MRI Brain Evaluation of brain diseases Stroke Stroke refers to a sudden or rapid onset of a neurologic deficit (in a vascular territory) due to a cerebrovascular disease. If the neurologic dysfunction lasts for less than 24 h, the term transient ischemic attack (TIA) is used. A cerebral infarct that lasts longer than 24 h, but less than 72 h, is called a reversible ischemic neurologic deficit (RIND).

Two major types of stroke can be discerned: Ischemic stroke Hemorrhagic stroke Stroke is a medical emergency and can cause permanent neurological damage, complications, and even death. Most common stroke etiologies: 1) Cerebral Infarction 80% 2) Primary Intracranial Hemorrhage 15% 3) Nontraumatic subarachnoid hemorrhage 5%

In a patient with acute stroke, the imaging protocol should be able to Sequence Rationale Axial DWI (trace images and ADC maps) to detect foci of diffusion restriction (cytotoxic edema) Axial turbo FLAIR to detect other signs of recent stroke (e.g., hyperintense vessel sign, subarachnoid or intraventricular hemorrhage) and to detect signs of preexisting cerebrovascular disease MRA 3D-TOF through base of skull and circle of Willis to detect occlusion of a major blood vessel Axial T2-W sequence (single echo) to assess white-matter hyperintensities in the brain, including the posterior fossa (where FLAIR is less sensitive) Axial gradient echo T2* or SWI to look for hemorrhage and blood breakdown products EPI MR perfusion with bolus injection of contrast Separates infarction on acute or chronic basis The acute infarct has a different diffusion signal due to intracellular edema Contrast-enhanced MR angiography to look for occlusion of a major blood vessel

Diffusion imaging Increased sensitivity for early changes of edema Becomes abnormal within 30 mins. Distinguish b/w old and new stroke New stroke = bright on DWI (diffusion weighted image) Old stroke (encephalomalacia) = low SI on DWI

MRI Acute Stroke T1 T2 Diffusion

Evaluation of brain tumors through: Definition Shape Site Size Enhancement Edema Mass effect Normal Findings

Meningioma Meningiomas are extra-axial tumours and represent the most common tumour of the meninges. They are a non-glial neoplasm that originates from the meningocytes or arachnoid cap cells of the meninges, and are located anywhere that meninges are found, and in some places where only rest cells are presumed to be located. Although they usually easily diagnosed, and are typically benign with a low rate of recurrence following surgery, there are a large number of histological variants with variable imaging features and, in some instances, more aggressive biological behaviour.

A broad division of meningiomas is into primary intradural (which may or may not have a secondary extradural extension) and primary extradural (rare). They can also be classified according to location (e.g. spinal, intraosseous, intraventricular etc.), by histological variants (e.g. clear cell, rhabdoid etc.), and by aetiology (e.g. radiation induced etc.). Typical meningioma appear as dural-based masses isointense to grey matter on both T1 and T2 weighted imaging enhancing vividly on both MRI and CT. Some of the variants as mentioned earlier can, however, vary dramatically in their imaging appearance.

Epidemiology Meningioma’s are more common in women, with a ratio of 2:1 intracranially and 4:1 in the spine. Atypical and malignant meningiomas are slightly more common in males. They are uncommon in patients before the age of 40 and should raise suspicion of neurofibromatosis type 2 (NF2) when found in young patients.