Treating Alzheimers by Transpositioning the Omentum into the Brain
Attention conservation notice: A brief summary of a relatively rare surgery that I know very little about, and loose extrapolations to what its relative success indicates about Alzheimers.
With all of the discussion about the connection between gut and brain health these days, it seems appropriate to discuss a surgical application of this: placing the omentum on top off the brain in an attempt to curb or in some cases even reverse dementia symptoms in AD (ht: J. Komisar).
First, here are some google image pictures of the greater omentum. It is certainly one of the less well understood parts of the human body, but it is well known that it is highly vascularized.
Next, here is a nice description of the procedure, written by Horatio Cabasares:
The procedure of omental transposition involves detaching a portion of the omentum from its location below the stomach; then, while keeping its main blood supply intact by a pedicle (pedicle flap), the omentum is tunneled underneath the skin of the chest to the neck and continued behind the ear to reach the brain.
While a general surgeon is performing this procedure in the abdomen, a neurosurgeon opens the skull to expose the brain. After the top of the brain is exposed, the surgery is completed by laying the omentum "like a towel” on the surface of the brain. Then, the wounds are sutured shut and, ta-da, the surgery is finished!
The procedure has been fairly successful -- for example, one case series reported at least a partial reversal of symptoms in 9/25, or 36% of, patients [1] -- and fairly successful is shocking for a disease that is routinely described as incurable.
Regardless of its usefulness in treating mild and/or severe cases of AD, the fact that it has had at least some success raises questions: why is it successful, and what does this say about the pathogenesis of AD?
1) Boosting cerebral blood flow. The omentum is highly vascularized, which makes this the obvious mechanism: the extra blood vessels in the omentum could anastamose with the existing arteries in the brain, re-perfusing the erstwhile inadequately perfused regions of the brain, such as the hippocampus, and thus restoring their function. On the molecular level, the omentum makes VEGF, which can stimulate the development of blood vessels. This is also consistent with a wealth of epidemiological data that vascular problems can increase the risk of AD.
2) Stimulating CSF drainage. The amyloid hypothesis is not necessarily inconsistent with the success of omental transposition for AD. One possibility is that omental surgery could stimulate the activity of the glymphatic system, via stimulating either the vessels that move CSF in or out of the CSF, or by stimulating the transparenchymal astrocyte channel-dependent CSF transport system. This could help remove soluble amyloid oligomers and reduce damage to neurons and neurites.
3) Providing stem cells or growth factors to the brain. The omentum contains cells that express CD34, which is commonly used as a marker for stem cells. Physiologically, it often plays a role in helping GI structures regenerate after injury [3]. It is eminently possible that the omental transposition therapy is helpful because it helps replace damaged astrocytes, OLs, endothells, or neurons.
[3]: Shivanee S, et al. 2012 Cellular Basis of Tissue Regeneration by Omentum.