This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diagnosis of Pregnancy, Subject name: Gynaecology & Obstetrics
THE MAIN DISTINCTIVE SIGN IN CORPUS CALLOSUM DEGENERATION ON USG IS? 
Select and explain. 
A. Tear drop sign, B. lemon sign, C. Banana sign, D. Ring sign
A: Tear drop sign
Answer: A: Tear drop sign 
Explanation: With complete agenesis of the corpus callosum, a normal cavum septum pellucidum cannot be visualized sonographically, and the frontal horns are displaced laterally. There is mild enlargement of the Atria posteriorly--such that the ventricle has a characteristic "Teardrop" appearance