What is an arachnoid cyst? Arachnoid cysts are the most common type of brain cyst. They are often congenital, or present at birth (primary arachnoid cysts). Head injury or trauma can also result in a ...

Noncancer (benign) breast lumps can have many causes. Two of the most common causes of benign single breast lumps are cysts and fibroadenomas. Several other conditions can also appear as lumps. These ...