Introduction

• Previously considered uncommon, cerebrovascular diseases (CVDs) are increasingly recognized in dogs or cats with the advance of neuro-imaging.
• Cause: obstruction or rupture of blood vessels in brain.
• Signs: acute onset (lateralizing) neurological signs improving with time.
• Diagnosis: clinical signs, neuroimaging.
• Treatment: supportive care and management of underlying disease.
• Prognosis: generally good but varies according to location, severity and underlying cause.

Pathogenesis

Etiology

• Cerebrovascular diseases (CVDs) divided into hemorrhagic and ischemic disease:
  • Obstruction of the blood vessels → ischemia, with or without infarction.
  • Rupture of the blood vessel wall → hemorrhage Intracranial hemorrhage.
• Pathologic processes of the blood vessel responsible for CVD include:
  • Occlusion of the lumen by thrombus or embolus.
  • Rupture of the vessel.
  • Any lesion or altered permeability of the vessel wall.
  • Increased viscosity or other change in the quality of the blood.
• CVDs are the underlying cause of cerebrovascular accidents Intracranial hemorrhage.
• The common mode of presentation of CVD is a stroke.

Predisposing factors

• Hemorrhagic stroke has been reported in dogs in association with:
  • Rupture of congenital vascular abnormalities.
  • Hemorrhage into primary and secondary brain tumors Brain: neoplasia.
  • Inflammatory disease of the arteries and veins.
  • Intravascular lymphoma.
  • Brain infarction (hemorrhagic infarction).
  • Impaired coagulation Hemostatic disorder: acquired.

• Lacunar infarctions in man are mostly due to microatheroma and thrombosis (with hypertension playing a prominent role) and less often due to microembolic occlusion. Although hypertension Hypertension may be more commonly seen in dogs with lacunar infarct than in any other type of infarct, its prevalence remains low as essential hypertension is not common in dogs. When hypertension is documented in dogs, an underlying cause (such as diabetes mellitus Diabetes mellitus , hyperadrenocorticism Hyperadrenocorticism and kidney (renal) disease Renal function assessment ) is typically found.

• Atherosclerosis Peripheral vascular disease is occasionally seen in dogs but is generally considered very rare. It has been reported in dogs with hypothyroidism Hypothyroidism or diabetes. Occasional encountered causes in dogs include thromboembolism associated with heart disease or neoplasia (embolism of neoplastic cells) as well as hypercoagulability secondary to hyperadrenocorticism and chronic renal failure Kidney: chronic kidney disease (CKD).

Specific

• Heart disease Heart: congestive heart failure.
• Hypertension (and potential underlying cause).
• Endocrine disease (diabetes, hyperadrenocorticism).
• Impaired coagulation Disseminated intravascular coagulation (and potential underlying causes).
  Hypothyroidism is commonly reported as a predisposing factor but evidence is lacking.

• Sepsis Shock: septic.
• Vascular malformations.
• Chronic kidney disease Kidney: chronic kidney disease (CKD).

• Primary or metastatic brain tumors.
• Heartworm (dirofilaria immitis) Canine cardiopulmonary dirofilariasis.

• Rocky Mountain Spotted Fever Rocky Mountain Spotted Fever (RMSF) , ie infectious vasculitis.

Pathophysiology

• Historically post mortem studies have shown that most forms of CVD occurring in man also occur in dogs.

Ischemic stroke

• The brain requires a continuous supply of glucose and oxygen to maintain ionic pump function.
• Supply requires adequate ventilation, hemoglobin concentration and saturation, glucose concentration, vascular patency, cardiac output, systemic blood pressure and cerebrovascular auto-regulation.
• When perfusion pressure falls to critical levels, ischemia develops.

Infarction

• Focal occlusion of one or more blood vessels compromises brain parenchyma and results in infarction.
• Occlusion due to:
  • Vascular obstruction developing within the occluded vessels (thrombosis) or
  • Obstructive material originating from another vascular bed traveling to the brain (thromboembolism).
• The pathogenesis of vascular occlusions of large and medium-sized arteries differs from that of small arteries.
• Arterial disease that involves a small penetrating branch of a large artery results in a small, deep infarct also called a lacunar infarct (specifically observed in dogs in the thalamus and midbrain in the territory of the paramedian branches of the basilar artery, thalamoperforating artery and lenticulostriate artery).
• Infarcts due to large vessel disease seems to preferentially affect the rostral cerebellar hemisphere secondary to involvement of the rostral cerebellar artery in dogs.
• Ischemic disease of the cerebral cortex is secondary to involvement of the rostral, middle or caudal cerebral artery. In man, this type of stroke is mainly due to atherosclerosis which is considered rare in dogs. This stroke may also be due to embolic infarction (cardioembolic or artery-to-artery embolism).

Hemorrhagic stroke

• In hemorrhagic stroke, blood leaks from the vessel directly into the brain, forming a hematoma in the brain parenchyma, or into the sub-arachnoid space. The mass of clotted blood causes physical disruption of the tissue and pressure on the surrounding brain.
• This alters CNS volume/pressure relationships with the possibility of increasing intracranial pressure and decreasing cerebral blood flow.
• Intracerebral hemorrhage resulting from spontaneous rupture of vessels is considered rare in dogs.
• Secondary hemorrhage has been reported in dogs in association with various causes such as rupture of congenital vascular abnormalities, hemorrhage into primary and secondary brain tumors, inflammatory disease of the arteries and veins or intravascular lymphoma, brain infarction (hemorrhagic infarction) or impaired coagulation.
• Non-traumatic subarachnoid hemorrhage has been reported in dogs but remains very rare when compared to its occurrence in man.
• Infarct of an individual brain region is associated with specific clinical signs that reflect the loss of function of that specific region.
• The clinical presentation of hemorrhagic stroke is different from ischemic disease as the hemorrhage usually involves the territory of more than one artery and pressure effects cause secondary signs. Neurological signs are largely related to increasing intracranial pressure, which gives rise to non-specific signs of forebrain or brainstem disease. Dogs with a large rostro-tentorial hematoma usually have a decreased level of consciousness as a result of increased intracranial pressure and direct compression or distortion of the thalamic and brainstem reticular activating system.

Timecourse

• Peracute onset of neurological signs.
• Signs usually improving over several weeks.

Epidemiology

• Published reports however do suggest that the disease is uncommon with only ~ 46 cases reported. Most reports are based on post-mortem results and probably skew the perceived severity and incidence of the disease.
• The true incidence in the dog population is unknown but since the wider availability of non-invasive imaging, ie MRI it has become apparent that CVD, whilst not common, does occur (with an incidence of ~ 4% of dogs having brain MRI).

Diagnosis

Treatment

Prevention

Outcomes