Dogpeople, a member of our community, recently related the following sad story
We just lost our otherwise perfectly healthy 5-year-old cat to a Brain Tumor. We are still in shock, and I am truly kicking myself for not noticing any changes prior to her pacing and head pressing that came up this Saturday. We rushed her to [the] emergency department where they immediately commented that her eyes were different from each other. She "failed" neurological tests also. By Sunday she was visibly "not in her right mind" and we could not get her comfortable or calm. We euthanized her that day. It was too much to ask to have her wait for an MRI midweek given her condition.
What a terrible and tragic case. Of course, I can’t comment specifically on what was going on with this particular cat, but I can point out a few things that are both typical and distinctive about this story.
First of all, finding a brain tumor in a five-year-old, otherwise healthy cat is not common. Take a look at my post Brain Tumors in Pets for some basic information. You’ll see there that I wrote, "Cancer affecting the brain is common in older dogs and cats but is rarely seen in younger animals." In one study, the researchers found "The mean age of the cats was 7.9 years within group A (median 8.5) and 9.3 years (median 10) within group B. The cats with lymphoma within both groups were significantly younger than cats with meningioma."
Now I’m not saying that dogpeople’s cat didn’t have a brain tumor (particularly if lymphoma was to blame), just that her age really stands out as being unusual. I wonder if she was suffering from an immunosuppressive disease like feline leukemia virus (FELV) or feline immunodeficiency virus (FIV). These diseases may cause young cats to develop tumors, particularly in the case of FELV, which can "hide out" in the neurologic system or bone marrow, making routine tests come back negative even when a cat is infected.
Other diseases can mimic the symptoms of a brain tumor in cats. This is what Linda Shell, DVM, DACVIM Neurology has to say on the matter in the Veterinary Information Network’s Associate entry on Intracranial Neoplasia
Differential diagnoses for cerebral type of signs are as follows: Ischemic encephalopathy can occur in age of cat and always has a sudden onset and usually asymmetrical signs as described above. Fungal granuloma is not as common as brain neoplasia but could have either a sudden or slow onset and may have asymmetric signs. Cryptococcus is the most common fungal disease to affect the brain of cats and it often causes a generalized encephalomyelomeningitis. Cerebral hemorrhage has a sudden onset of clinical signs and may be associated with bleeding at other sites or signs of systemic illness. The most common infectious organism affecting cats is feline infectious peritonitis virus and it may cause either a slow or sudden onset in clinical signs; often times the serum globulins are elevated and there are signs of systemic illness. Metabolic encephalopathies should be considered in the older, as well as the younger, cat that presents with cerebral signs and can often be ruled in/out with a hemogram, chemistry profile, urinalysis, and bile acid testing. Metabolic problems do not usually cause asymmetric deficits on the neurologic examination.
Frankly, reaching a definitive diagnosis is often a moot point. When I see a patient with significant neurological deficits that can be localized to the brain, and the cat’s condition deteriorates dramatically and rapidly, I tell the owners that even though I may not be able to tell them exactly what is going on without extensive testing, I can say that it is REALLY BAD. Medically treating diseases of the brain is difficult (a lot of drugs have difficulty getting past the blood-brain barrier), and surgery is expensive and often comes with a guarded prognosis (the exception to this rule is a meningioma — some of those cats do really well after surgery).
So, dogpeople, I think your decision to euthanize was totally reasonable. In my opinion, whatever was going on was unlikely to get better no matter what diagnostic/treatment protocol you embarked on, and your cat was obviously suffering. But no words can alleviate your anguish at having to come to the same conclusion.
For an excellent and extremely detailed look at brain tumors in cats, I refer you to the Veterinary Society for Surgical Oncology.