Page 817 - Clinical Small Animal Internal Medicine

71 Disorders of the Forebrain 785

Vascular Causes describe cases of peracute onset of clinical signs consist-
VetBooks.ir Cerebrovascular Accidents ent with a unilateral cerebral or brainstem problem caused
by ischemia. Although the cause remains unknown in
Cerebrovascular accident (CVA), also known as stroke, most cases, some of them have been linked to Cuterebra
migration. It is believed that the migrating parasite, or
is defined as a sudden onset of nonconvulsive and non- the host response to it, leads to vasospasm in the cerebral
progressive focal brain signs secondary to cerebrovascu- vasculature (typically middle cerebral artery).
lar disease (any pathology affecting the blood supply of Failure of blood supply (which results in decreased
the brain). By convention, these signs must remain for perfusion pressure within one area of the brain) leads to
more than 24 hours to qualify for the diagnosis of CVA; the development of ischemia, progressing to infarction if
if the clinical signs resolve within 24 hours, the episode is this is severe and persists. An infarct describes the area
called a transient ischemic attack or TIA. of compromised brain parenchyma that results from this
process. The initial drop in perfusion pressure may occur
Causes and Pathophysiology either secondary to vascular obstruction that develops
Ischemic strokes result from occlusion of cerebral blood within the occluded vessels (thrombosis) or due to
vessels by a thrombus or embolism while hemorrhagic obstructive material that originates from another vascu-
strokes result from rupture of blood vessel walls within lar bed and travels to the brain (thromboembolism). Two
the brain parenchyma or subarachnoid space. distinct regions of an infarct can be distinguished: the
core, where ischemia is severe and infarction develops
Ischemic Stroke rapidly; and the penumbra surrounding the core, which
Ischemic strokes have been reported infrequently in the shows a more moderate decrease of cerebral blood flow
veterinary medical literature when compared with the (CBF), allowing longer durations of ischemic stress to be
human medical literature. Suspected underlying causes tolerated. Tissue within the penumbra has the potential
identified in histopathologically confirmed cases include: for recovery and therefore is the target for interventional
therapy in acute ischemic stroke.
septic thromboemboli associated with bacterial endo-
●
carditis or other sources of infection
atherosclerosis associated with primary hypothyroidism Hemorrhagic Stroke
● In contrast to the high incidence in humans, intracere-
and miniature schnauzers with hypertriglyceridemia
aberrant parasite migration (Cuterebra) or parasitic bral hemorrhage resulting from spontaneous rupture of
● vessels is considered rare in dogs and cats. Secondary
emboli (Dirofilaria immitis)
embolic metastatic tumor cells hemorrhage has been reported in dogs in association
● with:
intravascular lymphoma
●
fibrocartilaginous embolism rupture of congenital vascular abnormalities
● ●
aortic or cardiac embolism. primary and secondary brain tumors
● ●
inflammatory disease of the arteries and veins
However, in those cases which are not severe enough to ● (vasculitis)
warrant admission to the postmortem room, a concur- intravascular lymphoma
rent medical condition can be found in just over 50% of ● brain infarction (hemorrhagic infarction)
dogs. The most commonly encountered conditions are: ●
● impaired coagulation.
hyperadrenocorticism
● Nontraumatic subarachnoid hemorrhage has been
chronic kidney disease
● reported in dogs but remains very rare when compared
hypothyroidism
● to its occurrence in humans, where aneurysmal rupture
hypertension.
is the most common underlying cause.
●
Chronic kidney disease and hyperadrenocorticism were In hemorrhagic stroke, blood leaks from the vessel
the most commonly suspected underlying causes for the directly into the brain, forming a hematoma within the
hypertension in one study. No underlying cause could be brain parenchyma, or into the subarachnoid space. The
identified antemortem in nearly half of the dogs; this type mass of clotted blood causes physical disruption of the
of infarct of unknown origin is referred to in humans as tissue and pressure on the surrounding brain. This alters
cryptogenic. No age, sex or breed predisposition has been CNS volume/pressure relationships with the possibility
identified in dogs but Cavalier King Charles spaniels of increasing intracranial pressure and decreasing cere-
(CKCS) and greyhounds appear to be overrepresented. bral blood flow. In addition, the tissue downstream of the
Reports of ischemic stroke in cats are scarce. The term ruptured vessel(s) undergoes ischemia as a result of the
feline ischemic encephalopathy (FIE) has been used to loss of blood supply. As the volume of the hematoma