This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Anatomy
Solitary hypoechoic lesion of the liver without septa or debris is most likely to be 
Select and explain. 
A. Hydatid cyst, B. Carolis disease, C. Liver abscess, D. Simple cyst
D: Simple cyst
Answer: D: Simple cyst 
Explanation: A solitary hypoechoic lesion without any septae or debris is most likely to be a simple cyst. However rarely a hydatid cyst can have a similar sonologic appearance. Simple cysts are the most common benign lesions found in liver. On imaging studies they appear as unilocular, homogenous fluid-filled structures with a thin wall without projections, septa or debris. Ultrasound appearances of - Hydatid cyst - It presents either as a simple cyst with hydatid sand or daughter cysts or floating endocyst or calcification. Caroli's disease - Its the type V choledochal cyst Multiple intrahepatic biliary cysts are seen on ultrasound. Sludge & stones may also be visible within the cysts. Liver abscess - Sonographic appearance may include a cystic lesion with floating internal echoes and irregular margins. Septations, debris and fluid-fluid interfaces may also be seen. Ref : Rumack's Diagnostic Ultrasound 3rd/e, p. 86, 89, 94, 1865