امراض نظري 1.docx

Stroke - - - - Epidemiology ============ [[Stroke]](https://radiopaedia.org/articles/stroke?lang=us) is the second most common cause of morbidity worldwide (after myocardial infarction) and is the leading cause of acquired disability. Risk factors for ischemic stroke [largely mirror] t...

Stroke - - - - Epidemiology ============ [[Stroke]](https://radiopaedia.org/articles/stroke?lang=us) is the second most common cause of morbidity worldwide (after myocardial infarction) and is the leading cause of acquired disability. Risk factors for ischemic stroke [largely mirror] the risk factors for [[atherosclerosis]](https://radiopaedia.org/articles/arteriosclerosis?lang=us) and include age, gender, family history, smoking, [[hypertension],](https://radiopaedia.org/articles/hypertension?lang=us) [[hypercholesterolemia],](https://radiopaedia.org/articles/hyperlipidaemia?lang=us) and [[diabetes] [mellitus].](https://radiopaedia.org/articles/diabetes-mellitus?lang=us) Clinical presentation: An ischemic stroke typically presents with rapid onset neurological deficit, which is determined by the area of the brain that is involved. The symptoms often evolve over hours and may worsen or improve, depending on the fate of the ischemic penumbra. The [[vascular territory]](https://radiopaedia.org/articles/brain-arterial-vascular-territories?lang=us) affected will determine the exact symptoms and clinical behavior of the lesion: - [[anterior circulation infarct]](https://radiopaedia.org/articles/anterior-circulation-infarct?lang=us) - [[anterior cerebral artery infarct]](https://radiopaedia.org/articles/aca-infarct?lang=us) - [[middle cerebral artery infarct]](https://radiopaedia.org/articles/middle-cerebral-artery-mca-infarct?lang=us) - [[lacunar infarct]](https://radiopaedia.org/articles/lacunar-infarct?lang=us) - [[striatocapsular infarct]](https://radiopaedia.org/articles/striatocapsular-infarct?lang=us) - [[posterior circulation infarct]](https://radiopaedia.org/articles/posterior-circulation-infarction?lang=us) - [[posterior cerebral artery infarct]](https://radiopaedia.org/articles/posterior-cerebral-artery-pca-infarct?lang=us) - [[cerebellar infarct]](https://radiopaedia.org/articles/cerebellar-infarct?lang=us) - [[brainstem infarct]](https://radiopaedia.org/articles/brainstem-infarct?lang=us) Pathology ========= Interruption of blood flow through an intracranial artery leads to deprivation of oxygen and glucose in the supplied vascular territory. This initiates a cascade of events at a cellular level which, if circulation is not re-established in time, will lead to cell death, mostly through liquefactive necrosis. The mechanism of vessel obstruction is important in addressing therapeutic maneuvers to both attempt to [reverse] or [minimize] the effects and to prevent future infarcts. - embolism - [[cardiac embolism]](https://radiopaedia.org/articles/missing?article%5btitle%5d=cardiac-embolism&lang=us) - [[paradoxical embolism]](https://radiopaedia.org/articles/paradoxical-embolism?lang=us) atherosclerotic embolism - [[fat embolism]](https://radiopaedia.org/articles/fat-embolism-syndrome?lang=us) - [[air embolism]](https://radiopaedia.org/articles/cerebral-air-embolism?lang=us) - thrombosis - perforator thrombosis: [[lacunar infarct]](https://radiopaedia.org/articles/lacunar-infarct?lang=us)  acute plaque rupture with overlying thrombosis. - [[arterial dissection]](https://radiopaedia.org/articles/arterial-dissection?lang=us) - [[Global cerebral hypoxia]](https://radiopaedia.org/articles/anoxic-brain-injury?lang=us) (as is seen in drowning or asphyxiation) is usually considered separately. Radiographic features --------------------- In many institutions with active stroke services which provide reperfusion therapies, a so-called code stroke aimed at expediting There is substantial heterogeneity in the terminology denoting time from onset. For the purposes of this article, the following definitions are used : **CT** ====== Non-contrast CT of the brain remains the mainstay of imaging in the setting of an acute stroke. It is fast, inexpensive and readily available. Its main limitation, however, is the limited sensitivity in the acute setting. Detection [depends] on the : - - - - For example, detection of MCA(middle cerebral artery) territory infarct has been shown to be approximately 60-70% in the first 6 hours , although changes in the deep grey matter nuclei (especially lentiform nucleus) can be visible within 1 hour of occlusion in up to 60% of patients. 1. exclude intracranial hemorrhage, which would preclude thrombolysis. 2. look for any \"early\" features of ischemia 3. exclude other intracranial pathologies that may mimic a stroke, such as a tumor Nonetheless, finding large areas of established infarction on acute non-contrast CT continues to play an important role in patient selection and management.  Immediate ----------- The earliest CT sign visible is a hyperdense segment of a vessel, representing direct visualization of the intravascular thrombus/embolus and as such is visible immediately. Although this can be seen in any vessel, it is most often observed in the middle cerebral artery (see [[hyperdense middle cerebral] [artery sign]](https://radiopaedia.org/articles/hyperdense-mca-sign-brain-1?lang=us) and [[middle cerebral artery dot sign])](https://radiopaedia.org/articles/mca-dot-sign-brain?lang=us). It may be of therapeutic and prognostic value to differentiate this hyperdense \'regular\' thromboembolic focus from a [[calcified cerebral embolus].](https://radiopaedia.org/articles/calcified-cerebral-embolus-1?lang=us)   Acute ------- The hypoattenuation and swelling become more marked with time, resulting in a significant mass effect. This is a major cause of secondary damage in large infarcts. ###  Subacute As time goes on, the swelling starts to subside and small amounts of cortical petechial hemorrhages (not to be confused with hemorrhagic transformation) result in elevation of the attenuation of the cortex. This is known as the [[CT fogging phenomenon].](https://radiopaedia.org/articles/ct-fogging-phenomenon?lang=us) Imaging a stroke at this time can be misleading as the affected cortex will appear near normal. ###  Chronic Later still the residual swelling passes, and [[gliosis]](https://radiopaedia.org/articles/gliosis?lang=us) sets in eventually appearing as a region of low density with a negative mass effect. Cortical mineralization can also sometimes be seen appearing hyperdense. ### CT perfusion CT perfusion has emerged as a critical tool in selecting patients for reperfusion therapy as well as increasing the accurate diagnosis of ischemic stroke among non-expert readers four-fold compared to routine non-contrast CT. It allows both the core of the infarct (that part destined to never recover regardless of reperfusion) to be identified as well as the surrounding [[penumbra]](https://radiopaedia.org/articles/ischaemic-penumbra?lang=us) (the region which although ischemic has yet to go on to infarct and can be potentially salvaged). CT perfusion may also demonstrate early evidence of associated [[crossed cerebellar] [diaschisis].](https://radiopaedia.org/articles/crossed-cerebellar-diaschisis?lang=us)  - [[cerebral blood volume (CBV)]](https://radiopaedia.org/articles/cerebral-blood-volume-cbv?lang=us) - [[cerebral blood flow (CBF)]](https://radiopaedia.org/articles/cerebral-blood-flow-cbf?lang=us) - [[mean transit time (MTT)]](https://radiopaedia.org/articles/mean-transit-time-mtt?lang=us) - [[time to peak (TTP)]](https://radiopaedia.org/articles/time-to-peak?lang=us) Areas that demonstrate matched defects in CBV and MTT represent the unsalvageable infarct core, whereas areas that have prolonged MTT but preserved CBV are considered to be the ischemic penumbra. ### CT angiography - may identify thrombus within an intracranial vessel, and may guide intra-arterial thrombolysis or clot retrieval. - evaluation of the carotid and vertebral arteries in the neck (e.g. [[atherosclerosis],](https://radiopaedia.org/articles/arteriosclerosis?lang=us) [[dissection],](https://radiopaedia.org/articles/arterial-dissection?lang=us) [[web],](https://radiopaedia.org/articles/carotid-web?lang=us)stenosis) - maybe necessary prior to thrombolysis in pediatric stroke cases. - assess [[collateral vessels]](https://radiopaedia.org/articles/collateral-vessels-in-acute-stroke?lang=us) using [[single-phase CTA].](https://radiopaedia.org/articles/single-phase-ct-angiographic-collateral-scores-in-acute-stroke-1?lang=us) #### Multiphase or delayed CT angiography [[Multiphase or delayed CT angiography]](https://radiopaedia.org/articles/multiphase-ct-angiography-in-acute-ischaemic-stroke?lang=us) is showing benefit either replacing CT perfusion or as an additional 4th step in the stroke CT protocol as it guides patient selection for endovascular therapy by assessing collateral blood flow in ischemic and infarct tissue. Thanks ======