I must revise a post from May 19, 2008 in which I quoted Dr. George R. Leichnetz, neuroanatomist at Virginia Commonwealth University and author of Digital Neuroanatomy: An Interactive CD Atlas with Text (Wiley-Liss, 2006). At that time, Dr. Leichnetz emailed me the following: “The 'interthalamic adhesion' or 'massa intermedia' is (as its name implies) an adherence of the ependymal lining of the midline third ventricle. Importantly, it is not a commissure, ie. there are no inter-thalamic fibers exchanged between the two thalami."
At that time, I said that I would confirm this view under the microscope by taking some sections of the interthalamic adhesion at autopsy. Well, it turns out that there are plenty of neuron cell bodies and nerve tracts within the massa intermedia. Above is pictured the massa intermedia from an 85-year-old lady with Alzheimer disease. Notice the bipolar neurons, particularly convincing is the neuron with the prominent nucleolus. Since this slide was stained with luxol fast blue, which stains myelin blue, you can see that there are indeed nerve tracts running through the massa intermedia. As I did further research on the internet, I found a consensus that the massa intermedia is indeed grey matter, and not simply an adherence of ependymal lining as was stated by Dr. Leichnetz. Sorry about any confusion I may have caused regarding this matter.