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