What is the difference between a brain aneurysm and avm?

Not much difference: An aneurysm expands under pressure and can leak or rupture. An avm is a cluster of veins and arteries that can leak, causing the same kind of problems. They are different in treatment but the damage is the same.

Aneurysm vs AVM: While both can bleed, an aneurysm is much more lethal based on its location off of a major artery at the base of the brain. Avm's are tangles of blood vessels typically located within the brain tissue and as a result any bleeding episode is more restricted and less fatal. An endovascular neurosurgeon should be consulted.

Multiple differences: Brain aneurysms occur at the junction of vessels at the base of the brain and are like a balloon or sac. These are under high pressure and can rupture leading to high mortality and morbidity. Brain avms occur with about 1/10th the frequency.These are a tangle of arteries and veins, where the blood from the arteries goes straight into the veins. These can also bleed and lead to serious problems.

Good question: Aneurysms are weakend areas of blood vessels that can rupture causing hemorrhage and even death. Avm's are twisting of blood vessels in the brain when arteries communicate directly with veins of the brain with intervening brain tissue. They cause increase blood flow through the weak walled veins causing them to become engorged and large. Avm's can also have aneurysms form on them.

Pathology differs: Brain aneurysms occur at the junction of blood vessels ususally at the base of the skull. They appear like a ballooning or sac that can rupture. When this happens this leads to subarachnoid hemorrhage that can be devastating. Avms are about 1/10 as common. These are a "tangle of vessels" where blood from the arteries goes directly into the veins. These also bleed leading to neurological problems.