmed/21048055)

A 5-Year-Old Boy Is Brought to the Office by His