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12.11.13 Neuroradiology review

SDH
  • 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

Subarachnoid haemorrhage
  • 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

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

Diffusion imaging

  • 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

Notes

  • 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

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