MRI in Temporal Lobe Epilepsy

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MRI in Temporal Lobe Epilepsy

• Val Adams

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Introduction

• Functional disorder of the brain
• Affects 0.5-1 of population in USA (Weiss et al
  1998)
• Classifications Partial (focal, local),
  Generalised, Unclassified
• Partial seizures include simple (no loss of
  consciousness) and complex (loss of
  consciousness)
• Generalised seizures generalised may be
  convulsive or non-convulsive.
• Unclassified classification for epilepsies that
  dont fit into the other classifications.

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Generalised Seizures convulsive or
non-convulsive

• Absence seizures
• Clonic seizures
• Tonic seizures
• Atonic seizures
• Tonic clonic seizures
• Myoclonic seizures

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Triggers

• Lack of sleep
• Stress
• Alcohol
• Flickering lights

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Causes of Epilepsy

• Mesial temporal sclerosis present in 65 of
  complex partial seizures (Jack 1994)
• Neoplasms present in 10-13.5 (Kido 1997)
• Adults oligodendrogliomas and astrocytomas
• Children gangliomas and pliocystic
  astrocytomas, more rarely pleomorphic
  xanthoastrocytomas, disembryoplastic
  neuroepithelial tumours and mixed gliomas. (Kido
  1997).
• Cortical dysplasia change from normal cortical
  pattern
• Trauma MTS (Arrastia 2001) Cortical scarring
  (Stevens 1995)
• Infection on increase (Friedland and Bronen
  1996)
• Vascular malformations

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Diagnosis

• EEG - may need several to detect abnormal brain
  activity. To determine if epileptic in origin
• Video EEG simultaneous monitoring and video
  recording to confirm if temporal lobe and whether
  unilateral or bilateral (Doherty and Cole 2001).
• MRI
• MEG
• PET, SPECT- Not widely used may be used for
  detecting the focus in difficult cases.

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Treatment

• Medication not all conditions respond to the
  medication.
• Surgery considered- if unilateral and resistant
  to drug therapy
• Stereotactic guided radiotherapy. (Grabenbauer
  2001).
• Vagus nerve stimulation (Alsaadi 2001)

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MEG and Epilepsy

• Sleep deprivation increases the likelihood of
  epileptic activity.
• Small changes in signal detected and localised.
• Localisation to within 2mm.
• Expensive.

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MRI

• MTS loss of volume, loss of T2 weighted signal,
  loss of internal architecture
• Tumours mass effect usually present.
  Astrocytomas have an increase in T2 signal
  greater than that seen in MTS. Some tumours may
  have calcification to aid differentiation (Kido
  1997). Not all tumours enhance.
• Cavernous angiomas have mixed signal intensities,
  with contrast enhancement in a minimum (Kido
  1997).
• Venous angiomas have smaller vessels draining
  into a larger vein usually enhance
• AVMs large vessels usually visible on MRI
• Infection High signal on T2 weighting.

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MRI Protocols

• Protocols vary across centres
• Volume scan
• High resolution coronal oblique
• FLAIR
• Diffusion
• Spectroscopy
• fMRI

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MARIARC Protocol

• Localiser
• MTL localiser
• T1 mprage volume coronal oblique
• T2 maps coronal oblique
• T2 tirm coronal fat sat dark fluid
• T2 TSE ICV
• T2 tirm coronal

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MR Images

• MTL Localiser for obliquity

• 3D MPRAGE

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MR Images

• T2 Maps

• T2 TIRM FS

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MR Images

• T2 TSE ICV

• T2 TIRM

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Anatomy
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Voxel based morphology

• T1 MPRAGE volumetry measurements for hippocampus,
  amygdala, temporal lobe
• T2 TSE ICV CSF bright for simple detection of
  brain hemisphere for volume
• Relative values to brain hemisphere used to avoid
  errors due to different brain sizes.
• Landmarks for cut off borders.

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Wada Test

• Invasive procedure involving injection of
  amobarbitol sodium to anaesthetise each
  hemisphere in turn.
• Patient woken during procedure to check if memory
  and language functions are ok.
• Alternatives available
• fTCD can detect relative changes in blood flow
  through the MCLs during language tasks.
• fMRI language tasks can detect areas of
  activation.

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T2 maps

• Echo time varied 16 different values
• Average of hippocampal head slice obtained
• Regions of interest placed on both sides
• Mean value used to determine if gliosis
  indicated.

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Spectroscopy

• Interictal proton CSI for presurgical
  localisation of TLE
• Decrease N-acetylaspartate (NAA) coupled with
  increased or unchanged choline (Cho). (Ng et al
  1994).
• Capizzano et al (2001)

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