Symptoms include chronic choke and swelling/deformation of the area where the esophagus is on the neck. Loss of weight (because of the swallowing complications) Some horses have nasal discharge from the backup of feed. (See photo).
This is a lot more than just a choking disorder, it's actually on the cellular level of the esophageal structure. The malformation results in impaired function of the esophagus which then results in choke and debris collecting in the esophagus. Some horses have mild cases and can be managed with moist food, frequent small mash meals, elevated eating and lifestyle adjustments. Decreased exercise can also help. This disorder is degenerative and develops as the horse ages so there is not cure, just treatment. Some have sever enough deterioration that they have to be put to sleep so evaluation of your horses situation and quality of life is very important.
There is some belief that because in Friesians the megaesophagus is related to abnormal collagen that it could be hereditary, there are no genetic tests in place to prove or disprove this but it's something that should be addressed. So if you have a horse with Megaesophagus and want to share their pedigree that would be appreciated. The more information we have the better chance we have at helping our horses. Fenway Foundation is trying to research Megaesophagus and it's link to the collagen disorder, they even believe it can be linked with CPL and Aortic Rupture. They are not disclosing blood lines, but if you would like to share that information either privately with me or publicly on the blog I'm happy to share whatever information I can.
Here is a postmortem of a torn esophagus.
Research Gate A
Slide show with some information, independent source