Answer:USMLE step 2 Mcq 148:a six week old male infant is noted to be tacchypneic and distressed

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Correct Answer: D

Explanation:
An aneurysmally dilated great vein of Galen causes high output congestive heart failure in neonates whilst in older children it obstructs the Aqueduct of Sylvius, producing non communicating hydrocephalus. This malformation is a congenital arteriovenous malformation with blood shunting from cerebral arteries into an aneurysmally dilated great vein of Galen and the straight sinus. The major feeding vessels are the posterior cerebral artery and its branches the posterior choroidal and posterior perforating artery Chest film shows cardiomegaly with right sided predominance. The superior mediastinum is widened due to dilation of the brachiocephalic arteries and veins. Pulmonary vascularity is frequently normal because of the pulmonary arterial hypertension of the newborn. On angiography rapid arteriovenous shunting into a dilated saclike vein of Galen and straight sinus is seen. The majority of patients diagnosed in the neonatal period present with life-threatening, intractable cardiac decompensation and high-flow arteriovenous fistulae, CHF due to AV shunting (L -> R) and predominantly RIGHT-sided cardiomegaly, a wide superior mediastinum and retrosternal fullness. In neonates it causes high output congestive heart failure. In older children it obstructs the Aqueduct of Sylvius, producing non communicating hydrocephalus.


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