A Chiari malformation (sometimes called an Arnold Chiari) means that the lower parts of your brain have been pushed downwards towards your spinal cord, so they are below the entrance to your skull. Most people will have a type 1 Chiari malformation, which is the least serious form of the disease.This is where the lowest part of the back of the brain (the cerebellar tonsils) drops down into the top of the spinal canal. Types 2 and 3 Chiari malformations are less common and more serious.sually, the lower parts of the brain are contained in a space within the skull, above the level of the foramen magnum (opening at the base of the skull). If you have a type 1 Chiari malformation, these brain parts are pushed downwards, because they are too big for the skull.
Types of Aortic Valve Replacements. There are two types of aortic valve replacements: a man-made mechanical valve and a tissue valve taken from an animal heart. Both types offer specific advantages and disadvantages. Mechanical valves are made from metal and plastic and may last the rest of the recipient's life.
If a valve can't be repaired, it may be replaced with a prosthetic valve. Two kinds of prosthetic heart valves are available: Mechanical valves are created from man-made materials. Lifetime therapy with an anticoagulant (sometimes called a blood thinner) is needed when these types of valves are used.