Aneurysma verum means 'real aneurysm', being a dilatation of a blood vessel. The wall of the aneurysm consists of all bloodvessel layers.

An aneurysma spurium or a false aneurysm actually is a hematoma lying adjacent to a bloodvessel, stemming from leakage out of the vessel. The wall of the aneurysm consists of surrounding tissues that are pushed away by the hematoma.

An aneurysma dissecans is an aneurysm with splitting (dissection) of the artery-wall, caused by blood intruding via a defect in the intima between the layers of the artery-wall. The wall of the aneurysm consists of one bloodvessel layer.