Thank you for your detailed response, one point of clarification if you could please. Other than the small hives all over her body she has no other lumps, I presume the lumps you refer to are something other than the hives themselves ? Are these mast cell tumours cancerous and/or treatable ?
Typically the lumps would be noticeable if on the body. But they don't have to be.Mast cell tumors can also be inside the body. They like to invade internal organs as well, including the liver. It is possible to have a mast cell tumor in the liver without changing the blood values of the liver very much at all. So, a normal blood work does not always mean a healthy pet. It helps, but it isn't everything.Mast cell tumors are a form of cancer. When on the skin they can be surgically removed. When in organs, it gets more complicated. Sometimes, they can not be removed. In these cases there is still some hope. Newer drugs like Mastinib have been invented over the last 5-10 years that can greatly reduce the size and clinical signs of these types of tumors. Mast cell tumors have a grading range. It used to be grade 1-2-3. The 1's weren't too bad, the threes are really aggressive, and the 2 range is what the pathologist used when they didn't want to call it it a three, but it was too aggressive to be a 1. Now they rank them on a hi-low system. High ranking is likely to spread and be aggressive. Low is likely to be more managable with removal and possible follow up modalities of treatment. The only way to know is to find it, biopsy it, remove it.One thing to consider is that you still don't have a diagnosis for the cause of the seizures. More tests are likely needed, ultrasound, etc. And in human cases, they would recommend an MRI/CT scan of the head. This is all possible, but costs and practicality keep some pet owners from using these diagnostic options. I understand completely in these cases.But, what that means, is sometimes in Veterinary Medicine we have to guess. Your Vet has made a good one in suspecting brain tumor. 9.5 out 10 times in an older dog, that is what it is going to be. But, there is a weird factor on this one. The hives. They just don't go along with that picture. So, I think it could be something else. More tests would be needed to be sure.I think an abdominal ultrasound might be a good idea to look for other causes of seizures/tumor. If not, then you have an even better chance of it being a brain tumor. At that point CT/MRI would be needed to know for sure. But, then, you might decide not to do that.