In Alzheimer’s disease there are two distinct forms of neurofibrillary tangles. These are not different stages of the same pathologic process. The above image is a pre-necrotic form of tangle. The neurofibrils are compactly contained in large bundles and they stain very darkly with the silver stain. The nucleus is intact and of fairly normal appearance. These cells do not die unless they also show granulovacuolar degeneration. In the hippocampus the nerve cells with these tangles tend to be spared the lethal granulovacuolar degeneration suggesting a protective role.
The above image is a post-necrotic neurofibrillary tange. The neurofibrils are not as darkly stained and they appear like bars and the cell looks like an empty cage.These structures appear only after death of the cell. There is never a viable cell nucleus or other sign of cell viability. The structure may be infiltrated by scavenger cells.
