through a given brain region. The transit time of blood

through the brain parenchyma varies depending on the

distance traveled between arterial inflow and venous outflow.

MTT equals CBV/CBF.

CBF/CBV mismatch correlates with stroke enlargement in

untreated or unsuccessfully treated patients. Those patients

with a CBF/CBV match or those with early complete

recanalization do not exhibit progression of the ischemic

stroke.

The general treatment guidelines for pCT are as follows. If

there is a CBF/CBV mismatch, with a larger CBF suggesting an

ischemic penumbra, the patient is likely a good candidate for

therapy. Many treatment guidelines suggest that a ≥ 20%

CBF/CBV mismatch should be present to consider

thrombolysis. Some authors propose that, if there is no

mismatch between CBV and CBF, treatment is unlikely to

benefit the patient.

CT Perfusion Interpretation Pearls

The MTT is the most sensitive parameter for perfusion

deficits. Although it is generally elevated due to a

thromboembolic process, it may be elevated in a patient with

significant arterial atherosclerotic narrowing. In early ischemia,

MTT is elevated, and CBF is decreased. However, the CBV can

be preserved or even elevated due to capillary bed dilatation

in very early ischemia. Once a CBF threshold is reached, CBV

starts to decline. This results in the ischemic core, which has a

matched decrease in CBF and CBV, whereas a mismatch

between CBF and CBV suggests a penumbra.

Differential Diagnosis

When considering stroke in a child or young adult, several

possible etiologies should be addressed, including arterial

dissection, vascular malformation with hemorrhage, drug

abuse, or clotting disorder. In young children, other

possibilities include congenital heart disease with emboli and

idiopathic progressive arteriopathy of childhood (moyamoya

disease).

In a middle-aged or older adult, the typical stroke etiologies

include arterial thromboembolism, hypertensive hemorrhage,

and cerebral amyloid angiopathy.

When evaluating a hemorrhagic stroke, etiologies in children

include vascular lesions, hematologic disorder, vasculopathy,

and venous infarct. In a young adult, considerations include

vascular malformations, drug abuse, and less commonly

venous occlusions or vasculitis. In older adults, common

considerations for intracranial hemorrhage include

hypertensive hemorrhage, neoplasm, cerebral amyloid

angiopathy, and, less commonly, dural sinus/cerebral venous

occlusion and coagulopathy.

Brain: Pathology-Based Diagnoses: Malformations,

Trauma, and Stroke

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