CT, CT-Angiography, and Perfusion-CT Evaluation of Stroke

Introduction

A stroke is a sudden loss of neurological function due to brain parenchyma damage caused by a cerebrovascular disorder. It can be caused either by the sudden loss or significant decrease of blood flow to a specific brain region (ischemic stroke), or by the rupture of blood vessels in the brain (hemorrhagic stroke). Together, stroke is the second most common cause of death worldwide, accounting for about 5.9 million deaths in 2010, almost equally distributed between ischemic and hemorrhagic strokes , but the latter accounts only for about 15% of all strokes. Stroke is also the leading cause of acquired disability in adults, and the third cause of loss of years of life. Ischemic stroke has a 6-month mortality rate of about 20%, and about 30% of patients who survive are handicapped at 6 months . Hemorrhagic stroke is an even more devastating disease, with a 30-day mortality rate of almost 50%, and only 20% of survivors being functionally independent at 6 months .

Patients with acute stroke usually present with a focal neurological deficit, such as a hemisyndrome if the stroke involves the motor cortex, or a loss of speech if the stroke involves the Broca area. The patients can also present nonspecific signs, such as headache, nausea, and seizures. In general, symptoms are not specific to the etiology of the stroke, and a large variety of diseases, such as an intracranial tumor, epilepsy, or posterior reversible encephalopathy syndrome, can mimic stroke clinically. Imaging is therefore used in the acute setting to differentiate between the various possible etiologies of the symptoms, which then help with the choice of the appropriate therapeutic approach.

Computed tomography (CT) remains the preferred imaging modality for the early evaluation of a patient suspected of acute stroke at most institutions, due to its broad availability, speed, relative lack of contraindications (except for contraindications for iodinated contrast, mainly allergy and renal insufficiency), and relative low cost. Its main drawbacks are the ionizing radiation used to make the images, and the reduced brain tissue contrast compared to magnetic resonance imaging (MRI).

In the setting of acute stroke, CT imaging has two main goals: (1) confirm the diagnosis of hemorrhagic or ischemic stroke, and exclude other possible causes of the clinical symptoms and (2) evaluate the risk:benefit ratio for each individual patient to triage for the optimal therapy.

Hemorrhagic Stroke

Acute Imaging

Intracerebral hemorrhage is typically diagnosed on a noncontrast head CT ( Fig. 131.1 ). When a large intracerebral hemorrhage is visualized, particular attention is required to identify signs of increased intracranial pressure: mass effect, displacement of the falx and the tentorium cerebelli, and the loss of visualization of the basal cisterns ( Fig. 131.2 ). CT angiography (CTA) and postcontrast CT are used to detect active extravasation of contrast and to exclude other causes of hemorrhage, such as an aneurysm, vessel anomalies, or blood–brain barrier breakdown in a glioblastoma.