Strokes in Dogs
Stroke is a term that describes a loss of blood flow to an area of the brain, causing neuronal cell damage. It is a relatively common occurrence in small animals, that is becoming far more widely diagnosed with the increased usage of MRI. They can cause a wide variety of clinical signs, often mimicking brain tumors in signalment, clinical presentation and sometimes imaging characteristics.
Stroke can be classified into two major groups: Ischemic or Hemorrhagic. Ischemic strokes are generally due to an occlusion of a blood vessel, often in association with a hypercoagulable state. This may be metabolic disease such as hypothyroidism, renal failure or cushings disease but can also be secondary to neoplasia, cardiac disease or other identifiable causes. Hemorrhagic strokes are caused by bleeding in the brain. Causes include hypertension, platelet disorders, coagulation disorders, metastatic neoplasia, metabolic disease or toxicity. Both ischemic and hemorrhagic stroke can also occur without any obvious underlying disease processes.
The first step to treatment is an early and accurate diagnosis. Baseline blood work including hematology, biochemistry profile and coagulation testing is required. MRI is the BEST and ONLY test to diagnose both ischemic and hemorrhagic disorders of the brain. MRI can readily differentiate, assess restriction of blood flow and often find the abnormal blood vessel in the brain. CT scan may, in certain cases show a lesion, but it can be nearly impossible to differentiate from a brain tumor. This is a major flaw of CT for imaging the brain. Accurate diagnosis is critical, as the prognosis between neoplasia such as a glioma and a hemorrhagic stroke vary considerably. Many conditions of that are consistent with stroke will recover normal or near normal given time.
Once a diagnosis of stroke is reached, further testing to help find the underlying cause of the stroke is recommended. This may require tests such as further blood work, abdominal ultrasound, coagulation profiles and blood pressure testing. Our board-certified neurologists at Southeast Veterinary can help you with these next steps.
These are two MRI images of an 11-year-old dog with acute onset of seizures, behavior change, walking in circles toward the left and weakness on the right side of the body. Note that these are common symptoms of a brain tumor in dogs. The MRI on the left shows a large, round grayish mass in the left cerebral cortex that is compressing the brain tissue toward the right. This is called a T2-weighted MRI. The image on the left is called a T2-star or gradient echo sequence. Blood products (hemorrhage) appears dark in this type of sequence. These imaging findings (and others) and the neurologists’ experience raised the suspicion of a stroke. Medical therapy was instituted. No radiation, chemotherapy or brain surgery was necessary. See below for the follow-up MRI performed 6 weeks later.
Here is the 6-week follow-up MRI. Note on the image on the left, that the previously large, gray mass is now smaller and darker. There is minimal to no compression of the brain or lateral ventricle. In the T2-star image on the right, the area of hemorrhage is much smaller but is still dark. By this time, the patient’s clinical signs had completely resolved and there were no further seizures. This information not only guides the recommended tests but also significantly improves the prognosis and allows our neurologists to stop unnecessary medications.
A CT scan would have likely led to the diagnosis of brain tumor, causing this patient unnecessary treatment or euthanasia. This is one of many reasons that we do not recommend CT for evaluating the brain.