• Crescent shape
• Doesn't cross midline
• Sub-falcine herniation
• Innermost part of the frontal lobe is scraped under part of the falx cerebri
• Can be caused when one hemisphere swells and pushes the cingulate gyrus by the falx cerebri
• May interfere with blood vessels in the frontal lobes that are close to the site of injury
• Symptoms not well defined
• Older patients
  
• cf Bridging veins
  

• Check for blood in ventricles
• Can cause non-communicating hydrocephalus

Lobes

• Frontal lobe is everything forward of the central sulcus
• i.e. Includes the primary motor cortex (pre-central gyrus)
• Parietal lobe includes the primary somatosensory cortex
  
• Omega sign is only present in 80% of people
• Everything looks a bit out of place on CT because of the tilt
• Central sulcus is quite far back
  
• cf Avoid the eyes
  

• Tightly packed stuff => Restricted diffusion
• Bright on DWI
• Dark on ADC
  

• DWI is bright where there is RESTRICTED DIFFUSION
• De-phase and then re-phase protons
• If they've moved, these won't cancel out => Signal loss
  
• ADC = Apparent Diffusion Coefficient
• => Measure of diffusion speed / Freedom
• So white = Free
  
• T2 shine-through
  
• Refers to high signal on DWI images that is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image
• T2 shine through occurs because of long T2 decay time in some normal tissue
• Therefore check the ADC scan, which should be dark if there is genuine DWI signal
  

• Sylvian Fissure MCA “Dot” Sign
• Represents a thromboembolus within a segmental branch of the MCA located within the sylvian fissure (M2 or M3 segment)
• Striatum
  
• Internal capsule runs down the middle
• Caudate nucleus on the inside
• Lentiform nucleus (putamen + globus pallidus) on the outside
  
• Periventricular or subcortical lesions in MS
  
• The posterior end of the corpus callosum is the thickest part, and is termed the splenium
• Genu is anterior