This article is from the Rhodesian Ridgebacks Breed FAQ, by firstname.lastname@example.org (Richard Gordon) with numerous contributions by others.
This condition occurs when the skin is not completely closed along the
dog's spine. While hard to detect at puppyhood, it can be done by
those experienced in the breed. If dormant, this condition causes no
problems and the dog can lead a normal life. Unfortunately these
sinuses or cysts don't often remain dormant. They become inflammed and
infected. The surgery to correct the sinus is expensive, painful and
frequently not successful. Most breeders euthanize puppies with
demoids as soon as they are detected. This condition is fairly rare.